Dire Dawa Administrative Council Integrated Resource

Water Works Design and Supervision Enterprise
Tertiary volcanic rocks (N2+P3Nl)
Tertiary volcanic rocks in the DDAC are mainly stratiod basalts and Alaji basalts
outcrops that occupy the elevated areas at the north and northeastern part of the Council
territory. Boreholes drilled on the basalts are practically dry except at Hurso area with a
maximum specific well discharge of 0.01 l/s/m.
Upper Sandstones (Ka) (main aquifer)
The upper sandstone outcrops in a small aerial extent at Haseliso, north of Dire Dawa at
the airport and Northwest of Dire Dawa town. The geophysical investigation results after
calibrating with the drilled test wells have preliminarily showed that the upper sandstone
forms a strip aquifer extending from Serkama (outcrops) to Dire Jara (overlain by
alluvium and basalts) in the northeast direction which could be one unit with the
extensive Dire Dawa town area upper sandstone. The width of the strip in north direction
from the foot of the escarpment is estimated in average about five kilometers. The drilled
wells in the aquifer show that the thickness of the aquifer is variable. The minimum
thickness of the aquifer penetrated at the Dire Jara well field is 36 meters (W-4) and at
TW4 is 108 meters and not completely penetrated. Although the only recorded data on
the groundwater strike is on test well TW4, the general information about the aquifer is
that it is confined aquifer. At TW4 the groundwater was struck at 98 meters depth and the
static water level stabilized at 31 meters. It is recorded in the Dire Jara well
accomplishment report as general conclusion that the groundwater was struck from 100-
120 meters and the static water stabilized at 50 to 60meters below the ground surface.
The sandstone at the Sabiyian area also considered as confined aquifer although the
pumping test results show leaky aquifer. In general the aquifer is confined aquifer where
the confining layer could be basalt, alluvium and intercalation of shale with in the
sandstone. The static water level varies from 9.3 meters (Sabiyian) to 69.3 meters (Dire
Jara) with the specific well discharge of 0.13 to 68.97 l/s/m. The transmissivity of the
aquifer varies from 9 to 5512 m 2 /day with a mean of 1810.9 and harmonic mean of 88
m 2 /day and the storage coefficient varies from 0.003 – 0.005 from pumping analysis.
Two groundwater flow regimes are identified in this aquifer, in the northwest direction
from Serkam to Shinile direction (along the strip), which joins the groundwater flow from
Dire Dawa town area of the aquifer in the area.
The water quality is generally hard and the water type is Ca-HCO3, Ca-Mg-HCO3 and the
water of Dire Dawa town and the Sabiyian has high chlorides and the water types
changes to- Ca-HCO3-Cl, Ca-Mg-HCO3-Cl, and Ca-Cl-HCO3-SO4 due to contamination
of the aquifer in the area.
Hamanaliei limestone (Jh)
The Hamanalei limestone outcrops in the Dire Dawa groundwater Basin together with the
upper sandstone a lesser aerial extent. Drilling results show that the limestone
Phase II- Data Collection - Site Investigation Survey & Analysis – DDAC - Main Report
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