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 To improve the quality of water draining irrigated farmland, a system of improvements may be
developed to treat site-specific problems. The system includes the crop, tillage, and chemical
application, irrigation water management, and improving, reorganizing, or converting the existing furrow
irrigation system.
The Rock Creek RCWP implemented improved irrigation, sediment basins, conservation tillage
and filter strips and reduced suspended sediment concentrations in return flows by 75% (EPA 1990)
and mass loadings of total phosphorus to the Snake River by 57% (Maret 1990).
Reducing the number of irrigation events, irrigating every other furrow
and additional water management BMPs have also been proposed. The applicability depends on the
crop and water requirements. Models to estimate irrigation runoff and nutrient losses in the irrigated
West have not been developed to the extent of models in the humid nonirrigated areas .
Water runoff from irrigated land has been estimated as 30-40% for the Magic Valley of Idaho
depending on the crop (McNeal 1982). Brockway (personal communication 1990) estimates return
flows at field ends for furrow gated pipe, and concrete ditch systems are 35-45% of the applied water.
He suggests that water reuse can reduce losses to 30% and cutback or surge irrigation return flows can
be reduced to 15% or less.
Control of slope through land leveling, grading, or contour furrowing can reduce erosion losses.
Israelson et al. (1946) showed that erosion losses increased with increasing furrow slope, and an
increase in slope from 1 to 6% increased erosion 16 times. From a compilation of several studies,
McNeal et al. (1982) found erosion to vary by the 2.2 power of the slope. Kemper et al. (1985) found
that erosion was commonly about a 2 to 3 power function of furrow slope.
Shortening the field or furrow run length also reduces erosion losses. Using a multiset system of
gated pipe, that can be removed to avoid damage by farm equipment, can reduce erosion by 40%
(Brockway 1986). Buried pipe can also convey water, reduce erosion losses, and farm equipment can
cross without damaging it. An approximate 83% sediment reduction efficiency with a range of 74-83%
was estimated for buried pipe in the Idaho RCWP by Carter and Berg (1982).
Crop and straw residues reduce the erosive energy of advancing irrigation water. Berg (1984)
found that straw-treated furrows reduced erosion by 30-70% compared to untreated furrows. Straw
significantly increased infiltration and lateral water movement. Straw-treated furrows also reduced net
sediment yields 52 to 71% with the greater soil savings during higher irrigation flow rates (Brown
1985). Sediment concentrations decreased 50 to 33% at low and high flows respectively. Miller et al.
(1987) found that straw residue was effective at reducing sediment yields up to 100 fold compared to
untreated furrows.
4.2-12
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