Dissertations / Theses on the topic 'Hydrologic modelling'

The capability of radar measured rainfall to enhance the simulation of storm hydrographs was assessed. Six rainfall events which occurred in 1986 and 1987 over an 8.13 km$ sp2$ agricultural watershed in south-western Quebec were used in model simulations. Radar measured rainfall rates were calibrated using measurements from a single tipping-bucket raingauge located at the study site.
A deterministic, event-based model, HYMO, was used to simulate streamflow using radar and gauge measured rainfall. The model utilized two rainfall abstraction techniques, i.e. the SCS Curve Number method and the Green-Ampt infiltration equation. Simulated streamflow hydrographs were compared with observed storm flows.
For short duration, high intensity, simple rainfall events, there were minor improvements in hydrograph simulations when calibrated radar measured rainfalls were input to the model, compared to tipping-bucket raingauge measurements. Complex, low intensity storms were poorly simulated by the model using either rainfall data source. Neither rainfall abstraction method proved consistently superior.

A distributed hydrological rainfall-runoff model has been developed using a GIS integrated with a dynamic programming module (PCRaster). The model has been developed within the framework of the EU-project TWINBAS at IVL Swedish Environmental Research Institute, and is intended for use in WATSHMAN – a tool for watershed management developed at IVL. The model simulates runoff from a catchment based on daily mean values of temperature and precipitation. The GIS input data consist of maps with soil type, land-use, lakes, rivers and a digital elevation model. The model is a hybrid between a conceptual and a physical model. The snow routine uses the degree-day method, the evapotranspiration routine uses the Blainey-Criddle equation, the infiltration routine is based on Green-Ampt, groundwater is modelled assuming a linear reservoir and the flow routing is done with the kinematic wave equation combined with Manning’s equation.

The GIS and the hydrologic model are embedded in one another, allowing calculation of each parameter in each grid cell. The output from the model consists of raster maps for each time step for a pre-defined parameter, or a time series for a parameter at a specified grid cell. The flow network is generated from the digital elevation model and determines the water flow on the grid scale. The smallest possible grid size is thus obtained from the resolution of the digital elevation model. In this implementation the grid size was 50 m x 50 m. The raster structure of the model allows for easy use of data from climate models or remotely sensed data.

The model was evaluated using the River Kölstaån catchment, a part (110 km2) of the Lake Mälaren catchment, which has its outflow in central Stockholm, Sweden. The integration of the GIS and the hydrologic model worked well, giving significant advantages with respect to taking lakes and land-use into account. The evaluation data consisted of observed run-off for the period 1981 to 1991. The result from the calibration period shows a great variation in Reff (Nash & Sutcliffe) between the years, the three best years having Reff-values of 0.70 – 0.80. The Reff-value for the entire calibration period was 0.55 and 0.48 for the validation period, where again there was great variation between different years. The volume error was 0.1 % for the calibration period and -21 % for the validation period. The evapotranspiration was overestimated during the validation period, which is probably a result of excess rain during the calibration period. The results are promising and the model has many advantages – especially the integrated GIS-system – compared to the present WATSHMAN model. It could be further developed by introducing a second groundwater storage and refining the evapotranspiration and infiltration routine. Given the promising results, the model should be evaluated in other larger and hillier areas and preferably against more distributed data.

En helt distribuerad GIS-baserad hydrologisk modell för modellering i avrinningsområden på lokal/regional skala har byggts upp i PCRaster. Arbetet utfördes på IVL Svenska Miljöinstitutet AB inom ramen för EU-projektet TWINBAS, som har som mål att identifiera kunskapsluckor inför implementeringen av EU:s ramdirektiv för vatten. Modellen är tänkt att användas i WATSHMAN (Watershed Management System), IVLs verktyg för vattenplanering i avrinningsområden där bland annat källfördelningsberäkningar och åtgärdsanalyser ingår. Den uppbyggda modellen är en hybrid mellan en fysikalisk och en konceptuell hydrologisk modell och predikterar vattenföring på pixelnivå i avrinningsområden. Simuleringen drivs av dygnsmedelvärden för temperatur och nederbörd och modellen tar hänsyn till markanvändning, jordart, topografi och sjöar. De modellekvationer som används är grad-dagsmetoden för snö, Blainey-Criddle för evapotranspiration, Green-Ampt för infiltration, linjärt magasin för grundvatten och Mannings ekvation för flödesrouting.

Det geografiska informationssystemet och den hydrologiska modellen är helt integrerade, vilket gör att alla parametervärden beräknas för varje enskild pixel. Som utdata ger modellen en rasterkarta för varje tidssteg för en i förväg bestämd parameter, eller tidsserier över parametervärden i definierade punkter. Vattnet transporteras i ett utifrån höjdmodellen genererat flödesnätverk och vattnets flödesväg bestäms därmed på pixelnivå. Minsta möjliga pixelstorlek bestäms således utifrån höjdmodellens upplösning, och var vid denna tillämpning 50 m gånger 50 m. Modellens uppbyggnad med raster gör det enkelt att använda data från klimatmodeller eller fjärranalys.

Avrinningsområdet för Kölstaån, ett biflöde till Köpingsån i Mälardalen, har använts för att utvärdera modellen. Integreringen av GIS och hydrologisk modell fungerade mycket väl och gav stora fördelar t ex vad gäller att ta hänsyn till sjöar och markanvändning. Modellen kalibrerades med data från åren 1981 till 1986 och det erhållna volymfelet var då 0,1 % och Reff-värdet (Nash & Sutcliffe) 0,55. Stora variationer erhölls dock mellan åren; för de tre bästa åren låg Reff-värdet mellan 0,70 och 0,80. Ett mycket kraftigt nederbördstillfälle samt regleringar i huvudfåran av vattendraget ligger troligtvis bakom de mindre väl beskrivna åren. Även under valideringsperioden (1987 till 1991) fungerade modellen väl, så när som på att avdunstningen överskattades på vårarna (antagligen beroende av det stora regnet under kalibreringen), och Reff-värde och volymfel hamnade på 0,48 respektive -21 %, även här med stora variationer mellan åren. Resultaten är lovande och modellen har många fördelar jämfört med den nuvarande WATSHMAN-modellen. Den skulle kunna förbättras ytterligare genom att dela upp grundvattnet i två magasin samt förfina evapotranspirations- och infiltrationsrutinerna. Den höjdmodellsbaserade modellen bör utvärderas även i andra mer kuperade områden samt mot mer distibuerade data.

This study proposes a pre-calibration approach using the Soil and Water Assessment Tool (SWAT) to quantitatively assess variability in model performance derived from input data sources in data-scarce dryland environment (the Wala catchment, Jordan 1743 km2). Eighteen scenarios combining different local and global land-use, soil and weather datasets (1979 - 2002) are constructed. Model outputs are statistically assessed against observed discharge and empirically-derived sediment load using r2, Nash-Sutcliffe efficiency (NSE), root mean square error standard deviation ratio (RSR) and percent bias (PBIAS). Global reanalysis weather data considerably improve model performance over discontinuous local datasets, while detailed local soil data perform significantly better than global maps. The approach presented aids selection of the most robust input datasets in regions where availability and quality of data are questionable. Attempting to rationalise modelling in data-poor regions, the catchment delineation produced by the SWAT model is used to design field sampling in October 2013 of channel bed sediments and reservoir sediment cores to investigate potential relationships via geochemical analysis and provide measured sediment information that may interpret model prediction. XRF and particle size analyses were performed on all samples and the data analysed in respect of geochemical signatures. No strong evidence of discrete event-driven deposition is detected, likely due to alternating high-flood and drought periods. Variations in pollutants geochemistry are consistent with land-use pattern with relatively higher levels of Pb, Co, Cu and Cr associated with urbanised regions. Although these concentrations are mostly below thresholds for health concern, higher water and sediment loadings from these regions, as estimated by the model, may increase them. Hence, future management of water quality must be considered. The optimised and calibrated SWAT model is used to assess hypothetical and object-based integrated catchment management interventions and their implications for the useable lifetime of the Wala Dam within the context of the UN-funded BRP Project. The modelled catchment response to different scenarios varies spatially based on type and extent of application. Changes in annual loadings delivered to the Wala reservoir are linked to a simple model of dam functional lifetime to support decision-making.

The Northern Rocky Mountains, home to the highest concentration of glaciers in the American West, are undergoing increased rates of climate warming, resulting in previously unseen ecological and hydrological outcomes. Globally, many glacier basins have experienced glacial recession to the threshold point of surpassing peak basin runoff, resulting in substantial decreases in local hydrological yield. Such findings call for models that do not alone examine glacial runoff but a complete examination of changes in the water budget. Alpine catchments are increasingly vulnerable to evapotranspirative losses due to climatic warming, and the rates of vegetation succession are often unable to keep up with the rate of warming. Basin scale analyses of glacial recession on streamflow are then confounded by ecohydrologic dynamics created by primary succession and the associated increase in evapotranspiration. In this study, I present a conceptual framework for modelling basin runoff in landscapes responding to paraglacial adjustment. The study goal was achieved by calibrating and running the Hydrologiska Byråns Vattenbalansavdelning (HBV) model in Swiftcurrent basin and investigating change across the basin water balance through baseflow analysis. The research findings indicate catchment scale changes in the timing and magnitude of the flow regime in the deglaciating Swiftcurrent basin, by employing HBV and empirical baseflow analysis. While most components of the water balance appear consistent across the study period, late summer baseflow values suggest the basin hydrology is undergoing changes, possibly a result of melt occurring earlier in the season. Ultimately, I advocate for an adaptable and accessible approach to understanding paraglacial basins by constructing an estimation of basin-scale water budgets.
Master of Science
Large scale trends in climate change are impacting a variety of ecosystems, especially alpine environments. Glacial recession has been well documented and studied in mountain chains across the globe, including the Rocky Mountains. Recession of these massive bodies of ice, which can be viewed as reservoirs of water in droughts or low flow months, has severe implications for society, the economy, and sensitive mountain environments. Furthermore, the new terrain exposed from beneath the melting glacier is dynamic and will undergo many adjustments geomorphically, in soil development, and ecologically as plants move up the glacier foreland. Ecological systems experiencing warming, deglaciation, and vegetation succession are not well understood and are complex environments due to the multiple inputs, interactions, and feedbacks. As such, this research examines how hydrologic conditions across a forty year period are changing in response to the complex feedbacks between glaciers, newly exposed terrain, and associated runoff. Through modeling and analysis, this study offers a method for understanding the water balance of Swiftcurrent basin in Glacier National Park, which can be used in other catchments experiencing similar changes.

Changes in watershed vegetative cover from natural and anthropogenic causes including, climatic fluctuations, wildfires and land management practices, can result in increased surface water runoff and erosion. Hydrologic models play an important role in the decision support process for managing these landscape alterations. However, model parameterization requires quantified measures of watershed biophysical condition to generate accurate results. These inputs are often obtained from nationally available land cover data sets that are static in terms of vegetation condition and phenology. Obtaining vegetative data for model input of sufficient spatiotemporal resolution for long-term, watershed-scale change analysis has been a challenge. The purpose of this research was to assess the implications of parameterizing the event-based, Rangeland Hydrology and Erosion Model (RHEM) with dynamic, remotely sensed foliar cover data. The study was conducted on a small, instrumented, grassland watershed within the Walnut Gulch Experimental Watershed surrounding Tombstone, Arizona. A time series of foliar cover rasters was produced by calibrating Landsat-based Soil Adjusted Total Vegetation Index (SATVI) scenes with field measurements. Estimates of basal and litter cover were calculated using allometric relationships derived from ground-based transect data. The model was parameterized using these remotely sensed inputs for all recorded runoff events from 1996-2014. Model performance was improved using the remotely sensed foliar cover compared to using an a priori value based on static national land cover classes. Significant (p<0.05) correlation was shown for the linear relationships between foliar cover and SATVI, foliar cover and basal cover, and foliar cover and litter cover. The integration of Landsat-based vegetative data into RHEM shows potential for modelling on a broadened spatiotemporal scale, allowing for improved landscape characterization and the ability to track watershed response to long-term vegetation changes.

The quality and sustainability of estuarine environments in large port-cities like Sydney are strongly impacted by increasing human activities. Investigations of water and sediment quality have identified urban stormwater as the most important contemporary source of chemical pollution in the estuary. A sound understanding of the transport of pollutants in an urbanised environment is a prerequisite to responsible management. An integrated hydrological model allowing estimation of pollutant distribution and loading from an urbanised catchment to the estuary should thus be a key tool to assist decision makers in testing and validating urban development impact. A GIS-based quantitative hydrological model coupled to a Decision Support System (DSS) for water quality management was developed to quantify stormwater runoff, and pollutant loading for diverse precipitation scenarios. The Urban PARC (Pollutant Area & Runoff Computation) Model consists in a series of workflows allowing assimilation of physiographic and environmental data, including topography, land use, pedology and precipitation at various temporal and spatial resolutions. The model was developed in ArcGIS and applied to simulate water and pollutant loading in stormwater for precipitation scenarios ranging from single events to average annual rainfall within the Sydney catchment. The Urban PARC Model was used to simulate the impact of remediation scenarios on pollutant loading. Tests presented here show that it can be successfully used as a DSS to predict the potential impact of remediation strategies on the urban environment and water quality management. The modelling applications and results for water and pollutants discharge produced by the current research are comparable with published data at various scales. Although additional work will be necessary to validate the model parameters for the entire Sydney catchment, the model provides a substantial platform for urban environment research and management.

Understanding the spatial and temporal dynamics occurring in headwater catchments enhances our ability to effectively manage the natural and unnatural inputs from the landscape to the stream. DOC is particularly important in northern peat dominated catchments, where concentrations in rivers have been increasing over recent decades. Due to the significant downstream impacts this increase has on the functioning of aquatic ecosystems and the quality of drinking water, it is vital to understand the tight coupling between the landscape and the stream. This study set out to explore the use of integrating high-frequency DOC data, stable isotopes and modelling as a novel way to increase our understanding of the hydrological and biogeochemical processes that control spatial and temporal DOC dynamics. By deploying in-situ FDOM sensors, across nested catchments, we captured 15 minute DOC dynamics. This yielded insights into seasonal, event and diel temporal variability, along with spatial variability. Results showed the utility of linking these DOC dynamics with stable isotopes and water ages, extracted from a tracer-aided runoff model. This allowed the main runoff generating processes, that transport the DOC from the sources to the stream, to be assessed, and showed the effects of hydrologic connectivity and antecedent conditions on DOC delivery. Incorporating modelling allowed the non-stationary hydrological processes influencing runoff generation, which cannot be easily measured by field techniques, to be evaluated. Overall, the findings of this thesis underline the utility of integrating highfrequency DOC data, stable isotopes and modelling to extract a highly informative dataset that helps produce a more complete symphony of the highly variable dynamics occurring in upland catchments. Such knowledge is crucial in order to effectively evaluate the influence of climate change on the water resources that both nature and humans so heavily depend on.

Hydrological responses vary from one catchment to another, depending on the nature of land use and cover changes. Modelling the hydrological responses to changes in land use and cover at different catchment spatial scales was the major focus of this study. This study assessed the hydrological responses attributed to changes in land use and extreme weather events resulting into increased sediment loading/concentration, rainfall-runoff generation/volume, streamflow fluctuation and modification of the river channel in the Malaba River Catchment, Eastern Uganda. The hydrological responses were assessed using hydrological models (IHACRES, SCS CN, and SHETRAN) to examine the effect of land use on soil physio-chemical properties susceptibility to rainfall-runoff generation and volume, frequency and severity of extreme weather events, changes in streamflow variations, sediment loading/concentration and river channel morphology. The preliminary study results showed that the frequency of extreme weather events reduced from 4-10 to 1-3 years over the catchment. The performance of the IHACRES model with a Nash-Sutcliffe Efficiency (NSE) of 0.89 showed that streamflow comparatively corresponded with the results obtained the drought indices in predicting the recorded events of severe drought (2005) and flood (1997). Changes in land use and cover types showed that the highest change in the gain of land was experienced from the agricultural land use (36.7 percent), and tropical forest (regeneration) (2.2 percent). The biggest losses in land were experienced in the wetlands (24.6 percent) and bushland and thickets (15.3 percent) land cover types. The SHETRAN model calibrated period had a NSE of 0.78 and 0.81 in the validation period showed satisfactory fits between the measured and simulated streamflow. The agricultural land use (crop growing) had a higher influence on the rainfall-runoff generation and increase in the streamflow than the tropical forest, and bushland cover types in the simulated period. Similarly, the curve number model estimated a comparatively higher surface rainfall-runoff volume generated from the agricultural land use (crop growing) (71,740 m3) than in the bushlands and thickets (42,872 m3) from a rainstorm followed by the tropical forest cover type. This was also reflected in the lower rates of saturated hydraulic conductivity from the agricultural land use (crop growing). The study also showed that human-induced sediment loading due to gold mining activities contributed a much higher impact on the concentration of suspended sediments and streamflow than sediments from rainfall-runoff from the sampled streams. The main contributor of human-induced sediments to the Malaba River were Nankuke River (130.6kg/annum), followed by Omanyi River (70.6kg/annum), and Nabewo River (66.8kg/annum). Human-induced sediment loading had a profound impact on the streamflow variations both in the dry and wet seasons from the sampled tributaries. Lastly, in regard to the effect of land use and cover types on the river channel morphology, tree plantation (cohesion=12, angle of internal friction=27) and bushland and thickets (cohesion=14, angle of internal friction=22) cover types had the most stable river banks compared to the wetland and agricultural land use and cover types that exhibited higher levels of sediment concentration.

Inverse geochemical modelling has been used frequently in groundwater systems between wells along a known flowpath and between precipitation and stream waters in catchments. This research expands the use of inverse geochemical modelling through a reaction path model (RPM) between waters in an alpine catchment to determine the geochemical connections and disconnections within the catchment. The data for this study are from the Green Lake 4 catchment in the Colorado Front Range during the 1996 snowmelt season, which has been divided into discrete time intervals based on snowmelt hydrology. Unique combinations of geochemical connections occur during these time intervals, and they show a dynamic hydrologic system. RPM results show notable disconnections; soil water is not geochemically connected to any other end member. These changes reflect changes in weathering reactions in the catchment that are dependent on the duration and timing of snowmelt. Previously end-member mixture analysis (EMMA) models have been used to discern the water sources in catchments. The combination of RPM and EMMA approaches offers the opportunity to connect the source of water to the internal hydrologic structure of the catchment, to better understand how catchments might respond to changes in climate or atmospheric deposition.

There is being observed high variability in the spatial and temporal rainfall patterns under changing climate, enhancing both the intensity and frequency of the natural disasters like floods. Pakistan, a country which is highly prone to climate change, is recently facing the challenges of both flooding and severe water shortage as the surface water storage capacity is too limited to cope with heavy flows during rainy months. Thus, an effective and timely predication and management of high flows is a dire need to address both flooding and long term water shortage issues. The work of this thesis was aimed at developing and evaluating different open source data based methodologies for floods detection and analysis in Pakistan. Specifically, the research work was conducted for developing and evaluating a hydrologic model being able to run in real time based on satellite rainfall data, as well as to perform flood hazard mapping by analyzing seasonality of flooded areas using MODIS classification approach. In the first phase, TRMM monthly rainfall data (TMPA 3B43) was evaluated for Pakistan by comparison with rain gauge data, as well as by further focusing on its analysis and evaluation for different time periods and climatic zones of Pakistan. In the next phase, TRMM rainfall data and other open source datasets like digital soil map and global land cover map were utilized to develop and evaluate an event-based hydrologic model using HEC-HMS, which may be able to be run in real time for predicting peak flows due to any extreme rainfall event. Finally, to broaden the study canvas from a river catchment to the whole country scale, MODIS automated water bodies classification approach with MODIS daily surface reflectance products was utilized to develop a historical archive of reference water bodies and perform seasonal analysis of flooded areas for Pakistan. The approach was found well capable for its application for floods detection in plain areas of Pakistan. The open source data based hydrologic modeling approach devised in this study can be helpful for conducting similar rainfall-runoff modeling studies for the other river catchments and predicting peak flows at a river catchment scale, particularly in mountainous topography. Similarly, the outcomes of MODIS classification analysis regarding reference and seasonal water and flood hazard maps may be helpful for planning any management interventions in the flood prone areas of Pakistan.

This thesis presents the outcomes of a comprehensive research study undertaken to investigate the influence of rainfall and catchment characteristics on urban stormwater quality. The knowledge created is expected to contribute to a greater understanding of urban stormwater quality and thereby enhance the design of stormwater quality treatment systems. The research study was undertaken based on selected urban catchments in Gold Coast, Australia. The research methodology included field investigations, laboratory testing, computer modelling and data analysis. Both univariate and multivariate data analysis techniques were used to investigate the influence of rainfall and catchment characteristics on urban stormwater quality. The rainfall characteristics investigated included average rainfall intensity and rainfall duration whilst catchment characteristics included land use, impervious area percentage, urban form and pervious area location. The catchment scale data for the analysis was obtained from four residential catchments, including rainfall-runoff records, drainage network data, stormwater quality data and land use and land cover data. Pollutants build-up samples were collected from twelve road surfaces in residential, commercial and industrial land use areas. The relationships between rainfall characteristics, catchment characteristics and urban stormwater quality were investigated based on residential catchments and then extended to other land uses. Based on the influence rainfall characteristics exert on urban stormwater quality, rainfall events can be classified into three different types, namely, high average intensity-short duration (Type 1), high average intensity-long duration (Type 2) and low average intensity-long duration (Type 3). This provides an innovative approach to conventional modelling which does not commonly relate stormwater quality to rainfall characteristics. Additionally, it was found that the threshold intensity for pollutant wash-off from urban catchments is much less than for rural catchments. High average intensity-short duration rainfall events are cumulatively responsible for the generation of a major fraction of the annual pollutants load compared to the other rainfall event types. Additionally, rainfall events less than 1 year ARI such as 6- month ARI should be considered for treatment design as they generate a significant fraction of the annual runoff volume and by implication a significant fraction of the pollutants load. This implies that stormwater treatment designs based on larger rainfall events would not be feasible in the context of cost-effectiveness, efficiency in treatment performance and possible savings in land area needed. This also suggests that the simulation of long-term continuous rainfall events for stormwater treatment design may not be needed and that event based simulations would be adequate. The investigations into the relationship between catchment characteristics and urban stormwater quality found that other than conventional catchment characteristics such as land use and impervious area percentage, other catchment characteristics such as urban form and pervious area location also play important roles in influencing urban stormwater quality. These outcomes point to the fact that the conventional modelling approach in the design of stormwater quality treatment systems which is commonly based on land use and impervious area percentage would be inadequate. It was also noted that the small uniformly urbanised areas within a larger mixed catchment produce relatively lower variations in stormwater quality and as expected lower runoff volume with the opposite being the case for large mixed use urbanised catchments. Therefore, a decentralised approach to water quality treatment would be more effective rather than an "end-of-pipe" approach. The investigation of pollutants build-up on different land uses showed that pollutant build-up characteristics vary even within the same land use. Therefore, the conventional approach in stormwater quality modelling, which is based solely on land use, may prove to be inappropriate. Industrial land use has relatively higher variability in maximum pollutant build-up, build-up rate and particle size distribution than the other two land uses. However, commercial and residential land uses had relatively higher variations of nutrients and organic carbon build-up. Additionally, it was found that particle size distribution had a relatively higher variability for all three land uses compared to the other build-up parameters. The high variability in particle size distribution for all land uses illustrate the dissimilarities associated with the fine and coarse particle size fractions even within the same land use and hence the variations in stormwater quality in relation to pollutants adsorbing to different sizes of particles.

LISEM, a physically-based distributed and dynamic erosion model within the PCRaster GIS, is used to investigate the influence of different spatial representations of input parameters on surface hydrologic and erosion processes at three antecedent soil moisture levels for a 6-hour heavy storm at catchment scale. Two derived DEMs viz. Cartometric and PulSAR DEMs and three public domain DEMs viz. Landmap, ASTER and SRTM were used in this study. These five DEMs of various original resolutions along with a land use and land cover map and a soil map of the Saltdean catchment were resampled into five spatial representations at 20, 40, 60, 80 and 100 m grid-cell sizes to create input parameters at each resolution. Spaceborne radar interferometry was investigated for generating a suitable DEM for modelling in the context of developing countries having poor availability of quality DEMs. The land use and land cover map was derived from SPOT-1 data and the infiltration parameters were estimated from the 1:250 000 soil map using pedotransfer functions. Crop, soil and soil surface parameters were estimated for possible field conditions in the catchment. Subsequently, twenty-five LISEM databases of 30 input parameters each were created in PCRaster and tested in the model. The results show that at increasing the grid-cell size of a DEM, the slope gradient flattens and the drainage length shortens. Both of these have competing effects on runoff and sediment flow routing. The catchment area also increases at larger grid-cell sizes and influences these processes, which are then normalised for the comparison of various resolution results. In the absence of observed runoff and average soil loss data, a relative evaluation across resolutions and DEMs was carried out in the context of developing countries. The results indicate that the PulSAR and Landmap DEMs have higher variations in runoff and average soil loss than the ASTER DEM, Cartometric DEM, and SRTM DEM at coarser resolutions at all three moisture levels with respect to their result at 20 m. The SRTM DEM has lower variability than other DEMs at finer resolutions. It is demonstrated that resampling a medium resolution SRTM DEM at smaller grid-cell sizes does not improve the prediction of runoff and soil erosion. At 100 m resolution, the runoff is over predicted as compared to an 80 m resolution. Hence, high resolution DEMs should be resampled to 80 m grid-cell size, but the resampling reduces the spatial variability drastically. The results also indicate that the prediction of runoff is improved for the PulSAR DEM and Landmap DEM, and is slightly improved for the ASTER DEM as compared to the Cartometric DEM, but it is not improved for the SRTM DEM. It is related with their slope gradients. The results support that the average soil loss is improved for the PulSAR DEM and Landmap DEM and is slightly degraded for the SRTM DEM as compared to the Cartometric DEM. It also suggests that both are suitable for erosion prediction due to higher slope gradient mapped by remote sensing. The ASTER DEM did not produce reliable soil losses at all the moisture levels. Therefore, it should not be used for the prediction of soil erosion. The results also indicate that small grid-cell size produces detailed soil erosion and deposition outputs, which help in identifying the exact location of sediment source and sink areas necessary for planning the effective conservation strategy in the catchment.

[Truncated abstract] Generally hydrologic and ecologic models operate on arbitrary time and space scales, selected by the model developer or user based on the availability of field data. In reality rainfall is highly variable not only annually, seasonally and monthly but also the intensities within a rainfall event and infiltration properties on semi-arid hillslopes can also be highly variable as a result of discontinuous vegetation cover that form mosaics of areas with vegetation and areas of bare soil. This thesis is directed at improving our understanding of the impacts of the temporal representation of rainfall and spatial heterogeneity on model predictions of hydrologic thresholds and surface runoff coefficients on semi-arid landscapes at the point and hillslope scales. We firstly quantified within storm rainfall variability across a climate gradient in Western Australia by parameterizing the bounded random cascade rainfall model with one minute rainfall from 15 locations across Western Australia. This study revealed that rainfall activity generated in the tropics had more within storm variability and a larger proportion of the storm events received the majority of rain in the first half of the event. Rainfall generated from fontal activity in the south was less variable and more evenly distributed throughout the event. Parameters from the rainfall analysis were then used as inputs into a conceptual point scale surface runoff model to investigate the sensitivity of point scale surface runoff thresholds to the resolution of rainfall inputs. This study related maximum infiltration capacities to average storm intensities (k*) and showed where model predictions of infiltration excess were most sensitive to rainfall resolution (ln k* = 0.4) and where using time averaged rainfall data can lead to an under prediction of infiltration excess and an over prediction of the amount of water entering the soil (ln k* > 2). For soils susceptible to both infiltration excess and saturation excess, total runoff sensitivity was scaled by relating drainage coefficients to average storm intensities (g*) and parameter ranges where predicted runoff was dominated by infiltration excess or saturation excess depending on the resolution of rainfall data were determined (ln g* <2). The sensitivity of surface runoff predictions and the influence of specific within storm properties were then analysed on the hillslope scale. '...' It was found that using the flow model we still get threshold behaviour in surface runoff. Where conditions produce slow surface runoff velocities, spatial heterogeneity and temporal heterogeneity influences hillslope surface runoff amounts. Where conditions create higher surface runoff velocities, the temporal structure of within storm intensities has a larger influence on runoff amounts than spatial heterogeneity. Our results show that a general understanding of the prevailing rainfall conditions and the soil's infiltration capacity can help in deciding whether high rainfall resolutions (below 1 h) are required for accurate surface runoff predictions. The results of this study can be considered a contribution to understanding the way within storm properties effect the processes on the hillslope under a range of overall storm, slope and infiltration conditions as well as an improved understanding of how different vegetation patterns function to trap runoff at different total vegetation covers and rainfall intensities.

Appropriately constructed pollutant export models can help set management priorities for catchments, identify critical pollutant source areas, and are important tools for developing and evaluating economically viable ways of minimising surface water pollution.¶ This thesis presents a comparison, an evaluation and an integration of models for predicting the export of environmental pollutants, in particular sediment, through river systems. A review of the capabilities and limitations of current water quality modelling approaches is made. Several water quality and quantity modelling approaches are applied and evaluated in the catchment of the upper Murrumbidgee River.¶ The IHACRES rainfall-runoff model and a simple hydrologic routing model are applied with the aim of developing a capacity to predict streamflow at various catchment scales and to enable integration with other pollutant load estimation techniques. Methods for calculating pollutant loads from observed pollutant concentration and modelled streamflow data are also investigated. Sediment export is estimated using these methods over a 10-year period for two case study subcatchments. Approaches for water quality sampling are discussed and a novel monitoring program using rising stage siphon samplers is presented. Results from a refinement of the Sediment River Network model in the upper Murrumbidgee catchment (SedNet-UM) are presented. The model provides a capacity to quantify sediment source, transport and to simulate the effects of management change in the catchment. The investigation of the model includes rigorous examination of the behaviour of the model through sensitivity assessment and comparison with other sediment modelling studies. The major conclusion reached through sensitivity assessment was that the outputs of the model are most sensitive to perturbation of the hydrologic parameters of the model.¶ The SedNet-UM application demonstrates that it is possible to construct stream pollutant models that assist in prioritising management across catchment scales. It can be concluded that SedNet and similar variants have much potential to address common resource management issues requiring the identification of the source, propagation and fate of environmental pollutants. In addition, incorporating the strengths of a conceptual rainfall-runoff model and the semi-distributed SedNet model has been identified as very useful for the future prediction of environmental pollutant export.

Thesis (Ph.D) (Microbiology and Plant Pathology)--University of Pretoria, 2006.
Summaries in Afrikaans and English. Includes bibliographical references. Available on the Internet via the World Wide Web.

El conocimiento de los procesos hidrológicos es esencial para la gestión de los recursos hídricos tanto desde el punto de vista cuantitativo (crecidas o sequías) como desde el punto de vista cualitativo (contaminación). El funcionamiento hidrológico de las cuencas mediterráneas es aún bastante desconocido a pesar de los diferentes estudios realizados desde hace una veintena de años. Los progresos realizados en la identificación y modelización de los procesos hidrológicos corresponden casi en la totalidad a investigaciones realizadas en clima templado-húmedo (Bonell y Balek, 1993; Buttle, 1994). Esta falta de información, fuerza según Bonell (1993) a la "transferencia de resultados", a pesar de la necesidad evidente de desarrollar aproximaciones diferentes, principalmente en el ámbito de la modelización (Pilgrim et al. 1988). Por lo que se refiere a la modelación hidrológica, los estudios disponibles (Durand et al., 1992; Parkin et al., 1996; Piñol et al., 1997 entre otros) muestran serias dificultades para reproducir las primeras crecidas de otoño, después del periodo estival seco. Para estas cuencas parece difícil modelizar correctamente uno o más años hidrológicos completos con un solo juego de parámetros (Piñol et al., 1997, Bernal et al., 2004). El clima mediterráneo está caracterizado por una dinámica estacional muy marcada del régimen de precipitaciones y de la evapotranspiración, que favorece la alternancia durante el año de periodos secos y húmedos. Esto modifica fuertemente el estado hidrológico de la cuenca, de lo que deriva un comportamiento hidrológico complejo y no-lineal (Piñol et al. 1999). La necesidad de comprender el funcionamiento hidrológico de un sistema responde a dos cuestiones importantes: por un lado es el procedimiento más indicado para proporcionar elementos útiles a la gestión integrada de los recursos hídricos y por otro lado es fundamental para la modelación del comportamiento de nutrientes por ejemplo como el nitrato.
Medici ., C. (2010). Progressive development of a hydrologic and inorganic nitrogen conceptual model to improve the understanding of small Mediterranean catchments behaviour [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8428
Palancia

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.

Thesis (M.Ing.)--Stellenbosch University, 2000.
ENGLISH ABSTRACT: The objective of this research has been to compare nonpoint sources assessment techniques for simulating phosphorous production in rural catchments which have a variety ofland use types. Four nonpoint source assessment techniques capable of simulating phosphorous production, operating at different spatial and temporal resolutions, were selected after an intensive literature review. The model selection criteria included the capability to simulate phosphorous production, the need for the study to cover a range of spatial and temporal resolutions, model data requirements, model affordability and availability in South Africa. The models selected using these criteria are the Phosphorous Export Model (PEM) (Weddepohl & Meyer, 1992), Impoundment and River Management and Planning Assessment Tool for Water Quality Simulation Model (IMPAQ) (DWAF,1995), the Hydrological Simulation Program Fortran (HSPF) (Bricknell,1993) and the Agricultural Catchments Research Unit Model (ACRU) (Smithers and Caldecott, 1994). Four ofthe study catchments were selected within the Berg River basin in the Western Cape and the remaining four were selected within the Amatole catchments in the Eastern Cape. The four subcatchments in the Berg River basin are the Twenty-Four Rivers, Leeu River, Kompanjies River and Doring River catchments and the four in the Amatole catchments are the Upper Buffalo, Cwencwe, Yellowwoods and Gqunube River catchments. The range of land use/cover types comprises: Western Cape catchments : wheat, grapes, natural vegetation and forestry Eastern Cape catchments : natural vegetation and forestry The PEM and IMPAQ models were applied reasonably successfully to all the catchments to simulate phosphorous production, with the observed flow as the input. The HSPF model could not successfully be applied to the catchments to simulate both the catchment hydrology and phosphorous production. Hence, the investigation into HSPF was abandoned, and in its place, the ACRU daily phosphorous yield model was incorporated at a fairly late stage in the research. ACRU was applied to only the Western Cape catchments. The estimated parameters for different land use types were compared to investigate the potential for parameter transfer in space and time. Both the PEM and IMP AQ models showed promise that land use parameters could be transferred in time for catchments located in the Western Cape catchments, but did not show promise for catchments located in the Eastern Cape. The IMPAQ model showed promise that land use parameters could be transferred in space for catchments located in the Eastern Cape, but did not perform as well in the Western Cape catchments. The PEM model showed promise that land use parameters could be transferred in space for catchments located in the Western Cape, but did not perform as well in the Eastern Cape. Since the ACRU phosphorous yield model was included at a late stage of the research, the potential for land use parameter transfer in space and time could not investigated. The model results were verified at the relevant flow and water quality gauging stations. The ACRU phosphorous model verification results showed promise for catchments located in humid parts of the Berg River basin, but did not perform as well in the catchment located in the semi-arid part. RECOMMENDATIONS FOR FURTHER RESEARCH: I. Intensive research should be undertaken to develop a database ofland use parameters/ export coefficients related to phosphorous production (and other non-conservative constituents) in South African catchments. Availability of these parameters would make phosphorous modelling much easier. HSPF should be configured and calibrated, more especially its water quality component, for catchments with hourly rainfall and rainfall stations located within/on the catchment boundaries, to investigate its performance under South African conditions. Given the complexity of the HSPF algorithms and the time required to familiarise oneself with the model, it is recommended that such an investigation be undertaken which is not inclusive of any other models. The spatial resolution ofPEM is extremely coarse, and should be improved to allow the user to partition the total flow in the catchment according to contributions from the variety ofland use types and to estimate soluble and particulate phosphorous parameters for each land use type. A study should be undertaken to investigate the potential for the ACRU phosphorous yield model parameter transfer in time and space. Sampling frequency of water quality data in South Africa should be improved, because it is difficult to assess the performance of the calibrated water quality models, more especially phosphorous export models, due to a lack of continuous data sets. Rainfall data collection in gauged catchments, more especially Western Cape catchments (e.g. Twenty-Four Rivers, Leeu, Kompanjies and the Doring River catchments), should be improved. There should be at least one rainfall gauging station located within the catchment boundaries. This would contribute towards achieving reasonable hydrological calibration or verification. Since runoff is the driving factor for water quality components, improved hydrological calibration/verification would result in reasonable water quality calibration/verification.
AFRIKAANSE OPSOMMING: Die doel van die navorsing was om die simulering van fosfaat produksie in landelike gebiede, wat 'n verskeidenheid grondgebruike het, met behulp van nie-punt bron evaluerings tegnieke te evulaeer. Vier nie-punt bron evaluerings tegnieke, met die vermoë om fosfaat produksie op verskillende ruimtelike en tyds resolusies te simuleer, is gekies na 'n intensiewe ondersoek van beskikbare literatuur. Die kriteria vir die keuse van die model het ingesluit die vermoë om fosfaat produksie te simuleer, die behoefte vir die studie om 'n reeks van ruimtelike en tyds resolusies te simuleer, model data vereistes, model bekostigbaarheid en beskikbaarheid in Suid Afrika. Die gekose modelle, gebaseer op bogemelde kriteria, was die PEM, IMPAQ, HSPF en ACRU modelle. Vier van die opvanggebiede gebruik in die studie, was in die Bergrivier bekken in die Wes-Kaap en vier was in die Amatole opvanggebiede in die Oos-Kaap. Die vier opvanggebiede in die Bergrivier bekken is die Vier-en- Twentigriviere, Leeurivier, Kompanjiesrivier en die Doringrivier en die vier opvanggebiede in die Amatole opvanggebiede is die Bo-Buffels, Cwencwe, Yellowwoods, en die Gunubierivier opvanggebiede. Grondgebruik beslaan die volgende: Wes-Kaap opvanggebiede : koring, druiwe, natuurlike weiding en plantasies. Oos-Kaap : natuurlike plantegroei en plantasies Die PEM en IMPAQ modelle is met redelike sukses in al die opvanggebiede gebruik vir die simulasie van fosfaat produksie, met die waargenome vloei as invoer. Die HSPF model kan nie met enige sukses gebruik word om beide die opvanggebied hidrologie en fosfaat produksie, te simuleer nie. Die HSPF model is dus uitgeskakel en in 'n redelike laat stadium van die studie met die ACRU daaglikse fosfaat leweringsmodel vervang. Die ACRU model is net op die Wes-Kaap opvanggebiede toegepas. Die beraamde parameters vir die verskillende grondgebruik tipes is vergelyk om die potensiaal vir parameter oordrag in ruimte en tyd te ondersoek. Beide die PEM en IMPAQ modelle het belowend vertoon ten opsigte van die oordrag van grondgebruik parameters in tyd vir opvanggebiede in die Wes- Kaap, maar het geensins belowend vertoon vir die Oos-Kaap opvanggebiede nie. Die IMPAQ model het belowend vertoon ten opsigte van die ruimtelike oordrag van grondgebruik parameters vir die Oos-Kaap opvanggebiede, maar het nie so goed vertoon in die Wes-Kaap opvanggebiede nie. Die PEM model het belowend vertoon ten opsigte van die ruimtelike oordrag dat grondgebruikte parameters in die Wes-Kaap opvanggebiede is, maar het nie so goed in die Oos-Kaap opvanggebiede vertoon nie. Aangesien die ACRU fosfaat leweringsmodel op 'n laat stadium van die navorsing ingesluit is, kan die potensiaal vir die oordrag van grondgebruik parameters in ruimte en tyd nie ondersoek word nie. Die model resultate is by die toepaslike vloei en waterkwaliteit meetstasies geverifiëer Die resultate van die ACRU fosfaat model verifikasie het belowend vertoon vir opvangebiede in die humiede gedeeltes van die Bergrivier bekken, maar het nie so goed vertoon in die semi-droeë deel van die opvangebied nie. AANBEVELINGS VIR VERDERE NAVORSING : Y4 Intensiewe navorsing moet onderneem word ten einde in 'n databasis van grondgebruik parameters/oordrag koëffisiente met betrekking tot fosfaat produksie (en ander niekonserwatiewe bestandelle ) in Suid Afrikaanse opvanggebiede op te bou. Beskikbaarheid van hierdie parameters sal fosfaat modellering vergemaklik. Die HSPF model moet opgestel en gekalibreer word, meer spesifiek ten opsigte van die waterkwaliteit komponent, vir opvanggebiede met uurlikse reënval en reënvalstasies binne of op die opvanggebied grense, om die model se vertoning onder Suid Afrikaanse omstandighede te ondersoek. Gegewe die kompleksiteit van die HSPF algoritmes en tyd benodig om met model vertroud te raak, word dit aanbeveel dat so 'n ondersoek onderneem word met uitsluiting van die ander modelle. Die ruimtelike resolusie van die PEM model is uitermatig grof, en behoort verbeter te word ten einde die gebruiker toe te laat om die totale vloei in die opvanggebied in ooreenstemming met die bydraes van die onderskeie grondgebruik tipes te verdeel en om oplosbare en partikulere fosfaat parameters vir elke grondgebruik tipe te beraam. 'n Studie om die potensiaal vir die ruimtelike en tydsoordrag van die ACRU fosfaat leweringsmodel parameters te ondersoek, moet onderneem word. Die frekwensie van waterkwaliteit monitering in Suid Afrika moet verbeter word, aangesien dit moelik is om, weens 'n gebrek aan deurlopend waargenome data, die vertoning van gekalibreerde waterkwaliteit modelle te ondersoek, meer spesifiek nog fosfaat uitvoer modelle. Reënval inligting versameling in gemete opvanggebied, meer spesifiek die Wes-Kaap opvanggebiede (bv.Vier-en-Twintigriviere, Leeu, Kompanjies en Doringrivier opvanggebiede), behoort verbeter te word. Daar behoort ten minste een reënval stasie binne die opvanggebied grense te wees. Dit sal bydra tot die bereiking van redelike hidrologiese kalibrasie ofverifikasie. Aangesien afloop die dryfveer van die waterkwaliteit komponente is, sal verbeterde hidrologiese kalibrasie/verifikasie lei tot redelike waterkwaliteit kalibrasie/verifikasie.

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.

Floods are a significant threat to communities around the world and require substantial resources and infrastructure to predict. Limited local resources in developing nations make it difficult to build and maintain dense sensor networks like those present in the United States, creating a large disparity in flood prediction across borders. To address this disparity, I operated the Iowa Flood Center Top Layer model to predict floods in Puerto Rico without relying on in-situ data measurements. Instead, all model forcing was provided by satellite remote sensing datasets that offer near-global coverage. I used three datasets gathered via satellite remote sensing to build and operate watershed streamflow models: elevation data obtained by the Space Shuttle Endeavour through the Shuttle Radar Topography Mission (SRTM), rainfall estimates gathered by a constellation of satellites through the Global Precipitation Measurement Mission (GPM), and evapotranspiration rate estimates collected by Moderate Resolution Imaging Spectroradiometer (MODIS) sensors aboard the Aqua and Terra satellites. While these satellite remote sensing datasets make observations of nearly the entire world, their spatiotemporal resolution is coarse compared to conventional on-the-ground measurements. Hydrologic models were assembled for 75 basins upstream of streamflow gages monitored by the United States Geologic Survey (USGS). Model simulations were compared to real-time measurements at these gages. Continuous simulations spanning 58 months achieve poor Nash Sutcliffe Efficiency and Klinge Gupta Efficiency of -112.0 and -0.5, respectively. The sources of error that influence model performance were investigated, underlining some limitations of relying solely on satellite data for operational flood prediction efforts.

Altered flow regimes following river regulation can result in significant changes in river bed geomorphology and subsequent negative ecological impacts caused by re-suspended sediments deposited on the riverbed. This study aimed to evaluate the consequences of implementing an ecological flow regime on sediments accumulated within the regulated river Juktån. Sediments were sampled and analysed for particle size distribution to estimate sediment stability. Flow alteration following the ecological flow regime was analysed with HEC-RAS unsteady flow simulation serving as a basis for calculations of forces acting to erode or retain deposited sediments. Additional analyses regarding critical flow were made with HEC-RAS steady flow simulation. Results show that 4 out of 15 cross-sections analysed would have the potential to erode and re-suspend sediments. The estimated average critical flow for when sediments become unstable with potential to re-suspend is 17 m3/s. The total sediment inventory of the studied reach is ~25000 ton, with ~3000-ton sediments potentially eroding into re-suspension. This is approximately 3% of river Umeälvens annual 100 000 ton suspended sediments before being regulated. Results indicate that river bed heterogeneity in river Juktån could benefit from implementing the ecological flow regime while not mobilizing such amounts of fine sediments that would cause clogging effects downstream the site of interest. The study also introduces the erosion rate equation which compares the annual erosion between two different flow regimes.

The connections between surface water and groundwater systems remain poorly understood in many catchments throughout the world and yet they are fundamental to effectively managing water resources. Managing water resources in an integrated manner is not straightforward, particularly if both resources are being utilised, and especially in those regions that suffer problems of data scarcity. This study explores some of the principle issues associated with understanding and practically modelling surface and groundwater interactions. In South Africa, there remains much controversy over the most appropriate type of integrated model to be used and the way forward in terms of the development of the discipline; part of the disagreement stems from the fact that we cannot validate models adequately. This is largely due to traditional forms of model testing having limited power as it is difficult to differentiate between the uncertainties within different model structures, different sets of alternative parameter values and in the input data used to run the model. While model structural uncertainties are important to consider, the uncertainty from input data error together with parameter estimation error are often more significant to the overall residual error, and essential to consider if we want to achieve reliable predictions for water resource decisions. While new philosophies and theories on modelling and results validation have been developed (Beven, 2002; Gupta et al., 2008), in many cases models are not only still being validated and compared using sparse and uncertain datasets, but also expected to produce reliable predictions based on the flawed data. The approach in this study is focused on fundamental understanding of hydrological systems rather than calibration based modelling and promotes the use of all the available 'hard' and 'soft' data together with thoughtful conceptual examination of the processes occurring in an environment to ensure as far as possible that a model is generating sensible results by simulating the correct processes. The first part of the thesis focuses on characterising the 'typical' interaction environments found in South Africa. It was found that many traditional perceptual models are not necessarily applicable to South African conditions, largely due to the relative importance of unsaturated zone processes and the complexity of the dominantly fractured rock environments. The interaction environments were categorised into four main 'types' of environment. These include karst, primary, fractured rock (secondary), and alluvial environments. Processes critical to Integrated Water Resource Management (IWRM) were defined within each interaction type as a guideline to setting a model up to realistically represent the dominant processes in the respective settings. The second part of the thesis addressed the application and evaluation of the modified Pitman model (Hughes, 2004), which allows for surface and groundwater interaction behaviour at the catchment scale to be simulated. The issue is whether, given the different sources of uncertainty in the modelling process, we can differentiate one conceptual flow path from another in trying to refine the understanding and consequently have more faith in model predictions. Seven example catchments were selected from around South Africa to assess whether reliable integrated assessments can be carried out given the existing data. Specific catchment perceptual models were used to identify the critical processes occurring in each setting and the Pitman model was assessed on whether it could represent them (structural uncertainty). The available knowledge of specific environments or catchments was then examined in an attempt to resolve the parameter uncertainty present within each catchment and ensure the subsequent model setup was correctly representing the process understanding as far as possible. The confidence in the quantitative results inevitably varied with the amount and quality of the data available. While the model was deemed to be robust based on the behavioural results obtained in the majority of the case studies, in many cases a quantitative validation of the outputs was just not possible based on the available data. In these cases, the model was judged on its ability to represent the conceptualisation of the processes occurring in the catchments. While the lack of appropriate data means there will always be considerable uncertainty surrounding model validation, it can be argued that improved process understanding in an environment can be used to validate model outcomes to a degree, by assessing whether a model is getting the right results for the right reasons. Many water resource decisions are still made without adequate account being taken of the uncertainties inherent in assessing the response of hydrological systems. Certainly, with all the possible sources of uncertainty in a data scarce country such as South Africa, pure calibration based modelling is unlikely to produce reliable information for water resource managers as it can produce the right results for the wrong reasons. Thus it becomes essential to incorporate conceptual thinking into the modelling process, so that at the very least we are able to conclude that a model generates estimates that are consistent with, and reflect, our understanding (however limited) of the catchment processes. It is fairly clear that achieving the optimum model of a hydrological system may be fraught with difficulty, if not impossible. This makes it very difficult from a practitioner's point of view to decide which model and uncertainty estimation method to use. According to Beven (2009), this may be a transitional problem and in the future it may become clearer as we learn more about how to estimate the uncertainties associated with hydrological systems. Until then, a better understanding of the fundamental and most critical hydrogeological processes should be used to critically test and improve model predictions as far as possible. A major focus of the study was to identify whether the modified Pitman model could provide a practical tool for water resource managers by reliably determining the available water resource. The incorporation of surface and groundwater interaction routines seems to have resulted in a more robust and realistic model of basin hydrology. The overall conclusion is that the model, although simplified, is capable of representing the catchment scale processes that occur under most South African conditions.

Predicted future precipitation is downscaled and used to drive a hydrologic model to assess future erosion potential in a semi-alluvial clay-bed watercourse, Watts Creek. The 21 km2 watershed is predominantly urban, with overall impervious cover of 22%, and the remaining land use split between agricultural and forested areas. Continuous simulations for the open water year, excluding spring freshet (April 1st to October 31st) were performed using the SWMHYMO (Stormwater Management Hydrologic Model) lumped hydrologic modelling platform. A shear stress exceedance and stream power erosion routine was added to the platform to calculate erosion potential. To account for uncertainty in the collected data, nine different observed discharge data sets were used to calibrate the model, each leading to a distinct set of calibrated parameter values. The difference between the observed data sets lies in the choice of rating curves and the collection period. The 2041-2080 precipitation outputs of the fourth version of the Canadian Regional Climate Model (CanRCM4) ran under Representative Concentration Pathways (RCPs) 4.5 and 8.5 at the MacDonald Cartier International Airport were downscaled using quantile matching and then used as input to the hydrologic model. For each set of calibrated parameters, a cumulative effective work index (CWI) based on the reach-averaged shear stress was calculated for Watts Creek during the open water year using both the historic (1968 2007) and projected future (2041-2080) flows, using a bed material critical shear stress for entrainment of 3.7 Pa. Results suggest an increase of 75% (resp. 139%) under RCP4.5 (resp. RCP8.5) in CWI compared to historic conditions for the average measured bed strength. The work index increase is driven by an increased occurrence of above-threshold events, and more importantly by the increased frequency of large events. The predicted flow regime under climate change would significantly alter the erosion potential and stability of Watts Creek. A channel adjustment sensitivity analysis, which balances future erosion potential with historic potential, was implemented and indicated that the channel could widen in the future from the current bankfull width of 6.1 m to 8.2 m for RCP4.5 and 10.2 m for RCP8.5. Specific morphological behaviour should be investigated in more detail, particularly to assess if the governing erosion mechanism is seasonally dependent, perhaps incising during spring freshet and widening when the bed is vegetated in the summer.

Forest harvesting has been shown to cause various changes in water quantity and water quality parameters, highlighting the need for comprehensive forest practice rules. Studies show a myriad of impacts to ecosystems as a result of watershed level changes, such as forest harvesting. Being able to better understand the impact that forest harvesting can have on stream temperature is especially critical in locations where federally threatened or endangered fish species are located. The overall goal of this research project is to assess responses in stream temperature to various riparian and forest harvest treatments in a maritime, mountainous environment. The results of this study aim to inform decision makers with additional information pertaining to the effects of forest harvest on water temperature. Modeling is done as a part of the third Caspar Creek Paired Experimental Watershed study. Located in Mendocino County, the site provides a place for California researchers and decision makers to learn about the cumulative watershed effects of forest management operations on peak flows, sediment production, anadromous fish, macro-invertebrate communities, nutrient cycling and more. Historic data was used to calibrate the Distributed Hydrology Soil Vegetation Model (DHSVM) and River Basin Model (RBM) to measured stream temperatures in the South Fork of Caspar Creek (SFC) for hydrologic years 2010-2016. Critical summer time periods, when temperatures are highest and flows are low, are the primary concern for this work. The key modeling scenarios evaluated were (1) varying percentages of Watercourse and Lake Protection Zones (WLPZ) canopy cover, (2) the 2018-2019 SFC forest harvest and (3) an experimental design converting dominant riparian vegetation along 300-yard stream reaches. Modeling results showed that stream temperatures begin to rise above third-growth conditions when canopy cover is reduced to 25% and 0% retention levels. Larger increases in Maximum Weekly Maximum Temperature (MWMT) values, compared to Maximum Weekly Average Temperature (MWAT) values, were seen across all scenarios. There was essentially no difference between altering buffer areas along only class I streams, compared to along all stream classes. At the 0% canopy retention, MWMT values consistently rose above recommended thermal limits for Coho salmon (Oncorhynchus kisutch) and state regulations prohibiting more than a 5 degree F increase in waters. Clearcutting the entire watershed produced less of an effect than simulations clearing on only the riparian area, suggesting that groundwater inflows act to mitigate stream temperature rises in the SFC. The 2018-2019 harvest showed a relatively consistent increase in MWAT values (avg. 0.11 degree C) and more varied increases in MWMT values (avg. 0.32 degree C). Simulations converting dominant riparian vegetation by clearing could not be considered conclusive due to sensitivity analyses suggesting potentially unrealistic tracking of downstream temperatures. Additional sensitivity analyses suggest that tree height and the monthly extinction coefficient (a function of Leaf Area Index) are most influential on stream temperature changes in SFC. This is consistent with other modeling studies and suggests stream temperature management focus on tall, dense buffers as opposed to wider buffer widths.

This study developed an innovative stormwater quality treatment design framework for effective mitigation of urban stormwater pollution. The research method is primarily based on a stormwater quality modelling exercise and an extensive statistical analysis for defining the relationships among rainfall, catchment and stormwater quality characteristics. The identified relationships were translated into a framework, enabling the determination of rainfall parameters and treatment system design specifications. Adopting this framework will enhance treatment system performances leading to greater protection of aquatic ecosystems.

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.

SMHI:s hydrologiska prognos- och varningstjänst använder sig av meteorologiska ensembleprognoser som indata i hydrologiska modeller. De hydrologiskaensembleprognoserna tar därmed hänsyn till framtida osäkerhet i temperatur och nederbördoch används som underlag vid utfärdandet av risker och varningar för höga flöden. För närvarande beaktas dock inte osäkerheten i modellens starttillstånd, vilket består av de tillståndsvariabler i modellen som beskriver bland annat markvattenhalt och snötäcke. I dennastudie undersöktes hur starttillståndet i den hydrologiska modellen HYPE inverkar på prognoser i syfte att kvantifiera osäkerheten och på sikt möjliggöra säkrare prognoser.Studien hade tre mål: 1) Ta fram ett förslag på hur starttillståndet kan varieras för att ge en god uppskattning av prognososäkerheten relaterat till det hydrologiska starttillståndet. 2) Undersöka sambandet mellan starttillståndens spridning och det hydrologiska prognosfelet. 3) Analysera hur årstider, avrinningsområdens area, sjöprocent, skogsprocent och höjd över havet inverkar på prognososäkerheten. En central hypotes var att mindre skillnad mellan starttillståndets vattenföring och den observerade vattenföringen vid prognosstart resulterar i mer träffsäkra prognoser. Studien begränsades av att starttillstånden endast genererades med hjälp av störningar i drivdata.Indata till HYPE-modellen var femton temperatur- och nederbördsserier som manipulerats i syfte att skapa en ensemble av olika starttillstånd. Denna ensemble användes sedan för att göra vattenföringsprognoser med observerad temperatur och nederbörd som drivdata. Studien omfattade 76 avrinningsområden från hela Sverige med data för perioden 1999-2008. Prognoser utfördes varje dygn och ensemblespridningen utvärderades 2, 4 och 10 dygn in i prognosen. Samma utvärderingar utfördes även på autoregressiva prognoser, vilket innebär att modellerad rättas utefter observerad vattenföring.Resultaten indikerade ett samband mellan ensemblespridning och prognosfel, vilket innebär att spridning kan användas som ett mått på starttillståndets osäkerhet. Prognosfelet korrelerade positivt med skogsprocent och negativt med avrinningsområdenas area, sjöprocent och höjd över havet. Samma samband uppvisades mellan dessa områdesvariableroch spridning. Spridningen var störst på vintern och våren då normalisering skett med medelvattenföring över tio år, och under vår och sommar då normalisering skett med medelvattenföring per månad. Hypotesen att mindre skillnad mellan starttillståndets vattenföring och den observerade vattenföringen vid prognosstart resulterar i mer träffsäkraprognoser bekräftades av resultaten. Implementering av en ensemble av olika starttillstånd i operationella prognoser vid SMHIs hydrologiska prognos- och varningstjänst föreslås i syfte att kvantifiera osäkerheten och därigenom utöka bedömningsunderlaget vid utfärdande av risker och varningar.
The Hydrological Forecast and Warning Service of The Swedish Meteorological and Hydrological Institute (SMHI) use meteorological ensemble forecasts as input in hydrological models. The hydrological ensemble forecasts take the uncertainty of future temperature and precipitation into account and serve as the basis of issued risks and warnings of high flows. Currently not considered is the uncertainty of the initial state, which consists of state variables in the model describing for instance soil water content and snow pack. This study assessed the impact of the initial state on forecasts in the hydrological model HYPE aiming to quantify the uncertainty and eventually enable more accurate forecasts.There were three aims of this study : 1) Evaluate a suggestion about how the initial state can be varied to give a good estimation of forecast uncertainty related to the hydrological initial state. 2) Examine the relationship between the spread of initial states and the hydrological forecast error. 3) Analyze the impact of seasons, catchment area, lake percentage, forest percentage and elevation on forecast uncertainty. A central hypothesis was that a smaller difference between the discharge of the initial state and the observed discharge results in more accurate forecasts. A restriction of the study was that the initial states only could be generated by disturbances of forcing data in before the forecast.Input data to the HYPE model were fifteen temperature and precipitation series, manipulated to generate an ensemble of different initial states. This ensemble was then used to make discharge forecasts with observed temperature and precipitation as forcing data. The study was performed on 76 catchments all over Sweden with data from the time period 1999-2008. Forecasts were made every day and the ensemble spread was evaluated 2, 4 and 10 days into the forecast. Autoregressive forecasts where the modelled discharge is corrected after the observed discharge were executed and evaluated as well. The results indicated a relationship between ensemble spread and forecast error, which implies that the spread can be used as a measure of the uncertainty of the initial state. The forecast error and ensemble spread correlated positively to forest percentage and negatively to catchment area, lake percentage and elevation. The same trend was detected between spread and catchment characteristics. The spread was biggest in winter and spring when normalization was made with mean discharge for the ten-year period and in spring and summer when normalization was done with mean discharge per month. The hypothesis that a smaller difference between the discharge of the initial state and the observed discharge results in more accurate forecasts was confirmed by the results. An implementation of an ensemble of different initial states in operational forecasts at SMHI’s Hydrological Forecast and Warning Service is suggested in order to further quantify the uncertainty of hydrological forecasts, and thereby improve the basis of judgment when issuing risks and warnings.

Orientador: Jose Teixeira Filho
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola
Made available in DSpace on 2018-08-03T23:55:35Z (GMT). No. of bitstreams: 1 Ferreira_Lucia_D.pdf: 1500242 bytes, checksum: f168afe0384add0cf44eeb8198bdd9c6 (MD5) Previous issue date: 2004
Doutorado
Agua e Solo
Doutor em Engenharia Agrícola

The main objectives of this work were to investigate Geographical Information Systems techniques for modelling a cross-country trafficability. To accomplished stated tasks, reciprocal relationships between the soil deposits, local hydrology, geology and geomorphology were studied in relation to the study area in South-Eastern Sweden.

Growing awareness of nowadays users of GIS in general is being concentrated on understanding an importance of soil conditions changed after cross-country trafficability. Therefore, in this thesis, constructing of the Soil Knowledge Database introduced to the genuine geological soil textural classes a new, modified geotechnical division with desirable for off-road ground reasoning measurable factors, like soil permeability, capillarity or Atterberg’s consistency limits.

Digital Elevation Model, the driving force for landscape studies in the thesis, was carefully examined together with the complementary datasets of the investigated area. Testing of the elevation data was done in association to the hydrological modelling, which resulted with the Wetness Index map. The three distinguishable soil wetness conditions: dry, moist and wet, were obtained, and used consequently for creation of the static ground conditions map, a visible medium of soils susceptibility to for example machine compaction.

The work resulted with a conceptual scheme for cross-country trafficability modelling, which was put into effect while modeling in GIS. As a final outcome, by combining all processed data together, derivatives were incorporated and draped over the rendered 3D animating scene. A visually aided simulation enabled to concretized theoretical, hypothetical and experimental outcomes into one coherent model of apprised under Multicriterial Evaluation techniques standardized factor maps for ground vehicle maneuverability. Also further steps of research were proposed.

In many parts of the world snow melt runoff influence discharge from combined sewer overflows (CSO) and flooding in urban drainage systems. Despite this, urban snow hydrology is a field that has received little attention from the urban drainage community. The objectives of this research were to better understand urban snow hydrology and through field work and hydrological modelling quantify effects of anthropogenic activities (AA) on snow distribution, and melt in an urban environment. This means in principle how the presence (design geometry) and operation of roads and buildings influence the snow distribution and melt in urban areas. The Risvollan urban catchment (20 ha) located in Trondheim, Norway, was used as a study area. A literature review of urban snow hydrology was also carried out.

A gridded urban hydrology model (GUHM) was developed as part of the study. The principal idea of the GUHM is to subdivide an urban catchment into orthogonal equal area grid cells. The snow routine in the GUHM is based on an energy balance approach, which together with a soil-runoff routine is used to calculate a time series of rain, snow water equivalent (SWE), snow melt, and runoff, for each grid cell. In GUHM, processes such as snow clearing of roads, locally low albedos, heat/shadowing from buildings, and effects of slope and aspect are included in the model structure.

A technique for observing time series of snow covered area (SCA) for an urban catchment is presented. The method is based on image processing and neural network technology to calculate SCA from a time series of images taken from a tall building in the Risvollan catchment. It was shown that SCA on roads and roofs in general becomes more rapidly snow free during melt periods compared to the park areas of the Risvollan catchment. This can be explained by snow clearing of roads, snowdrift from roofs and high snow melt rates on roofs and roads. The high melt rates was attributed to locally low albedos in vicinity to roads, rooftop snow packs exposure to wind and solar radiation, in addition to anthropogenic heat release from the roofs themselves.

Field observations of SWE were carried out in the Risvollan catchment and it was shown that areal mean SWE located on/or nearby roads and buildings were significantly lower during mid and end of the winter, than in park areas. This can be attributed to higher melt rates caused by AA. A time series of SCA and SWE was obtained through field work for the period from 2000 to 2003 in the Risvollan catchment.

The GUHM was applied and calibrated for the Risvollan catchment for a three year period. Two seasons were used as validation period. Comparison between the simulated and observed SWE, SCA and runoff data showed that the GUHM was able to simulate snow accumulation and melt for whole seasons with short time resolution (1 hour) satisfactory.

The GUHM was used to quantify effects of AA on snow distribution and melt for six different land use scenarios in the Risvollan catchment for the period June 1998 to June 2003. The modelling results showed that when the area coverage of buildings and roads increased, the SCA and SWE more rapidly decreased during melt periods. Because of this more runoff will be produced in the early winter season (Jan-March) compared to if the catchment had been covered with only sparsely vegetated areas.

The simulation results showed that when the impervious surface covers of a catchment increase, the peak and volume runoff will also increase, as expected.

Both the field observations and the hydrological model study carried out in this work showed that AA lowers SCA and SWE more rapidly in an urban environment compared to more untouched terrain. The reasons for this are redistribution of snow, and strong snow melt rates on roads, roofs, and in snow deposit areas. Low albedos and anthropogenic heat release are the main reasons for the enhanced snow melt rates.

L'objet de la présente thèse est de caractériser, quantifier et modéliser les flux d'eau au sein de la Réserve Naturelle Nationale de la Tourbière des Dauges, située en Limousin (Massif Central, France) et qui inclue une tourbière acide de fond de vallon et son bassin versant. Un ensemble de techniques, incluant la description de coupes superficielles existantes, la réinterprétation de sondages géologiques profonds, la tomographie de résistivité électrique et une modélisation de la distribution spatiale des formations affleurantes, ont été utilisées pour caractériser la nature et la géométrie des formations d'altération du granite. Les dépôts alluviaux et tourbeux ont été caractérisés et cartographiés par sondage à la tarière et à la tige filetée, et leur conductivité hydraulique estimée par choc hydraulique. Les précipitations, les paramètres météorologiques nécessaires au calcul de l'évapotranspiration potentielle, les débits et niveaux dans les ruisseaux, et les niveaux piézométriques dans la tourbe et les formations minérales sous jacentes ont été mesurés en continu pendant trois ans. Le modèle hydrologique distribué à base physique MIKE SHE / MIKE 11 a été utilisé pour modéliser les écoulements et les niveaux piézométriques au sein de la tourbière et de son bassin versant avec un pas de temps quotidien et une résolution spatiale de IO m. Il est montré que les apports souterrains issus de la zone fissurée du granite et suintant au travers du dépôt tourbeux constituent une part quantitativement importante et fonctionnellement essentielle de la balance hydrique de la zone humide. La présence d'une nappe affleurante entraîne une évacuation rapide vers les cours d'eau des apports par ruissellement ou par précipitation directe du fait de la saturation des histosols. Toutefois, il est montré que le fonctionnement hydrologique à l'échelle locale peut s'éloigner de ce schéma général du fait d'une grande hétérogénéité du taux d'humification et de la conductivité hydraulique de la tourbe, de la présence de dépôts alluviaux très perméables sous ou au sein du dépôt tourbeux et de perturbations anthropiques passées. Une fois calibré, le modèle hydrologique, qui représente la zone fissurée du socle granitique comme un milieu poreux équivalent, donne des résultats satisfaisants à très bons selon les indicateurs de performance utilisés: il est capable de reproduire les débits dans les cours d'eau au niveau des quatre stations de jaugeage disponibles, et le niveau de la nappe dans la plupart des piézomètres installés. A l'échelle du bassin versant étudié, le niveau moyen de la nappe simulé par le modèle montre une très bonne concordance avec la distribution observée des végétations de zone humide, cartographiée de manière indépendante. Les analyses de sensibilité ont montré que la porosité efficace et la conductivité hydraulique horizontale de la zone fissurée du granite sont les paramètres auxquels les débits et les niveaux de nappe (y compris dans la tourbe) simulés par le modèle sont les plus sensibles, ce qui démontre l'importance d'une meilleure caractérisation des formations d'altération du granite dans tout le bassin versant pour la compréhension et la modélisation du fonctionnement hydrologique de ce type de zone humide. Le modèle a été utilisé pour simuler l'impact potentiel d'un changement d'occupation des sols au sein du bassin versant sur la balance hydrique et les niveaux de nappe dans la zone humide, ainsi que sur les débits dans les cours d'eau. Le modèle suggère que le remplacement des végétations conduirait à une réduction substantielle des apports de surface et souterrains à la tourbière et à un abaissement conséquent des niveaux de nappe dans les histosols en période estivale
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. lt 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 see page 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 of past human interference including drainage. The equivalent porous medium approach used to mode 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 parameter to which simulated stream discharge and groundwater table depth, including in peat, are most sensitive. The model was forced with new vegetation pararneters to assess the potential impacts of changes in catchment land use on the mire hydrological conditions. Replacement of the broad leaf woodlands that currently cover most of the catchment with conifer plantations would lead to a substantial reduction in surface and groundwater intlows to the mire and to a substantial drop in summer groundwater table depths, particularly along the mire margins

L'infiltration à la source des pluies courantes est largement encouragée par les pouvoirs publics. Pourtant, les conséquences d’une systématisation de ces pratiques à l’échelle du quartier ou de la ville restent mal connues, notamment du point de vue du compartiment souterrain. Outre la question de l’éventuelle pollution des nappes par l’eau issue du ruissellement urbain, différents travaux démontrent le risque d’introduire une recharge excessive des aquifères ou mettent en lumière les fortes incertitudes quant à la proportion des volumes infiltrés participant effectivement à la recharge des nappes et aux débits de base ou à celle regagnant finalement le réseaud’assainissement par infiltration des eaux souterraines dans les conduites. Le faible nombre d’études et le caractère spécifique des sites d’application limitent toutefois la compréhension des mécanismes en jeu et de l’influence du contexte naturel et urbain.Cette thèse vise à préciser les effets potentiels d’une systématisation de l’infiltration à la source des eaux pluviales sur le fonctionnement hydrologique de petits bassins versants urbanisés et les facteurs gouvernant ces effets (caractéristiques du contexte climatique, hydrogéologique, d’occupation des sols et de la stratégie d’infiltration mise en œuvre). Il s’agit par ailleurs d’apporter des éléments de compréhension quant aux apports et limites des modèles hydrologiques distribués pour l’évaluation de stratégies d’infiltration à l’échelle du quartier ou de petits bassins versants.La réponse à ces objectifs s’appuie sur l’utilisation du modèle URBS qui permet de simuler en continu et de manière distribuée le fonctionnement hydrologique de zones urbanisées. La représentation du compartiment souterrain a été enrichie et consolidée pour simuler plus finement les écoulements en zone non-saturée et saturée et modéliser une plus grande variété de sols, d’aquifères et de structures souterraines.Le fonctionnement hydrologique d’un ensemble de bassins versants fictifs a été modélisé en faisant varier les caractéristiques du contexte climatique, hydrogéologique, d’occupation des sols et de la stratégie d’infiltration. Les résultats confirment l’intérêt des ouvrages d’infiltration pour la maîtrise du ruissellement et mettent en évidence leurs limites pour rétablir les autres composantes du bilan hydrologique, en particulier le flux d’évapotranspiration. Les ouvrages d’infiltration entraînent en conséquence un accroissement de la recharge pouvant se traduire par une élévation de la nappe générant des interactions complexes entre volumes infiltrés, nappe, végétation et structures souterraines, en particulier en présence d’une nappe peu profonde et d’un aquifère peu transmissif. Outre le contexte hydrogéologique, le climat (e.g. répartition des précipitations et de la demande évaporative) et les caractéristiques de l’occupation des sols (e.g. densité) et sous-sols (e.g. type et répartition des structures souterraines) sont déterminants dans la capacité à retrouver un fonctionnement hydrologique pré-développement. Les résultats suggèrent ainsi que les stratégies d’infiltration doivent être adaptées localement aux spécificités du contexte et envisagées en combinaison d’une maîtrise de l’imperméabilisation et/ou d’autres ouvrages (e.g. toitures végétalisées).La simulation du fonctionnement hydrologique d'un secteur en cours d'urbanisation situé en région parisienne a montré la pertinence d'un tel outil pour l’étude du fonctionnement hydrologique des milieux urbanisés mais aussi ses limites dans un contexte opérationnel. Elle a permis d'illustrer la forte incertitude liée à la méconnaissance du sous-sol et d'identifier des pistes d'amélioration du modèle, notamment sur la description de la transpiration
Source-control infiltration practices are widely promoted by public authorities. However, the consequences of a systematization of these methods at the neighborhood or city scale remain poorly known, especially with regard to the underground compartment. In addition to the question of the possible pollution of groundwater by urban runoff, various studies demonstrate the risk of introducing an excessive recharge of aquifers or highlight the strong uncertainties regarding the proportion of infiltrated volumes that actually contributes to groundwater recharge and to base flows or that finally returns to the sewerage system by groundwater seepage into the pipes. However, the small number of studies and the site-specific nature of the applications limit the understanding of the mechanisms involved and of the influence of the natural and urban context.This thesis aims at specifying the potential effects of a systematization of stormwater source-control practices on the hydrological functioning of small urbanized watersheds and the factors governing these effects (characteristics of the climatic, hydrogeological and land use context and of the implemented infiltration strategy). It also aims to provide insights into the contributions and limitations of distributed hydrological models for the evaluation of infiltration strategies at the neighborhood or small watershed scale.The response to these objectives is based on the use of the URBS model which allows continuous and distributed simulation of the hydrological functioning of urbanized areas. The underground compartment depiction has been enriched and consolidated to more finely simulate unsaturated and saturated flows and to model a wider variety of soils, aquifers and underground structures.The hydrological functioning of a set of hypothetical watersheds is modeled varying the characteristics of the climatic and hydrogeological context, the land use and the infiltration strategy. Results confirm the benefits of infiltration systems for runoff control and highlight their limitations in restoring the other components of the water balance, especially the evapotranspiration flow. As a consequence, infiltration devices increase groundwater recharge, which can lead to a rise in the water table, generating complex interactions between infiltrated volumes, water table, vegetation and underground structures, especially in the presence of a shallow water table and a low-transmissive aquifer. Besides the hydrogeological context, the climate (e.g. distribution of precipitation and evaporative demand) and the characteristics of the land use (e.g. density) and subsoil (e.g. type and distribution of subsurface structures) are determinant in the ability to recover a pre-development hydrological functioning. Results suggest that source-control infiltration strategies should be locally defined according to the specificities of the context and considered in combination with a control of imperviousness and/or other types of devices (e.g. green roofs).The simulation of the hydrological functioning of a partially urbanized watershed located in the Paris region highlights the relevance of such a tool to study the hydrological functioning of urbanized environments, but also its limitations for operational purposes. This application illustrates the high uncertainty linked to the lack of knowledge of the subsurface compartment composition and to identify ways to improve the model, especially regarding the description of transpiration

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

Kunskap om grundvattenbildningen är nödvändig för att man ska kunna förutsäga konsekvenserna av grundvattenuttag och underjordsbyggande. Grundvattenbildningen i berggrunden är dock svår att uppskatta. Syftet med avhandlingen var att öka förståelsen av grundvattenbildningen i kristallin berggrund, att undersöka hur grundvattenbildningen ska uppskattas samt att utveckla nya modeller för att beskriva grundvattenbildningen. Studien grundades på tre angreppssätt: grundvattendatering med freoner (CFC), geohydrauliska observationer och matematisk modellering.

Koncentrationerna av CFC-11 och CFC-113 befanns vara låga i det undersökta berggrundvattnet, vilket i kombination med låga syrgashalter tyder på anaerob nedbrytning. Koncentrationerna av CFC-12 och tritium överensstämde ganska väl, vilket betyder att den skenbara åldern kan vara den sanna åldern. Resultaten tyder på att CFC-datering inte är pålitlig i skogsmiljöer med finkornigt jordtäcke.

Vid nederbörd observerades ett snabbt gensvar i den hydrauliska potentialen i den studerade bergakviferen, trots det 10 m mäktiga moräntäcket. En avsevärd del av de observerade potentialvariationerna befanns vara belastningseffekter, som inte innebar någon magasinsförändring eller något vattenflöde. Berggrundens belastningseffektivitet uppskattades, ur potentialens svar på lufttrycksförändringar, till 0,95. Ytbelastningen beräknades från mätningar av lufttryck, vatten i jordtäcket och snö. Omkring 20 % av årstidsvariationen hos den hydrauliska potentialen uppskattades bero på enbart belastningsförändringar. En enkel begreppsmässig modell kunde användas för att simulera den observerade hydrauliska potentialen. För att beskriva enskilda grundvattenbildningstillfällen på bästa sätt var det nödvändigt att ta hänsyn till effekten av ytbelastningen.

Numeriska experiment gjordes med en modell av en jord–bergprofil. När berget modellerades som ett heterogent kontinuum bildades omättade zoner i berget vid stora hydrauliska gradienter. Fenomenet uppträdde i områden där låggenomsläppliga zoner låg uppströms höggenomsläppliga zoner, och ledde till minskad hydraulisk konduktivitet i berget.

Knowledge about the groundwater recharge is essential for the prediction of impacts of groundwater withdrawal and underground construction. Recharge in the bedrock is, however, difficult to estimate. The objectives of this thesis were to increase the understanding of groundwater recharge in crystalline bedrock, to investigate how the recharge could be estimated, and to develop new models to describe the recharge. The study was based on three approaches: groundwater dating using chlorofluorocarbons (CFCs), geohydraulic field measurements, and mathematical modelling.

Low concentrations of CFC-11 and CFC-113 were found in the bedrock groundwater, which in combination with low dissolved-oxygen levels indicated anaerobe degradation. The CFC-12 and tritium concentrations agreed fairly well, which means that apparent ages could be true ages. The results suggest that CFC dating may not be reliable at forested, humid sites covered by fine-grained soil.

A quick response in hydraulic head to precipitation was observed in the studied bedrock, despite the 10-m thick till cover. A substantial portion of observed head variations was found to be loading effects, involving no storage changes or water flow. The loading efficiency of the bedrock was estimated, from the air-pressure response, to be 0.95. The surface loading was calculated from measurements of air pressure, water in the soil, and snow. About 20% of the seasonal variation of the hydraulic head was estimated to be related to loading changes only. A simple conceptual model could be used to simulate the observed hydraulic heads. The loading effect had to be included to properly describe individual recharge events.

Numerical experiments were performed with a soil–bedrock profile. When the rock was modelled as a heterogeneous continuum, unsaturated zones developed at high hydraulic gradients. The phenomenon appeared in areas where low-conductive zones were located upstream of high-conductive zones, decreasing the effective hydraulic conductivity of the material.