| Abstrakt: |
On November 23, 2018, cascading rainfall events that occurred in the upstream section of wadi Al-Lith, which is located in the western part of the Kingdom of Saudi Arabia, caused a failure in the Al-Lith earthen dam. This event was followed by a large-scale devastating flood that inundated the area downstream of the dam, damaging infrastructure and property. The main scope of this work was to identify the causes of catastrophic flooding and ways to prevent and mitigate the potential consequences of a future flood occurrence in the study area. For this purpose, remote sensing images, DEM, field observations, and rainfall data were used. A geospatial integrated approach using a GIS, remote sensing, hydromorphological analysis, and rainfall-runoff modeling was utilized to provide a better understanding of the hydrology of the wadi Al-Lith catchment. Various methods were used for rainfall frequency analyses; supervised classification was applied on Landsat (OLI), in which land-use types were classified to identify the curve number values. Rainfall-runoff modeling was conducted using the catchment characteristics and rainfall analysis to calculate flood volumes and peak discharges. Peak discharge results at the flood event on November 23, 2018, and at 5- and 100-year return periods were used for the prediction of flood extent using the 2D HEC-RAS model. Water inundated depth and velocity were mapped. The result of the 5-year return period simulated model showed a good correlation with the flood extent of the event on November 23, 2018 that extracted from the sentinel-2 image. This model was validated using field observation data and remote sensing interpretation at the real flood event of November 2018. The flood model indicated that a dam failure with the substantial release of an enormous amount of water in a short period created exacerbates the problem. Also, the simulated model of the 100-year return period showed high-risk of the whole floodplain area of Wadi Al-Lith and the urbanized zone, where utterly devastation could be occurred. Finally, the results showed that a new dam proposal is urgently required to prevent the area from future flood events to replace the failed dam with a 45 m high dam. In this case, the reservoir capacity is estimated to be ~147.4 million m3, which is above the runoff volume for a 200-year return period. |
