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Hydrological assessment of flash flood hazards and the constructed mitigation measures in Wadis affecting Ain Al Soukhna, Northwest Gulf of Suez, Egypt
  • Hanaa Megahed,
  • Mohammed El Bastawesy
Hanaa Megahed
National Authority for Remote Sensing and Space Sciences
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Mohammed El Bastawesy
National Authority for Remote Sensing and Space Sciences
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Abstract

Considerable stretches of barren coastal areas of the Gulf of Suez and the Red Sea have been covered by various anthropogenic activities during the past few decades. Several dykes have been erected on the wadi beds constituting the catchment of Wadi Ghuwaiba, which encloses the industrial zone of Ain Al Soukhna on its large alluvial fan. The multitude of optical remote sensing data, Digital Elevation Model (DEM) and thematic geological data have been integrated into Geographic Information System (GIS) to estimate the hydrological parameters of flash floods, pathways and storage capabilities of the constructed dykes upstream of the industrial zone. Due to the absence of rainfall/runoff data for these ungagged wadis, a semi-distributed hydrological model was developed using the extracted morphometric parameters from the DEM from the analyses of satellite images. Manning equation was used to compute the open channel flow velocities, and the spatial functionalities into GIS were used to estimate the cumulative flow times. Next, the catchments were subdivided into cascading time-area zones using the derivatives of flow direction, accumulation and length from the DEM. Then, the spatially distributed unit hydrograph was computed using a hypothetical rainfall distribution and runoff coefficients, and the obtained time-area zones. The dykes have been visited in the field to measure the distribution of entrapped sediment loads due to the accumulation of torrential flows in these specific areas. The magnitudes of flash floods developed from an effective rainfall of 20 mm will not be fully contained in the storage areas of these dykes and overflows will reach the industrial zone via uncontrolled pathways, thus the area is prone to flash flood vulnerability and additional mitigation measures are still needed. The slack deposits are accumulating with notable rates and have reached 60 cm in some areas. It is strongly recommended to construct a conveying channel downstream of the dykes to collect the surplus overflow and discharge it into the Gulf of Suez via a well-defined channel-pathway