Groundwate Potential Evaluation Pydrochemistry Of Sululta Cacthment

Sululta catchment is located in the north part of Addis Ababa with east north-south stretch of 9°05'rnOI"N to 9° 18' 45"N latitude and east west stretch of 38° 33' 15"E to 38° 50' 45" E longitude. It is arn. sub-catchment of Abay drainage basin with a total area of about 480.80 km2rnThe main rock outcrops in the catchment are alluvial deposit of Quaternary age, basaltic, trachytic,rnrhyolitic lava flows & pyroclastic deposits of Tertiary age.rnFrom long term mean monthly rainfall data annual precipitation of the catchment is calculated asrn1201.31 mm per year. The potential and actual evapotranspiration for the catchment are 959.81 mmrnand 684.82 mm respectively. The area has an estimated overland flow of 178mm/year. Hence, thernarea's annual recharge value is 342 nun/year. When the value of annual base flow is subtractedrnI 32mm/year depth of water is being added to the groundwater reservoir. This value is very impOliant torncategorize the groundwater development of the catchment exactly knowing the entire groundwaterrnwithdra,wal per year.rnThe vertical electrical survey (VES) interpreted results, borehole logs, pumping test and qualitativerninterpretation have indicated that the. upper 3-20 ,meters in most part of the central plain area isrn,rnpotential for hand dug well and shallow groundwater. This same area is potential for borehole ofrnmaximum depth 120 following the main fracture zones. The main aquifer in catcl1l11ent is fracturedrnand/or weathered basaltic lava. Hand dug wells are potential sources of water in the area wherernquaternmy alluvial deposits followed by thick weathered basaltic lava. Even though, the yield is low tornmoderate both rhyolitic and trachyatic flow are aquifers near the Intoto ridge,rn. Based on the qualitative and quantitative analysis of aquifer characteristics the catc!unent is categorizedrninto tln'~e permeability zones, The high permeable zone has transmissivity greater than 22 m2/c'ay andrnthe yield of wells is 2 to 4 Usec with partial penetration. The low permeable zone have trasmissivityrnless than 5,5 nl Iday and yield less thanillsec. the formation mapped as m~derate permeable zone has - ., ~rnvalues of transmissivity and yield between these zones.rnrnThe water in the catchment is mainly of Ca- Mg-HC03-C03 and Ca- Na-HC03-C03 water type. Inrnmost samples percentage of Ca2+ +Mg2+ is greater than Na+ +K+. The TDS obtained for the catchment isrngenerally below 256mg/1 and maximum EC is 540 microsiemens (~lS). Redox Potential (Eh) isrngenerally positive nearby the recharge area and gradually decreases downstream part of the catchment.rnConcerning water quality, except for turbidity, color and bacteria the rest parameters are within thernlimit of acceptable value of WHO (World Health Organization) water quality standards fo), waterrnsupply, 'irrigation and industries excluding trace elements. Hand dug well shows the bacterial pollution because of its shallow water table.

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