Investigation of seepage in water supply distribution channels in St George, Queensland

The annual loss of water in agricultural storage and supply channels due to evaporation and seepage is estimated to exceed several thousand gigalitres representing billions of dollars lost to the Australian economy. There is a need for water-saving measures and a structured approach to assess water loss in earthen supply channels. The focus of this study (the St George Irrigation Area) [GDA94 S 28.048953°, E 148.582.746°] is the only public dam supplemented agricultural water supply system in southwest Queensland supplied by earthen channels and it is a major contributor to the fibre (mainly cotton lint) produced in Australia. This study measured the seepages losses in 9 km of a 50 year old agricultural channel water supply system constructed in St George, Queensland. The results of the study were compared to the seepage losses measured in other Australian studies. The expected seepage loss was less than 0.035 md-1. The ponding test method was used to calculate the daily seepage losses through the bed and walls of the channel supply system at three sites. The sites were selected based on soil types and the nature of the use. Absolute pressure sensors installed in three isolated channel sections measured the rate of drop of the free water surface in the channel. The daily seepage loss rate was calculated by subtracting the daily evaporation from the rate of drop of the free water surface. The estimated seepage loss during May 2015 at Site 3: Buckinbah B2/2 Channel(designed capacity of 29 MLd-1) was 0.008 md-1 ± 0.002 m (95%)