The effect of in-stream activities on the Njoro River, Kenya. Part I: Stream flow and chemical water quality

Abstract

For shallow streams in sub-Saharan Africa, in-stream activities could be described as the actions by people and livestock, which take place within or besides stream channels. This study examined the nature of in-stream activities along a rural stream in Kenya and established the inequality in water allocation for various livelihood needs, as well as the negative impact they have on dry weather stream flow and chemical water quality. Seven locations along the stream were studied in wet and dry weather of 2006. Enumeration consisted of making head counts of people and livestock and tallying visitors at hourly intervals from 6 a.m. to 7 p.m. To estimate water abstraction, filled containers of known volume were counted and the stream was sampled to examine the impact on water quality. Water samples were obtained upstream and downstream of in-stream activities before (6 a.m.) and during (11 a.m., 6 p.m.) activities. Samples were analyzed for suspended solids, turbidity, BOD 5, total nitrogen and total phosphorus. The daily total abstraction at the middle reaches during dry weather was 120–150 m 3 day −1. More than 60% of abstraction was done by water vendors. Vended water from the stream was sold at US$ 3.5–7.5 per m 3 and vendors earned between US$ 3–6 a day. Abstracted water contributed approximately 40–60% of the total daily consumptive water use in the riparian area during dry weather but >30% of the morning stream flow was abstracted thereby upsetting stream flow in the lower reaches. The daily total water abstraction correlated positively ( R 2, 0.98) and significantly ( p < 0.05) with the daily total human visit, which was diurnally periodic with two peaks, occurring between 9 a.m. and 10 a.m. and from 4 p.m. to 5 p.m. This diurnal pattern of visits and the corresponding in-stream activities affected water quality. In particular, suspended solids, turbidity and BOD 5 levels increased significantly ( p < 0.05) downstream during in-stream activities. It was concluded that the positive contribution of in-stream activities, in particular, water abstraction to livelihoods and the daily water needs was overshadowed by the apparent disregard of the impact on stream flow and water quality. Therefore, measures are required to control in-stream activities along the stream but authorities should be mindful of the implications of any management strategy on the livelihoods of the riparian inhabitants.