Academic literature on the topic 'Geomorphological Instantaneous Unit Hydrographs'

The construction of design flood hydrographs for ungauged drainage areas has traditionally been approached by regionalization, i.e. the transfer of information from the gauged to the ungauged catchments in a region. Such approaches invariably depend upon the use of multiple linear regression analysis to relate unit hydrograph parameters to catchment characteristics and generalized rainfall statistics. In the present study, Geomorphologic Instaneous Unit Hydrograph (GIUH) was applied to simulate the rainfall-runoff process and also to determine the shape and dimensions of outlet runoff hydrographs in a 37.1 km² area in the Ammameh catchment, located at northern Iran. The first twenty-one equivalent rainfall-runoff events were selected, and a hydrograph of outlet runoff was calculated for each event. An intercomparison was made for the three applied approaches in order to propose a suitable model approach that is the overall objective of this study. Hence, the time to peak and peak flow of outlet runoff in the models were then compared, and the model that most efficiently estimated hydrograph of outlet flow for similar regions was determined. Statistical analyses of the models demonstrated that the GIUH model had the smallest main relative and square error. The results obtained from the study confirmed the high efficiency of the GIUH and its ability to increase simulation accuracy for runoff and hydrographs. The modified GIUH approach as described is therefore recommended for further investigation and intercomparison with regression-based regionalization methods.

Abstract. The construction of design flood hydrographs for ungauged drainage areas has traditionally been approached by regionalisation, i.e. the transfer of information from the gauged to the ungauged catchments in a region. Such approaches invariably depend upon the use of multiple linear regression analysis to relate unit hydrograph parameters to catchment characteristics and generalised rainfall statistics. The concept of the geomorphological instantaneous unit hydrograph (GIUH), in relating the shape and scale of the catchment transfer function to stream network topology and channel characteristics, offers an alternative methodology. GIUH derivation depends upon a series of assumptions, including that of estimating a "characteristic velocity"; these continue to attract attention and debate. However, if this velocity is expressed in terms of the kinematic wave approximation, the peak and time-to-peak of the IUH may be expressed in terms of a group of catchment and channel characteristics and the intensity of rainfall excess, giving the so-called geomorphoclimatic IUH (GCIUH). Previous studies involving the GCIUH have developed a single IUH relating to the total duration of rainfall excess. In this study, the rainfall excess duration was divided into several (equal) time increments, with separate IUHs being generated for each interval. This quasi-linear approach was applied to 105 storm events from nine catchments in the south-west of England, ranging in size from 6 to 420 (km)2 . The results showed that, providing the time interval chosen is fine enough to capture the shape of the runoff hydrographs, a comparable level of goodness-of-fit can be obtained for catchments covering a range of about 1:75 in area. The modified GCIUH approach as described is therefore recommended for further investigation and intercomparison with regression-based regionalisation methods. Keywords: floods; geomorphology; rainfall-runoff modelling

Flood forecasting at Wonogiri Reservoir is restricted on the availability of hydrologic data due to limited monitoring gauges. This issue triggers study of unit hydrograph modeling using Geomorphological Instantaneous Unit Hydrograph (GIUH) which is based on Geographic Information System (GIS). Analysis of physical watershed parameters was conducted on Digital Elevation Model (DEM) data using software Watershed Modeling System (WMS) 10.1 and ArcGIS. Nash model and S-curve method were used to process triangular GIUH into hourly Instantaneous Unit Hydrograph (IUH) and Unit Hydrograph (UH) and then was compared with the observed UH of Collins method. A sensitivity analysis was conducted on parameter of RL and Nash-model k. Evaluation of accuracy of the simulated GIUH runoff hydrograph was also conducted. The GIUH model generated UH with smaller peak discharge Qp, also slower and longer of tp and tb values than the observed UH. Accuracy test of the simulated GIUH runoff hydrograph using Nash-Sutcliffe Efficiency (NSE) shows that Keduang watershed gives a satisfying result, while Wiroko watershed gives less satisfactory result. The inaccuracies occur due to limited flood events used to derive the observed UH and stream tributaries that were not properly modeled based on Strahler method.

Abstract. The theory of the geomorphological unit hydrograph (GUH) is examined critically and it is shown that the inherent assumption that the operation of the drainage network may be modelled by a corresponding network of linear reservoirs so restricts the instantaneous unit hydrograph (IUH) shape that the effects of further restrictions, reflecting the constraints imposed by the geomorphological laws of the channel network, cannot easily be identified. Without such identification, the geomorphological unit hydrograph theory is untestable and must remain only a plausible hypothesis providing an indication of a two-parameter IUH whose shape and scale factors must still be related empirically to appropriate catchment characteristics.

The geomorphological instantaneous unit hydrograph (IUH) proposed by Gupta et al. (1980) was compared with the IUH derived by commonly used time-area and Nash methods. This comparison was performed by analyzing the effective rainfall-direct runoff relationship for four large basins in Central Italy ranging in area from 934 to 4,147 km2. The Nash method was found to be the most accurate of the three methods. The geomorphological method, with only one parameter estimated in advance from the observed data, was found to be little less accurate than the Nash method which has two parameters determined from observations. Furthermore, if the geomorphological and Nash methods employed the same information represented by basin lag, then they produced similar accuracy provided the other Nash parameter, expressed by the product of peak flow and time to peak, was empirically assessed within a wide range of values. It was concluded that it was more appropriate to use the geomorphological method for ungaged basins and the Nash method for gaged basins.

Rainfall-Runoff modeling is among the classical applications of hydrology. This paper examines the results of 3 hydrologic approaches, particularly Clark Model, Nash Model, and Geomorphic Instantaneous Unit Hydrograph Model. Assumptions are forwarded for the long run use of the Rawalpindi Division, Pakistan’s Small Dam Organization. The catchment of Shahpur Dam was an area under consideration for the study. The Digital elevation model (DEM) was implicated to measure the Nash and Clark model’s geomorphic parameters. Using ArcGIS, catchment satellite imagery was processed to estimate geomorphological parameters. The models have been applied to multiple storm cases. Geographic Instantaneous Unit Hydrograph (GIUH) model gave direct surface runoff hydrograph, whereas, on measured precipitation excess rainfall hyetograph was obtained. Four types of statistical parameters, namely efficiency of the model (EFF), percentage defect in time to attain peak (PETP), percent defect in attained peak Q (PEP), percentage defect in runoff rate (PEV) are used to check model’s efficiency. The comparison is done between the findings of Clark and Nash GIUH models and the original Clark and Nash models. It was observed that GIUH models are equally good even when optimization is done for Clark and Nash model’s parameters. Since the results obtained from these models are more credible, so, these models can be used in ungauged catchments to estimate the hydrographs.

Estimates of design flood are necessary at locations of hydrologic structures (e.g., flood control dams, barrages) in studies related to their planning, design and risk assessment. In situations, where failure of hydrologic structures could have catastrophic consequences on environment and mankind owing to the presence of thickly populated areas and/or nuclear facilities downstream, the design flood estimate is considered to be the probable maximum flood (PMF). The PMF could be estimated by convoluting probable maximum precipitation (PMP) for catchment contributing flow to the target location with Unit hydrograph (UH) of the catchment. For the purpose of convoluting PMP with UH, their effective durations should be the same. Geomorphological Instantaneous Unit Hydrograph (GIUH) could form the basis to arrive at UH of any required effective duration. There is ambiguity in GIUH constructed for gauged locations, as parameters of GIUH are sensitive to (i) scale of map and support/threshold area for initiation of the first order streams, and (ii) the position of outlet of catchment. To address this, recently a strategy based on the hypothesis of self-similarity of stream networks was proposed by Moussa (2009) to estimate GIUH parameters and the resulting GIUH is referred to as equivalent GIUH (E-GIUH). Previous studies on the self-similarity hypothesis were confined to a few French catchments, and did not examine digital elevation model (DEM) based uncertainty. In this perspective, hypothesis of self-similarity‖ was tested on 200 catchments in four Indian river basins (Mahanadi, Godavari, Krishna and Cauvery) having wide range in their areas (19 km2 to 3,00,870 km2) by using the Shuttle Radar Topography Mission (SRTM) DEM data. Results indicated that the self-similarity hypothesis is valid for all the 200 catchments. Parameters required to construct E-GIUH for each of the catchments are provided. In addition, investigations were carried out on 42 gauges in two river basins (Mahanadi and Cauvery) to examine (i) validity of the hypothesis of "self-similarity" with change in DEM source, and (ii) the effect of DEM source (30m resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and 90m resolution SRTM) on morphometric properties of the channel networks, equivalent H-S ratios and the corresponding equivalent GIUH constructed for the catchments. The results indicated that the hypothesis of "self-similarity" was valid for all the 42 catchments irrespective of the DEM source considered for the analysis. Further, SRTM DEM was found to be reliable (when compared to ASTER DEM) for extracting morphometric descriptors for the catchments. Overall the results indicated that uncertainty associated with DEM source cannot be ignored in hydrological studies involving E-GIUHs. To account for spatial variability in extreme rainfall, catchment of a target location (e.g., dam) is often delineated into sub-catchments, many of which could be ungauged. There is dearth of studies to predict E-GIUH for ungauged catchments. To address this, entropy based regionalization approach is proposed which utilizes catchment geomorphological descriptors suggested by Moussa (2008a). Effectiveness of the approach was evaluated by application to 55 catchments of reasonable size (< 5200 km2) in four Indian river basins (Mahanadi, Godavari, Krishna and Cauvery). The analysis yielded three regions, which were shown to be effective in arriving at E-GIUH for ungauged locations through leave-one-out cross-validation experiment. The PMP estimates necessary to arrive at PMF could be determined based on various approaches. Douglas and Barros (2003) proposed multifractal approach (MA) which is deemed to be effective as it considers both physics and statistics of the rainfall process, in contrast to the conventional approaches which are based either on statistical concepts or physical aspects. Their study was confined to eastern United States, and the MA has seldom been used elsewhere possibly due to its theoretical complexity. Investigations were carried out on Mahanadi and Godavari river basins to examine if PMP estimates corresponding to 1-day to 5-day durations obtained using this approach are consistent with estimates obtained using two commonly used approaches [Hershfield method (HM) and Storm Model approach (SMA)]. The SMA is based on physical aspects responsible for causing the storm event at target location, whereas HM is based on statistical concepts. For investigation, 0.5˚ resolution gridded rainfall data was considered, and PMP estimates obtained at grid scale were considered to prepare PMP maps for the basins and to arrive at PMP estimates for catchments in each of the basins. The results indicated that HM and SMA underestimate PMP (relative to MA) for larger durations (>3 days), as storm events whose accumulated rainfall forms the basis to arrive at PMP estimates are less likely to be uninterrupted. Further, among HM and SMA, PMP estimates based on the former method are found to be higher than those based on the latter method for majority of grids over all the durations. In addition, fractal maximum precipitation (FMP) and design PMP (DPMP) maps corresponding to various durations (and return periods) were prepared by applying multifractal approach to 0.25˚ gridded daily rainfall data (3890 grid points) covering the entire India (excluding high altitude Himalayan region). Results indicated that FMP/DPMP estimates cannot be obtained for 651 grid points using the approach. Majority of those 651 grid points are located in north-west (Rajasthan and Punjab states) and north-east of the country, and some parts of Maharashtra and Tamil Nadu states. In addition, a new cluster analysis based regionalization procedure is proposed to address issues associated with construction of envelope curve in Hershfield method, which helps in averting overestimation of PMP for majority of gauges (sites) in the study area. As engineering designs of large-scale hydrological structures are conventionally based on PMF derived from PMP, reduction in PMF estimates is likely to have economic implications. The procedure involves delineation of the study area into zones (regions) on the basis of extreme rainfall characteristics. Those zones are suggested to be considered as the basis for construction of envelope curve and estimation of PMP by Hershfield method. Application of the proposed procedure to India yielded 20 homogeneous PMP zones when regionalization was performed using global K-means (GKM) clustering algorithm for both 1-day and 2-day durations. When the analysis was repeated by considering global fuzzy c-means (GFCM) clustering algorithm, the procedure yielded 17 homogeneous PMP zones. Envelope curve constructed for each of the zones (resulting from GKM and GFCM cluster analysis) was considered as the basis to estimate PMP for each of the 0.25˚ resolution grid points in the zone. The following inferences were drawn from comparison of the PMP estimates with those obtained for the grid points by considering (a) a single envelope curve for the entire India, (b) two envelope curves (one prepared for grid points which are towards north of 20˚ latitude and another prepared for grid points towards south of the latitude) as considered by Rakhecha et al. (1992) and Rakhecha and Soman (1994). (i) PMP estimates obtained based on single/two envelope curve(s) for the entire India are significantly higher than estimates obtained using GKM- and GFCM-based zones (regions),(ii)The differences in GKM and GFCM zone-based PMP estimates appear marginal across India, except for south-eastern part of Rajasthan, Jharkhand and Maharashtra states (in the case of 1-day PMP) and north-eastern part of India (in the case of 2-day PMP), (iii) The differences in PMP estimates obtained based on single/two envelope curve(s) appear (a) marginal for most part of the country in the case of 1-day PMP, but (b) significant for northern part of the country in the case of 2-day PMP (owing to higher values for estimates obtained by fitting a single envelope curve for the entire India) Additional investigations were carried out by fitting river basin specific envelop curves to estimate 1-day and 2-day PMP for each of the 0.25˚ resolution grid points in four river basins (Mahanadi, Godavari, Krishna, Cauvery). Those PMP estimates were found to be generally lower than the corresponding estimates obtained based on single/two envelope curve(s) for the entire India. The river basin based 1-day PMP estimates were significantly lower in the case of Cauvery and Mahanadi river basins. Further it was noted that GKM- and GFCM-based 1-day PMP estimates could be higher/equal/lower than the corresponding PMP estimates obtained based on single/two envelope curve(s) for the entire India or river basin-based region. The GKM- and GFCM-based 2-day PMP estimates for grid points in the river basins are lower than (i) PMP estimates obtained based on single/two envelope curve(s) for the entire India in the case of all the river basins, (ii) river basin-based PMP estimates for Mahanadi, Krishna and Godavari basins, but higher than those for Cauvery river basin. As regions delineated using cluster analysis are based on attributes affecting/depicting rainfall, PMP estimates based on those regions could be considered reliable. On the other hand, river basin constitutes a geographical area demarcated based solely on area draining streamflow on land surface which has no effect on PMP, while other regions (India-, 20˚ latitude-based regions) that formed the basis for PMP estimation are based on political boundary which has no influence on PMP. The utility of E-GIUH and PMP estimates in arriving at probable maximum flood (PMF) for catchment of Hirakud dam in Mahanadi river basin (India) is demonstrated. Further, the sensitivity of PMF estimate to PMP estimates obtained by using Hershfield method, storm model approach and multifractal approach was examined for 1-day and 2-day durations. This involved (i) delineation of catchment of Hirakud dam into sub-catchments of reasonable size (< 5200 km2), (ii) construction of E-GIUH for the sub-catchments (using the proposed entropy based regionalization approach in the case of ungauged sub-catchments), (iii) derivation of 1-day and 2-day unit hydrographs for each of the sub-catchments from its E-GIUH, (iv) determination of 1-day and 2-day PMP estimates for each of the sub-catchments, (v) convoluting PMP estimate with unit hydrograph of corresponding effective duration to arrive at PMF for the sub-catchment, and (vi) routing the PMFs of the sub-catchments through the channel network in catchment of Hirakud dam to arrive at PMF at the dam location.

碩士
國立臺灣大學
農業工程學研究所
88
This study aims at building up a geomorphologic instantaneous unit hydrograph model (GIUH model) that appropriately reflects the characteristics of the real structure of a stream network. Introduced into the model are two main ideas: On the one hand, the width function obtained by River Tools software is proposed to explain the structure of a river network; details of the theory and calculation steps of this method will be given in the paragraphs. On the other hand, in order to deduce travel time distributions in channel links that clarifies the motion tendency of water particles, the kernel function of the GIUH model is decided using the diffusion analogy. The GIUH theory containing the concept of probability is subsequently combined with the width function that represents the structure of river network of watershed to build up a width-function based GIUH in the form of a general formula. Thirty-five typhoon events are included in this study to test and verify the suitability of this model, using data from Bao-Qiao, Heng-Xi, San-Xia and De-Ji watersheds in Taiwan. Errors between the simulation results and the observation values are within acceptable range. In addition to the verification, it can be observed by comparing among results obtained from the four watersheds that different structures of river networks have different GIUHs, which lead to different effects on the outcomes of simulations. The results of this research show that the shape of a river network is an important physiographic factor of the rainfall-runoff process. To this end, the width-function based GIUH proposed in this study can be used to simulate typhoon events for hillslope watersheds in Taiwan and plays a referential role on the planning of flood mitigation and the administering of water-soil conservation in Taiwan.