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International Institute for Geo-Information Science and Earth Observation (ITC) 2006

Assessment of artificial groundwater recharge using greenhouses runoff, North East Naivasha, Kenya.

Mohammedjemal, A. (Abdulwhab)

Titre : Assessment of artificial groundwater recharge using greenhouses runoff, North East Naivasha, Kenya.

Auteur : Mohammedjemal, A. (Abdulwhab)

Etablissement de soutenance : University of Twente International Institute for Geo-Information Science and Earth Observation (ITC)

Grade : Master of Science in Geo-Information Science and Earth Observation 2006

Résumé
Feasibility study on artificial recharge was conducted in the horticultural area north of Lake Naivasha. The use of groundwater for irrigation purposes has tremendously increased since the last 8 years. This causes a decline of about 10m of the water level. This study is targeted to assess the feasibility of artificial ground water recharge using the runoff harvested from the greenhouses. The quality and quantity of the available water resource, identification of suitable sites for various alternatives and scenarios, and economics based on preliminary cost assessments are discussed. During field study, Injection and pumping test was carried out to determine the intake capacity and hydraulic property of the aquifer. In addition soil and ground water samples were taken for grain size and water quality analysis respectively. A spreadsheet model developed to analyze the recharge efficiency and cost per cubic meter of recharge water for 31 years duration of daily rainfall. The field experiment result shows the existence of vertical and horizontal variations of hydraulic parameters with the transmissivity value ranging from 800 to 1200 m2 day-1 . The porosity and specific yield of the aquifer are estimated 0.3 and 0.15 respectively. The injection rate with a pressure head of 30m with a hole of 40m deep is in the order of 160m 3 hr-1 . It is known that the 40-60m deep part of the aquifer has very high transmissivity. So the actual recharge potential may be double or more than the injection rate. Unfortunately this could not be tested due to collapsing of the boreholes starting around 38m depth. The runoff volume calculated by rational empirical method results in a maximum of 35,000m 3 day-1 . Runoff coefficient of 0.89 is found for the present study using the field experiment of rainfall-runoff record. The scenario analysis of the water balance in the area shows that about 46% of the ground water abstraction can be saved by utilizing the runoff from greenhouses for aquifer recharge. A cost per cubic meter surface (storage capacity vs recharge rate) was established from the spreadsheet model allowing finding the most cost effective scenario ; a basin of 9600m 3 combined with recharge wells with a total potential of 7000m 3 day-1 is an optimum solution. In this case the the recharge efficiency is 89% and the cost per meter cube is 0.56 KES (Kenyan shilling) .The model set up implemented based on the work of Kibona (2000) results in 3.4m and 5m rise in water level around the productive wells and recharge wells respectively. The water budget simulated in two scenarios with and without artificial recharge indicates that 90% of the inflow is from constant heads boundaries simulating inflow from the lake and in the second scenario this value is lowered to 50% due to the artificial recharge.

Version intégrale (ITC)

Page publiée le 28 janvier 2018