In 2016 Urban Water Solutions was engaged by Goulburn Valley Water to undertake an inflow/infiltration analysis study on four sewerage catchments under its control – the Wandong, Kilmore, Alexandra and Eildon catchments.  The purposes of the study were to:

1. Provide Goulburn Valley Water with a better understanding of the impact of inflow/infiltration on the sewerage systems under its control; and
2. Provide Goulburn Valley Water with a robust methodology for assessing inflow/infiltration which could then be applied to other sewerage catchments.

Goulburn Valley Water provided calibrated InfoWorks CS models for each of the catchments which Urban Water Solutions updated in consultation with Goulburn Valley Water.  Then, using historic data provided by Goulburn Valley Water, Urban Water Solutions undertook the following analyses:

• Rainfall time series analysis
• Pump station analysis
• Treatment plant analysis
• Infiltration and inflow reduction effectiveness, measured by reduction in predicted manhole flooding; and reduction in flows to the treatment plants and the resultant reduction in operating costs.

The results of the study showed that, of the four catchments studied, only the Kilmore catchment had predicted infiltration and inflows levels that were high enough to warrant further evaluation of the effectiveness of an infiltration and inflow reduction program.  Other catchments had predicted manhole flooding during 1 in 5 year design storms, however this was caused by local capacity constraints rather than excessive wet weather inflows.  The study indicated that in the Kilmore catchment potential savings in treatment plant operating costs of $50,000p.a. could be achieved with a 45% reduction in infiltration and inflow.