A study of stormwater runoff from Alexandra township in the juskei river

[摘要] South Africa, like many other developing countries, is faced with rapid urbanisationwith the associated increase in the pollution load. Much of this pollution is destinedfor our watercourses, that eventually run into storage reservoirs which may be usedfor drinking water or recreational purposes. This pollution is usually attributed tohuman waste products which include nitrogenous wastes, phosphates, microorganisms,organic material and litter,A 6km stretch of the Jukskei river just downstream of Alexandra Township, wasused to determine the different biological, physical and chemical processes thatpollutants undergo during natural assimilation, their rates and efficiencies ofassimilation in rivers and their impact Oil the environment downstream of the urbanarea. Grab samples were taken over a period which included both low-flow andstorm events. Due to the high concentration of nutrients in the run-off fromAlexandra Township, the major changes seen were in the biological conversion oforganic nitrogen compounds and ammonia to nitrates, in the BOD and in theconcentration of dissolved oxygen in the river, with lows of 1.1 to 1.5 mg/l 02being recorded at Alexandra. A rapid rise in the concentration of faecal coliformshas been seen with a high of 31 million/100 ml being recorded at Alexandra inSeptember, 1994. Sedimentation at the Alexandra site is also a common occurrencewith a lot of adsorbed pollutants being effectively removed from the water columnwith the suspended solids.The QUAL2E water quality model, used by the EPA in the United States, was usedto model the reactions that the nutrients, BOD and DO undergo. BOD and DOwere modelled very well with r of 0.98 and 0.94 being calculated respectively.QUAL2E did not model tile dissolved potlutants, dissolved phosphorus andammonia very well with the observed results showing a greater reduction ill thesepollutants. A method by which these pollutants adhere to SS and settle out was

[发布机构] University of the Witwatersrand