Web tool to get us tanked up

Collecting urban rainwater is becoming more crucial for our fast-growing cities and towns.

This under-used water source and the commercial approach to capturing it is driving Swinburne's Dr Monzur Imteaz to develop a number of simple tools to analyse and design stormwater systems.

Imteaz has already developed STORMKIT, an internet-based tool that helps water managers and other uses to analyse and design stormwater systems.

He is now developing a similar tool to help householders establish the rainfall capture capacaity of their roofs that could also be available this year.

Imteaz is concerned that many urban rainwater tanks are half-empty, or worse, cannot hold any more water, just because theire's no simple tool to help people better match storage with catchment.

"House tanks are a good example," Imteaz said. "People want to catch the stormwater collected on their own roofs, but tanks are often installed with little or not planning as to whether they are the right size. There are plenty of tanks which will never fill and there are plenty which are too small to capture all the water that is available."

Using information such as contributing catchment size, tank volume, geographic location, weather conditions and the water's intended use, Imteaz's proposed calculation tool will determine the volume of water likely to be captured each year according to different rainfall scenarios.

Near his office on Swinburne's Hawthorn campus are two large rainwater tanks with which Imteaz has put his theory to practice and establish their effectiveness and payback period. Applying his calculations to the capture area he was able to measure by how much one tank was far too large to readily fill, and to the extent the other was too small to capture all available rainfall.

Based on an average and worst case rainfall scenario, Imteaz found the smaller tank connected to the larger rood area would save $110,000 worth of water over three years, covering the cost of its construction. The other, larger tank (connected to a smaller roof area) would take 10.5 average of 18.5 worst-case years to pay off.

The point Imteaz makes is that better analysis and design before constructing such facilities would significantly improve their cost-benefit and effectiveness.

Initially the proposed tool is for stormwater capturing analysis for impervious roofs only. But by incorporating soil loss parameters it can be extended for pervious surfaces such as golf courses and playing fields.