Hydrological models are one of the currently used techniques for simulating runoff produced from rainfall. These models by simulation of rainfall-runoff process, are able to estimate runoff values in ungauged cachments without spending high cost and long time. AWBM rainfall-runoff model developed by Boughton in 1993, can calculate runoff based on hourly and daily rainfall. Daily and hourly results obtained from the modelling are used in flood management and planning, respectively. This model includes set of surface storage parameters (C1, C2, C3), partial area parameters (A1, A2, A3), and using daily rainfalls and discharges, monthly runoffs and evaporations. In this study, in order to evaluate the model performance, six sub-catchments located in the south of Sistan and Balochestan province were chosen under a case study. The analysis was carried out by the available data from these sub-catchment including Bah in Sistan and Balochstan Province. Daily rainfall data by using TPSS method were converted to regional data and daily diacharge to specific discharge in mm. Finally, accurancy and efficiency of the AWBM model in simulating runoff evaluated by efficiency was and determination cofficients. The results show the model can simulate runoff reasonably in all sub-catchments under study and other ungauged catchments, and also can be used as a useful tool for research and modelling hydrological process of rainfall-runoff in catchments located in arid and semi-arid regions.

Quantifying the impact of climate change and human activities on hydrological processes is of great importance for regional water-resource management. In this study, trend analysis and analysis of the short-term variations in annual streamflow in the Sajasrood Watershed (SW) during the period 1987– 2012 were conducted using linear regression and the Pettitt test. The time series for streamflow in SW exhibits declining trends. The results show that its break point is 1998, so that the streamflow can be divided into the baseline period and the evaluation period. The Soil and Water Assessment Tool (SWAT) was employed to simulate the hydrological processes. SWAT was first calibrated at monthly time step. The NSE, PBIAS, and RSR for the calibration period (1988-1992) were 0. 7, 7. 3, and 0. 55, respectively. The NSE, PBIAS, and RSR for the validation period (1993-1995) were 0. 65,-9. 4, and 0. 58, respectively. The results suggest that SWAT performance was good during calibration and validation periods. The results show that the contribution rates of climate change and human activities to runoff are 33% and 67% during 1999-2012. The proposed framework can help policy makers to regulate the policies accordingly so that the river may restore to a better level and ecosystem may get improved.

The present study aimed to analyze the comprehensive relationships between suspended sediment yield, and rainfall and runoff characteristics on storm basis in Khamsan Representative Watershed with an area of 4193 ha in Kurdistan Province, Iran. In due course, 9 storm events occurred during study period were analyzed 4 of which generated runoff and consequently yielded sediment. Different bivariate regression models were then applied for estimating sediment yield. The results of the analysis verified better performance of linear regression developed based on maximum rainfall intensity with respective determination and efficiency coefficients, and estimation error of 0.843, 0.84 and 39%.

Structure of runoff. rainfall mathematical model comprises of separation base flow discharge and determining infiltration, effective rainfall and direct runoff. These processes are calculated by various methods. Instantaneous unit hydro graph which Nash model in its index sample has considered as a conceptual model, applied widely in runoff. Rainfall models. Here, the author produces a conceptual mathematical model with some proposed methods for determining separation processes of baseflow infiltration, effective rainfall runoff and direct runoff. Non. Linear mathematical optimization is used for calculation of the model's parameters. Performance results of the model prove the superiority of the proposed method over the other common ones. For doing the research, both methods of artificial neural networks and mathematical optimization of instataneous unit hydrograph are used, because the artificial neural network only, requires a lot of information and the results may not always be obtainable, but an artificial neural network. mathematical optimization combination makes possible a quick convergence and assured results.

Due to the global water crisis, having the right information for managing the planning and optimization in different locations is essential. The conventional methods of measuring are very costly, time-consuming and difficult. In recent years in order to reduce this problem and estimate runoff the watershed, the Geographic Information System (GIS) has been used. In this study, by using daily rainfall data in the SMADA software, return period of 2and 50 years was obtained. ArcCN-Runoff tool with respect to the accuracy and precision in numerous research studies have been made to creat maps and volume of runoff curve number and height were used in the watershed KESHAR. KESHAR area into three groups hydrological B -C-D and was divided into seven land use. The results showed that land use and vegetation and importance of the area in the basin is the most important parameter determines the loss of significant influence and impact on runoff .Curve Number Basin KESHAR shows, rocky outcrops small surface area occupied by the greatest CN (91), The highest volume and highest runoff in the user's area Hydro Group C with 08.56 percent, With low permeability and high potential of runoff is derived, Which puts the area at risk of flooding.

The use of GIS and remote sensing to estimate basin runoff has increased in recent years. In this study, curve number and runoff maps of maximum rainfall of 6 hours with 2 year return period were required to map the height of the runoff. Runoff curve number maps were provided in the GIS environment with ArcCN-Runoff. Since runoff curve number is determined based on factors such as soil hydrology, land use, land cover, and hydrological conditions, ETM+images of 2002 in Erdas software and supervised classification were used to develop the land cover map. In addition, the normalized difference vegetation index (NDVI) was used and accordingly pastures were categorized as good and medium, and forests as dense and mid dense. Maps of maximum rainfall of 6 hours were drawn based on the relations and equations of the raining basin by using the DEM map in the GIS environment. Integrating the obtained maps and the equations, the runoff height map was drawn. As a result, the average runoff was 3.18 mm which is more accurate than the findings of traditional methods (about 3.98 mm).

Surface water collection networks are responsible for collecting, transporting and directing runoff to the nearest acceptable outlet. In this research, simulation and evaluation of Ilam City runoff system with the ASSA mathematical model developed by the Autodesk Inc. was carried out. In the present research, the entire study area, which includes in-city and outsides, was divided into 46 sub-basins. The physical properties of each sub-basin were determined using the ArcGIS software and field investigation. Within the Ilam City there are four main channels that lead the runoff of sub-basins out of the city. The runoff from sub-basins was calculated using three methods of rational, modified rational and SWMM. The results of the study showed that the collecting system only had a flood transfer ability during the two year return period and during the return periods greater than five years the major part of the main channels in the city were waterlogged and damaged.

Diverse factors affect the characteristics of the watershed that lead to spatial and temporal variations in the runoff and sediment production processes. Runoff and sediment are the main important elements in the hydrological cycle, and their changes directly affect river systems and sedimentary environments; and their spatial and temporal variations change the morphology of the rivers. Due to differences in soil characteristics, source materials and geological formations, vegetation and slope in different parts of a region, the amount of runoff and sediment produced in these areas can vary with spatial variations. The purpose of this study is to evaluate the spatial variations of runoff and sediment and runoff threshold using rainfall simulation data in the Gharehshiran watershed in Ardebil Province. Considering the importance of spatial distribution of sampling points across the catchment area, the locations of the samples were determined, taking into account the access path to the points, as well as sampling in different formations through determining the boundaries of the study area. The field experiments and simulation of precipitation were carried out using a 1×1m rainfall simulator in 45 points in different geologic formations of the watershed area. The amount of runoff and sediment were measured in each experiment along with recording the threshold time of runoff generation. The measured variables were mapped and interpolated by using Kriging method over the study area. To assess the accuracy of the interpolation results, 7 samples were selected randomly and the Root Mean Square Error (RMSE), Mean Absolute Error (MAE) and Mean Bias Error (MBE) statistical measures were calculated by comparing observational and estimated values. Then, the correlation between the studied variables in various geological formations was evaluated using Pearson correlation analysis. The relationship between sediment and runoff amount, and runoff threshold time were also evaluated using a triple diagram model. The results of the interpolated maps showed that the lowest values of runoff time threshold (1. 99-3. 17 min) were observed in the geological formations of upper part of the watershed having dacite and tracite igneous, volcanic rocks. While the runoff time thresholds were increased (6. 13-7. 25 min) in the low land areas with the old alluvial terraces. The amount of generated runoff in the upper hillslopes of the watershed with dacite and tracite rocks was estimated as (6. 07-7. 25 lit/m2), and the amount of sediment was low (1. 25-1. 66 g/l). Meanwhile, in the lower parts of old alluvial terraces, the amount of runoff production was low (2. 20-3. 50 lit/m2) and the amount of produced sediment was higher with values of (2. 25-3. 5 g/l). The results of correlation analysis showed that the correlation coefficients between runoff threshold and runoff volume were significant at 0. 01 significant level (r =-0. 802). Also, a significant negative correlation (r =-0. 672), were observed between runoff and sediment values. The relationship between the runoff time threshold and the sediment content was positive at significant level of 0. 01 (r = 0. 900). The results of interdependency between the sediment, runoff and runoff time threshold values using triple diagram models showed that the sediment amount was about 2g/l at high runoff time thresholds of 4 minutes with 2. 5-5. 5 lit/m2 runoff amounts. In general, it can be said that the sediment production in the study area is strongly under the effects of runoff amounts in lower time thresholds of runoff. As a remark, the results pointed out that the internal relationship of runoff and sediment production are affected by a variety of effective factors which requires comprehensive studies to reach a final conclusion.

Run off simulation is one of the most important topics in hydrology And its study is based on rainfall-run off models. Several rain fall and run off models have been developed and the most appropriate model should be selected for each catchment. By applying the appropriate model the water consumption will be optimized. The model should be selected for each catchment based on the model abilities and limits. In this study, the performance of two rain fall and runoff models, GR2M and GR4J were compared in Darehtakht Basin in Lorestan Province during 1379 to 1392. The Nash coefficient was used as a decision criteria for comparing two model performances. Nash coefficient for GR4J and GR2M were 42. 7 and 65. 5, respectively. Results showed that both models can predict the performance of the catchment accurately, but, based on Nash coefficient the GR2M is more accurate than the GR4M.

Surface gravel cover is an important factor for contoroling of soil erosion in dry area specially in area that plant can not grow because of excessive dryness and salinity. The objective of this study was investigation effect of different surface gravel cover on runoff and sediment yeild. For this porpose, 36 field plots with 20 meter length and 0. 5 meter width at 3 percent slope were constructed in research field of agriculturev faculty, Shahrekord university. Treatments were including four level gravel cover (0, 10, 20 and 30 percent) and three surface flow rate (2. 5, 5 and 7. 5 L min-1) at three replications that expriment was done in a factorial with randomized complete block design. The results showed that as increasing surface gravel cover decresed the runoff rate and sediment yield significanty (p<0. 001) in comparision with control treatment as linear and exponential, respectively. Aso, statisticaly comparision of the effect different gravel cover on runoff and sediment indicated that the effective gravel cover on runoff and sediment was different with increasing surface flow rate, as suitable gravel cover for surface flow 2. 5 and 5 L min-1 was 20 percent and for surface flow 7. 5 L min-1 was 30 percent gravel cover.