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
