THE EFFECT OF DIFFERENT URBAN-DEVELOPMENT TYPES ON STORMWATER RUNOFF QUALITY - A COMPARISON BETWEEN 2 JOHANNESBURG CATCHMENTS

The quality of urban stormwater runoff can be greatly affected by the type of development within the catchment and the level of management o f the engineering services. This was investigated using water quality data from 2 areas near Johannesburg, namely Alexandra and Sunninghill Park. Alexandra township supports a mixture of formal and informal (sq uatter-type) developments, while Sunninghill Park comprises only a for mal development. The level of maintenance of the services is considera bly different between the 2 areas. The results of the monitoring perio d have shown that the stormflow off Alexandra is similar to raw sewage , for a number of pollutant concentrations, and the dry weather flow i s comparable to settled sewage. The concentrations in the storm- and d ry-weather flow off Sunninghill Park are considerably lower. Pollutant loads are greater from the Alexandra catchment by factors of between 20 and 130.