Stormwater impact on water quality of rivers subjected to point sources and urbanization - the case of Addis Ababa, Ethiopia

Urbanization of a catchment often causes degeneration of rivers. We studied the water quality of three rivers in Addis Ababa based on the impact of stormwater and non-point sources, and urbanization. Along these rivers several point sources were registered, with direct discharge of industrial and domestic wastes into them. To distinguish the impact of these year-round point-sources from stormwater, we analysed physicochemical parameters, nutrients and heavy metals sampled from upstream to downstream sections of each river in the dry and wet season. Dissolved oxygen (DO), NO2-N, NH4-N, PO4-P, (Cr(VI) and Cu) exceeded international standards, pointing to a generally poor water quality of the rivers in both seasons. NO3-N, Mn and Zn were problematic in dry season only. Although stormwater improved DO, conductivity, PO4-P, Cr(VI) and Zn, the levels were still critical, pointing to construction sites, agriculture and pit latrines, somewhat offsetting the effect of stormwater dilution. No clear impact of urbanization pressure was found.