Flow Regimes
Physical factors play a crucial role in the ecology of flowing (aka lotic) waterways. One of the most important physical factors is flow rate. The flow rate can influence the creek or river bed, with fast flowing waterways generally having rocky bottoms as small particles are carried away and slower moving creeks and rivers generally have muddy bottoms as the sediments settle out.
Different rates of flow as water moves through pools and riffles result in a variable substrate which provides different opportunities for aquatic plants (flora) and animals (fauna) to establish and contribute to a functioning ecosystem.
The volume of water in a creek can change dramatically over a very short period of time, like during a storm, which strongly influences the flow rate. Water moving rapidly through a creek or river can cause scouring of the substrate, removing aquatic plants and animals. In a natural system, these plants and animals generally have high reproductive rates and can re-establish quickly.
In urban areas, this natural variability in flow has been intensified by the increase in impervious surfaces such as roads, roofs, and car parks, which cause a higher runoff volume and flow rate than occurs naturally. In addition, water that is used in developed areas (e.g. runoff from washing cars or watering gardens) is directed through stormwater infrastructure into local creeks, which has led to many urban streams now having unnaturally permanent flows.
As a consequence of urbanisation, the Shire has seen significant land use changes that have caused considerable modification to creeks, streams and rivers. One of the aims of waterway management is to mimic natural flow regimes, allowing the waterways to function naturally to provide social, economic and environmental benefits.