Simulation of Basin Hydrological Processes Considering Air Resistance Effect
2018, 33 (8):
In the process of rainfall infiltration, part of the air will be trapped in the soil, which affects soil moisture infiltration. However, when simulating the basin hydrological processes, the current distributed hydrological models fail to consider the effect of air resistance on rainfall infiltration. This effect is mainly reflected in two aspects: 1) The air trapped in the soil results in that the actual moisture content and hydraulic conductivity of the soil profile are less than the saturated water content and saturated hydraulic conductivity, respectively. 2) Air trapped in the soil creates air pressure, which reduces soil infiltration rate. Consequently, the applicability and simulation accuracy of existing models are hindered. Based on the Green-Ampt model, the saturation coefficient related to soil moisture content and saturation coefficient related to soil water conductivity were introduced in this paper to correct the saturated water content and saturated hydraulic conductivity of the distributed hydrological model. Simultaneously, this paper introduced the air bubbling pressure and water bubbling pressure to quantify the effect of air pressure on soil water suction at wetting front. Using these four parameters, the rainfall infiltration module in the distributed hydrological model (WEP-L model) was modified. Finally, the traditional WEP-L model and the modified model were used to simulate the rainfall-runoff process in the Qingshui River Basin and the Liujiang River Basin, and the simulation results were compared and analyzed using the rainfall runoff data at Qingbaikou Station and Liuzhou Station, respectively. The results show that when using the modified WEP-L model in the Qingshui River Basin, a small watershed, the simulation accuracy was significantly improved, especially in rainstorm periods. For the simulation of monthly runoff in Qingbaikou Station, when using the modified WEP-L model the relative error between simulated and measured values decreased from 53.71% to 23.50% compared when using the traditional model, and Nash-Sutcliffe efficiency coefficient increased from 0.63 to 0.90 during the calibration period. Moreover, during the validation period, the relative error decreased from 50.39% to 20.87%, and Nash-Sutcliffe efficiency coefficient increased from 0.78 to 0.84. For the simulation of daily runoff in rainstorm periods, the absolute relative error of flood peaks decreased from 23.64% to 14.63%. While using the modified model in the Liujiang River Basin, a large watershed, the improvement of simulation accuracy was not obvious. The reason may be that: 1) Compared with the small watershed, the impact factors of rainfall-runoff in the large watershed are more complicated and diverse, and the adaptability of the catchment to the changes in rainfall intensity and underlying surface conditions is stronger, which make the effect of air resistance more difficult to be significantly reflected. 2) The climatic zones and runoff mechanisms of the two basins are different. Qingshui River Basin is located in the semi-humid and semi-humid area where the runoff yield is dominated by excessive infiltration, so the effect of air resistance is relatively greater.
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