P. Yillia, N. Kreuzinger, J. Mathooko:
"The effect of in-stream activities on the Njoro River, Kenya. Part I: Stream flow and chemical water quality";
Physics and Chemistry of the Earth, 33 (2008), 8-13; S. 722 - 728.

Kurzfassung englisch:
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, BOD5, total nitrogen and total phosphorus. The daily total
abstraction at the middle reaches during dry weather was 120-150 m3 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 m3 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 (R2, 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 BOD5 levels increased significantly (p < 0.05) downstream during instream
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.

Abstraction; In-stream activities; Water quality

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