Arid hydrological modeling at Wadi Alaqiq, Madinah, Saudi Arabia

Abstract

Madinah is one of the urban centers that have experienced several devastating floods during the past 50 years. The objectives of this study are to estimate the flood hydrograph and peak discharge in the Wadi Alaqiq in Madinah and its major sub-catchments based on daily rainfall distribution. Daily annual maximum records are chosen for rainfall distribution in the study area. Wadi Alaqiq is located in the western part of the Madinah city and consists of five major sub-catchments, namely, Aqiq, Ruwawah, Reem, Al-Yutmah and Annaqi. The HEC-HMS and modified Talbot models are applied to estimate design flood for various average recurrence intervals (ARI). The analysis involves two stages, where stage one is concerned with modeling of the Wadi Alaqiq sub-catchment and comparison of the peak flow values obtained by previous studies and empirical formulae based on rainfall distribution analysis. In the second stage, the HEC-HMS is run separately for the five sub-catchments of Wadi Alaqiq. The model parameter values are then used to simulate for 25-year, 50-year and 100-year flood hydrographs. The HEC-HMS model is used to analyze the hydrologic behaviour of the wadi catchments. Initial and constant rate loss method is used to determine the hydrologic loss and the excess rainfall was transformed using the Clark\x92s Unit Hydrograph. The peak flow simulations are very close with reported values and those derived by modified Talbot. Also, the peak discharges are applied to model discharges from the HEC-HMS and modified Talbot equations of the five sub-catchments for a set of selected return periods. The direct runoff ratio for Madinah region in wadis Al-Yutmah, Annaqi, Aqiq, Reem and Ruwawah ranged from 25 to 28 of the total rainfall. This is due to topography condition, wadi catchment area and the use of predicted maximum daily rainfall results. The model results are reasonable for rainfall-runoff application and can be used for wadi corridor management in arid region.