Abstract
Complex processes of sediment transport in a river impact on overall aquatic system and result in the productivity decrease of socio-economic development projects taking the river as a source of water. The present study was designed to estimate Sebeya river sediment load and assess its impacts on Lake Kivu, Gihira water treatment plant and various hydropower plants constructed in Sebeya catchment located in Western Province of Rwanda. Water samples were hand-collected from five different sampling points along Sebeya river during rainy and dry seasons. Laboratory analysis for turbidity, total suspended solids, sieve analysis for bed load materials and NPK content of water samples were conducted. The results revealed that the average turbidity was found to be high during rainy season compared to dry season. The same trend was found in total suspended solids concentrations. At all 5 sampling sites and during rainy season compared to dry season, the average mass flowrates of bed load materials were 7.84 and 2.96 kg/hr respectively. Sieve analysis results showed that all bed load sediments were mainly composed of high proportions of fine sand of more than 70% which adversely causes damages on hydropower turbines and the effect of high soil erosion rates on Gihira water treatment plant was traduced by high turbidity of raw water and excessive costs of reagents. At Sebeya outlet, nutrients load and high turbidity reduce significantly the aesthetic quality of Lake Kivu, having a harmful impact on recreation and tourism, aquatic life and affect the livelihoods of people living in the vicinity. Researchers recommend two options of reducing the amount of sediment load in Sebeya river: either to prevent soil erosion or to trap eroded sediment at the upstream of the hydropower and the water treatment plants. Assessing the sediment load fluctuations in Sebeya river is useful for water managers and planners to adjust operations accordingly at water treatment and hydropower plants.
Highlights
Surface water plays a significant role in the development of a country and individual citizens as sources of food, water, transport, hydropower and recreation [1]
The present study was designed to estimate Sebeya river sediment load and assess its impacts on Lake Kivu, Gihira water treatment plant and various hydropower plants constructed in Sebeya catchment located in Western Province of Rwanda
The results revealed that the average turbidity was found to be high during rainy season compared to dry season
Summary
Surface water plays a significant role in the development of a country and individual citizens as sources of food, water, transport, hydropower and recreation [1]. High concentration of sediments in water retrogrades the economy of a country and the polluted water affect the livelihoods of people living in the vicinity and can kill aquatic life. Soil erosion increases the amount of sediment transported in rivers at a rate of 2.3 billion tons per year [2]. In most watersheds of Rwanda, sediment transported in rivers varies proportionally to the rate of erosion, river runoff and the land slope [3] while soil nutrients (organic materials, nitrogen, phosphorus and potash) were lost due to soil erosion at rates of 945,200, 41,210, 200 and 3055 tons/year respectively [4]. For the case of Sebeya river in the Western part of Rwanda, the transported sediments lead to scour on bridge, increase pollutants in water bodies and reduce the performance of hydro power plants [5]. The measurements revealed excessive turbidity and Total Suspended Solids (TSS) of 1102 NTU and 4414.5 mg/L respectively [6]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call