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.

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.

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.

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.

Given the increasing trend of application of Geographic Information System (GIS) for natural resources study in one hand and complication of biological, geomorphological, hydrological and ecosystem mechanisms on the other hand, scale is an overlooked but very impressive and flourishing concept. As for any natural resources study consistent with its phase, various maps are used and produced so in order to make the achieved results usable for planning as well as management of resources, determination of scale of the study and application domain for the results is very significant. Since using GIUH model in the basins without hydrological data have been widely recommended by hydrologist and this model developed in accordance to the relationship between geomorphological properties of basins and their effects on hydrological responses, so before using that it is essential to determine the optimal scale (in view points of accuracy, time and cost) which in this paper will be selected from 1: 50000 and 1: 25000 scales, inclusively used in topographic maps in Iran, using multi-scale analysis. Of course, it should be mentioned that giving a comparison between the results of GIUH and the recorded data as well as the model’ s effectiveness in our research basin has not been the purpose.

Time of concentration is one of the main topics of physiographic and hydrology studies in watersheds, and it has relatively large impact in calculation of other hydrology parameters, especially flood peak discharge. Moreover, it is used to derive the Unit Hydrograph of watershed. Fractal geometry can be used as a qualitative tool in order to examine the geomorphology of rivers and also modeling of complex natural phenomena. The most important feature which is analyzed about the phenomena is the fractal dimension that has a great importance to understand and predict the behavior of river changes. This article is aimed to find relationships for time of concentration based on fractal dimension using the production of fractal triangular Unit Hydrograph of Walnut Gulch watershed. Accordingly, all sub-watersheds and waterways of Walnut Gulch watershed were separated using the GIS software, image of sub-watersheds were digital image processed and the fractal dimension of waterways were calculated using box counting method. Then, by fitting the curve of watershed fractal dimension with the concentration time, which had been calculated by the Kirpich method, a new time of concentration relation was obtained based on the fractal dimension. Finally, fractal triangular Unit Hydrograph was developed using the new time of concentration. Results showed that the developed triangular Unit Hydrographs had a relatively appropriate match with NRCS triangular Unit Hydrograph.

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.

Historical researches concerning Unit Hydrograph (UH) demonstrate significant variation and presence of noise due to error in measurements and the assumption of linearity in rainfall–runoff relation. In this study, first, the UH is calculated for 16 storm events based on The least square method in a 449 hectare basin located in the vicinity of Riesel city, USA. In order to recognize noise frequencies, spectrums of the UHs are calculated for each UH by Fourier transformation. The results obtained from the spectral analysis are used for the noise reduction of the UH via a normal - weighted moving average method. From 16 smoothed UHs, one UH is selected as the representative UH of the basin by crossvalidation method. The results showed that the methods of the weighted moving average and cross– validation are suitable for obtaining a non – oscillatory and unique UH.

An extensive data collection on precipitation and runoff is required for development and implementation of soil and water projects. The Unit Hydrograph (UH) is an appropriate base for deriving flood Hydrographs and therefore provides comprehensive information for planners and managers. However, UH derivation is not easy job for whole watersheds. The development of UH by using easily accessible rainfall data is then necessary. Besides that, the validity evaluation of different statistical modeling methods in hydrology and UH development has been rarely taken into account. Towards the attempt, the present study was planned to compare the efficiency of different modeling procedures in Hydrograph and 2-h representative UH relationship in Kasilian watershed with concentration time of some 10 h. The study took place by using 23 storm events occurred during four seasons within 33 years and applying two and multivariable regression models and 36 variables. According to the results, the median of estimated errors in estimation of 2-h UH dependent variables for verification stage varied from 37 to 88%. The results verified the better performance of cubic and linear bivariate models and logarithm-transformed data in multivariable model as well. The efficiency of multivariable models decreased when they were subjected to principle component analysis. The performance of backward method was frequently proved for estimation of dependent variables based on evaluation criteria, whereas the forward was found to be more efficient for time-dependent factors estimation.