Geomorphologic Instantaneous Unit Hydrograph Research Articles

Flood Hydrograph Estimation for Ungaged Wadis in Saudi Arabia

Flood hydrograph determination under arid climate for countries like Saudi Arabia is essential for the assessment of water resource potential and for the design of various hydraulic structures. To meet such objectives, hydrological and morphological data from different regions of Saudi Arabia are evaluated for their suitability and tested for model application. The suggested model used in the present study, geomorphologic instantaneous unit hydrograph (GIUH), is applied by the researchers for its application in the selected thirteen representative basins. The calibrated model for gaged wadis can be applied to other ungaged wadis by following the proposed procedure. The mathematically and graphically derived relations are found to be the key elements in the prediction of flood hydrographs for ungaged wadis.

Hydrologic Parameter Estimation Using Geographic Information System

The use of geographic information systems (GIS) can make the task of compiling necessary spatial data and the required hydrologic parameters for modeling watershed runoff relatively easy. Furthermore, recent advances in hydrologic modeling of watersheds have favored the use of physically based methods such as the geomorphological instantaneous unit hydrograph (GIUH) for simulating watershed runoff. A hydrologic model that uses such a procedure is called the watershed hydrology simulation (WAHS) model. The application of this model in hydrology can be facilitated by using a GIS to compile the required data base, composed of various geomorphic and other hydrologic characteristics as spatial‐data input. This process is demonstrated in this paper for select watersheds within the Big Sandy River basin in northeastern Kentucky using a GIS software program called ARC/INFO. Although runoff simulation results using the WAHS model did not compare well with the observed data, this study clearly demonstrates the advantages and disadvantages of using a GIS in runoff modeling that require geomorphic and other spatial data bases.

A deterministic gamma‐type geomorphologic instantaneous unit hydrograph based on path types

A geomorphological instantaneous unit hydrograph is obtained by dividing the whole catchment into subcatchments, according to the different “path types” which water follows to the outlet of catchment. Each subcatchment produces, at its own outlet, an impulse response which is described by a two‐parameter (n, K) gamma function. In traveling to the outlet of whole catchment, each impulse response undergoes a further pure translation with delay time τ, thus producing at the outlet of the catchment a partial impulse response described by three parameters (n, K, and τ). Summation of these partial impulse responses with area weights W forms the impulse response of whole catchment. The parameters K and τ are estimated from catchment characteristics and the flow velocity of each flood event. Area weights W can be calculated from maps after defining the subcatchments. The parameter n is estimated by optimization. The proposed model is tested in two catchments in China and shows encouraging results.

Incorporating hillslope effects into the geomorphologic instantaneous unit hydrograph

Use of gamma distributions of stream holding times, rather than the traditional exponential distributions, results in geomorphologic instantaneous unit hydrographs (GIUHs) that better fit data‐based IUHs. In this paper, hillslope effects are incorporated into the gamma GIUH (GGIUH) model by assuming that the hillslope travel distance in an area of a given order is approximated by the inverse of twice the local drainage density and introducing a hillslope velocity term. A method of moments fitting procedure is developed to estimate the channel and hillslope velocity terms in the GGIUH model from the moments of rainfall input and basin discharge output. It was found that hillslope velocities are 2 orders of magnitude smaller than channel velocities. The values found for the latter are reasonable given the range of values given in the literature for channel velocities. Similarly, the hillslope velocity term found by the method of moments procedure matches macropore velocities reported in the literature.

Geomorphologic Rainfall‐Runoff Model: Incorporating Philip's Infiltration Expression

This paper presents a watershed discharge hydrograph simulation model, based on the hydraulically based geomorphologic instantaneous unit hydrograph (IUH), developed by Kirshen and Bras (1983). This IUH was derived as a function of watershed geomorphology and the response of streams to lateral inflows, determined by solving one‐dimensional linearized equations of motion. The effective rainfall is calculated here to be equal to the gross rainfall minus the infiltration losses, presented with Philip's expression coupled with an empirical equation for soil moisture computation. Consideration is given to the role of mountainous terrain in runoff generation. For mountainous watersheds, the mountain runoff is regarded as a water depth on the alluvial channels. The effective rainfall depth is calculated to be equal to this water depth plus the rainfall depth minus the infiltration losses. The simulation model is verified through applications for three gauged watersheds in Saudi Arabia. A comparison is made between the observed and simulated hydrographs, and evaluation of the model results and limitations is provided.

Case study evaluation of geomorphologic rainfall ‐ runoff model, incorporating linear infiltration expression

AbstractThis paper presents case study applications for the hydraulically‐based geomorphologic Instantaneous Unit Hydrograph (IUH), developed by Diaz‐Granados et al. (1986). This IUH was derived as a function of watershed geomorphology and stream response to lateral inflows. This response was determined by solving one‐dimensional linearized equations of motion including a simple infiltration expression approximated by an infiltration coefficient multiplied by the streamflow discharge. Three gauged watersheds in Saudi Arabia are selected as case studies. A procedure for estimating the stream response parameters (the flow depth, the flow velocity, and the infiltration coefficient) is provided. A comparison is made between the observed and computed hydrographs and an evaluation of the IUH results and limitations is provided.

A streamflow model using physically-based instantaneous unit hydrographs

The Geomorphologic Instantaneous Unit Hydrograph watershed modeling approach is extended to account for subsurface runoff. Watershed response to rainfall is modelled as a Markov process whose parameters can be related to physical watershed characteristics. Time-varying instantaneous unit hydrographs are subsequently derived and convoluted with antecedent rainfall intensities to generate total streamflow discharges. This watershed model was applied to simulate the Little River Watershed in southeast Georgia. Predicted streamflows were found to be in good agreement with streamgage measurements.

Estimation of the time scale of the geomorphologic instantaneous unit hydrograph from effective streamflow velocity

The greatest difficulty in applying the geomorphologic instantaneous unit hydrograph is the estimation of the time scale of the hydrologic response of a basin. We derive the time scale from the effective streamflow velocity of the highest‐order stream and the spatial distribution of velocity throughout the stream network. The latter is described by a dimensionless geomorphologic function with a single‐shape parameter. The proposed method is applied to some Italian basins.

Case study evaluation of the geomorphologic instantaneous unit hydrograph

Several issues related to the probabilistic and hydraulic structure of the geomorphologic instantaneous unit hydrograph (GIUH) are addressed. These issues are: (1) accuracy of the geomorphologic expressions of the probabilities of surface runoff movement in a watershed, (2) identifying, for a given storm, a representative time-average velocity for surface runoff, (3) estimation of this velocity for the ungauged watersheds and effect of velocity estimation errors on the GIUH predictability, and (4) suitability of incorporating a linear expression for infiltration in the GIUH as well as the estimation problem of the infiltration coefficient and its effect on the reliability of predicted hydrographs. These issues are analyzed through application of the GIUH for two gauged watersheds in the southwestern region of Saudi Arabia. Twelve storm events are used in the analysis and the results are presented.

Application of the geomorphological instantaneous unit hydrograph theory to development of forecasting models in Poland

Geomorphological instantaneous unit hydrograph (GIUH) theory has been applied for the estimation of the parameters of two conceptual models: a linear cascade model and a Laurenson-type model. Conceptual models, especially the linear cascade model, are more convenient for operational forecasting than the original GIUH model. A single linear reservoir model is suggested, with limited storage to represent the subsurface flow component. Subsurface flow is significant in Polish mountainous river catchments. Preliminary results of applying the model to operational flood forecasting are described.

A Comparison of Some Methods of Deriving the Instantaneous Unit Hydrograph

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.

The linear channel and its effect on the geomorphologic IUH

The instantaneous unit hydrograph (IUH) is derived as a function of the basin's geomorphological and physiographic characteristics. Inherent in the basin IUH is the response of the individual channels composing the basin. The response of the individual channels is derived by solving the continuity and momentum equations for the boundary conditions defined by the IUH. Both the effects of upstream and lateral inflow to the channels is taken into account in the derivation of the basin's IUH. The time to peak and peak response are used as a basis for comparison between the results produced by this model and those produced by a model where the channel's response is assumed to be an exponential distribution. The comparisons indicate that of the approach taken in this paper is indeed accurate, for example, the assumptions used do not invalidate the model, then the type of channel response used for the basin's IUH is significant, and future efforts must be directed towards parameter estimation.

A rainfall‐runoff analysis of the geomorphologic IUH

The instantaneous unit hydrograph (IUH) derived from the geomorphologic characteristics of a basin and a timing component, the velocity of the discharge, was presented by Rodríguez‐Iturbe and Valdés (1979). To analyze this geomorphologic IUH in real world basins, a study was carried out on several basins in Venezuela and Puerto Rico. The gemorphologic IUH for each basin was compared with the IUH's derived from the discharge hydrograph produced by a physically based rainfall‐runoff model of the same basins. The effects that the nonlinearities of the rainfall‐runoff model have on the derivation of the IUH are analyzed, and further, controlled experiments are carried out in which the IUH is derived under constant velocity conditions. The geomorphologic IUH's and the ones obtained in the experiments are remarkably similar in all the basins analyzed.

Discharge response analysis and hydrologic similarity: The interrelation between the geomorphologic IUH and the storm characteristics

It is shown that the dynamic parameter v of the geomorphologic instantaneous unit hydrograph (IUH) can be taken as the velocity at the peak discharge time for a given rainfall‐runoff event in a basin. This transforms the time variant IUH throughout the event into a time invariant IUH in each storm occurrence. The errors which the a priori estimation of the velocity in the IUH may cause in the calculation of the peak and time to peak of the runoff discharge are estimated for different types of basins and storms; the relative weights of the storm characteristics and the drainage network parameters in the prediction procedure are also studied in detail. Drainage basins are defined as hydrologically similar if they have the same IUH when kinematic conditions are kept the same; through the geomorphologic IUH theory it is shown that the controlling parameter in hydrologic similarity is RL0.43/LΩ.