To install and maintain the measures during the 20-year installation period will require about 17,716 man-years of labor (table 20). The labor to install and maintain cropland and pasture-improvement measures will be supplied largely through more complete use of the available time of cooperators and will not usually require hiring extra assistance. Measures of a public nature, such as the forest land and highway treatments, will furnish 6,246 man-years of employment during the 20-year period or average yearly employment amounting to 312 man-years. This will provide additional part-time employment to local people and will help to offset temporary reductions in income which may sometimes result from carrying out necessary land-use adjustments. Labor requirements for maintaining the program after the twentieth year are relatively small and amount to only 781 man-years.

TABLE 20.-Labor requirements to install and maintain a remedial program

CHAPTER IV. BENEFITS FROM THE REMEDIAL PROGRAM

Benefits from the recommended program are of two major classes: (1) The off-site or flood-control benefits and (2) the on-site or conservation benefits. Off-site benefits of the program will accrue on flood-plain property as a result of reduced flooding and sedimentation. On-site benefits will accrue on treated lands as a direct result of conserving water and building up the soil and will consist of increased yields of crops, forage, and timber or reduced operating or maintenance costs.

OFF-SITE BENEFITS TO VALLEY LANDS AND FLOOD CONTROL WORKS

Off-site benefits provide ample justification for the recommended flood-control program. The benefits are public in character, since they accrue to society at large and result from control measures which are applied to lands other than those benefited. Inasmuch as 82 percent of all farms in the watershed include some bottom land, most people incurring costs of land treatment will also share in the flood-control benefits. Substantial off-site benefits will accrue to lands in the alluvial fans which are unattached to any lands participating in the program.

20

10

3A

x

18

3A

48

4C

3C

38

WORK UNIT SA-Entrenched streams-Deep loess - Western Coldwater 38-Deep loess - North bluff

"

- Yalobusha

-Yalobusha

4A-Brown loam-Yocona

3C

48

4C-Entrenched streams-Brown loam - Bogue

1

Benefits from run-off reductions.

Storm run-off will be reduced materially soon after control measures are installed, even on severely eroded lands where forest plantings will check surface run-off substantially in only a few years. There will be a delay in the attainment of benefits on a watershed-wide scale because of the impracticability of effecting major land-use adjustments over the entire area in a short period of time. As planned, the program will be installed over a 20-year period and more than 65 percent of the off-site benefits from reducing floodwaters will be attained by that time. In the tenth year after the program is completely installed, almost 90 percent of the ultimate floodwater benefits will be realized and 100 percent of yearly benefits will be attained 25 years after all installations are complete.23 When the program becomes fully effective flood flows will be decreased on the average by the percentages shown by the curves of figures 4 and 5.

Floods formed the alluvial valleys of this basin long before the land was subjected to improper use and floods cannot be entirely eliminated even when all lands are properly devoted to their best potential uses. The recommended adjustments in land use, however, will cause a marked reduction in surface run-off, with a result that some floods will be entirely prevented and others will be so reduced as to permit much more profitable utilization of the alluvial lands. There are now from 1 to 13 24 floods annually on any one stream system; in the future this frequency will roughly be halved and on an average the aggregate acreage of flood plain inundated annually will be only about 50 percent of that now flooded.25

Within 25 years after the program is installed, annual floodwater benefits will amount to approximately $890,000, of which 93 percent will be a direct reduction in damage to crops and property. The remaining 7 percent will represent the enhanced value of land within flood-control reservoir areas, the presently wooded flood plain of the main stem of the Coldwater River; and alluvial fan areas of the delta. More intensive use of these lands will be feasible when the frequency of flooding has been reduced; land that now is flooded more often than once in 4 years, and usually every year, will be flooded less frequently and thus will be available for crop production. In the reservoir areas, this benefit will result from more land being available for leasing to private interests, as a common rule of thumb for determining leasable land is that it be flooded no more frequently than once in 4 years. Along the main stream of the Coldwater and on the delta alluvial fans, most of the land capable of yielding this class of benefit is now in woods because of frequent flooding. Additional small areas of woodland occur on flood plains in other parts of the watershed and undoubtedly will receive benefits of this type; however, such benefits have not been evaluated for these scattered areas, since the latter are intermingled with other flood-plain lands, the preponderance of which have already been developed intensively for farming use.

23 See appendix, exhibit E.

24 This does not mean that the entire stream system will be flooded the total number of times shown, but that the number of floods given will occur on some streams in the system. It is not uncommon at present, however, to have as many as 4 to 6 floods on one stream during one growing season.

25 Some areas are inundated several times in the same year by successive floods and the aggregate acreage inundated in a year may be several times the flood-plain area.

A summary of floodwater benefits by drainage units is shown in table 21.

Benefits from reduced sedimentation.

Benefits from reducing sedimentation will not accrue as rapidly as those resulting from reductions in floodwater. The recommended remedial measures will curtail sharply soil-erosion rates long before the infiltration capacity of soils has been fully restored. Although these influential effects will confer some immediate benefits, reductions in sedimentation will increase progressively and will not reach a maximum for many years.

Present trends in sedimentation damage by deposition and swamping are upward. Consequently the stabilization of erosion will check these trends immediately and reverse them by the time all measures are installed. This will result in relatively early benefits from the prevention of future damage. As the rate of erosion is further decreased and sediment contributions fall below the critical rate,* the benefits from alleviating past damage will begin to accrue and finally will surpass in value all other types of off-site benefits.

Calculations show that at present the annual contribution of sediment to stream systems totals about 89,000,000 tons for the watershed (table 22). Twenty years after the program has been installed, the annual contribution will total an estimated 33,000,000 tons instead of increasing to 137,000,000 tons.

TABLE 21.-Monetary value of off-site benefits resulting from anticipated reductions in run-off

[Benefits shown have not been reduced to present values]

1 Land on which the frequency of flooding will be reduced by the proposed measures sufficiently to permit cultivation. Values for Coldwater unit apply to 4,155 acres of flood plain in the main stream of Coldwater River above the Arkabutla Reservoir and to 1,124 acres within the reservoir proper. Values for Yococs unit apply to 995 acres within the Enid Reservoir. In the Yalobusha unit, 2,539 acres in the New Grenads Reservoir will be benefited, whereas in the delta 583 acres of alluvial fan areas adjacent to the North Bluf unit and 1,338 acres of similar land adjacent to the South Bluff unit will have their value enhanced through more intensive use.

Approximately twenty-fifth year after program installation is completed.
Actually future without conversions.

Flood reduction benefits in the delta consist of $10,787 accruing to overflow areas along the main stream and $217,896 on alluvial fans formed by streams draining the North and South Bluff units. All delta benefits are the result of land treatment in the North and South Bluff units.

28 The critical rate is defined as the number of tons of sediment per year which stream systems can receive and safely dispose of without causing any net harmful effects from sedimentation. This rate amounts to about 36,000,000 tons per year for the watershed as a whole and will be reached about 10 years after the comr plete installation of the program.