Dissertations / Theses on the topic 'Hydrological modelling'

Technological advances in computer science, namely cloud computing and data mining, are reshaping the way the world looks at data. Data are becoming the drivers of discoveries and strategic developments. In environmental sciences, for instance, big volumes of information are produced by monitoring networks, satellites and model simulations and are processed to uncover hidden patterns, correlations and trends to, ultimately, support policy and decision making. Hydrologists, in particular, use models to simulate river discharges and estimate the concentration of pollutants as well as the risk of floods and droughts. The very first step of any hydrological modelling exercise consists of selecting an appropriate model. However, the choice is often made by the modeller based on his/her expertise rather than on the model's suitability to reproduce the most important processes for the area under study. Since this approach defeats the ''scientific method'' for its lack of reproducibility and consistency across experts as well as locations, a shift towards a data-driven selection process is deemed necessary. This work presents the design, development and testing results of a completely novel data mining algorithm, called AMCA, able to automatically identify the most suitable model configurations for a given catchment, using minimum data requirements and an inventory of model structures. In the design phase a transdisciplinary approach was adopted, borrowing techniques from the fields of machine learning, signal processing and marketing. The algorithm was tested on the Severn at Plynlimon flume catchment, in the Plynlimon study area (Wales, UK). This area was selected because of its reliable measurements and the homogeneity of its soils and vegetation. The Framework for Understanding Structural Errors (FUSE) was used as sample model inventory, but the methodology can easily be adapted to others, including more sophisticated model structures. The model configuration problem, that the AMCA attempts to solve, can be categorised as ''fully unsupervised'' if there is no prior knowledge of interactions and relationships amongst observed data at a certain location and available model structures and parameters. Therefore, the first set of tests was run on a synthetic dataset to evaluate the algorithm's performance against known outcomes. Most of the component of the synthetic model structure were clearly identified by the AMCA, which allowed to proceed with further testing using observed data. Using real observations, the AMCA efficiently selected the most suitable model structures and, when coupled with association rule mining techniques, could also identify optimal parameter ranges. The performance of the ensemble suggested by the combination of AMCA and association rules was calibrated and validated against four widely used models (Topmodel, ARNOVIC, PRMS and Sacramento). The ensemble configuration always returned the best average efficiency, characterised by the narrowest spread and, therefore, lowest uncertainty. As final application, the full set of FUSE models was used to predict the effect of land use changes on catchment flows. The predictive uncertainty improved significantly when the prior distributions of model structures and parameters were conditioned using the AMCA approach. It was also noticed that such improvement is due to constrains applied to both model and parameter space, however the parameter space seems to contribute more. These results confirm that a considerable part of the uncertainty in prediction is due to the definition of the prior choice of the model configuration and that more objective ways to constrain the prior using formal data-driven techniques are needed. AMCA is, however, a procedure that can only be applied to gauged catchment. Future experiments could test whether AMCA configurations could be regionalised or transferred to ungauged catchments on the basis of catchment characteristics.

Testing and trying out of the applicability and utility of watershed hydrological models in different; catchment sizes, hydro-geologic conditions, soil conditions and with different time resolutions is necessary for a range of spatial scales to assess the utility of these models in water shade management means like flood protection, land slide prevention, erosion control etc. The main purpose of this thesis is to tryout TOPLAND hydrological model, i.e. the new developments to the LANDPINE model allowing for using TOPMODEL distributed runoff generation, with different precipitation input methods. It focuses on the simulation of precipitation events with time resolution of one hour. Short term time resolution event simulations are important to capture flow events in small and large catchments; since these events are responsible for local flood, land slide etc., especially in areas where they are strongly localized. The model simulation has been carried out using three different precipitation input methods; gauge IDW interpolation, gauge simulated and radar based precipitation data for the selected hourly events of 2006 (27-07-2006 00:00 to 29-07-2006 23:00) and 2009 (19-07-2009 05:00 to 25-07-2009 20:00). 2009 Event The 2009 event is characterized by high peak and uniformly distributed event. For the bias corrected radar precipitation, the objective method of result comparison showed an excellent correspondence between observed and simulated flows with NS (R2) of 0.98, correlation (R2) of 0.98 and PBIAS of 0.48% at the calibration point (Gaulfoss). The bias corrected radar precipitation also showed a very good performance of the model at the interior uncalibrated gauging stations with average values of NS (R2) 0.85, correlation (R2) 0.93 and PBIAS 16.6% of the HugdalBru, Lillebudal and Eggafoss gauging stations. The gauge IDW interpolation and gauge simulated precipitation input methods also showed a very good performance of the model both at the calibration and internal uncalibrated gauging stations. 2006 Event The 2006 event is characterized by low peak and unevenly distributed (localized) event. The bias corrected radar precipitation is the only precipitation input method that made possible for calibration of the model. The objective method of result comparison showed a very good result for NS (R2) of 0.96, correlation (R2) of 0.97 and PBIAS of 5.1% at the calibration point (Gaulfoss). At the internal uncalibrated gauging stations, the correlation and PBIAS showed a good performance with average correlation (R2) of 0.77 and PBIAS of 21.3% and a poor average NS (R2) of 0.3.

In many areas of the world, the absence of streamflow data to calibrate hydrological models limits the ability to make reliable streamflow predictions. Whilst a large and increasing number of regions are insufficiently gauged, there are also many highly monitored catchments. Transferring the knowledge gained in data-rich areas to data-scarce regions offers possibilities to overcome the absence of streamflow observations. In this thesis knowledge is transferred in the form of signatures, which reflect hydrological response characteristics of a particular catchment. Several signatures may be required to capture different aspects of catchment functional behaviour. Using a large dataset of catchments, observed signatures are regressed against physical and climatic catchment descriptors. Signatures for an ungauged location with known descriptors are then estimated utilising the derived relationships. A Bayesian procedure is subsequently used to condition a conceptual model for the ungauged catchment on the estimated signatures with formal uncertainty estimation. Particular challenges related to the Bayesian approach include the selection of signatures, and specification of the prior distribution and the likelihood functions. A methodological development is based on an initial transformation of the commonly adopted uniform parameter prior into a prior that maps to a uniform signature distribution, aimed at cases where limited prior knowledge regarding the model structure adequacy and the parameters distribution exist. The suggested methodology contributes to improved estimation of response signatures, and is particularly relevant when regionalised information is highly uncertain. A further contribution of this thesis refers to the integration of several regionalised signatures into the model, accounting for the inter-signature error covariance structure. By increasing the number and regionalisation quality of signatures in the conditioning process, better predictions are obtained. Additionally, the consideration of the inter-signature error structure may improve the results when correlations between errors are shown to be strong. When regionalised signatures are integrated into the model, it is shown that model structural inadequacy has a strong effect on the prediction quality.

The aim of this thesis was to test and evaluate whether parameter regionalization of a hydrological model can be used to model the impact of forest clearcutting on streamflow in Sweden. This is an important task to be able to perform water management and impact assessments adequately. The HBV conceptual rainfall-runoff model was applied for 218 Swedish catchments of different sizes that were spread across the country and covered a wide range of different forest cover percentages. The modelling approach included calibration of the model for each catchment using a genetic algorithm and then associating the resulting optimal parameter values with the percentage of forest cover. The obtained relationship between different model parameters and forest cover was validated with help of a paired catchment study site in northern Sweden where a clear cut was done in 2006: calibrated optimal parameter sets of pre- and post-clearcutting conditions were compared to parameter sets obtained from the Sweden-wide analysis. Correlations were found for about half of the fifteen hydrological model parameters, but the validation with the paired catchment study site could only partially confirm these obtained relationships. The results suggest that the adopted parameter regionalization approach is too basic. However, some of the results seem promising and emphasize the need for further research and development of the approach to provide a more reasonable method to model the impact of forest clearcutting on streamflow.
Det huvudsakliga målet med detta examensarbete var att testa och utvärdera om parameterregionalisering av en hydrologisk modell kan vara en lämplig metod för att modellera och kvantifiera påverkan från skogsavverkning på vattenbalansen i Sverige. Detta är en viktig uppgift för att kunna hantera våra vattenresurser och utföra konsekvensanalyser på ett tillfredsställande sätt. En konceptuell hydrologisk modell tillämpades på 218 avrinningsområden av olika storlekar och som var geografiskt utspridda i hela Sverige där även andelen skog i avrinningsområdena hade ett brett spektrum. Den använda modelleringsmetoden innefattade kalibrering av varje avrinningsområde genom att använda en genetisk algoritm, varefter de optimala parametervärdeana korrelerades mot andelen skog i avrinningsområdet. Idén med denna metod är att använda dessa potentiella samband för att justera modellparametrarna och därmed simulera en skogsavverkning. De erhållna sambanden mellan modellparametrarna och skogstäcket validerades med hjälp av data från en försöksstudie i norra Sverige där en skogsavverkning gjordes under 2006. Skillnaden mellan de bäst fungerande parametervärdena före och efter skogsavverkningen jämfördes med de tidigare sambanden från andra avrinningsområden i Sverige. Signifikant korrelation hittades för ungefär hälften av de 15 hydrologiska modellparametrarna, men valideringen mot den riktiga skogsavverkningen kunde bara delvis bekräfta de erhållna sambanden. Resultaten visar att detta sätt att använda parameterregionalisering antagligen är för grundläggande. Vissa resultat är ändå lovande och fortsatt forskning och utvidgning av metoden är nödvändig för att kunna tillhandahålla en rimlig metod för att kvantifiera en skogsavverknings effekter på vattenbalansen.

There is currently worldwide interest in the effect of human activity on tile global environment, especially the effect of greenhouse gases and land-use change on the global climate, and models are being developed to study both global change and the local effects of global change. The research reported here (funded by CNPq-Brazil) involves the development of GRASP:Groundwater Recharge modelling Approach with a Scaling up Procedure. GRASP has been integrated into the UP (Upscaled Physically-based) macromodel, developed under the UK NERC TIGER programme, which is designed for studying the effects of climate and land-use change on the availability and quality of water resources. The UP macromodel will be coupled to the UK Meteorological. Office's Unified (weather and climate) model to create a state-of-the-art coupled atmospheric/hydrological model. Several important requirements for the design of new large-scale hydrological models are identified in a wide ranging review on GCMs; (General Circulation Models) and physically -based hydrological modelling, and these requirements have been applied in the development of GRASP(and UP). The main requirements are a physical basis, proper treatment of spatial variability, and simplicity. Using the concept of partial analysis, two point-scale models, SM (Soil Moisture content approach) and TF (Transfer Function approach), are developed for recharge, both based on the one-dimensional Richards' equation. SM is a simple two-parameter model relating recharge to water storage in the unsaturated zone, and several unsuccessful attempts are made to link its parameters to physical propcrties. TF is a transfer function model, and is parameterised using the matric potential and unsaturated hydraulic conductivity functions using a new approach developed especially for GRASP. Both SM and TF are verified against numerical solutions of Richards' equation.

NewAge-JGrass system for forecasting and modelling of water resources in general at the basin scale. As a modern hydrological modelling, it is composed of two parts: (i) the system for data and results visualization based on the Geographic Information System uDig and (ii) the component based modelling system. All the system is based on Java because of its portability. Java is a modern and mature language aware of the web and has features such as multithreading that are essential to build scalable modelling platform. There are a few open source frameworks available that allow adaptation for our task, such as the GeoTools project by the Open GIS Consortium, representing a solid foundation for spatial analysis. OMS was chosen for facilitating model connectivity because of it low invasiveness in code practice and capability in production of leaner and more descriptive modelling code . uDig as visualization/GIS platform, including GIS services, and its integration with the JGrass GIS, developed by http://udig.refractions.net/, offers a spatial toolbox which contains the features previously offered by JGrass. Compared to traditional hydrological models, which are built upon monolithic code, JGrass-NewAge allows for multiple modelling solutions for the same physical process, provided they share similar input and outputs constraints. Modeling components are connected by means of a concise scripting language NewAge-JGrass components can be grouped in several categories. The geomorphic and DEM analyses which solves the problem of basin delineation; the tools for making spatial extrapolation/interpolation of the meteorological data; the estimation of the radiation forcing; the estimation of evapotranspiration; the estimation of the runoff production; the channel routing and tools for automatic model parameter calibration such as DREAM, Particle Swarm and LUCA. NewAge requires interpolated meteorological variables (such as air temperature, precipitation, and relative humidity) as input data for each hillslope. They can be computed by a deterministic or geostatistic approaches. The energy model includes both, shortwave and longwave radiation calculation components for each hillslope. The first implements algorithms that take into account shade and complex topography and cloud cover. Evapotraspiration can be modelled using two different solutions: the Fao-Evapotraspiration model and the Priestley-Taylor model. A snow melting and snow water equivalent model is also part of the system. Duffy's model and Hymod model are the runoff production models implemented in NewAge. In both cases the model is applied for each hillslope. Finally, the discharge generated at each hillslope is routed to each associated stream link. Modeling solutions (connections of different components) are applied in three different river basin and verifications against measured data (discharge, radiation fluxes, snow water equivalent) are presented by using traditional goodness of fitting indices.

NewAge-JGrass system for forecasting and modelling of water resources in general at the basin scale. As a modern hydrological modelling, it is composed of two parts: (i) the system for data and results visualization based on the Geographic Information System uDig and (ii) the component based modelling system. All the system is based on Java because of its portability. Java is a modern and mature language aware of the web and has features such as multithreading that are essential to build scalable modelling platform. There are a few open source frameworks available that allow adaptation for our task, such as the GeoTools project by the Open GIS Consortium, representing a solid foundation for spatial analysis. OMS was chosen for facilitating model connectivity because of it low invasiveness in code practice and capability in production of leaner and more descriptive modelling code . uDig as visualization/GIS platform, including GIS services, and its integration with the JGrass GIS, developed by http://udig.refractions.net/, offers a spatial toolbox which contains the features previously offered by JGrass. Compared to traditional hydrological models, which are built upon monolithic code, JGrass-NewAge allows for multiple modelling solutions for the same physical process, provided they share similar input and outputs constraints. Modeling components are connected by means of a concise scripting language NewAge-JGrass components can be grouped in several categories. The geomorphic and DEM analyses which solves the problem of basin delineation; the tools for making spatial extrapolation/interpolation of the meteorological data; the estimation of the radiation forcing; the estimation of evapotranspiration; the estimation of the runoff production; the channel routing and tools for automatic model parameter calibration such as DREAM, Particle Swarm and LUCA. NewAge requires interpolated meteorological variables (such as air temperature, precipitation, and relative humidity) as input data for each hillslope. They can be computed by a deterministic or geostatistic approaches. The energy model includes both, shortwave and longwave radiation calculation components for each hillslope. The first implements algorithms that take into account shade and complex topography and cloud cover. Evapotraspiration can be modelled using two different solutions: the Fao-Evapotraspiration model and the Priestley-Taylor model. A snow melting and snow water equivalent model is also part of the system. Duffy's model and Hymod model are the runoff production models implemented in NewAge. In both cases the model is applied for each hillslope. Finally, the discharge generated at each hillslope is routed to each associated stream link. Modeling solutions (connections of different components) are applied in three different river basin and verifications against measured data (discharge, radiation fluxes, snow water equivalent) are presented by using traditional goodness of fitting indices.

This thesis explores several important hydrological modelling topics surrounding the use of continuous rainfall-runoff simulation for flood frequency estimation. A continuous simulation methodology suitable for flood frequency estimation is developed. The methodology features a rainfall-runoff model (TOPMODEL, e.g. Beven, 1997), a new profile-based stochastic rainfall model (developed in this thesis), and an uncertainty estimation procedure (Generalised Likelihood Uncertainty Estimation, or GLUE e.g. Beven and Binley, 1992). By explicitly accounting for a catchment's soil moisture conditions, allowing the direct simulation of long return period flood events (via the coupling of TOPMODEL with the stochastic rainfall model), and quantifying the uncertainty associated with the simulated flood estimates, this methodology is an attractive alternative to the more traditional statistical and event-based techniques available for flood frequency estimation. It is tested successfully using data obtained from five, gauged, UK catchments. In addition to exploring the possible consistency between flood peak and continuous flow rainfall-runoff model parameterisations, the methodology is used to examine the potential impacts of climatic change upon flood frequency. Two further issues are also addressed. These are: the choice of stochastic rainfall model (for use within continuous simulation studies), and the modification of a pulse-based stochastic rainfall model for enhanced extreme rainfall simulation.

A physically-based, distributed sediment yield component has been developed for the SHE hydrological modelling system. This new component models the hillslope processes of soil detachment by raindrop impact, leaf drip impact and overland flow, and transport by overland flow. If the eroded soil reaches a river system it is routed downstream along with any inobilised river bed material. Deposition on land or in a river is simulated and the river bed material size distribution is continuously updated with allowance for armour layer development. The equation developed for soil detachment by raindrop and leaf drip impact was successfully tested using data from a field plot with a range of soybean canopy covers and rainfall intensities. The soil detachment coefficient in this equation was determined for a range of soil types and showed a variation consistent with that which may be expected from a consideration of the physics of a soils resistance to detachment. At present two soil detachment coefficients need calibration. In order to investigate the variation in these coefficient values, as well as to test the component, various applications were carried out. The hilislope sub-component was applied to rainfall simulator plots with a variety of surface conditions. Two sets of calibration parameters, distinguishable on a physical basis according to the degree of soil disturbance, were found to be appropriate for all the plots. To investigate scale effects, parameters calibrated at the rainfall simulator plot scale were transferred to a 1-ha rangeland sub-catchment. With no further calibration, the catchmerit response for four events was poorly simulated for both water and sediment. However, with reasonable variations in the antecedent soil moisture content but no variation in plot calibrated sediment parameters, the sediment yield for two of the four events could be successfully simulated. These applications suggest that parameter transfer is feasible if the sediment yield characteristics at the different scales are similar. Further applications of the hilislope sub-component were carried out for two small agricultural catchments. The sediment response could be simulated to at least the same accuracy as achieved by two existing distributed soil erosion models. The channel sub-component was applied to the East Fork River, Wyoming. Although the complex sediment storage/supply effects could not be reproduced completely, the simulated response was nevertheless of similar accuracy to that achieved by two existing alluvial river models. The new component is considered to be a valuable contribution to sediment yield modelling as a physically-based approach is used for both the hilislope and channel phases of the catchinent sediment system, within the framework of an advanced hydrological modelling system.

The recent high profile flooding events – that have occurred in many parts of the world – have drawn attention to the need for new and improved methods for water resources assessment, water management and the modelling of large-scale flooding events. In the case of the Zambezi Basin, a review of the 2000 and 2001 floods identified the need for tools to enable hydrologists to assess and predict daily stream flow and identify the areas that are likely to be affected by flooding. As a way to address the problem, a methodology was set up to derive catchment soil moisture statistics from Earth Observation (EO) data and to study the improvements brought about by an assimilation of this information into hydrological models for improving reservoir management in a data scarce environment. Rainfall data were obtained from the FEWSNet Web site and computed by the National Oceanic and Atmospheric Administration Climatic Prediction Center (NOAA/CPC). These datasets were processed and used to monitor rainfall variability and subsequently fed into a hydrological model to predict the daily flows for the Zambezi River Basin. The hydrological model used was the Geospatial Stream Flow Model (GeoSFM), developed by the United States Geological Survey (USGS). GeoSFM is a spatially semi-distributed physically-based hydrological model, parameterised using spatially distributed topographic data, soil characteristics and land cover data sets available globally from both Remote Sensing and in situ sources. The Satellite rainfall data were validated against data from twenty (20) rainfall gauges located on the Lower Zambezi. However, at several rain gauge stations (especially those with complex topography, which tended to experience high rainfall spatial variability), there was no direct correlation between the satellite estimates and the ground data as recorded in daily time steps. The model was calibrated for seven gauging stations. The calibrated model performed quite well at seven selected locations (R2=0.66 to 0.90, CE=0.51 to 0.88, RSR=0.35 to 0.69, PBIAS=−4.5 to 7.5). The observed data were obtained from the National Water Agencies of the riparian countries. After GeoSFM calibration, the model generated an integration of the flows into a reservoir and hydropower model to optimise the operation of Kariba and Cahora Bassa dams. The Kariba and Cahora Bassa dams were selected because this study considers these two dams as the major infrastructures for controlling and alleviating floods in the Zambezi River Basin. Other dams (such as the Kafue and Itezhi-Thezi) were recognised in terms of their importance but including them was beyond the scope of this study because of financial and time constraints. The licence of the reservoir model was limited to one year for the same reason. The reservoir model used was the MIKE BASIN, a professional engineering software package and quasi-steady-state mass balance modelling tool for integrated river basin and management, developed by the Denmark Hydraulic Institute (DHI) in 2003. The model was parameterised by the geometry of the reservoir basin (level, area, volume relationships) and by the discharge-level (Q-h) relationship of the dam spillways. The integrated modelling system simulated the daily flow variation for all Zambezi River sub-basins between 1998 and 2008 and validated between 2009 and 2011. The resulting streamflows have been expressed in terms of hydrograph comparisons between simulated and observed flow values at the four gauging stations located downstream of Cahora Bassa dam. The integrated model performed well, between observed and forecast streamflows, at four selected gauging stations (R2=0.53 to 0.90, CE=0.50 to 0.80, RSR=0.49 to 0.69, PBIAS=−2.10 to 4.8). From the results of integrated modelling, it was observed that both Kariba and Cahora Bassa are currently being operated based on the maximum rule curve and both remain focused on maximising hydropower production and ensuring dam safety rather than other potential influences by the Zambezi River (such as flood control downstream – where the communities are located – and environmental issues). In addition, the flood mapping analysis demonstrated that the Cahora Bassa dam plays an important part in flood mitigation downstream of the dams. In the absence of optimisation of flow releases from both the Kariba and Cahora Bassa dams, in additional to the contribution of any other tributaries located downstream of the dams, the impact of flooding can be severe. As such, this study has developed new approaches for flood monitoring downstream of the Zambezi Basin, through the application of an integrated modelling system. The modelling system consists of: predicting daily streamflow (using the calibrated GeoSFM), then feeding the predicted streamflow into MIKE BASIN (for checking the operating rules) and to optimise the releases. Therefore, before releases are made, the flood maps can be used as a decision-making tool to both assess the impact of each level of release downstream and to identify the communities likely to be affected by the flood – this ensures that the necessary warnings can be issued before flooding occurs. Finally an integrated flood management tool was proposed – to host the results produced by the integrated system – which would then be accessible for assessment by the different users. These results were expressed in terms of water level (m). Four discharge-level (Q-h) relationships were developed for converting the simulated flow into water level at four selected sites downstream of Cahora Bassa dam – namely: Cahora Bassa dam site, Tete (E-320), Caia (E-291) and Marromeu (E-285). However, the uncertainties in these predictions suggested that improved monitoring systems may be achieved if data access at appropriate scale and quality was improved.

The cryosphere is defined as the portions of the earth where water is in solid form. It represents a very important part of the hydrologic cycle, affecting ecological, human and climate systems. A number of component models describing the energy and mass balances of a snowpack have been developed and these component models are finding their way into watershed models and land surface schemes. The purpose of this thesis is to examine the incorporation of a number of snow processes in the coupled land-surface-hydrological model WATCLASS. The processes under consideration were mixed precipitation, variable fresh snow density, maximum snowpack density, canopy interception and snow-covered area (SCA). The first four of these processes were based on similar work done by Fassnacht (2000) on a watershed in Southern Ontario. In the case of this thesis, the work was completed on a basin in Northern Manitoba. A theory of the relationship between snow-covered area and average snow depth was developed and an algorithm was developed to implement this theory in WATCLASS. Of the five snow processes considered, mixed precipitation was found to have the greatest impact on streamflow while the new canopy interception algorithm was found to have the greatest impact on sensible and latent heat fluxes. The development of a new relationship between SCA and average snow depth was found to have a minimal impact in one study case, but a significant impact on the sensible and latent heat fluxes when snow fell on a pack that had begun to melt and was partially free of snow. Further study of these snow processes in land-surface-hydrologic models is recommended.

The rigorous development, application and validation of distributed hydrological models obligates to evaluate data in a spatially distributed way. In particular, spatial model predictions such as the distribution of soil moisture, runoff generating areas or nutrient-contributing areas or erosion rates, are to be assessed against spatially distributed observations. Also model inputs, such as the distribution of modelling units derived by GIS and remote sensing analyses, should be evaluated against groundbased observations of landscape characteristics. So far, however, quantitative methods of spatial field comparison have rarely been used in hydrology.

In this paper, we present algorithms that allow to compare observed and simulated spatial hydrological data. The methods can be applied for binary and categorical data on regular grids. They comprise cell-by-cell algorithms, cell-neighbourhood approaches that account for fuzziness of location, and multi-scale algorithms that evaluate the similarity of spatial fields with changing resolution. All methods provide a quantitative measure of the similarity of two maps.

The comparison methods are applied in two mountainous catchments in southern Germany (Brugga, 40 km²) and Austria (Löhnersbach, 16 km²). As an example of binary hydrological data, the distribution of saturated areas is analyzed in both catchments. For categorical data, vegetation zones that are associated with different runoff generation mechanisms are analyzed in the Löhnersbach. Mapped spatial patterns are compared to simulated patterns from terrain index calculations and from satellite image analysis. It is discussed how particular features of visual similarity between the spatial fields are captured by the quantitative measures, leading to recommendations on suitable algorithms in the context of evaluating distributed hydrological models.

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Interdisziplinäres Zentrum für Musterdynamik und Angewandte Fernerkundung
Workshop vom 9. - 10. Februar 2006

Lake Tana Basin is of significant importance to Ethiopia concerning water resources aspects and the ecological balance of the area. The growing high demands in utilizing the high potentials of water resource of the Lake to its maximal limit, pictures a disturbing future for the Lake. The objective of this study was to assess the influence of topography, soil, land use and climatic varia-bility on the hydrological and hydrodynamic processes of the Lake Tana Basin. The physically based SWAT model was successfully calibrated and validated for flow and sediment yield. Se-quential uncertainty fitting (SUFI-2), parameter solution (ParaSol) and generalized likelihood un-certainty estimation (GLUE) calibration and uncertainty analysis methods were compared and used for the set-up of the SWAT model. There is a good agreement between the measured and simulated flows and sediment yields. SWAT and GIS based decision support system that uses multi-criteria evaluation (MCE) was used to identify the most vulnerable areas to soil erosion in the basin. The results indicated that 12 to 30.5% of the watershed is high erosion potential. Pro-jected changes in precipitation and temperature in the basin for two seasons were analyzed using outputs from fifteen global climate models (GCMs). A historical-modification procedure was used to downscale large scale outputs from GCM models to watershed-scale climate data. The results showed significant changes in streamflow and other hydrological parameters in the period between 2045-2100. SWAT was combined with a three dimensional hydrodynamic model, GEMSS to investigate the flow structure, stratification, the flushing time, lake water balance and finally the Lake‘s water level response to planned water removal. We have found an alarming and dramatic fall of the water levels in Lake Tana as response to the planned water withdrawal. The combination of the two models can be used as a decision support tools to better understand and manage land and water resources in watersheds and waterbodies. The study showed that the Lake Tana Basin may experience a negative change in water balance in the forthcoming decades due to climate change as well as over abstraction of water resources.
QC 20100720

A good understanding of the local and regional water cycle and how it is modified by landscape changes may help policymakers take the pertinent decisions in order to avoid adverse effects of future hydro–climatic changes. This knowledge is of particular interest in the most vulnerable areas of the world such as the African continent. In this context the aim of this project is to model hydrological responses to possible changes in climatic conditions in Lake Babati, northern Tanzania. For this reason a water balance model specially designed to simulate lake level changes was adapted to Lake Babati and calibrated with the available local meteorological and hydrological data record covering the last decades. The necessary ambient condition changes to produce a dry–out and an overflow of the lake were investigated and the response of the system to future IPCC climate change projections was studied. The results show that for instance a temperature change of less than 3ºC or a precipitation change of around 100 mm/year could eventually bring the lake from a dry–out situation to an overflow situation. Furthermore, the IPCC derived scenarios show a clear tendency of the lake to increase its volume and reach the overflow level in a relatively short time.

There are a number of engineering situations where fluid-saturated geological media can be subjected to thermal effects. These include the disposal of heat-emitting nuclear fuel wastes in saturated geological formations, extraction of energy resources such as oil and natural gas by steam injection and the recovery of geothermal energy by ground source heat exchangers. The objective of this thesis is to study the coupled thermal-hydrological-mechanical (T-H-M) response of fractured geological media by the computational implementation of mathematical models. From the generalization of Biot's classical theory of consolidation of a saturated porous elastic medium to include thermal effects, we first derived the equations governing coupled T-H-M processes in saturated geological media. In order to obtain numerical solutions for the governing equations, the finite element method was used. A finite element computer code, FRACON (FRActured media CONsolidation), was developed in order to simulate plane strain and axisymmetric problems. Eight-noded isoparametric elements were developed to represent the intact regions of the geological medium, while special joint elements were developed to simulate discrete joints. The intact regions of the geological medium was assumed to exhibit linear elasticbehaviour. The joints between intact regions were modelled by constitutive relationships which reproduced both linear elastic and nonlinear elasto-plastic responses. The elasto-plastic stress-strain relationship of the joint, was formulated by appeal to classical theories of interface plasticity. The elasto-plastic model for joint behaviour thus formulated is capable of reproducing many of the fundamental features of mechanical behaviour associated with naturally occuring joints, such as dilation under shear and strain softening due to surface asperity degradation. Furthermore, the thesis presents a physically-based hydraulic model of the joint that permits the inclusion of the effec
The development of the FRACON code followed an extensive procedure of code verification via analytical solutions and intercode comparison. A unique set of benchmark problems was proposed in order to perform code verification for coupled T-H-M.
The FRACON code was used to interpret certain laboratory and field experiments, including the following: (1) coupled T-H-M laboratory experiment on a block of cementitious material; (2) lab experiments on joint shear behaviour under constant normal stress and constant normal stiffness conditions; (3) coupled shear-flow laboratory experiment on a joint; (4) Field experiments of fluid injection in a horizontal fracture in a granitic rock mass.
Lastly, the FRACON code was used to simulate the coupled T-H-M response of a rock mass to radiogenic heat from nuclear fuel wastes buried in the rock formation. The coupled H-M response of this rock mass to a future glaciation scenario was also simulated. It was shown that the mechanical/hydraulic regimes of the rock mass could be significantly changed by the above two factors. The importance of the consideration of T-H-M processes in the overall scheme of safety assessment of sites targeted for nuclear fuel waste repositories is supported by the findings of this thesis.

The management of large scale strategic urban combined drainage systems is becoming increasingly dependent upon weather radar systems which can provide quantitative precipitation information to improve the overall efficiency of a system's operational performance. Thus, there has been an increasing requirement for a more detailed knowledge of the radar rainfall data accuracy and the development of a mathematical rainfall-runoff model that can be used to analyse and control a system in real-time. Within this context, several important factors including signal attenuation, temporal and spatial data resolutions and rainfall quantisation schemes that determine the accuracy of radar rainfall estimates were examined in this thesis. In order to facilitate real-time flow simulation and forecast, a Conceptually Parametrised Transfer Function (CPTF) model has been developed based on Dynamic Linear Reservoir theory. The model is structurally simple and operationally reliable. It can be easily identified and robustly updated following a pulse response-to-CPTF procedure in which Genetic Algorithms play a key role. Using the model, the accuracy of areal rainfall estimates obtained by the Hameldon Hill radar has been assessed, firstly by comparing the radar rainfall estimates with `ground truth', and then by comparing the simulated hydrographs with the actual flow observations. Finally, a case study was conducted using radar rainfall data to highlight the potential benefit of real-time control for the strategic urban drainage system in the Fylde Coast. The major achievements documented in this thesis are: 1) A rule for determination of an appropriate input data resolution for hydrological models; 2) A general probability density function for describing the sampled radar rainfall intensities; 3) An efficient quantising law (ß-Law) and an associated adaptive rainfall quantisation scheme; 4) Three general conceptual pulse-response functions developed based on Dynamic Linear Reservoir theory; 5) CPTF model; and 6) A case study on the potential benefit of real-time control in the Fylde urban drainage system.

This research applies, evaluates and compares approaches to hydrological modelling and stream flow forecasting within a GIS environment. Three different approaches to modelling stream flow were investigated, namely; TOPMODEL, a regression approach and a GIS-based model, HydroGrid. TOPMODEL is a parametrically simple, physically-distributed model that allows the topological modelling of catchment processes. Regression modelling is a statistical technique that derives an empirical equation based on the assumption that the values of a dependent variable will depend upon the values of the independent variables. HydroGrid is a purpose-built GIS-based model for catchment modelling using the functionality that GIS offers for modelling the spatial variations of catchment characteristics. All three approaches were evaluated using readily available data for a lowland catchment, in Staffordshire, U.K. Model validation used six years of data covering the period 1991-92 through to 1996-97 - with years running from March-February. Five performance indicators were used to assess the models enabling both for detailed evaluation of the models and comparisons to be drawn with other research. The performance of the three models tested showed great similarities, with all approaches tending to over-predict stream flow. Model performance was also evaluated using three different evapotranspiration models - the Penman formula, the Crowe-irrigation method and the sine curve method. All three models performed best during wet years or wetter seasons indicating a common weakness in the accurate modelling of low stream flows. Despite similarities in performance, clear benefits of hydrological modelling within a GIS framework are identified. Overall, the results show that although the methods used here can help in daily flow modelling, there is a major need to improve methods for catchment modelling with routine data sources. An important development could be to loose-couple hydrological models with a GIS to improve their ability to use available information but also, as shown in this work, to model catchment processes directly within a GIS.

This thesis identifies, quantifies and models water fluxes within the Dauges National Nature Reserve, an acidic valley mire in the French Massif Central. A range of techniques were used to investigate the nature and geometry of granite weathering formations and of peat deposits. Rainfall, reference evapotranspiration, stream discharge, stream stage, groundwater table depths and piezometric heads were monitored over a three-year period. The distributed, physics-based hydrological model MIKE SHE/MIKE 11 was used to model water flow within the mire and its catchment. It was shown that the mire is mostly fed by groundwater flowing within the densely fissured granite zone and upwelling through the peat deposits. Upwelling to the peat layer and seepage to overland flow were highest along the mire boundaries. However hydrological functioning differs from this general conceptual model in some locations due to the high variability of the peat hydraulic characteristics, the presence of highly permeable alluvial deposits or past human interference including drainage. The equivalent porous medium approach used to model groundwater flow within the fissured granite zone gave satisfactory results: the model was able to reproduce discharge at several locations within the high-relief catchment and groundwater table depth in most monitoring points. Sensitivity analyses showed that the specific yield and horizontal hydraulic conductivity of the fissured zone are the parameters to which simulated stream discharge and groundwater table depth, including in peat, are most sensitive. The model was forced with new vegetation parameters to assess the potential impacts of changes in catchment landuse on the mire hydrological conditions. Replacement of the broadleaf woodlands that currently cover most of the catchment with conifer plantations would lead to a substantial reduction in surface and groundwater inflows to the mire and to a substantial drop in summer groundwater table depths, particularly along the mire margins.

Aid In Action Porthcawl (a registered South Wales Charity Organisation) has been carrying out charity work in the town of Rubik in the Mirdita Region of North Albania for many years. Rubik lies within the Catchment of the River Fani which is remote, ungauged and characterised by frequent flooding, erosion and deforestation. Over the years these processes have had a huge environmental and socioeconomic impact on the residents of Rubik. Aid In Action was concerned about this situation and wished to provide a sustainable solution. Following discussions with staff at the University of Glamorgan, it was agreed that a sustainable solution was the development of an integrated hydrological decision support system for the whole River Fani Catchment. Hydrological models can be a valuable tool, providing a common platform for experts, decision-makers and stakeholders for the sustainable management of catchments, especially when used within the framework of a Geographic Information System (GIS). Such models and systems require quantitative data of good quality over appropriate spatial and temporal scales. For remote mountainous ungauged river catchments in developing countries the development of a catchment model and management system is often complicated due to limited availability of such data. Very often, any available data are difficult to obtain; they could, for example, be scattered among local authorities and are generally in the national language of the country concerned, thus adding the challenge of having records translated into the study language. Over the last few decades, advances in hydrological data capture (e.g. using remote sensing) and data management systems (e.g. GIS) have provided opportunities for overcoming some of the challenges of modelling ungauged catchments. However, the data captured is often from different sensors and sources and at different scales. This research project sought out to creatively use multi-source and multi-scale data to develop a GIS based hydrological model of the River Fani Catchment in the North of Albania to provide, a long term solution for the sustainable management of the Fani Catchment, thus improving the quality of life for the residents of Rubik and the rest of the Catchment. Data from various remote sensing sensors (e.g. Landsat, MODIS, ASTER) and other sources such as published maps, limited gauged flow and rainfall records, local library archives, digital datasets (e.g. CORINE and radar rainfall) and interviews with residents were used to develop the integrated GIS-based hydrological (using WMS hydrological modelling environment) and hydraulic (HEC-RAS) model of the Fani Catchment. The model was then used to not only map significant environmental change in the Catchment (e.g. deforestation using various vegetation indices), but also to assess flooding impact and to analyse various “What-if” scenarios of conservation strategies (e.g. deforestation, afforestation and provision of runoff attenuation systems). The results suggest that the changes in vegetation cover (apart from farming practices) are not considerably extensive in the Catchment between 1984 and 2000. It was observed that afforestation as a flooding mitigation measure did not play a decisive role in runoff reduction compared with attenuation measures. This study has demonstrated the effectiveness of remote sensing and GIS in generating quantitative information on land classification, change detection, soil erosion and general catchment management for remote and ungauged catchments in developing countries. This has been particularly so, owing to recent developments in sensor technologies and increasing available datasets from data providers and the global scientific community at little or no cost.

Evapotranspiration as a major component of the water balance has been identified as a key factor in hydrological modelling. Water management can be improved by means of increased use of reliable methods for estimating evapotranspiration. The limited availability of measured climate and discharge data sets, particularly in the developing world, restricts the reliability of hydrological models in these regions. Furthermore, rapid changes in hydrological systems with increasing development mean uncertainties in water resource estimation are growing. These changes are related to the modification of catchment hydrological processes with increasing human activity. Dealing with data uncertainty and quantifying the impacts of catchment activities are significant challenges that scientists in the field of hydrology face today. Uncertainties in hydrometeorological data are associated with poor observation networks that provide data at point scales which are not adequately representative of the inherent heterogeneity within catchment processes. Using uncertain data in model applications reduces the predictive power of hydrological models as well as the ability to validate the model outcomes. This study examines the potential of using remote sensing-based evapotranspiration data to reduce uncertainty in the climatic forcing data and constraining the output of a rainfall-runoff hydrological model. It is common to use fixed seasonally variable potential evapotranspiration (PET) instead of temporally varying PET data as inputs to standard rainfall-runoff models. Part of the reason is that there are relatively few stations available to measure a variety of meteorological input data needed to compute PET, as well as the apparent lack of sensitivity of rainfall-runoff models to different types of PET inputs. As hydrometeorological data become more readily available through the use of earth observation systems, it is important to determine whether rainfall-runoff models are sensitive to time-varying PET derived from these earth observations systems. Further potential includes the use of actual evapotranspiration (ETa) from this type of data to constrain model outputs and improve model realism. It is assumed that a better representation of evapotranspiration demands could improve the efficiency of models, and this study explores some of these issues. The study used evapotranspiration estimates (PET and ETa) from the MOD16 global product with one of the most widely used hydrological models in South Africa. The investigation included applying the Pitman model in a number of case study catchments located in different climatic regions of the country. The main objectives of the study included (i) the establishment of behavioural model parameter sets that generate acceptable hydrological response under both naturalised and present-day conditions, (ii) the use of time-varying PET estimates derived from MOD16 data to force the model, and (iii) the use of MOD16 ETa estimates to constrain model-simulated ETa. Before examining the use of different PET forcing data in the model, a two-step modelling approached was employed both a single-run and an uncertainty version of the Pitman model. During the first step (using a single-run version), available information on catchment physical properties and regionalised groundwater recharge together with model calibration principles were used to develop model functionality understanding and establish initial parameter sets. The outcomes from the first step were used to define uncertain parameter ranges for the use in the uncertainty version of the Pitman model (second step). Further, catchment water uses were quantified to ensure comparability with present-day flow conditions represented by the stream flow records. The effects of forcing the Pitman model with MOD16-based time-varying PET data inputs were evaluated using static and dynamic sensitivity analysis approaches. In the static approach, parameter sets calibrated using fixed seasonal distributions of PET data remain unchanged when forcing the model with other forms of PET, whereas in the dynamic method, the model is recalibrated with changing PET inputs. In both approaches, model sensitivity was assessed by comparing objective function statistics of reference flow simulations with those simulations incorporating changing PET data inputs. The use of the MOD16 ETa data to constrain model- simulated evapotranspiration losses was conducted by calibrating the parameters such that the simulated-ETa matched the evapotranspiration loss estimated from the MOD16 data. Despite issues around model equifinality and significant uncertainty within water use information, the Pitman model simulations were generally satisfactory and compared with observed stream flow data where available. The use of time-varying PET data does not improve the efficiency of the model when both static and dynamic sensitivity approaches are used. This was highly expected with the static approach where fixed model parameter sets do not account for the changes in evapotranspiration demands. However, with the dynamic approach, it was difficult to conclude why the model efficiency did not improve given the flexibility of the model to achieve appropriate parameter sets to different forms of PET. The study noted that the insensitivity of the model to changes in PET demands could be due to uncertainties in the model structure and MOD16 data. Attempts to constrain the model-simulated actual evapotranspiration with MOD16 ETa estimates were hampered by large errors in the MOD16 data and resulted in the non-closure of the catchment annual water balance, even when likely errors in the other components of the water balance were accounted for. There is still a great deal of work that needs to be done to reduce uncertainties associated with the use of earth observation data in hydrological modelling. This study has identified some of the specific gaps within the application of evapotranspiration data from earth observation information. While the MOD16 data applied with the Pitman model did not achieve improved simulations, the study has demonstrated the enormous potential of the data product in the future should the identified uncertainties be resolved. Lastly, the investigation highlighted some of the possible model structural uncertainties specifically associated with the simplified soil-moisture accounting routines within the model. It is possible that amending the model structure through investigating the dynamics of the relationship between soil moisture and evapotranspiration losses would assist in the improved utilisation of earth observation products related to the MOD16 ET data.

In order to effectively manage river basin systems, a full understanding of the effects of land use change on hydrological processes, as well as knowledge on spatial heterogeneity of surface runoff with associated catchment characteristics, is required. This thesis employed the SWAT2009 model and SUFI-2 tool to understand the hydrological response to land use change in the Daning River catchment, Three Gorges Reservoir area, China. Firstly, appropriate landscape representations for the SWAT-based hydrological modelling were examined. DEM spatial resolution, catchment delineation scale and HRU definition were identified so that the inputs uncertainty could be reduced to a minimal level. Secondly, a consistent underestimation of discharge using station-based climatic records disclosed there was insufficient precipitation due to the location of the rain gauge at relatively low altitude. Considering the orographic effects on precipitation, Daning hydrological models were well calibrated and validated with the sparse climate observations. The model prediction uncertainty was also quantified. Thirdly, using the calibrated hydrological models of the Daning River catchment, this study quantified the effects of land use change (1990 and 2004) on the hydrological processes in the whole basin and sub-catchment levels. In 1982-1993, the change of land use pattern from 1990 to 2004 resulted in an increase of surface runoff, whereas, in 1996-2007 reverting the land use from 2004 to 1990 caused a slight decrease of river flows. Increased forest cover decreased surface runoff at the sub-catchment level. A concurrent increase of agricultural land, which brought about more surface runoff, weakened the forest‘s ecological function of water retention at the catchment scale. This thesis highlights that the strategy of land use exploration for human use along with the afforestation is not always effective in ecological protection. With the changing land use in future, composition of forests and agricultural land is a significant element being considered.

Shallow landslides are important as geomorphic agents of erosion, sources of catchment sediment and potential hazards to life and infrastructure. The importance of these mass movements is difficult to define using solely field- based approaches because these are often too limited in both duration and resolution to fully determine the magnitude and frequency of these processes. Modelling is a powerful alternative tool for providing insight into underlying processes governing shallow landslides and for testing new hypotheses regarding environmental and land-use change impacts. The explanatory power of models is a function of their process representation and predictive ability. Current models suitable for catchment-scale application provide valuable probabilistic information on failure, but not detailed deterministic predictions. Using the English Lake District as a study area, this thesis addresses three issues necessary to provide the process-basis of these probabilistic analyses. First, poorly constrained or spatially variable input parameters such as soil depth, root reinforcement or material properties are often used to explain the locations of failure within a larger area that has a high, sometimes equal, probability of failure. The thesis develops rigorous new methods to quantify and minimise error in these parameters, representing them as distributions to capture both their natural variability and the error in their measurement. Results suggest that lateral root reinforcement even for grasses and shrubs may provide important additional strength (as much as 6 kPa) in the top 0.5 m of the soil. Second, infinite slope stability analysis neglects important additional lateral friction and root reinforcement effects at the margins of an unstable block. More sophisticated three-dimensional stability analyses can represent this process but are limited in their applicability by computational and data resolution requirements. This thesis derives from first principles a set of analytical governing equations for three-dimensional analysis; tests these against benchmark geotechnical methods; and applies them to establish key landslide scaling relationships. Third, shallow landslides in the UK are almost exclusively hydrologically triggered, resulting from local high pore water pressures. In line with the current paradigm existing stability models assume that the topography plays a dominant role in defining the spatial pattern of soil moisture and therefore pore water pressures in the landscape. This hypothesis is tested: first at the hillslope scale (10(^1) km(^2)) with a network of ֊100 wells; then the catchment scale (10(^2) km(^2)) using high resolution orthorectified aerial photographs to identify vegetation indicative of wet habitats and applying these as a proxy for soil moisture. These studies indicate that, for the case-study, wet areas are controlled at the landscape scale by a set of broad topographic limits in terms of slope and contributing area. Within these there is considerable scatter, resulting from the interplay of local factors such as: bedrock topography, preferential flow and soil stratification. Lateral root cohesion represents an important source of additional strength which can be included within analytical stability equations to create a threshold dependence on landslide size. Patterns of instability will then depend on the spatial pattern of other influencing factors (e.g. soil strength and pore pressure). At present the limits to available data and our understanding of hillslope hydrology constrain our ability to predict slope instability in environments like the Lake District. Future research might usefully identify landscape scale controls on this predictability.

An increase in the frequency and intensity of storm events is predicted by numerous climate researchers for the north of Europe. Not only this but also landuse change in form of clear-cutting can have an impact on the discharge of rivers and with that on road drainage structures. Extensive societal costs can be the consequences of blockage and underdimensioned structures. Hydrological models are powerful instruments that can be used to assess the future dimension requirements for road drainage structures especially in specifically vulnerable areas. In this thesis the hydrological model MIKE SHE was set up to study the discharge and water level at two pipe bridges and one culvert within the catchment of the river Hakerud in Västra Götaland, Sweden. Three scenarios were considered including a changing climate until 2050 and 2100 and a clear-cut scenario aiming to find out if the current design is sufficient for the future. This model can be used as an example model set-up for similar studies taking the recommendations of the experience gained in this thesis into consideration. For the Swedish Transport Administration further studies on this basis can contribute to decision making on the dimensioning of road drainage structures in the future to ensure a safe and robust infrastructural system.

Thesis (M.ScEng.)--Stellenbosch University, 2001.
ENGLISH ABSTRACT: Historically, urban waterresources have too often been managed without recognition that the flow in a river integrates many landscape and biological features. This has often resulted in the elimination of natural processes and their replacement by man-made streamlined structures with the effects of increased urbanisation being primarily addressed from an engineering and economics point of view to the detriment of environmental and social issues. Catchment Management, as legislated in the Water Act, No. 36 of 1998, is a management approach to address the negative consequences of an urban stormwater design philosophy restricted to flood restriction. It is a systems approach that integrates engineering and scientific skills, socio-economic concerns, and environmental constraints within a new multidisciplinary decision-making process that recognises the different components of the hydrological and aquatic cycles are linked, and each component is affected by changes in every other component. In order to make effective management decisions, catchment managers require tools to provide reliable information about the performance of alternative arrangements of stormwater management facilities and to quantify the effects of possible management decisions on the water environment. A deterministic hydrological model is such a tool, which provides the link between the conceptual understanding of the physical catchment characteristics and the empirical quantification of the hydrological, water quality and ecological response. In order to provide effective computer based decision support, the hydrological model must be part of an integrated software application in which a collection of data manipulation, analysis, modelling and interpretation tools, including GIS, can be efficiently used together to manage a large potion of the overall decision process. This decision support system must have a simple and intuitive user interface able to produce easily interpreted output. It must have powerful graphical presentation capabilities promoting effective communication and be designed to solve ill-structured problems by flexibly combining statistical analysis, models and data. The Great Lotus River canal, situated on the Cape Flats, Cape Town, has been designed and controlled through extensive canalisation and the construction of detention pond facilities to avoid the flooding of urban areas of the catchment. This approach has resulted in these channels becoming stormwater drains, transporting waste and nutrients in dissolved and particulate forms, and reducing their assimilatory capacity for water quality improvement. In order to investigate the use of hydrological modelling in decision support for Catchment Management, the semi-distributed, physically based model, SWMM, was applied to the Great Lotus River canal. SWMM consists of a number of independent modules allowing the hydrological and hydraulic simulations of urban catchments and their conveyance networks on an event or continuous basis. In order to ease the application of the Fortran based SWMM model, the GUl, PCSWMM98, was developed by Computational Hydraulics Inc (CH!). This provides decision support for SWMM through large array of tools for file management, data file creation, output visualisation and interpretation, model calibration and error analysis and storm dynamic analysis thus easing any simulations with SWMM. In addition, PCSWMM was developed with a GIS functionality for graphically creating, editing and/or querying SWMM model entities and attributes, displaying these SWMM layers with background layers and dynamic model results, and exporting data to SWMM input files thus providing an interface between a GIS and SWMM. In terms of Catchment Management, the above DSS can be used effectively to assist decisionmaking. This is to address tensions between the fundamental catchment management considerations of physical development, social considerations and maintaining ecological sustainability. It is at the stages of Assessment and Planning that the model can play the most significant role in providing decision support to the Catchment Management process. Assessment in the Catchment Management process refers to the collection, storage, modelling and interpretation of catchment information. It is in this quantification, interpretation and assessment of catchment information that a hydrological model contributes to an increase in knowledge in the Catchment Management process. In identifying and quantifying, at a sufficient temporal and spatial scale, the dominant cause and effect relationships in the urban physical environment, a hydrological model is able to highlight the main contributing factors to an issue. This is used in the Planning stage of the Catchment Management process and when combining these contributing factors with assessments of the socio-economic and administrative environments, enables the prioritisation of the principal issues requiring attention in a Catchment Management Strategy. It is possible to link the multiple decision-making requirements of Catchment Management with the abilities of a hydrological model to provide information on these requirements in a conceptual framework. This framework consists of the fundamental catchment considerations of Physical Development, Environmental Management and Social Development and resolves these considerations into the various management issues associated with each consideration ~s well as its management solution. The management solutions are linked to the model through formulating the solution in terms of the model parameters and perturbing the affected parameters in ways to simulate the management solution. This results in model output and graphical interpretation of the effects of the suggested management solution. A comparison between the simulated effects of each management solution allows the Catchment Management body to identify optimal management solutions for the various management Issues. The present model of the Great Lotus River catchment is sufficient to simulate the overland and subsurface flows from individual parts of the catchment and to route these flows and associated pollutant loadings to the catchment outlet. At its present level of complexity, the finely discretised model subcatchment and conveyance network provides decision support for Catchment Management through the simulation, at a pre-feasibility stage, of various Catchment Management issues and their proposed solutions. Given more detailed canal and drainage network dimensions and water quality data, it is possible for the model to incorporate hydraulic calculation routines to assess the implications of alternative river rehabilitation techniques and waste management strategies. This would allow greater capability in assessing the role of the various BMPs in ameliorating stormwater impacts and pollutant loading. In addition, a detailed level survey of the stormwater pipe and canal network could result in hydrological modelling being utilised to identify critical areas where stormwater upgrading would be necessary. In order to facilitate future complex, finely discretised catchment hydrological models, it is imperative that complete and detailed drainage patterns and stormwater network characteristics are available. In addition, to minimise model generation costs and time of model setup, this spatially representative data must be captured in a GIS for rapid inclusion into the model. Furthermore, complete spatially representative precipitation datasets are necessary to ensure that model error is reduced. These two issues of available spatial data and comprehensive precipitation records are crucial for the generated models to function as effective decision support systems for Catchment Management.
AFRIKAANSE OPSOMMING: Histories is stedelike waterbronne te dikwels bestuur sonder inagneming dat die vloei van die rivier baie landskap- en biologiese kenmerke insluit. Dit het dikwels daartoe gelei dat natuurlike prosesse uitgeskakel is en vervang is deur mensgemaakte, stroombelynde strukture waarvan die effek van toenemende verstedeliking hoofsaaklik aangespreek word vanuit 'n ingenieurs- en ekonomiese oogpunt tot nadeel van omgewings- en sosiale kwessies. Opvangsgebiedsbestuur, soos bepaal deur die Waterwet, Wet 36 van 1998, is 'n bestuursbenadering om die negatiewe gevolge van 'n stedelike stormwaterontwerpfilosofie wat beperk is tot vloedbeperking aan te spreek. Dit is 'n stelselbenadering wat ingenieurs- en wetenskaplike vaardighede, sosio-ekonomiese probleme en omgewingsbeperkings integreer in 'n nuwe multidissiplinêre besluitnemingsproses wat erkenning daaraan gee dat die verskillende komponente van die hidrologiese en watersiklusse verbind is, en elke komponent beïnvloed word deur veranderings in elke ander komponent. Om doeltreffende bestuursbesluite te neem, benodig opvangsgebiedsbestuur die hulpmiddels om betroubare inligting oor die prestasie van alternatiewe moontlikhede VIr stormwaterbestuurfasiliteite en om die effek van moontlike bestuursbesluite op die wateromgewing te kwantifiseer. 'n Deterministiese hidrologiese model is so 'n hulpmiddel wat die skakel daarstel tussen die konseptueie begrip van die fisiese opvangsgebiedskenmerke en die empiriese kwantifisering van die water-, waterkwaliteit- en ekologiese reaksie. Om doeltreffende rekenaarbesluitnemingsteun te verskaf, moet die hidrologiese model deel wees van 'n geïntegreerde sagteware-aanwending waarin 'n versameling datamanipulasie-, analise-, modellerings- en interpreteringshulpmiddels, insluitend GIS, doeltreffend saam gebruik kan word om 'n groot deel van die algehele besluitnemingsproses te bestuur. Hierdie besluitnemingsteunstelsel moet 'n eenvoudige en intuïtiewe gebruikersvlak hê wat in staat is om maklik interpreteerbare uitsette te lewer. Dit moet goeie grafiese voorleggingsvermoëns hê wat doeltreffende kommunikasie vergemaklik en ontwerp wees om swak gestruktureerde probleme deur die buigsame samevoeging van statistiese analise, modelle en data op te los. Die Groot Lotusrivierkanaal op die Kaapse Vlakte, Kaapstad is ontwerp en word beheer deur uitgebreide kanalisasie en die konstruksie van detensiedamfasiliteite om die oorstroming van stedelike opvangsgebiede te vermy. Hierdie benadering het daartoe gelei dat hierdie kanale stormwaterafvoerpype geword het wat afval en nutriënte in opgelosde en partikelvorm vervoer en hulle assimilasievermoë vir die verbetering van waterkwaliteit verminder. Om die gebruik van hidrologiese modelle in besluitnemingsteun vir Opvangsgebiedsbestuur te ondersoek, is die semi-verspreide, fisiesgebaseerde model, SWMM, op die Groot Lotusrivierkanaal toegepas. SWMM bestaan uit 'n aantalonafhanklike modules wat die hidrologiese en hidroulika simulasies van stedelike opvangsgebiede en hulle vervoemetwerke per geleentheid of deurlopend monitor. Om die aanwending van die Fortran gebaseerde SWMM model te vergemaklik is die GUl, PCSWMM98 deur Computational Hydraulics Inc (CHD ontwikkel. Dit verskaf besluitnemingsteun vir SWMM deur 'n groot aantal hulpmiddels vir lêerbestuur, die skep van datalêers, uitsetvisualisering en interpretasie, modelkalibrasie, foutanalise en stormdinamikaanalise om enige simulasies met SWMM te vergemaklik. Daarby is PCSWMM ontwikkel met 'n GIS funksionaliteit vir die grafiese daarstelling, redigering en/of navraagfunksie van SWMM model entiteite en kenmerke, wat hierdie SWMM vlakke met agtergrondvlakke en dinamiese modelresultate vertoon en data in SWMM inset1êers plaas en op daardie manier 'n koppelvlak tussen 'n GIS en SWMM verskaf. Volgens Opvangsgebiedsbestuur kan bogenoemde DSS doeltreffend gebruik word in besluitneming. Dit IS om die spanning tussen fundamentele opvangsgebiedsbestuursoorwegings van fisiese ontwikkeling, sosiale oorwegings en ekologiese volhoubaarheid aan te spreek. Dis in die stadiums van Waardebepaling en Beplanning wat die model die belangrikste rol kan vervul in die verskaffing van besluitnemingsteun vir die Opvangsgebiedsbestuursproses. Waardebepaling in die Opvangsgebiedbestuursproses verwys na die versameling, berging, modellering en interpretasie van opvangsgebiedsinligting. Deur hierdie kwantifisering, interpretasie en waardebepaling van opvangsgebiedsinligting dra 'n hidrologiese model by tot 'n verhoging in kennis in die Opvangsgebiedsbestuur. Deur die identifisering en kwantifisering, op 'n ruim genoeg tydelike en ruimtelike skaal, van die dominante oorsaak en gevolg verhoudings in die stedelike fisiese omgewing, kan die hidrologiese model die hoof bydraende faktore uitlig. Dit word gebruik in die Beplanningsfase van die Opvangsgebiedproses en wanneer hierdie bydraende faktore by die waardebepaling van die sosio-ekonomiese en administratiewe omgewings saamgevoeg word, maak dit moontlik om die belangrike kwessies wat aandag behoort te kry in 'n Opvangsgebiedsbestuurstrategie in volgorde van voorrang te plaas. Dit is moontlik om die verskeidenheid besluitnemingsvereistes van Opvangsgebiedsbestuur met die vermoëns van 'n hidrologiese model te koppel om inligting oor hierdie vereistes in 'n konseptuele raamwerk te verskaf. Die raamwerk bestaan uit die fundamentele opvangsgebiedsoorwegings van Fisiese Ontwikkeling, Omgewingsbestuur en Sosiale Ontwikkeling en los hierdie oorwegings op in die verskillende bestuursaangeleenthede wat met elke oorweging en die bestuuroplossing geassosieer word. Die bestuursoplossings word aan die model gekoppel deur die formulering van die oplossing volgens die modelparameters en versteuring van die relevante parameters op sekere manier om die bestuursoplossing te simuleer. Dit lei tot modeluitset en grafiese interpretasie van die effek van die voorgestelde bestuursoplossing. 'n Vergelyking tussen die gesimuleerde effek van elke bestuursoplossing laat die Opvangsgebiedsbestuursliggaam toe om die optimale bestuursoplossings vir die verskeie bestuursaangeleenthede te identifiseer. Die huidige model van die Groot Lotusrivieropvang is genoegsaam om die bo- en ondergrondse vloei vanaf individuele dele van die opvangsgebied te simuleer en om die watervloei en geassosieerde besoedelstofladings na die opvangsgebiedsuitlaatplek te lei. Op sy huidige vlak van kompleksiteit verskaf die fyn gediskretiseerde model subopvangsgebied en vervoernetwerk besluitnemingsteun aan Opvangsgebiedsbestuur deur die simulasie, teen 'n voor-lewensvatbaarheidstudie, van verskeie opvangsgebiedsbestuurkwessies en die voorgestelde oplossings. Indien meer gedetailleerde kanaal- en dreineringsnetwerkdimensies- en waterkwaliteitdata ingevoer word, is dit moontlik vir die model om hidroulikaberekeningsroetines te inkorporeer om die implikasies van alternatiewe rivierrehabilitasietegnieke en afvalbestuurstrategieë te beoordeel. Dit sou die vermoë verbeter om die waarde van die verskeie BMPs te bepaal om die impak van stormwater en besoedelstoflading te versag. Daarby kan 'n gedetailleerde vlakopname van die stormwaterpyp en -kanaalnetwerk daartoe lei dat hidrologiese modelle gebruik kan word om kritieke areas te identifiseer waar stormwateropgradering nodig is. Om toekomstige komplekse, gediskretiseerde opvangsgebiedshidrologiese modelle te verbeter, is dit noodsaaklik dat volledige en gedetailleerde dreineringspatrone en stormwaternetwerkkenmerke beskikbaar is. Om die model-ontwikkelingskoste en tyd bestee aan die opstel van 'n model te minimiseer, moet hierdie ruimtelik verteenwoordigende data ingelees word in 'n GIS vir vinnige insluiting in die model. Daarbenewens is volledige, ruimtelik verteenwoordigende presipitasie datastelle nodig om te verseker dat modelfoute verminder word. Hierdie twee kwessies van beskikbare ruimtelike data en omvattende presipitasierekords is van die uiterste belang sodat die gegenereerde modelle as doeltreffende besluitnemingsteun vir Opvangsgebiedsbestuur kan funksioneer.

Hydrological models are a simplified representation of hydrological processes and can be very used for the water resources assessment and gain an integral view of the water resources status for integrated water resources management IWRM. Furthermore, they can be used to investigate the possible impacts and trends resulting from different types of scenarios, such as climate change impact studies. Accordingly, with IWRM as the future application, the primary objectives of this study is to use a hydrological model, SWAT for the modelling of a highly-regulated river basin through the physical flow control (reservoirs release in the upstream region), the Dee River Watershed in the United Kingdom. Moreover, an essential aspect of model input uncertainty, i.e. precipitation is investigated on the simulated streamflow where different methods of rainfall pre-processing are used. Furthermore, a quantile regression method is employed for analysing the long-term historical trend of rainfall, river flow and catchment water yields focusing on the patterns of the data close to 'extreme' regimes, to link them to the events of interests for the climate change impact studies. Additionally, a reliable simulation of both land surface and groundwater hydrological processes is a far important step for IWRM. One way to achieve such purpose is the coupling of surface and groundwater models. The land surface model (SWAT) is coupled with the groundwater flow model (MODFLOW) to improve the baseflow simulation of the SWAT standalone in the study area. Another critical aspect of this study is the investigation of parameter uncertainty of the coupled SWAT-MODFLOW. Finally, the climate projection data from the CMIP5 project is utilised with allocation model, Water Evaluation and Planning software WEAP to address climate change impact for future scenarios on water resources. All presented models performed well in demonstrating the study conditions, as indicated by the statistical performance. The research approach of the integrated models can generally apply to any catchment and inspired by the need of considering all aspects related to hydrological models for IWRM to bridge the gap of between stakeholder involvement and natural hydrological processes in building and applying integrated models to ensure acceptability and application in decision-making for IWRM.

The world is undergoing rapid changes and the future is uncertain. The changes are related to modification of the landscape due to human activities, such as large and small scale irrigation, afforestation and changes to the climate system. Understanding and predicting hydrologic change is one of the challenges facing hydrologists today. Part of this understanding can be developed from observed data, however, there often too few observations and those that are available are frequently affected by uncertainties. Hydrological models have become essential tools for understanding historical variations of catchment hydrology and for predicting future possible trends. However, most developing countries are faced with poor spatial distributions of rainfall and evaporation stations that provide the data used to force models, as well as stream flow gauging stations to provide the data for establishing models and for evaluating their success. Hydrological models are faced with a number of challenges which include poor input data (data quality and poorly quantified human activities on observed stream flow data), uncertainties associated with model complexity and structure, the methods used to quantify model parameters, together with the difficulties of understanding hydrological processes at the catchment or subbasin. Within hydrological modelling, there is currently a trend of dealing with equifinality through the evaluation of parameter identifiability and the quantification of uncertainty bands associated with the predictions of the model. Hydrological models should not only focus on reproducing the past behaviour of a basin, but also on evaluating the representativeness of the surface and subsurface model components and their ability to simulate reality for the correct reasons. Part of this modelling process therefore involves quantifying and including all the possible sources of uncertainty. Uncertainty analysis has become the standard approach to most hydrological modelling studies, but has yet to be effectively used in practical water resources assessment. This study applied a hydrological modelling approach for understanding the hydrology of a large Tanzanian drainage basin, the Great Ruaha River that has many areas that are ungauged and where the available data (climate, stream flow and existing water use) are subject to varying degrees of uncertainty. The Great Ruaha River (GRR) is an upstream tributary of the Rufiji River Basin within Tanzania and covers an area of 86 000 km2. The basin is drained by four main tributaries; the Upper Great Ruaha, the Kisigo, the Little Ruaha and the Lukosi. The majority of the runoff is generated from the Chunya escarpment, the Kipengere ranges and the Poroto Mountains. The runoff generated feeds the alluvial and seasonally flooded Usangu plains (including the Ihefu perennial swamp). The majority of the irrigation water use in the basin is located where headwater sub‐basins drain towards the Usangu plains. The overall objective was to establish uncertain but behavioural hydrological models that could be useful for future water resources assessments that are likely to include issues of land use change, changes in patterns of abstraction and water use, as well the possibility of change in future climates.

Semi-arid areas are, due to their climatic setting, characterized by small water resources. An increasing water demand as a consequence of population growth and economic development as well as a decreasing water availability in the course of possible climate change may aggravate water scarcity in future, which often exists already for present-day conditions in these areas. Understanding the mechanisms and feedbacks of complex natural and human systems, together with the quantitative assessment of future changes in volume, timing and quality of water resources are a prerequisite for the development of sustainable measures of water management to enhance the adaptive capacity of these regions. For this task, dynamic integrated models, containing a hydrological model as one component, are indispensable tools.
The main objective of this study is to develop a hydrological model for the quantification of water availability in view of environmental change over a large geographic domain of semi-arid environments.
The study area is the Federal State of Ceará (150 000 km2) in the semi-arid north-east of Brazil. Mean annual precipitation in this area is 850 mm, falling in a rainy season with duration of about five months. Being mainly characterized by crystalline bedrock and shallow soils, surface water provides the largest part of the water supply. The area has recurrently been affected by droughts which caused serious economic losses and social impacts like migration from the rural regions.
The hydrological model Wasa (Model of Water Availability in Semi-Arid Environments) developed in this study is a deterministic, spatially distributed model being composed of conceptual, process-based approaches. Water availability (river discharge, storage volumes in reservoirs, soil moisture) is determined with daily resolution. Sub-basins, grid cells or administrative units (municipalities) can be chosen as spatial target units. The administrative units enable the coupling of Wasa in the framework of an integrated model which contains modules that do not work on the basis of natural spatial units.
The target units mentioned above are disaggregated in Wasa into smaller modelling units within a new multi-scale, hierarchical approach. The landscape units defined in this scheme capture in particular the effect of structured variability of terrain, soil and vegetation characteristics along toposequences on soil moisture and runoff generation. Lateral hydrological processes at the hillslope scale, as reinfiltration of surface runoff, being of particular importance in semi-arid environments, can thus be represented also within the large-scale model in a simplified form. Depending on the resolution of available data, small-scale variability is not represented explicitly with geographic reference in Wasa, but by the distribution of sub-scale units and by statistical transition frequencies for lateral fluxes between these units.
Further model components of Wasa which respect specific features of semi-arid hydrology are:
(1) A two-layer model for evapotranspiration comprises energy transfer at the soil surface (including soil evaporation), which is of importance in view of the mainly sparse vegetation cover. Additionally, vegetation parameters are differentiated in space and time in dependence on the occurrence of the rainy season.
(2) The infiltration module represents in particular infiltration-excess surface runoff as the dominant runoff component.
(3) For the aggregate description of the water balance of reservoirs that cannot be represented explicitly in the model, a storage approach respecting different reservoirs size classes and their interaction via the river network is applied.
(4) A model for the quantification of water withdrawal by water use in different sectors is coupled to Wasa.
(5) A cascade model for the temporal disaggregation of precipitation time series, adapted to the specific characteristics of tropical convective rainfall, is applied for the generating rainfall time series of higher temporal resolution.
All model parameters of Wasa can be derived from physiographic information of the study area. Thus, model calibration is primarily not required.
Model applications of Wasa for historical time series generally results in a good model performance when comparing the simulation results of river discharge and reservoir storage volumes with observed data for river basins of various sizes. The mean water balance as well as the high interannual and intra-annual variability is reasonably represented by the model. Limitations of the modelling concept are most markedly seen for sub-basins with a runoff component from deep groundwater bodies of which the dynamics cannot be satisfactorily represented without calibration.
Further results of model applications are:
(1) Lateral processes of redistribution of runoff and soil moisture at the hillslope scale, in particular reinfiltration of surface runoff, lead to markedly smaller discharge volumes at the basin scale than the simple sum of runoff of the individual sub-areas. Thus, these processes are to be captured also in large-scale models. The different relevance of these processes for different conditions is demonstrated by a larger percentage decrease of discharge volumes in dry as compared to wet years.
(2) Precipitation characteristics have a major impact on the hydrological response of semi-arid environments. In particular, underestimated rainfall intensities in the rainfall input due to the rough temporal resolution of the model and due to interpolation effects and, consequently, underestimated runoff volumes have to be compensated in the model. A scaling factor in the infiltration module or the use of disaggregated hourly rainfall data show good results in this respect.
The simulation results of Wasa are characterized by large uncertainties. These are, on the one hand, due to uncertainties of the model structure to adequately represent the relevant hydrological processes. On the other hand, they are due to uncertainties of input data and parameters particularly in view of the low data availability. Of major importance is:
(1) The uncertainty of rainfall data with regard to their spatial and temporal pattern has, due to the strong non-linear hydrological response, a large impact on the simulation results.
(2) The uncertainty of soil parameters is in general of larger importance on model uncertainty than uncertainty of vegetation or topographic parameters.
(3) The effect of uncertainty of individual model components or parameters is usually different for years with rainfall volumes being above or below the average, because individual hydrological processes are of different relevance in both cases. Thus, the uncertainty of individual model components or parameters is of different importance for the uncertainty of scenario simulations with increasing or decreasing precipitation trends.
(4) The most important factor of uncertainty for scenarios of water availability in the study area is the uncertainty in the results of global climate models on which the regional climate scenarios are based. Both a marked increase or a decrease in precipitation can be assumed for the given data.
Results of model simulations for climate scenarios until the year 2050 show that a possible future change in precipitation volumes causes a larger percentage change in runoff volumes by a factor of two to three. In the case of a decreasing precipitation trend, the efficiency of new reservoirs for securing water availability tends to decrease in the study area because of the interaction of the large number of reservoirs in retaining the overall decreasing runoff volumes.
Semiaride Gebiete sind auf Grund der klimatischen Bedingungen durch geringe Wasserressourcen gekennzeichnet. Ein zukünftig steigender Wasserbedarf in Folge von Bevölkerungswachstum und ökonomischer Entwicklung sowie eine geringere Wasserverfügbarkeit durch mögliche Klimaänderungen können dort zu einer Verschärfung der vielfach schon heute auftretenden Wasserknappheit führen. Das Verständnis der Mechanismen und Wechselwirkungen des komplexen Systems von Mensch und Umwelt sowie die quantitative Bestimmung zukünftiger Veränderungen in der Menge, der zeitlichen Verteilung und der Qualität von Wasserressourcen sind eine grundlegende Voraussetzung für die Entwicklung von nachhaltigen Maßnahmen des Wassermanagements mit dem Ziel einer höheren Anpassungsfähigkeit dieser Regionen gegenüber künftigen Änderungen. Hierzu sind dynamische integrierte Modelle unerlässlich, die als eine Komponente ein hydrologisches Modell beinhalten.
Vorrangiges Ziel dieser Arbeit ist daher die Erstellung eines hydrologischen Modells zur großräumigen Bestimmung der Wasserverfügbarkeit unter sich ändernden Umweltbedingungen in semiariden Gebieten.
Als Untersuchungsraum dient der im semiariden tropischen Nordosten Brasiliens gelegene Bundestaat Ceará (150 000 km2). Die mittleren Jahresniederschläge in diesem Gebiet liegen bei 850 mm innerhalb einer etwa fünfmonatigen Regenzeit. Mit vorwiegend kristallinem Grundgebirge und geringmächtigen Böden stellt Oberflächenwasser den größten Teil der Wasserversorgung bereit. Die Region war wiederholt von Dürren betroffen, die zu schweren ökonomischen Schäden und sozialen Folgen wie Migration aus den ländlichen Gebieten geführt haben.
Das hier entwickelte hydrologische Modell Wasa (Model of Water Availability in Semi-Arid Environments) ist ein deterministisches, flächendifferenziertes Modell, das aus konzeptionellen, prozess-basierten Ansätzen aufgebaut ist. Die Wasserverfügbarkeit (Abfluss im Gewässernetz, Speicherung in Stauseen, Bodenfeuchte) wird mit täglicher Auflösung bestimmt. Als räumliche Zieleinheiten können Teileinzugsgebiete, Rasterzellen oder administrative Einheiten (Gemeinden) gewählt werden. Letztere ermöglichen die Kopplung des Modells im Rahmen der integrierten Modellierung mit Modulen, die nicht auf der Basis natürlicher Raumeinheiten arbeiten.
Im Rahmen eines neuen skalenübergreifenden, hierarchischen Ansatzes werden in Wasa die genannten Zieleinheiten in kleinere räumliche Modellierungseinheiten unterteilt. Die ausgewiesenen Landschaftseinheiten erfassen insbesondere die strukturierte Variabilität von Gelände-, Boden- und Vegetationseigenschaften entlang von Toposequenzen in ihrem Einfluss auf Bodenfeuchte und Abflussbildung. Laterale hydrologische Prozesse auf kleiner Skala, wie die für semiaride Bedingungen bedeutsame Wiederversickerung von Oberflächenabfluss, können somit auch in der erforderlichen großskaligen Modellanwendung vereinfacht wiedergegeben werden. In Abhängigkeit von der Auflösung der verfügbaren Daten wird in Wasa die kleinskalige Variabilität nicht räumlich explizit sondern über die Verteilung von Flächenanteilen subskaliger Einheiten und über statistische Übergangshäufigkeiten für laterale Flüsse zwischen den Einheiten berücksichtigt.
Weitere Modellkomponenten von Wasa, die spezifische Bedingungen semiarider Gebiete berücksichtigen, sind:
(1) Ein Zwei-Schichten-Modell zur Bestimmung der Evapotranspiration berücksichtigt auch den Energieumsatz an der Bodenoberfläche (inklusive Bodenverdunstung), der in Anbetracht der meist lichten Vegetationsbedeckung von Bedeutung ist. Die Vegetationsparameter werden zudem flächen- und zeitdifferenziert in Abhängigkeit vom Auftreten der Regenzeit modifiziert.
(2) Das Infiltrationsmodul bildet insbesondere Oberflächenabfluss durch Infiltrationsüberschuss als dominierender Abflusskomponente ab.
(3) Zur aggregierten Beschreibung der Wasserbilanz von im Modell nicht einzeln erfassbaren Stauseen wird ein Speichermodell unter Berücksichtigung verschiedener Größenklassen und ihrer Interaktion über das Gewässernetz eingesetzt.
(4) Ein Modell zur Bestimmung der Entnahme durch Wassernutzung in verschiedenen Sektoren ist an Wasa gekoppelt.
(5) Ein Kaskadenmodell zur zeitlichen Disaggregierung von Niederschlagszeitreihen, das in dieser Arbeit speziell für tropische konvektive Niederschlagseigenschaften angepasst wird, wird zur Erzeugung höher aufgelöster Niederschlagsdaten verwendet.
Alle Modellparameter von Wasa können von physiographischen Gebietsinformationen abgeleitet werden, sodass eine Modellkalibrierung primär nicht erforderlich ist.
Die Modellanwendung von Wasa für historische Zeitreihen ergibt im Allgemeinen eine gute Übereinstimmung der Simulationsergebnisse für Abfluss und Stauseespeichervolumen mit Beobachtungsdaten in unterschiedlich großen Einzugsgebieten. Die mittlere Wasserbilanz sowie die hohe monatliche und jährliche Variabilität wird vom Modell angemessen wiedergegeben. Die Grenzen der Anwendbarkeit des Modell-konzepts zeigen sich am deutlichsten in Teilgebieten mit Abflusskomponenten aus tieferen Grundwasserleitern, deren Dynamik ohne Kalibrierung nicht zufriedenstellend abgebildet werden kann.
Die Modellanwendungen zeigen weiterhin:
(1) Laterale Prozesse der Umverteilung von Bodenfeuchte und Abfluss auf der Hangskala, vor allem die Wiederversickerung von Oberflächenabfluss, führen auf der Skala von Einzugsgebieten zu deutlich kleineren Abflussvolumen als die einfache Summe der Abflüsse der Teilflächen. Diese Prozesse sollten daher auch in großskaligen Modellen abgebildet werden. Die unterschiedliche Ausprägung dieser Prozesse für unterschiedliche Bedingungen zeigt sich an Hand einer prozentual größeren Verringerung der Abflussvolumen in trockenen im Vergleich zu feuchten Jahren.
(2) Die Niederschlagseigenschaften haben einen sehr großen Einfluss auf die hydrologische Reaktion in semiariden Gebieten. Insbesondere die durch die grobe zeitliche Auflösung des Modells und durch Interpolationseffekte unterschätzten Niederschlagsintensitäten in den Eingangsdaten und die daraus folgende Unterschätzung von Abflussvolumen müssen im Modell kompensiert werden. Ein Skalierungsfaktor in der Infiltrationsroutine oder die Verwendung disaggregierter stündlicher Niederschlagsdaten zeigen hier gute Ergebnisse.
Die Simulationsergebnisse mit Wasa sind insgesamt durch große Unsicherheiten gekennzeichnet. Diese sind einerseits in Unsicherheiten der Modellstruktur zur adäquaten Beschreibung der relevanten hydrologischen Prozesse begründet, andererseits in Daten- und Parametersunsicherheiten in Anbetracht der geringen Datenverfügbarkeit. Von besonderer Bedeutung ist:
(1) Die Unsicherheit der Niederschlagsdaten in ihrem räumlichen Muster und ihrer zeitlichen Struktur hat wegen der stark nicht-linearen hydrologischen Reaktion einen großen Einfluss auf die Simulationsergebnisse.
(2) Die Unsicherheit von Bodenparametern hat im Vergleich zu Vegetationsparametern und topographischen Parametern im Allgemeinen einen größeren Einfluss auf die Modellunsicherheit.
(3) Der Effekt der Unsicherheit einzelner Modellkomponenten und -parameter ist für Jahre mit unter- oder überdurchschnittlichen Niederschlagsvolumen zumeist unterschiedlich, da einzelne hydrologische Prozesse dann jeweils unterschiedlich relevant sind. Die Unsicherheit einzelner Modellkomponenten- und parameter hat somit eine unterschiedliche Bedeutung für die Unsicherheit von Szenarienrechnungen mit steigenden oder fallenden Niederschlagstrends.
(4) Der bedeutendste Unsicherheitsfaktor für Szenarien der Wasserverfügbarkeit für die Untersuchungsregion ist die Unsicherheit der den regionalen Klimaszenarien zu Grunde liegenden Ergebnisse globaler Klimamodelle. Eine deutliche Zunahme oder Abnahme der Niederschläge bis 2050 kann gemäß den hier vorliegenden Daten für das Untersuchungsgebiet gleichermaßen angenommen werden.
Modellsimulationen für Klimaszenarien bis zum Jahr 2050 ergeben, dass eine mögliche zukünftige Veränderung der Niederschlagsmengen zu einer prozentual zwei- bis dreifach größeren Veränderung der Abflussvolumen führt. Im Falle eines Trends von abnehmenden Niederschlagsmengen besteht in der Untersuchungsregion die Tendenz, dass auf Grund der gegenseitigen Beeinflussung der großen Zahl von Stauseen beim Rückhalt der tendenziell abnehmenden Abflussvolumen die Effizienz von neugebauten Stauseen zur Sicherung der Wasserverfügbarkeit zunehmend geringer wird.

Sustainability of water resources is imperative for the continued prosperity of Sri Lanka where the economy is dependent upon agriculture. The Mahaweli river is the longest in Sri Lanka, with the upper catchment covering an area of 3124 sq km. The Mahaweli Development programme, a major undertaking in the upper catchment has been implemented with the aims of providing Mahaweli water to the dry zone of the country through a massive diversion scheme and also for generating hydropower. Under this programme, seven large reservoirs have been constructed across the river and large scale land use changes in the catchment have occurred during the last two decades. Critics now say that the hydrological regime has been adversely affected due to indiscriminate land use changes and, as a result, river flows have diminished during the last two decades, thus jeopardising the expectations of this massive development programme. Reforestation programmes have been recommended because of the benefits of forest in resource conservation and also the water derived from fog interception. Selection of the best sites for these forest plantations for maximum benefits, especially in terms of water yield from fog interception has the utmost importance. This created the need for a comprehensive model to represent the hydrology and to simulate the hydrological dynamics of the catchment In conceptual terms, GIS is well suited for modelling with large and complex databases associated with hydrological parameters. However, hydrological modelling efforts in GIS are constrained by the limitations in the representation of time in its spatial data ,structures. The SPANS GIS software used in this study provided the capability of linking spatially distributed numerical parameters with corresponding tabulated data through mathematical and statistical expressions while implicitly representing temporality through iterative procedures.The spatial distribution of land use was identified through the supervised classification of IRS-IA LISS II imagery. Daily rainfall data for a 30 year period and corresponding gauging locations derived from GPS were managed and retrieved through a Lotus 1-2- 3 database. The fog interception component was estimated based on elevation and the monsoon season. Hydrological processes such as interception and evapotranspiration were derived from individual sub models and finally combined within the overall hydrological model structure. The model was run with daily time steps on numerical 'values of each quad cell of the thematic coverage. The information on flow derived from the model was depicted as a series of thematic maps in addition to the time series of numerical values at subcatchment and catchment outlets. The results confirmed that the model is capable of simulating catchment response of the UMCA successfully. The time dimension was accommodated through a senes of non-interactive REXX programmes in developing the customised version of the model. It is concluded that the software architecture of SPANS GIS is capable of accommodating spatiotemporal modelling implicitly in its spatial data structures although changes in the model structure may necessitate considerable reprogramming. Sensitivity of the model for different spatial interpolation techniques was evaluated. Further, sensitivity of the model for the defined hydrological parameters, spatial 'resolution and land use was also assessed. The model is sensitive to land use changes in the catchment and it shows 15-35% annual increase of runoff when forests are converted to grassland. Further studies are required to develop a more detailed set of hydrological parameters for the model.

Doutoramento em Ciências e Engenharia do Ambiente
Forest fires implications in overland flow and soil erosion have been researched for several years. Therefore, is widely known that fires enhance hydrological and geomorphological activity worldwide as also in Mediterranean areas. Soil burn severity has been widely used to describe the impacts of fire on soils, and has being recognized as a decisive factor controlling post-fire erosion rates. However, there is no unique definition of the term and the relationship between soil burn severity and post-fire hydrological and erosion response has not yet been fully established. Few studies have assessed post-fire erosion over multiple years, and the authors are aware of none which assess runoff. Small amount of studies concerning pre-fire management practices were also found. In the case of soil erosion models, the Revised Universal Soil Loss Equation (RUSLE) and the revised Morgan–Morgan–Finney (MMF) are well-known models, but not much information is available as regards their suitability in predicting post-fire soil erosion in forest soils. The lack of information is even more pronounced as regards post-fire rehabilitation treatments. The aim of the thesis was to perform an extensive research under the post fire hydrologic and erosive response subject. By understanding the effect of burn severity in ecosystems and its implications regarding post fire hydrological and erosive responses worldwide. Test the effect of different pre-fire land management practices (unplowed, downslope plowed and contour plowed) and time-since-fire, in the post fire hydrological and erosive response, between the two most common land uses in Portugal (pine and eucalypt). Assess the performance of two widely-known erosion models (RUSLE and Revised MMF), to predict soil erosion rates during first year following two wildfires of distinctive burn severity. Furthermore, to apply these two models considering different post-fire rehabilitation treatments in an area severely affected by fire. Improve model estimations of post-fire runoff and erosion rates in two different land uses (pine and eucalypt) using the revised MMF. To assess these improvements by comparing estimations and measurements of runoff and erosion, in two recently burned sites, as also with their post fire rehabilitation treatments. Model modifications involved: (1) focusing on intra-annual changes in parameters to incorporate seasonal differences in runoff and erosion; and (2) inclusion of soil water repellency in runoff predictions. Additionally, validate these improvements with the application of the model to other pine and eucalypt sites in Central Portugal. The review and meta-analysis showed that fire occurrence had a significant effect on the hydrological and erosive response. However, this effect was only significantly higher with increasing soil burn severity for inter-rill erosion, and not for runoff. This study furthermore highlighted the incoherencies between existing burn severity classifications, and proposed an unambiguous classification. In the case of the erosion plots with natural rainfall, land use factor affected annual runoff while land management affected both annual runoff and erosion amounts significantly. Time-since-fire had an important effect in erosion amounts among unplowed sites, while for eucalypt sites time affected both annual runoff and erosion amounts. At all studied sites runoff coefficients increase over the four years of monitoring. In the other hand, sediment concentration in the runoff, recorded a decrease during the same period. Reasons for divergence from the classic post-fire recovery model were also explored. Short fire recurrence intervals and forest management practices are viewed as the main reasons for the observed severe and continuing soil degradation. The revised MMF model presented reasonable accuracy in the predictions while the RUSLE clearly overestimated the observed erosion rates. After improvements: the revised model was able to predict first-year post-fire plot-scale runoff and erosion rates for both forest types, these predictions were improved both by the seasonal changes in the model parameters; and by considering the effect of soil water repellency on the runoff, individual seasonal predictions were considered accurate, and the inclusion of the soil water repellency in the model also improved the model at this base. The revised MMF model proved capable of providing a simple set of criteria for management decisions about runoff and erosion mitigation measures in burned areas. The erosion predictions at the validation sites attested both to the robustness of the model and of the calibration parameters, suggesting a potential wider application.
As implicações dos fogos florestais na escorrência superficial e erosão dos solos têm sido objeto de estudo desde há vários anos. Como tal, é do conhecimento geral, que os fogos tendem a aumentar a atividade hidrológica e geomorfológica em todo o mundo e também nas zonas mediterrânicas. A severidade da queima do solo tem sido utilizada para descrever o impacto dos fogos nos solos e reconhecida como um fator decisivo no controle das taxas de erosão pós-fogo. No entanto, não existe uma definição única do termo e a relação entre severidade de queima do solo com a resposta hidrológica e erosiva não é ainda totalmente conhecida. Por outro lado, escasseiam os estudos com registos de taxas de erosão pós-fogo durante um período de quatro anos, nenhum dentro desse período com registos de escorrência superficial pós-fogo. Menos estudos ainda, que retratem a resposta erosiva pós-fogo, mencionando práticas de gestão florestal anteriores ao mesmo. No caso da modelação de erosão dos solos, apesar dos modelos aplicados ‒ a Equação Universal de Perdas do Solo Revista (RUSLE) e o modelo de Morgan-Morgan-Finney (MMF) ‒ serem bem conhecidos, a informação referente à sua aplicabilidade para prever taxas de erosão em solos florestais após o fogo é bastante limitada. No caso da aplicabilidade destes modelos, considerando tratamentos de mitigação após incêndio, ainda menos informação existe. O objetivo deste trabalho é o aprofundar do conhecimento relativo à resposta hidrológica e erosiva após incêndios florestais através do estudo dos efeitos da severidade de queima nos ecossistemas e das suas implicações na resposta hidrológica e erosiva em todo o mundo. Para este fim, testámos também o efeito de diferentes práticas de gestão florestal (não lavrado, lavrado no sentido do declive e lavrado segundo as curvas de nível), executadas previamente ao incêndio florestal, entre dois dos usos do solo mais comuns em Portugal: o pinheiro e o eucalipto. Testámos ainda a eficiência com que dois modelos, amplamente conhecidos (RUSLE e MMF revisto), conseguem prever, em duas severidades distintas e com tratamentos de reabilitação pós fogo, as taxas de erosão durante o ano que seguiu ao incêndio florestal. Com essa informação, que veio melhorar as estimativas, alterámos o modelo e verificámos a sua eficiência, tanto nas previsões de escorrência superficial como na erosão do solo em pós-fogo e em pós-fogo com tratamentos de reabilitação. Essas alterações, que consistiam em (1) passar todos os inputs numa escala sazonal para incorporar as variações sazonais sentidas na formação de escorrência superficial e erosão do solo, e (2) inclusão do efeito hidrófobo do solo à água nas previsões da escorrência superficial. Adicionalmente, validar estas melhorias noutra área florestal independente no centro de Portugal para pinhal e eucaliptal, pós-fogo e pós-fogo com tratamentos de reabilitação. A revisão e a meta-análise demonstraram que a ocorrência de um fogo florestal provoca alterações significativas na resposta hidrológica e erosiva. No entanto, este efeito só é significativamente diferente com o aumento da severidade da queima do solo para a erosão e não para a geração de escorrência superficial. Este estudo também aludiu a incoerência entre várias classificações de severidade de queima e propõe ainda uma classificação não ambígua. No caso das parcelas de erosão com chuva natural, verificou-se que o uso do solo é um fator que afeta a geração de escorrência; em contrapartida, a gestão florestal afeta tanto a escorrência como a erosão do solo. O tempo decorrido desde o incêndio surge como fator de elevada importância entre locais não lavrados, relativamente às perdas de solo, e entre eucaliptais, relativamente à escorrência e erosão. Em todos os locais os coeficientes de escorrência aumentaram do primeiro para o quarto ano de estudo. Noutra nota, notou-se um decréscimo nas concentrações de sedimentos na escorrência durante o mesmo período. Foi explorada a discrepância entre este estudo e entre os modelos clássicos de recuperação pós-fogo; também o curto intervalo entre fogos e as constantes práticas de gestão florestal são vistas como as principais razões pela severa e continuada degradação dos solos. O modelo de MMF revisto apresentou uma razoável acuidade nas previsões enquanto que, o RUSLE claramente sobrestimou as taxas de erosão observadas. Ambos os modelos demonstraram capacidades para serem usados como ferramentas operacionais para ajudarem gestores a determinar áreas de risco de erosão pós-fogo e a tomarem ações prioritárias. O Modelo MMF revisto permitiu determinar as taxas de erosão durante o primeiro ano, após o fogo, para os dois usos do solo estudados: o pinheiro e o eucalipto. Essas previsões melhoraram com a implementação da modelação sazonal e com a inclusão da hidrofobia do solo à água para as previsões de escorrência. Por fim, o modelo de MMF revisto provou ser capaz de providenciar um conjunto de critérios para ajudar à tomada de decisões por parte dos gestores relativamente à escorrência, erosão e tratamentos de mitigação em áreas recentemente ardidas. Este modelo sugere, segundo os resultados obtidos aquando da validação e calibração, uma elevada robustez e um potencial de ser aplicado a outras áreas.