Journal of Spatial Analysis

The runoff simulation have  particular importance in Civil works, river training, design and planning of ground water resources, flood control and prevention of environmental hazards and reduction of erosion and sedimentation in the watershed. The runoff in each region varies according to climatic conditions, hydrological, soil and vegetation in the basin. Simulate these processes need to provide the necessary information on the spatial variation of these factors.  In this context, given the diversity of hydrological models, to achieve the most appropriate simulation of hydrologic models and choose the appropriate model requires the evaluation of their performance in each area is commensurate with hydrological conditions. So hydrologicl models, need to recognize the capabilities and limitations of basins.  In this study, the performance of the two models of rainfall – runoff including IHACRES and SWAT models was compared and evaluated in runoff simulation for two watersheds Yalfan and Sulan in Hamedan province in West of Iran .  

     The SWAT model uses various information, including;  hydrometry, climate , soil , topography, vegetation and land use . SWAT (Soil & Water Assessment Tool) is a river basin scale model developed to quantify the impact of land management practices in large and complex watersheds. SWAT model is a hydrology model with the following components: weather, surface runoff, return flow, percolation, evapotranspiration, transmission losses, pond and reservoir storage, crop growth and irrigation, groundwater flow, reach routing, nutrient and pesticide loading. SWAT model uses a two-level disaggregation scheme; a preliminary sub-basin identification is carried out based on topographic criteria, followed by further discretization using land use and soil type considerations. Areas with the same soil type and land use form a Hydrologic Response Unit (HRU), a basic computational unit assumed to be homogeneous in hydrologic response to land cover change.

     IHACRES model is a catchment-scale rainfall – stream flow modeling methodology whose purpose is to characterize the dynamic relationship between rainfall and stream flow, using rainfall and temperature (or potential evaporation) data, and to predict stream flow. The model can be applied over a range of spatial and temporal scales - from small experimental catchments to basins; using minute, daily or monthly time steps. It can be used to fill gaps in data, extend stream flow records, as well as explore the impact of climate change and identify effects of land use changes.

    Data used in this study includes temperature, precipitation and runoff in the period of 2010-1983. Rainfall and temperature data were used from weather stations and runoff gauging stations from basin Sulan  and Yalfan hydrometry stations. In this study we select two periods, first period from 1983 to1999 for calibration and the second period from 1999 to 2009 for validation. Some of the required basic information such as soil, vegetation, topography and land-use maps were used to carry out the research were received from the Research Center of Agriculture and Natural Resources of Hamedan province.      Accordingly, after collecting basic data and analysis of the sensitivity parameters, then calibrate and validate the models. To determine the ability of models Nash Sutcliffe (NS) and determination coefficient ( R2) were evaluated .

    The results showed that both models are acceptable in simulating runoff in both basins. According to the results obtained in the simulation by SWAT model in both basins, Nash Sutcliffe on a monthly scale in the Yalfan basin for calibration period is 0.68 and verification period is 0. 74 and for Sulan basin calibration period is 0.69 and verification period 0.76.

    The flow rate during validation periods have high accuracy. In the Yalfan basin observed daily flow 1.17 cubic meters per second and simulated flow is 1.10 cubic meters per second. As well as an overview of the values of the coefficient of determination can be seen in both basins, amount represents the high precision simulation in monthly and daily scales. Based on the results obtained in the two basins, IHACRES model has been good performance on a monthly scale, so that the Nash Sutcliffe in the Yalfan basin for calibration period 0.68 and for verification periodic 0.72 in the Sulan basin for calibration period 0.64 and for verification periodic 0. 65. In general, both models can be seen by comparing the SWAT model was calibrated and validated with the highest Nash Sutcliffe on the monthly and daily scales. Generally it can be concluded that to simulate the daily and monthly runoff, the SWAT model is recommended for evaluation hydrology process in the Yalfan and Sulan basins. It is essential in most similar studies to determine of rainfall-runoff models with respect to variability of rainfall-runoff models in different climate periods of dry and wet years.

 
In Iran, there is a general risk of runoff and flood, and since this country has a dry to semi-arid climate, its predominant rainfall is not evenly distributed in terms of time and place. Routine runoff at the earth's surface can lead to risks such as groundwater abatement, social issues such as population migration, erosion and loss of soil fertility, sedimentation in reservoirs and water quality in rivers. Also, damage to the agricultural sector, subsidence, the destruction of residential buildings and the reconciliation of the urban, rural and nomadic order are all examples of controversy about the risks that runoff and flooding are due to. The severity of these hazards in the Afje watershed is due to the geographical location, the specific climate, geology and pond factors, and a large volume of flooding every year causes the destruction of residential areas, agricultural lands and many financial and financial losses.                            
In this research, data collection was carried out through library and field resources. The main tools of this research were topographic map of 1: 25000 which was used by GIS software for the separation of layers and determining the boundaries of the basin; Land use maps and user data and hydrologic groups of the study area were also used to estimate runoff height using curve number method and Arc-CN Runoff instrument. Then Arc-CN Runoff tool was used to prepare layers and curve number map (CN). Finally, the runoff height of the studied basin was prepared in the GIS software.
Soil Hydrology Group: According to the studies, in terms of breadth and extent, the Hydrologic Groups C has the largest area with relatively high runoff potential. By matching the map of Hydrologic Soil Groups and the mineralogical units of the basin it can be stated that the green mass tuff and thick conglomerates are in the hydrologic group D, and the thick layers of green tuff, marl and sandstone in the hydrologic group C and the rocky layer of limestone in The hydrological group B is located.
Land use: The hydrological status of the land and types of uses in the Afje watershed basin are as follows. Most of the catchment area is covered by medium-sized meadows, which comprises 53.77% of the basin area and is located in the hydrological group C with relatively high potential of runoff production. The rock outcrops are in the next rank, which is in the hydrological group D.
Runoff curve number (CN): Land use maps and soil hydrologic groups were combined and extracted for each curve number range (CN) and CN map was prepared. The Afjeh basin has a curtain number of 66 to 100. The highest value of the curve number is 100, which is related to the outflow of the Afjeh watershed basin, which is practically inert, so all precipitation becomes runoff. The Afjeh basin has a curtain number of 66 to 100. The highest value of the curve number is 100, which is related to the outflow of the Afjeh watershed basin, which is practically Impervious, so all precipitation becomes a runoff. In fact, the curve number 100 in stone is 5.59 square kilometers from the area of the Afjeh watershed. But gardens and Agricultural land have the lowest CN (curve numbers 66 to 77) in the Afjeh basin, and include 4.53 square kilometers of basin area. Therefore, the lower parts have a lower CN than the upstream of basin.               
The runoff height in the four seasons was calculated based on the daily precipitation values occurring at mentioned times.
Based on the average daily rainfall of spring with a value of 10.79 mm and runoff classification, in a small part of the gardens in catchment area due to high permeability of the soil, 2.54 mm of precipitation has become runoff, although it is due to stone due to The Impervious of the surface, 10.66 mm of precipitation, turned into runoff.
According to the studies carried out and according to the potential maps of runoff production in the Afje watershed, in the garden with the value of the curve number 66 and daily precipitation (for example, in the winter with a rainfall of 4.04 mm), the runoff height is 0.76 mm And the peak of discharge of 0.47 cubic meters per second And has the lowest runoff potential. In winter, the upstream sediments of the basin with curve number 100, runoff height of 3.81 mm and peak of discharge of 2.65 cubic meters per second and almost all rainfall becomes runoff. Therefore, the shortage of water resources, the presence of dry and semi-arid climates in the country and the achievement of sustainable development leads to the optimal use of water resources.
 
keywords: hazard, Arc- CN Runoff, GIS, high runoff, catchment Afjeh