Sediment and polyacrylamide effects on seepage from channeled flows

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, and silt), sediment concentration (0, 0.5, and 2 g Lj1 ), and water-soluble anionic polyacrylamide (PAM) concentration (0, 0.4, and 2 mg Lj1 ) inf luences seepage loss of irrigation water (electrical conductivity = 0.04 S mj1 ; sodium adsorption ratio = 2.2) from unlined channels in silt loam soil. In a minif lume, a preformed channel with 7% slope was supplied with 40 mL minj1 simulated irrigation water inf lows 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 inf lows, 2.8 L for clay-loaded inf lows, and 6.4 L for f lows without sediment. Increasing inf low clay concentrations, 0, 0.5, and 2 g Lj1 clay, decreased cumulative seepage volume (23 h) for the no-PAM treatment from 12.4 L to 6.7 and 0.2 L, respectively. Increasing inf low silt concentrations in no-PAM treatments resulted in a curvilinear response with a seepage volume maximum occurring for the 0.5-g Lj1 treatment (12.4, 47.1, and 9.8 L, respectively). Increasing inf low PAM concentrations increased seepage volumes for 2-g Lj1 silt and 2-g Lj1 clay treatments but decreased seepage for the 0.5-g Lj1 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 inf lows. Their effects on induced seepage changes are complex, strongly controlled by factor interactions, and appear to involve a number of mechanisms