Hydrologic Modelling for Flood Threshold and Hazard Prediction in the Black Volta River Basin, West Africa

Abstract

The Black Volta River Basin (BVRB) is one of the flood-prone subbasins in the West African subregion experiencing frequent and severe flood-related disasters in recent times. Flood prediction systems embedded with hydrological models are important non-structural measures for effective flood management. This study adopted a Hydrological Modeling approach using Hydrological Engineering Center’s Hydrological Modeling System (HEC-HMS) software to simulate flood events within the BVRB. The future average frequency of occurrence of flood events in terms of peak flows was simulated using the calibrated and validated model and Intensity-Duration-Frequency (IDF) curves for the basin. This was followed by the application of a rating curve to obtain floodwater levels corresponding to the predicted peak discharges and subsequently, a flood hazard classification ranging from moderate, high, and very high severity levels in terms of peak flow and water levels. The Nash–Sutcliffe model efficiency (NSE) coefficient results of > 0.70 for both calibration and validation indicate the model’s good performance in the basin. The model application for flood threshold prediction and hazard classification in terms of peak flows and flood water levels in the basin particularly at the Chache station reveals that a severe flood of magnitude (flood water level >= 8 m and equivalent discharge >= 1935 m3/s) is likely to be experienced in the basin for a rainfall event of at least 25-year return period. Moderate flooding is likely to be experienced for at least a 5-year return period rainfall event (7.0 m =< flood water level < 7.5 m and 1365 m3/s =< peak flow < 1635 m3/s) in the study area. The outcomes of this study help to better understand the hydrological response and flood characterization due to extreme rainfall events for flood monitoring purposes in the BVRB.