Verification of Water Infiltration in the Soil in the Flood Occurrence Model Using SCS Probability Distribution Equations and HEC-HMS Model

Subject Areas : Hydrology, hydraulics, and water transfer buildings

Sohrab  Alizadeh ¹ (Department of Civil Engineering, Roudehen Branch, Islamic Azad University, Roudehen, Iran.)
Alireza  Zamani Nouri ² (Department of Civil Engineering, Shahr_e_Qods Branch, Islamic Azad University, Tehran, Iran.)
Babak  Aminnejad ³ (Department of Civil Engineering, Roudehen Branch, Islamic Azad University, Roudehen, Iran.)

Received: 2023-04-25 Accepted : 2023-08-16 Published : 2023-11-22

Keywords: SCS probability distribution equations, HEC-HMS model, flood occurrence model, Infiltration verification,

Abstract :

Background and Aim: One of the biggest challenges of the rainfall-runoff model is to accurately determine the rate of water infiltration into the soil as one of the parameters that determine the size and shape of the hydrographs of historical floods. The studies conducted in different climates that show different morphometry of the earth indicate the weakness of widely used methods such as SCS-CN in determining the rate of water infiltration into the soil. For the SCS-CN method, as the soil storage index approaches infinity, the soil moisture ratio approaches 1, and this is due to the limitation of the SCS-CN method. In this research, focusing on this weakness in the basic relationships of loss calculations, and an integrated approach in determining the infiltration of water into the soil, the magnitude of the historical floods in the watershed was analyzed. The importance of this analysis can be in verifying the magnitude of floods, which is the criterion for determining structures or crisis control programs.Method: Considering that in order to solve the problem of infiltration calculations at the basin scale, and based on the new equations to determine flow losses, a homogeneous but raster criterion is needed, in this research, based on the sensitivity of the produced flow to the amount of losses in the probabilistic investigation of the index humidity and flow ratio, a depth-infiltration model was prepared from the two-dimensional comprehensive model in the range. In this study, based on the new relationships of losses determination, numerical calculations were done in the software and script environment sequentially and based on the outputs of the hydrological model. First, the HEC-HMS rainfall-runoff model structure was generated with Arc Hydro and HEC_GeoHMS extensions in Shadegan catchment. Then, infiltration parameters were determined by SMA method in the analysis of remote sensing images from the basin. In the next stage, the development of the primary continuous model, calibration and validation was done focusing on soil moisture information. After determining the soil moisture relationship based on the results of the soil wetting model, the artificial unit occurrence hydrograph was determined by determining the flood volume based on the SCS-CN and VIC combined method. Results: The general results of the implementation of the hydraulic model of the flood plain showed that the maximum inflow was equal to 3023 cubic meters per second at the 90th hour of the event, and the maximum outflow flood was at the 93rd hour with a figure of 2137 cubic meters per second. The discharge value is assumed to be 0 at the beginning of the calculations. The flow volume at the end of the calculations was equal to 141.03 million cubic meters, which is the remaining volume of 918.36 million cubic meters in the whole event. The difference between the inlet and outlet discharge was calculated as a deficiency of about 6.14%. Also, the layer of flow depth changes shows that the water level in the plain is trying to be at a possible and reasonable level by filling the lower points. So that a large part of the volume of water from the southern strip of the borders of Trava for the active area of modeling will eventually flow into the sea. However, the direction of water movement has even been estimated to be perpendicular to the direct path towards the sea in some cases. These results indicate a maximum depth of 16.4 units in some areas, with a minimum depth of 5.3 units. The important point is that in the plains, according to the cell size, definitely in some cases much lower depths can be calculated. The average depth in active cells is 11.9 meter calculated locally. These figures can change according to different rainfall events.Conclusions: The results showed that it is possible to verify the infiltration based on the new base distribution equations with a probabilistic condition in the estimation of the basin shape parameter. The amount of hydrograph calibration in response to water infiltration in soil is dependent on the correct estimation of initial soil moisture. Flow losses in large-scale watersheds are obtained more suitably based on SCS-based distribution equations. Numerical and hydrological models such as HEC-HMS or modelers such as HEC_GeoHMS are completely dependent on the DEM raw layer introduced for the purpose of upstream demarcation. Changes in land cover in flat areas can actually produce a closed border of the watershed compared to the reality of the land in different simulation models. According to the basic assumptions such as calibration coefficients, the single hydrograph method can be a good substitute for areas without rainfall-runoff statistics. The TUFLOW software model gave the best response to one-dimensional to two-dimensional flow for Shadgan plain according to the type of boundary conditions.

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