Assessment of the renewable groundwater resources of Wadi ... Kid watersheds covers an area of 1500-3500 km2 , and each of the remaining 12 ... Strategic Initiatives Program through US Department of Energy Contract W-3 l-109-Eng-38.
Remole Sensing and Hydrology 2000 (Proceedings of a s y m p o s i u m held at Santa Fe, N e w Mexico, U S A , April 2000). IAHS Publ. no. 267, 2 0 0 1 .
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Assessment of the renewable groundwater resources of Wadi El-Arish, Sinai, Egypt: modelling, remote sensing and GIS applications
H A Z E M M. GHEITH EMH&T,
South
East Building,
140 North
High Street,
Gahanna,
Ohio 43230,
USA
e-mail: h g h e i t h @ e m h t . c o m
M O H A M E D I. SULTAN Argonne National Laboratory, Environmental Argon ne, Illinois 60439, USA
Research
Division,
9700 South
Cass
Avenue,
Abstract Recharge of the alluvial aquifers flooring Wadi El-Arish in central and northern Sinai, Egypt was investigated. A hydrological model that combined the spatial and temporal distribution of rainfall, suitable infiltration parameters, and appropriate sub-basin unit hydrographs to estimate rainfall excess, transmission losses along stream networks, and downstream runoff was developed. The Wadi El-Arish watershed receives an annual average rainfall of 981.3 x 10 m in the rainy season (November-March) of which our model indicates that 938.7 x 10 m is the initial upstream loss, 32.5 x 10 m is the transmission loss recharging the alluvial aquifers flooring the stream network, and 10.1 x 10 m is downstream runoff. 6
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K e y w o r d s alluvial aquifer; arid r e g i o n ; g r o u n d w a t e r r e c h a r g e ; L a n d s a t T M ; r e m o t e s e n s i n g ; Sinai, transmission losses
INTRODUCTION Sporadic storms over the Sinai hills (Egypt) are channelled as surface runoff and subsurface waters through a network of minor valleys, which join into a few valleys that ultimately drain towards the Mediterranean Sea, the Gulf of Suez, or the Gulf of Aqaba. The largest of these drainage basins is the Wadi El-Arish watershed (22 000 km ), which collects over 6 0 % of Sinai's precipitation. W e constructed a hydrological model to calculate initial upstream loss, transmission loss, and downstream runoff for the Wadi El-Arish watershed. The model integrated Landsat Thematic Mapper (TM), Digital Terrain Elevation (DTED), meteorological, and geological data in a geographic information system (GIS) environment. 2
METHOD Digital mosaics were generated and co-registered. Three data sources were used: threearc-second DTED, TM data (Fig. 1(a)), and geological maps. Watersheds and channel networks (Fig. 1 (b)) were then delineated from the D T E D and verified by comparison to co-registered TM scenes and geology maps. Monthly mean precipitation values averaged between 1920 and 1980 m m (Legates & Wilmott, 1997) and an archival
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Hazem M. Gheith & Mohamed I. Sultan
Fig. 1 (a) Mosaic of four Landsat TM band-5 images covering the Precambrian volcanic-sedimentary rocks cropping out in southern Sinai (dark) and the Cretaceous and Tertiary outcrops (bright) to the north, which are largely composed of sandstone and limestone, respectively. The outlet of Wadi El-Arish, covered by box A, is enlarged in Fig. 2. (b) Distribution of watersheds and streams network in Sinai Peninsula. Also shown are the areas (in km ) covered by the identified watersheds. 2
hyetograph were adopted as input to the hydrological model. W e assumed a single rain event for each month. The US Soil Conservation Service (SCS) curve number method (SCS, 1985) was adopted to calculate upstream initial losses in the sub-basins. Soils were classified into three types: Quaternary valley deposits as type A; Nubian Sandstone (NSS) as type B; and massive Tertiary limestone and basement rocks as impervious areas. Runoff calculations were enabled by adopting the SCS unit hydrograph (SCS, 1985) and by using the Riverside County lag-time equations for mountainous, foothill, and valley areas (Riverside County Flood Control, 1978). Channel routing was conducted by using the Muskingum routing method (McCarthy, 1938), whereby the average Manning's coefficient for gravel bed rivers was calculated according to procedures developed by Jarrett (1984). W e adopted expressions developed for a similar arid environment (Saudi Arabia) to calculate transmission losses (groundwater recharge) in the stream networks from the known volume of runoff upstream (Walters, 1990). The aerial extents of soil types and various geomorphic features (valleys, mountains, and foothills) were identified from coregistered TM, DTED, and geological digital mosaics.
Assessment of the renewable groundwater resources of Wadi El-Arish, Sinai, Egypt
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Fig. 2 Enlargement of the area covered by box A in Fig. 1(a). Also shown are contoured elevations (in metres) that were extracted from DTED data.
DISCUSSION AND RESULTS 2
W e identified 18 watersheds across Sinai, the largest (22 000 k m ) of which is the Wadi El-Arish watershed (Fig. 1(b)). Each of the El-Watir, Awag, Girafi, Dahab and Kid watersheds covers an area of 1500-3500 k m , and each of the remaining 12 watersheds covers an area less than 1500 k m . The hydrological model was applied to calculate the upstream initial loss, transmission loss, and runoff in the Wadi El Arish watershed for each of the rainy months of November, December, January, February and March (Table 1). Average annual recharge rates for the El-Arish aquifer were obtained by adding the transmission losses deduced for the five rainy months (Table 1). Our estimate for the annual recharge rate (32.5 x 10 m ) is conservative because it is based on average monthly precipitation values, whereas in reality rain storms in Sinai are more likely to occur as infrequent events or as rare large or extreme events. Large (26 mm) and extreme (76 mm) rainstorms were reported to occur once every ten years and sixty years, respectively in the St Catherine area (JICA, 1999). Assuming that these rare events cover an area 150 km long and 50 1cm wide, centred on St Catherine, we found that the recharge and initial losses from the 60-year events (76 mm) are sub-equal, each amounting to approximately 5 0 % of the total precipitation. Considerably lower 2
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Hazem M. Gheith & Mohamed I. Sultan
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Table 1 Results of hydrology model for Wadi El-Arish watershed (all values x 10 Transmission losses
6
Downstream runoff
Total precipitation
Upstream losses
144 202.5
139.6
4
December
192.7
5.7
0.4 4.1
January
201.1
193.4
4.6
3.1
February
270.6
254.4
March
163.1
158.6
4.2
0.3
Average annual
981.3
938.7
32.5
10.1
92.8
63
29.5
0.3
271.9
131.8
135.4
4.8
November
10-year event (26 mm) 60-year event (76.2 mm)
14
2.2
recharge (32% of precipitation) and higher initial losses (68% of precipitation) were computed for the relatively smaller (26 mm), 10-year events (Table 1). Unfortunately, records for the temporal and spatial distribution of these infrequent-to-rare events are incomplete and thus could not be used to evaluate the recharge of the Wadi El-Arish alluvial aquifer. Future studies will benefit from Egypt's current efforts to further develop Sinai's meteorological network. A fairly large (100 k m ) depression outlined by the 200-m contour on Fig. 2 at the outlet of Wadi El-Arish could potentially be used to enhance both the recharge of the alluvial aquifer under investigation and local agricultural activity (e.g. area B on Fig. 2) if the outlet (point C on Fig. 2) of the depression was dammed. 2
Acknowledgements We thank Professors Mofeed Shehab, Farouk Ismail, Naguib El Helaly, Fathy Saad, Hamdy Ibrahim and Zeinhom El Alfy for facilitating collaborative scientific research between Cairo University and the Argonne National Laboratory. Efforts at Argonne National Laboratory were supported by Cairo University and by Argonne's Strategic Initiatives Program through US Department of Energy Contract W-3 l-109-Eng-38.
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