WSP10974 - Laserfiche WebLink

Home Browse Search

.-oj '-' '- ,- '- - c There are wi de variatl ons in the amount of leveling required for the different soil conditions that prevail within the project. Considerable areas of project lands are unsuited for any but the IIlOst limi ted of leveling operations. Where leveling is restri cted to smoothing of the ground surface to remove minor irregularities, such as might be accomplished by farm 'equipment, it has been estimated as an operating cost rather than as a development cost. In making the analysis for these locations, increased labor inputs and lowered irrigation efficiencies have been used. The lower yields associated wi th this level of development are also reflected in the analysis. Farm Irri gation Sys tems Existing farm ditches are generally stabilized by vegetation or by plating with gravel and rock. Those on steeper slopes or in IIlOre erosive soils are usually plated. In some areas di tches have eroded down to the underlying sandstone or shale. Banks are general'ly well stabilized by the gravelly soils and by plant growth. Little improvement of existing di tches is expected, particularly in connection with hay and pasture crops. Other than routine replacement of existing control gates and diViders, there probably will be only limited installation of irrigation structures. Disposal of irrigation waste water is a significant item. In areas where deep, shale-derived soils predominate, the erosion of gully channels by waste water has been, or can become, a serious farm management problem. Cost estimates for farm irrigation systems on nonirrigated lands include an allowance for waste water disposal structures. The weighted average estimate for addi tional development of existing farm irrigation systems is adequate to cover what few addi tional on-far!ll structures ma,y be required for this purpose. Drainage A considerable area of land now irrigated but wet or seeped, or presently recognized as susceptible to damage from this cause, has been excluded from the project. Some project lands temporarily have shallow water tables after irrigation. These lands have steep gradients and permeable soils, and natural drainage is effective. No cost estimate has been made for on-farm drainage. Findings Only limi ted amounts of addi tional development can be accomplished on most project lands. Levels of projected development have been related to physical requirements of the soils as they will be handled under project condi tions, and to the economic capabilities of the project. Weighted average develop- ment cost estimates are summarized by evaluation areas in table 5. >1 ';1 .' - 18 -