Seepage losses as affected by condition and composition of channel banks

Extensive measurements from farm channels in Pakistan showed that about half of the water leaving the canals, was lost before it reached the farmers’ field. However, studies were needed to identify causes contributing to this huge loss of water. This study was conducted to evaluate effects of condition and composition of channel banks on water loss and to develop and evaluate methods to reduce this loss. Measurements showed that loss rates, while influenced by soil texture, were even more strongly influenced by the condition and composition of channel banks. It was also observed that 80% of the water losses occurred within the top 8 cm of the banks of the old channels. Reconstructed channels with moderately compacted banks reduced the water losses to less than 2% of the flowing water per 100 m length of the channels. Compacted soil cores in channel banks reduced water losses to less than 25% of the losses prior to compaction. Cost of water saved by core compaction would be about US$ 0.06 per 100 m3 as compared to US$ 2.50 per 100 m3 currently charged for water from tubewells. Another benefit of installing compacted cores in banks is that the improvement can take place while water is running in the channel. This helps to maintain water supplies at farmers’ fields and provides flexibility in timing so it can be done when laborers have free time.