Assessment of Flood Frequency Pattern in a Complex Mountainous Terrain Using the SWAT Model Simulation

Abstract

Understanding the relationship between rainfall and runoff is one of the requirements and necessities in flood modeling, predicting, and recording annual runoff contributions. This study aimed to evaluate the use of hydrological modeling and flood frequency analysis (FFA) in studying the extent and occurrence of floods in complex mountain basins and the impact of dams on downstream flooding. The N’fis subbasin, the study area, is located in the High Atlas Mountains of Morocco; it drains a total area of 1700 km2 and is characterized by an arid to semi-arid climate in the plains and a subhumid climate in the mountains. Flood modeling in this catchment is very difficult due to the lack of sufficient spatial and temporal flood data available for FFA. Therefore, the SWAT (Soil and Water Assessment Tool), a physics-based continuous model, was used to simulate and reproduce the hydrological behavior upstream of N’fis. The model’s parameters were calibrated and validated using data collected from 2000 to 2016, and the model performed well using Nash–Sutcliffe statistics with a calibration period of 0.52 and a validation of 0.69. Finally, using daily flood data (1982–2016), we performed FFA using the L-moments method (Gumbel, normal, and log-Pearson III). Furthermore, a comparison of the goodness of fit of the Gumbel, GEV, and LP3 distributions to the flood frequency analysis in the N’fis basin highlighted that the GEV distribution gave good results and appears to be the more appropriate distribution. This research will enable better assessment of floods and help water managers and decision makers to better plan and manage flood mitigation.