The project is expected to prevent approximately 1,150 tons of sediment and 2,385 pounds of phosphorus from entering the Snake River annually and will help the Twin Falls Canal company
meet their reduction requirement under the Snake River Total Maximum Load Management Plan.
In southern Idaho for example, the Twin Falls Canal Company is 75 percent surface irrigated and about 10 percent of the diverted water returns back to the Snake River while the Northside Canal Company is 95 percent sprinkler irrigated and returns about 5 percent of the diverted water back to the river.
Applying alum reduced soluble P below the inflow concentrations at Twin Falls Canal Company I-drain (0.18 mg P [L.sup.-1]) and Cedar Draw (0.09 mg P [L.sup.-1]), with soluble P reductions increasing as alum application rate increased (Figure 8a).
As with soluble P, there was little difference between the reductions in total P in the two ponds on the Twin Falls Canal Company I-drain while at Cedar Draw the total P concentrations increased in the second cell as soluble P concentration increased.
The alum efficiency at the field sites varied, with the Al:P ratios being smaller at the Twin Falls Canal Company I-drain site than at Cedar Draw.