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P. Yillia, N. Kreuzinger, K. Mwetu:
"Temporal variability of two contrasting transient pollution events in a pastoral stream";
Water Science and Technology, 61 (2010), 4; 1053 - 1063.

Two transient pollution events were monitored in a pastoral stream in southwestern Kenya to evaluate their relative contribution to diffuse pollution. Peak loads of pollutants during storm-induced transients were within 3-4 orders of magnitude higher than the short-lived (30-60 minutes) diurnal episodes provoked by in-stream activities of people and livestock.
Transient yields were striking during storm-induced events; 778,000, 8,400, 550 and 100 kg/day for suspended solids, BOD5, total P and total N, respectively, compared to wet weather base flow
(150, 30, 0.8 and 1.4 kg/day, for the same parameters, respectively). Two forms of concentration-discharge relationships were observed: increases in concentration for turbidity,
suspended solids, BOD5, total P and the faecal indicator bacteria at the peak of the stream hydrograph, and concurrent decreases in concentration for conductivity and total N. Following each storm-induced transient event, a marked improvement in water quality was observed within 48-72 hrs of the receding limb of the stream hydrograph before the next base low was established. It was concluded that storm-induced transients are exceedingly important for the mobilization of pollutants from diffuse sources but both transient events affect stream-channel processes, especially water quality, with the possibility of attendant consequences on the health
of riparian inhabitants.

diffuse pollution, in-stream activities, rainstorm, stream hydrograph, transient events