Water Allocation Assessment and Hydrological Simulation on Mukurumudzi River Basin in Kenya

Water Allocation Assessment and Hydrological Simulation on Mukurumudzi River Basin in Kenya

Jacob Mutua Katuva (University of Nairobi, Kenya), Christian Thine Omuto (University of Nairobi, Kenya) and John P. O. Obiero (University of Nairobi, Kenya)
DOI: 10.4018/978-1-5225-2719-0.ch003
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Lack of water allocation plans in semi-arid river basins increases the risks of hydrological droughts. The Mukurumudzi river basin was experiencing extremely low flows which led to a water allocation assessment to quantify the available resource amidst competing demands from domestic, commercial and environmental needs. An abstraction survey was conducted along the entire length of the river followed by a low flow study and water balance modelling using rainfall-runoff Model. Observed flows at source and mouth were 0.028 m3/sand 0.043 m3/s respectively. Simulated flows estimated an environmental flow (Q95) deficit of0.023 m3/s and 0.010 m3/s in July and August respectively. Normal flow (Q80) of 0.190 m3/s and flood flow (Q50) of 0.520 m3/s were estimated. Compensating the environmental flow deficit in July and August was recommended. A more detailed hydrogeological study should be conducted to elucidate the potential of the groundwater resource in meeting current demands.
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Study Area

The Mukurumudzi River basin (MRB) covers an area of 207 km2 and is located in the southern part of the Kenya coast approximately 50 km south of Mombasa. The basin has a bi-modal rainfall pattern with half of the mean total annual rainfall falling in April, May and June. The annual average precipitation ranges between 1,000 mm and 1,200 mm. The Mukurumudzi river starts 30 km inland from the Indian Ocean. The river is about 40 km long, originating from the Shimba Hills and draining into the Indian Ocean. The catchment has one River Gauging Station coded 3KD06 (sited at location L3 in Figure 1) that covers 69 km2. The catchment also has two major industries, a mining company and a sugarcane irrigation farm. The mining is conducted by the Kwale Mineral Sands Project (KMSP) while the irrigation of 5,500 ha of land is conducted by the Kwale International Sugar Company Limited (KISCOL). Both the mining and irrigation companies have so far developed 3 dams (Mukurumudzi dam, Lower and Upper Koromojo dam) with a total storage of 14 Million m3 on the Mukurumudzi River basin to meet their water demands.

Figure 1.

Study area

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