| 520 |
|
|
|b This paper has emphasized the need for comprehensive water resources assessment in Sennar State. Sennar state lies mostly in the semi-arid zone where water availability forms the bottleneck for all developmental activities. Available surface water resources comprise the Blue Nile River and surface water (run off). Availability of groundwater links very much with the geological formations which have resulted into the Nubian aquifer, El Atshan Aquifer, the alluvium basins and the fractured basement aquifers in Sennar region. Groundwater of good quality can be tapped fewer than 60% of the state area and occur in the sand and sandstone layers of the Nubian sandstone and El Atshan sediments in the sand layers of River deposits. In the Nubian aquifer groundwater occurs under semi-artesian conditions, owing to the presence of overlying formation and its clays on top of Nubian aquifer. The average saturated thickness of the Nubian aquifer penetrated into the area is about 20 m. The depth to water level is shallow (15 meter average), and increases with distance from the Blue Nile, and consequently the well depths increases in the same manner. The groundwater moves from the Blue Nile (influent River), this is continued by low salinity close to the River. The high values of Transmissivity are generally found in areas that are fairly close to Blue Nile with an average of 10,000 g/day/ft. However, loss of circulation is recorded in the western part due to the relatively compact and fractured rocks through which water tend to seep laterally. The Nubian sandstone in sennar state can be regarded as moderately to hard water. In the eastern part of the state, El Atshan formation characterized by very coarse sands and gravels, and represent the most promising aquifer in state, and it is also characterized by good hydraulic properties, with is depths to water is relatively shallow (18 meter average), increasing away from the River until it reaches its maximum depth at central part between the Dinder and the blue Nile. However, due to high possibilities of recharge and consequently high water circulation, this area is characterized by very low mineral contents. Both the Nubian and El Atshan aquifers cover about 55% of the total area. Groundwater in the alluvial aquifers generally occurs at an average depth of lm 10m below ground level. Specific capacities of the tube wells tapping the alluvium (Wadi-fill) aquifers are as high as 100 m3/m/h. Groundwater tapped from the alluvium aquifers is generally fresh with a low content of Total Dissolved Salts (TDS), rarely exceeding 300 mg/1. However the water suffers from a deficiency in dissolved iodine. Alluvium aquifers, due to their shallowness, high permeability and wider use in watering animals, are susceptible to pollution, especially in the urban centers. The basement complex rocks lie in south-western part of sennar state, and cover about 45% of the total area Presently in Sennar State there are more than 167 water-yards of which about 27% are non-functional. However, the remaining working ones operate at about 60% efficiency, due to aging, poor design, lack of overall maintenance and rehabilitation, and the low capacity of the installed reciprocating pumps and the technical staff and the absence of institutional back up to the community efforts in management of water yards. Several water yards in Sennar State have been (partially) destroyed and affected by the bad management and they are in need of rehabilitation, while in Es Swki and El Dindir province, out of a total of 26, and are in need of rehabilitation works. The majority of existing water yards are single boreholes, with no fence, no house connections, and many are with or without leaky storage tanks. Development and utilization of groundwater resources in Sennar State for drinking, irrigation purposes and for livestock (for the nomads) is constrained by deep water levels(deep aquifers), high construction and rehabilitation costs of the water supply sources and poor and inefficient back-up operation and maintenance services
|
