California Agriculture

Irrigation tailwater can transport sediments and sediment-associated agricultural pollutants to nearby waterways. To help protect the biota of surface waters, we evaluated the use of polyacrylamide (PAM, a synthetic material that flocculates sedi-ments when added to water), vegetated ditches and sediment traps to mitigate sediment losses from furrow-irrigated fields. In a 2-year study, liquid PAM injected into irrigation source water most effectively reduced suspended-sediment concentrations in runoff from different soil types. Dry tablet and granule PAM formulations were also effective, as long as their placement in the furrows promoted their dissolution in irrigation water. Vegetated ditches resulted in intermediate reductions in suspended sediments in tailwater. The sediment traps were limited in their effectiveness by insufficient holding time for fine-grained particulates to settle out of the runoff.