HYDROLOGIC ASSESSMENT OF WADI SUDR AND VICINITIES, SOUTH SINAI, EGYPT

Abstract

The present thesis is mainly concerned with the evaluation and assessment of both surface water and groundwater hydrological conditions for Sudr major catchment which occupies about 2389km2 in south Sinai. It includes three main drainage basins namely from north to south:- Wadi Lahata (260 km2), Wadi Sudr (743km2) and Wadi Wardan (1385 km2) running in NE-SW direction. In the study area, the shallow groundwater aquifers are directly influenced by the local seasonal rainfall in general and the flash flood storms in particular. In the present study, the rainfall-runoff relationship, and the quantitative and qualitative impacts of rainfall upon the groundwater have been deeply discussed and assessed for each basin, based on the prevailing climatological and hydro-morphological conditions: On the other hand, the interrelation between different water bearing formations in the study area, have been investigated and evaluated through a representative number of a samples for detailed chemical and isotopic analyses aiming to identify the source of each aquifer recharge. The hydrological and hydrogeological studies are categorized and summarized under the following items: Climatology; the study area has a long summer, from April to October; and a short winter from January to March, separated by a transitional period (November-December). Climatic data are collected from the Egyptian Meteorological Authority and the net sites at NASA for the period 1976-2013. The mean daily maximum temperature in July reaches about 36.4°C.while January has the lowest temperature with mean value 8.1°C. The annual average precipitation is 10.58mm, mostly occurs during the autumn and winter seasons. Highest rates of daily evaporation (16.20mm/day) are recorded in June, while October is the most humid month with a relative humidity of about 60%. The area of study is sometimes subjected to a heavy storm in a short time causing flash flood. The storm of January 2010, which is the most severe storms in this area, is used to estimate the runoff volume. Geologically; the sedimentary rocks that prevail in the studied basins range in age from Upper Cretaceous carbonate rocks, Lower Miocene sandstone and evaporites to Quaternary clastic deposits. Such rock units are classified into formations having different lithological characteristics. The main dominant rock units are:- 1. Carbonate Rocks; they occupy a total area of about 1200Km2. This carbonate terrain is mainly covering the upstream portion of the study basins. They consist the main bulk of Jalalah, Wata, Matallah, Duwwi, and Thebes Formations. Such part of studied wadis is mainly related to Upper Cretaceous-Lower Eocene age. Actually this Carbonate terrain occupies the major Eastern part of study area and forms the main mountainous region in the studied wadis, where most of the sub catchments are represented. 2. Sandstone and Evaporites;It belongs mainly to the Lower Miocene age and covering the midstream area of studied wadis. This rock type is actually classified into Sumar, Rudays, Uyun Musa, Karim, Balaim, Hammam Faroun, South Garib and Zayat Formations. It occupies the middle parts of studied wadis, where it is characterized by hilly features. Such Miocene rocks are responsible for the abundance of sulfate salts in the groundwater in the delta, as well as for sabkha deposits along the Gulf of Suez. 3. Quaternary alluvial deposits;they occupy most of the main trunk of such wadis and its tributaries, as well as, the deltas of the studied wadis (Downstream area), which cover a total area of 200 km2. Such deposits are related to the Quaternary in general and the Pleistocene in particular. The thickness of these deposits varies widely from upstream to downstream where it is encountered at the outlets of the wades dissecting Gebel Sin Bisher, Gebel El Raha and Gebel Somar with a thickness of less than 5 m. In the delta the thickness of Quaternary deposits reaches about 50m and increases towards the Gulf of Suez. Geomorphologically;the Digital Elevation Model (DEM) of the study area indicates that, the study area is surrounded at its upstream part by a number of mountains which represent the main watershed area receiving most of the rainfall. Its elevation ranges from 600m above mean sea water level in Gebel El Raha to 916m above mean sea water level in Gebel Dahak. The general surface slopes towards the Suez Gulf. The dominated geomorphological features of the study area are structural plateau, elevated plateau and coastal plain.The study area is greatly influenced by several structure trends W-S, E-W, NW-SE and NNE-SSW comprising normal faults and reverse faults dipping 75°-85° E. The average length of these faults in South Sinai is about 3.6 km and the longest one is Ragabet El-naam fault which has the length of 150 km. It is cutting Sinai from east to west from the El Nakab region until Wadi Sudr. Morphometrically; the main features of the studied basins are as follows:- • All the studied basins have an area exceeds 100 Km2; therefore, all basins can be grouped as large size basins. The main stream order is: - (5th order for Lahata basin, 6th order for Sudr basin and 7th order for Wardan basin). • The number of streams and its lengths are negatively correlated with their order. Basins of high bifurcation ratio (Rb) (Lahata and sudr basins) are usually elongated in shape and permit the passage of runoff over an extended period of aquifers. On the other hand basins of low bifurcation ratios (Wardan basin) is circular in shape, allowing the runoff to pass in short time (low time of concentration) forming a sharp peak. • The drainage texture analysis of studied basins (Stream frequency, drainage density, length of overland flow, drainage pattern) were carried out, no major different exists in the stream frequency of the studied basins; hence, all studied basins have a nearly similar high stream frequency and show consequently a high possibility of runoff water collection. For Wadi Wardan, the drainage density is relatively high and hence the permeability is low. There are no significant difference between the length of the over land flow values of studied basins. But there are relatively decrease southward. This reflects that water concentrates faster in Wardan basin than in other basins. The dominate drainage pattern of the studied basins are dendritic. • The shape characteristics of the basins (circularity, elongation and form factor ratios), reflect that Lahata and sudr basins are elongated, while Wardan basin is relatively near circular in shape.