
Seepage from water streams into unlined channels determines the proportion of water distributed to adjacent soil for plant use or soil or groundwater recharge, or conveyed to downstream reaches.� We conducted a laboratory study to determine how sediment type (none, clay, silt), sediment concentration (0, 0.5, and 2 g L-1), and water soluble, anionic polyacrylamide (PAM) concentration (0, 0.4, 2 mg L-1) influences seepage loss of irrigation water (electrical conductivity = 0.04 Sm-1; sodium adsorption ratio = 2.2) from unlined channels in silt loam soil.� In a miniflume a preformed channel with 7% slope was supplied with 40 mL min-1 simulated irrigation water inflows containing the different treatment combinations.� �Runoff and seepage rates and runoff sediment were monitored for 24-h.� Average 23-h cumulative seepage loss was 11.8 L for silt-loaded inflows, 2.8 L for Clay loaded inflows, and 6.4 L for flows without sediment.� Increasing inflow clay concentrations, 0, 0.5, 2 g L-1 clay, decreased cumulative seepage volume (23-h) for the No-PAM treatment from 12.4 to 6.7, and 0.2 L respectively. Increasing inflow silt concentrations in No-PAM treatments resulted in a curvilinear response with a seepage volume maximum occurring for the 0.5-g L-1 treatment (12.4, 47.1, 9.8 L respectively).� Increasing inflow PAM concentrations increased seepage volumes for 2-g L-1 Silt and 2-g L-1 Clay treatments, but decreased seepage for the 0.5-g L-1 Silt treatment.� ��Seepage losses from these unlined channels can be significantly altered relative to untreated controls by manipulating the sediment particle size and concentration, and PAM concentration of irrigation water inflows.� Their effects on induced seepage changes are complex, strongly controlled by factor interactions, and appear to involve a number of mechanisms.�
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