The findings of numerous
studies on the responses of stream quality indicators
to different levels of watershed development have been integrated into an impervious cover model. The focus on one development stressor, namely the
impervious cover, allows the decision makers to use the impervious cover model as a watershed planning tool
to forecast stream response. In evaluating stream
quality, the studies used various indicators such as pollutant loads, habitat
quality, aquatic species diversity and abundance, and others. This study
aims to test the applicability of the impervious
cover model as a tool to set the threshold of catchment area development
based on the targeted water quality index. The
model is represented by a linear relationship between the water quality index
as a response variable and catchment area imperviousness as an explanatory
variable. The study area is an urbanized catchment area of a cascade-pond
system located at the campus of Universitas Indonesia, Depok, West Java.
Estimation of catchment area imperviousness is based on digital globe imagery
and digitized based on identified rooftops. The water quality data to compute
the water quality indices are collected from previous studies and related
reports. The targeted water quality index is determined
based on water use suitability referring to the Indonesian government
regulation number 82/2001. Based
on the available data, an increasing tendency of temporal variation of
catchment area imperviousness for each pond can be recognized, while water
quality index of each pond tends to decrease over time. In accordance with land
cover distribution, spatial tendency indicates that imperviousness is
decreasing in downstream direction, while water quality index is increasing in
downstream direction, in line with the characteristics of cascade ponds. The
results demonstrate that despite the fact that the available data are very
limited, it is possible to use the linear relationship between catchment area
imperviousness and water quality index as a tool to set the threshold for
future development on the catchment area of the cascade-pond system at the
campus of Universitas Indonesia with a minimum water quality index suitable
just for recreation activities.