34 5. NAIROBI DAM Facts about Nairobi Dam The Nairobi Dam is by paulj


									5.      NAIROBI DAM

Picture 7: Nairobi Dam Spillway at Low Flow

Facts about Nairobi Dam
    The Nairobi Dam is shallow. Average depth is 2.76m
    It has a surface area of about 356,179 m2 and a volume of 98,422 m3
    The dam inlet is about 1700m. Dam crest is about 1680m above sea level
    Geological formation on which the dam rests comprises the Middle and
    Upper Kerichwa Valley Tuffs
    Inflow is constituted of tributary runoff, over-dam precipitation and
    wastewater from the non-sewered Kibera settlement
    Outflow is composed of dam evapotranspiration, outflow from the river
    channel through the spillway and groundwater flow from the dam
    The dam is heavily silted by sediments from erosion and solid waste
    dumped at various places to reclaim land for agriculture

     Water Hyacinth has infested the water body disrupting fisheries and
     The total contribution of rainfall to the dam is 311,656m3 per year.
     The total water loss as a result of evapotranspiration is about
     711,289m3 per annum.
     Evapotranspiration from the Water Hyacinth may be higher than
     potential evaporation
Fig 7: Schematic representation of the water budget for the Nairobi Dam. Note that river discharges
into and out of the reservoir have not been included. Infiltration rates into the aquifer are also
excluded. This information should be collected in subsequent studies to arrive at a more accurate
water budget.

    629,459 m3 y-1

                     311,656 m3 y-1
                                                    711,289 m3 y-1

                        Precipitation (inflow)
                        Evaporation       and   evapotranspiration
                        Infiltration (outflow)
                        Nairobi Trachyte (Permeable)
                        Nairobi Phonolite (Impermeable)
                        Water hyacinth


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