Flash floods and their effects on the development in El-Qaá plain area in South Sinai, Egypt
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Abstract
The arid regions are dominated to a much larger degree than humid regions by
major catastrophic events. Although most of Egypt lies within the great hot desert belt;
it experiences especially in the north some torrential rainfall, which causes flash floods
all over Sinai Peninsula. Flash floods in hot deserts are characterized by high velocity
and low duration with a sharp discharge peak. Large sediment loads may be carried by
floods threatening fields and settlements in the wadis and even people who are living
there.
The extreme spottiness of rare heavy rainfall, well known to desert people
everywhere, precludes any efficient forecasting. Thus, although the limitation of data
still reflects pre-
satellite methods, chances of developing a warning system for floods in
the desert seem remote. The relatively short flood-to-peak interval, a characteristic of
desert floods, presents an additional impediment to the efficient use of warning
systems.
The present thesis contains introduction and five chapters, chapter one points
out the physical settings of the study area. There are the geological settings such as
outcrop lithology of the study area and the deposits. The alluvial deposits of Wadi
Moreikh had been analyzed using OSL dating to know deposits and palaeoclimatic
conditions. The chapter points out as well the stratigraphy and the structure geology
containing main faults and folds. In addition, it manifests the pesent climate conditions
such as temperature, humidity, wind and evaporation. Besides, it presents type of soils
and natural vegetation cover of the study area using unsupervised classification for
ETM+ images.
Chapter two points out the morphometric
analysis of the main basins and their
drainage network in the study area. It is divided into three parts: The first part manifests
the morphometric analysis of the drainage networks which had been extracted from two main sources, topographic maps and DEM images. Basins and drainage networks are
considered as major influencing factors on the flash floods; Most of elements were
studied which affect the network such as stream order, bifurcation ratio, stream lengths,
stream frequency, drainage density, and drainage patterns. The second part of this
chapter shows the morphometric analysis of basins such as area, dimensions, shape and surface. Whereas, the third part points the morphometric analysis of alluvial fans which
form most of El-Qaá plain.
Chapter three manifests the surface runoff through rainfall and losses analysis.
The main subject in this chapter is rainfall which has been studied in detail; it is the
main reason for runoff. Therefore, all rainfall characteristics are
regarded here such as
rainfall types, distribution, rainfall intensity, duration, frequency, and the relationship
between rainfall and runoff. While the second part of this chapter concerns with water
losses estimation by evaporation and infiltration which are together the main losses
with direct effect on the high of runoff. Finally, chapter three points out the factors
influencing desert runoff and runoff generation mechanism.
Chapter four is concerned with assessment of flood hazard, it is important to
estimate runoff and tocreate a map of affected areas. Therefore, the chapter consists of
four main parts; first part manifests the runoff estimation, the different methods to
estimate runoff and its variables such as runoff coefficient lag time, time of
concentration, runoff volume, and frequency analysis of flash flood. While the second
part points out the extreme event analysis. The third part shows the map of affected
areas for every basin and the flash floods degrees.
In this point, it has been depending
on the DEM to extract the drainage networks and to determine the main streams which
are normally more dangerous than others. Finally, part four presets the risk zone map of
total study area which is of high inerest for planning activities.
Chapter five as the last chapter concerns with flash flood Hazard mitigation. It
consists of three main parts. First flood prediction and the method which can be used to
predict and forecast the flood. The second part aims to determine the best methods
which can be helpful to mitigate flood hazard in the arid zone and especially the study
area. Whereas, the third part points out the development perspective for the study area
indicating the suitable places in El-Qaá plain for using in economic activities.