Hydrological assessment of flash flood hazards and the constructed
mitigation measures in Wadis affecting Ain Al Soukhna, Northwest Gulf of
Suez, Egypt
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