Dire Dawa Administrative Council Integrated Resource

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Water Works Design and Supervision Enterprise Figure 5 Isohyetal Map Phase II- Data Collection - Site Investigation Survey & Analysis – DDAC - Main Report 21
Water Works Design and Supervision Enterprise 2.3.3 Water Resources a) Surface water The surface water potential of the DDAC has been estimated using indirect methods as there are not gauged data. Table 7 summarizes mean annual runoff values estimated for different watersheds in the DDAC. All the rivers within the Council are seasonal and with short duration flood, practically without base flow. Table. 6 Mean Annual Flow (Mm 3 ) of the Rivers in the Dire Dawa Council No. Rivers Area (km 2 ) Weighted Rainfall (mm) Phase II- Data Collection - Site Investigation Survey & Analysis – DDAC - Main Report Mean Annual Flow (Mm 3 ) 1 Kelaad and all the tributaries 1078 728.4 116.5 2 Dichato (& tributaries) 473 683.4 109.3 3 Lege Oda 115 672.1 107.5 4 Kalicha tributaries 448 717.1 114.7 Total 448 b) Groundwater The DDAC is found at the margin of the eastern part of the Ethiopian Rift Valley. The geological formation and hydrogeological conditions of the area is a function of geomorphology, on the escarpment-outcrops pre-Cambrian rocks, Adigrat sandstone, Hamanalei limestone, upper sandstones and basalts, the down thrown plain (foot of the escarpment) is dominantly covered by alluvial deposits. Both the plains (down thrown block) and the escarpment are highly dissected by east-west trending faults. The groundwater occurrence, distribution and flow regime is highly governed by topography, tectonics, geological formation, aerial and topological relationship of the geological formation. Based on these major factors, the DDAC can be categorized into two groundwater systems i.e. the escarpment and the foot of the escarpment (groundwater basin of Dire Dawa) Fig6. i) The Escarpment Groundwater The escarpment occupies the southern, southeastern and eastern parts of the Council. It is highly rugged areas and intensively faulted by east-west trending faults. Geologically, the western part is dominated by sedimentary formations (limestone and sandstones) at the central part south of Dire Dawa town sedimentary and basement rocks dominates, to the east volcanic and sedimentary rocks dominates. At the eastern part of the escarpment (from Kalicha to the east) downstream of the sedimentary formation, basement rocks outcrops and the topography highly enhances complete drainage of the groundwater of the sedimentary formation. From analysis of the ground water point inventory, which was carried out from August to September 2002 the groundwater potential of the escarpment is estimated to be about 4.8 Mm3/year (151.71/s). ii) The Dire Dawa groundwater basin (foot of the escarpment) 22
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Dire Dawa Administrative Council Integrated Resource

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