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Show PART IV FUTURE DEMAND These drainage costs are summarized in Table 37 and discussed in greater detail in the following sections. On-farm drainage In addition to drainage already provided for presently irrigated lands in the region, as discussed in Part II, on-farm drainage will "be needed on 436,900 acres of presently irrigated land in the region, re- quiring 4,093 miles of open ditches and tile drains for a total installa- tion cost of $43,223,000 by 2020. One mile of on-farm drain is expected to provide relief for approximately 106 acres of drainage deficient land. The cost will be an average of $100 per acre of drainage-deficient irri- gated land or $21 per acre of total land presently irrigated. This cost could be reduced significantly by more efficient use of irrigation water than has been used historically. Projected on-farm drainage required for presently irrigated lands is shown by Eydrologic Subregions and States for each projected time period in Table 38. An estimated 176,300 acres, comprising about 30 percent of the new land projected to be developed by 2020 in the region, will need on-farm drainage. Approximately 1,651 miles of drains will be needed to provide drainage for this additional acreage at an estimated total cost of $17,434,*J-OO and at an average cost of $100 per acre. On-farm drains re- quired for new lands are listed by Eydrologic Subregions and States for each projected time period in Table 39. Project-type drainage It is not only essential to provide on-farm drainage for presently irrigated, and potentially irrigable lands to be developed for irrigation but also to provide project-type subsurface drains and outlet channels to serve a group of several farms. These drains are installed as part of Federal and occasionally non-Federal project developments which are usually riot a direct cost to individual landowners. Costs for installing approximately 1,060 miles of project-type open ditch and. tile drains on 436,900 acres of presently irrigated land need- ing additional drainage relief will total about $27,588,500 by 2020, as shown in Table 40. This averages approximately $60 for each acre of drainage-deficient irrigated land and each mile of drain will provide an outlet or* relief for about 400 acres. Project drainage requirements on presently irrigated lands in the Upper Main Stem Subregion are well below those of other subregions. This is attributed to the unusually rough to- pography and high elevation of much of this subregion which limit many irrigated lands to meadow hay and pasture production and to small local- ized seepage areas not requiring or susceptible to project-type drainage. In other areas where the terrain is more even and occurs in broader tracts, 84 |