The present study has been conducted to evaluate the efficiency of Clark Instantaneous Unit Hydrograph Model in regenerating flood unit hydrograph in Bazoft watershed in Chaharmahal and Bakhtiari Province. The comparative evaluation is conducted between the 2h-Unit hydographs simulated using Clark model and the one obtained from averaging the observed ones. This comparison is made with the help of statistical criteria viz. relative error, root mean square of error, coefficient of efficiency and bias. It verified high level of compatibility between two unit hydrographs using the dark model and the hydrograph obtained by averaging the observed data.

Among the main objectives in hydrology are to forecast quantitatively the process of rainfall-runoff, and to determine flood discharge at the outlet of a watershed. Flood discharge can be estimated using rainfall-runoff models which explain hydrological phenomena for unmeasured watersheds. Relationship between hydrology and geomorphologic parameters can lead to the estimate of hydrologic response of a basin. The purpose of this study is to investigate the consistency, accuracy and reliability of geomorphologic model (GIUH) in estimating the shape and discharge of flood resulting from a rainfall with certain intensity and duration. The results of this model were compared with SCS (Soil Conservation Service), Snyder, triangular, Rosso and Geomorphoclimatic (GCIUH) unit hydrographs. The results showed that in Kasilian basin with the area of 67/78 km2, GIUH model had the least amounts of main relativity (MRE) and square error (MSE). Furthermore the result showed that the efficiency of geomorphologic model ratio to Snyder, SCS, Triangle, Rosso and GCIUH in Kasilian Basin are 91.06, 99.11, 88.642, 48.19 and 4.94 respectively. Therefore the result of Geomorphologic model compared to other models (based on this study) is the most efficient model to estimate flood discharge.

Efficacy in estimation of storage coefficient in Clark method, as one of the applicable techniques for development of instantaneous unit hydrograph, may have great effect on ultimate unit hydrograph. The present study was therefore conducted in Bazoft watershed in Chaharmahal and Bakhtiari Province to determine the efficiency of developed hydrograph using Clark method and to compare the Muskingum storage coefficient obtained through graphical, Clark and Linsley methods. Firstly, the time-area histogram of the watershed was developed. The 2h-unit hydrograph was then derived using the data collected in Chelgerd climatological and Morghak hydrometric stations. The efficiency of Clark's instantaneous unit hydrograph developed based on graphical, Clark and Linsley methods for calculation of Muskingum storage coefficient was ultimately evaluated. The results of the study revealed that the Clark's instantaneous unit hydrograph resulted from graphical method for estimation of storage coefficient is more compatible with average unit hydrograph existed for the watershed than other two methods.

The Clark method is one of the most applicable techniques for development of instantaneous unit hydrograph whose efficacy depends upon the accuracy in estimating storage coefficient. The present study was conducted in Kasilian watershed in Mazandaran Province to determine the efficiency of developed hydrograph using Clark's method and to compare the Muskingum storage coefficients obtained through graphical, Clark, Linsley, Mitchell, Johnstone-Cross and Eaton methods. To this aim, the time-area histogram of the study watershed was initially developed. The 3h-unit hydrograph was then derived using the data collected in Sangedeh climatological and Valikbon hydrometric stations. The efficiency of Clark’s instantaneous unit hydrograph developed based on 6 methods for calculation of Muskingum storage coefficient was ultimately compared with the observed average 3h-unit hydrograph of the study area. The results of the study revealed that the Clark’s instantaneous unit hydrograph obtained from graphical method for estimation of storage coefficient with estimation error of less than 33.33% and efficiency coefficient of 83% could suitably simulate different components of the observed average unit hydrograph for the study watershed.

Sediment graph is an important tool for soil and water resources management of watersheds. It is therefore important to find an appropriate procedure to simulate sediment graph data in different watersheds with inadequate and unreliable suspended sediment data. However, achieving simple procedures based on easily accessible data has been less considered. Hence, the present study was conducted in Galazchai Watershed in West-Azerbaijan Province, Iran, with an area of some 103 km2 to investigate the ability of synthetic sediment graph development by using hydrograph. Towards this attempt, a databank of 18 storm events occurred during autumn 2011 and spring 2014 was developed and corresponding total and direct hydrographs and sediment graphs were prepared. All total and direct sediment graph components were simulated using corresponding hydrograph components with the help of different bivariate regression models and the best performed model was ultimately determined by applying different criteria. The results showed that the simulation of different total sediment graph components was possible using hydrograph components except for base time and ordinates of 50 and 75 percent of peak. Direct sediment graph simulation results also verified the simulation ability of all components except for ordinates of 75 percent of peak. According to the results, simulation of temporal components with the lower relative errors had better performance than the other components. So that, for total sediment graph, the lowest relative estimation and validation errors for time to peak were 48. 86% and 45. 65%, respectively. Also, the best performed model developed for the direct sediment graph base time had the lowest relative estimation and validation errors of 23. 03% and 21. 75% and the highest coefficient of efficiency of 0. 93.

Estimating runoff from ungauged catchments has been an important subject for experts in planning, development and operation of various water resources projects. Focus of this study was on application and evaluation of Clark instantaneous unit hydrograph in predicting direct runoff hydrograph of Jafar-Abad watershed, Golestan Province. Isochron map and time-area histogram were extracted using GIS technique and IUH of study area was also simulated by Clark IUH model. The direct runoff hydrograph was simulated for six storm events. Time of concentration and storage coefficient were considered for sensitivity analysis of Clark IUH model. The efficiency of Clark IUH model in predicting direct runoff hydrographs was evaluated by Nash-Sutcliffe, relative error of peak discharge, time to peak and volume, and root mean square error criteria. The results showed that Clark IUH model just predicted time to peak and peak discharge with good accuracy. Sensitivity analysis of input parameters (storage coefficient and time of concentration) indicated that model outputs were strongly affected by value of calculated time of concentration for watershed.

The usage of geomorphologic parameters for estimating of unit hydrograph are a basic role in hyrological science. Due to lack of observed data in basins. Relationship between hydrology and geomorphologic parameters can lead to estimate hydrologic response of a basin. Dynamics and static parameters such as velocity and rainfall intensity plus bifraction ratio length ratio, area ratio length and slope of the main stream affect on response of basin. To make relation between these two elements can estimate the output hydrograph of a basin. In this research project by this method for representative basin of Kasilian in north Iran hydro graph were estimated and then by other synthetic methods such as Snayder, SCS and triangular SCS were compared. It is mentioned that the giuh by ROSSO method also acquised. After then these methods compared by observed hydrograph, the result was satisfied and they have no significant differences.

Applications of rainfall-runoff models, are to determine the hydrologic behavior of watershed and to simulate the flow, for designing hydraulic structures and specially evaluating the impacts of operations on the flow regime. According to deficiency of hydrometer data in most of Iran’s watersheds, using simple and convenient hydrologic models and developing them for watersheds without stations is essential. In this context, several methods have been proposed.This study has been compared the consistency, accuracy and reliability of geomorphologic, geomorphoclimatic and nash instantaneous unit hydrographs, in estimating outlet runoff hydrograph characteristics, in Manshad watershed.For this purpose, six storm events were chosen, by using the area’s hydro-meteorological data. Then, the methods’needing parameters, including the area’s morphometric characteristics and the events properties, were calculated.Thus, outlet runoff hydrographs, for each method were determined. Evaluations that have been carried out by using the mean relative error, the root mean square error and the Nash-Sutcliffe indices, confirmed the higher efficiency of Nash model, in estimating peak discharge, with an error of 23.75, time to peak with an error of 28.21 and the complete shape of hydrograph, with efficiency criterion of 0.4, than the other methods. In addition, this method has a high potential in simulating the actual amount of flood volume, with an error of 9.90. Thus, nash model, compared to other models (based on this study), is the most efficient mod el for estimating flood discharge.

Accurate prediction of floods is especially important in arid areas with more irregularities and intensities. Lack of hydrometric stations in these areas of our country, along with the important advantage of the GIUH model, which allows the simulation of precipitation-runoff of a basin with the least information data, led the researchers to evaluate the above model in the basin. Consider the catchment of Minab as their goal. The quantitative values ​​of each of the geomorphological parameters of the GIUH model, the most important of which are the bifurcation ratio, length ratio and area ratio, have been calculated using GIS technology and with the help of HECGeoHMS add-on. In ranking waterways, the Strahler method was used as a basis. The hydrograph model of the geomorphology unit in the study basin has had acceptable results according to the calculated average error equivalent to 17. 22% for the peak discharge of 4 selected events. However, in estimating the peak occurrence time, the amount of error is higher and in all events, the peak discharge time is less than the real time. In addition, the results of this model in the same basin under study also provided acceptable results with an average error rate of about 30% in calculating the peak discharge. The GIUH in Minab catchment has had acceptable results according to the mean error calculated for the peak discharge of 4 selected events. Therefore, it is possible to achieve the desired results from this model in similar conditions and by applying changes.