Factors Affecting the Estimation of Seepage Rates from Channel Automation Data

Abstract

Seepage is the dominant process by which water is lost from well-managed earthen distribution channels. Pondage tests are acknowledged as the best direct method for seepage measurement, and the recorded water level data from automated systems during periods of gate closure can be treated as pondage test data. A new computer model that applies pondage test methodology to automated channel control data during periods of shutdown to estimate seepage rates in different channel reaches was developed recently by the authors. In this paper, the model is applied to the total channel control (TCC) data for the entire Coleambally irrigation area during three consecutive irrigation seasons between 2009 and 2012 to estimate the seepage rate for each depth gauge, pondage, and pool. Various features affecting the estimated seepage rates were evaluated for selected pools. The evaluation considered two groups of factors. The first group consists of factors that affect the estimation of the seepage rate, including rainfall and evaporation during the pondage period, number of water level measurements in the pondage, and duration of gate shutdown. The second group consists of factors that affect the rate of seepage, including surface water elevation at the start of the pondage condition and its relation to supply level of the channel at each gauge, seasonal variations in seepage rate, and suspected leakage through macropores in banks of the channels.