Sahar Daraei; Abdolreza Bahremand; Hamid Karimi
Abstract
The land use changes cause changes in components of the hydrological cycle and increase or reduce the amount of runoff. Subsurface runoff is one of the most important parts of the runoff in wet areas, especially in steepy lands with higher vegetation. Given the advantages and capabilities of distributed ...
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The land use changes cause changes in components of the hydrological cycle and increase or reduce the amount of runoff. Subsurface runoff is one of the most important parts of the runoff in wet areas, especially in steepy lands with higher vegetation. Given the advantages and capabilities of distributed hydrological models, these models are appropriate to assess changes in land use and quantitative estimates of changes. In this study, evaluation of the effects of land use change scenarios on the subsurface flow rate was investigated using WetSpa model on daily basis in Horo-Dehno Watershed with an area of 263.43 Km2. Daily hydro-meteorology data including evapotranspiration, precipitation and temperature from 2006 to 2010 were used to run the model, . The model input maps included DEM, land use and soil texture maps. According to the watershed potentials, four scenarios of land use change were planned in ArcGIS and entered in the calibrated model for simulation. In order to use model to simulate the effects of land use change scenarios, sensitivity and uncertainty analysis and calibration were performed manually and afterwards with the PEST optimization program. In addition, to compare the output hydrograph of subsurface flow in current situation of four scenarios with simulated results, changes in hydrological processes and parameters were evaluated. This analysis showed that improving land use is the reason of increasing of subsurface flow, increasing of deep infiltration, reducing of surface runoff and increasing of watershed time of concentration . Whereas, land degradation reduces the amounts of subsurface flow, permeability to deep and surface aquifers and increases runoff volume. Therefore, maintaining and improving current land uses are one of the major alternatives for watershed surface runoff management.
Touraj Sabzevari; Mehdi Mokhberi; Sadegh Hosseini khotbehsara
Abstract
Catchments consist of a series of sloping pervious overland whose surface and subsurface runoffs are transmitted to their outlet through stream networks. In the catchments with high perviousness and good vegetation cover, the amount of subsurface gains more significance and it might have a considerable ...
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Catchments consist of a series of sloping pervious overland whose surface and subsurface runoffs are transmitted to their outlet through stream networks. In the catchments with high perviousness and good vegetation cover, the amount of subsurface gains more significance and it might have a considerable share in the direct runoff. In this study, a hydrologic rainfall simulator model with the length of 1.92 meter and width of one meter and depth of 0.35 meter has been used which its surface and subsurface amount of flow have been measured by means of two different weirs. The texture of soil in Estahban Watershed was loamy sand. The experiments were conducted under three slope angles of 0.1, 3, 6 and 9 degrees and under rainfall intensity of 31.73, 47.6 and 63.46 millimeter per hours. Based on the results, the slope changes from 0.1 to 3 degrees resulted in 50 percent decrease in the subsurface flow and 10 to 15 percent increase in the surface flow in different rainfalls, but, from the slope of 3 to 9 degrees, no significant change was observed in the two flows and in the slope change from 6 to 9 percent of subsurface flow and 2 percent of surface flow, there was surface flow observed. The increase in rainfall intensity causes rise in hydrograph amount of surface and subsurface flow. The proportion of surface to subsurface flow changed on average between 7.5 and 14.5 times the subsurface flow under three rainfalls for the loamy sand. With the increase in slope, the surface flow amount increases and infiltration decreases. In this study, two non-linear regression equations were presented for measuring surface and subsurface peaks which is a function of length, slope and rainfall intensity of the slope.
