nonowners to exploit the land. Markets for such items as poultry and dairy products are largely located in centers of greater population and the difficulties of marketing special produce have discouraged many farmers from producing these supplementary sources of income. In the Memphis trade area, there has been a marked development of the dairy industry and some other towns have recently become the sites for cheese plants and condenseries. Such developments, however, are of too recent origin to have influenced much the desirable transition from cotton to a more stable economy based on diversification of enterprises and supplying adequate outlets for labor during the entire year.

GENERAL ECONOMIC-SOCIAL PROBLEMS

Population, in excess of that which basic resources can sustain on a permanent basis is a major economic and social factor underlying the problems of this watershed. There are practically no industries in the watershed which are not directly associated with the production of crops or timber. In spite of decreasing agricultural opportunities, the population has remained fairly constant in recent decades, hence the pressure on the land has accelerated as its fertility has declined. This pressure will increase when the proposed reservoir program is complete. Relief through the development of other outlets for labor is not at all promising. In recent years there have been some exploratory developments for oil and gas, but there is little evidence indicating important underground resources. Aside from products of the soil, the area appears to have few other major resources which can profitably be developed.

As the soil and timber resources have been exploited, the tax base has decreased. Local governments are faced with the necessity of either increasing assessments or maintaining valuations on lands of decreasing value. This procedure normally results in taxation in excess of the productive capacity of the land and ultimately leads to tax delinquency. Delinquency, however, has not yet developed into a serious problem as revenue from leases based on speculative underground values and Federal conservation payments to landowners have in recent years provided funds for the payment of taxes. If underground resources prove valueless or subsidies are eliminated, a delinquency problem will inevitably develop.

Sickness and disease tend further to depress the area. Although public-health agencies have made considerable progress in preventing and controlling diseases, precautionary measures are not in common Low family incomes definitely limit medical attention with the result that death rates are relatively high especially in the younger ages.

use.

Education facilities in the watershed are not adequate. Only about one-third of the people have had limited or formal education. Although improved transportation facilities have made consolidation of rural schools possible and conditions have been bettered in recent years, high-school enrollment lags. Low salaries paid to teachers, especially in Negro schools, and the mistaken opinion of many rural people that only limited education is necessary in farming enterprises, re barriers to educational progress and to the care of the soil resource. A growing need is for more vocational training covering the fields of

agriculture, soil conservation, forestry, and the manual trades. Various land-use agencies have carried on some land-use educational work among owners and operators, but this work has not been on a sufficient scale to reach the vast majority of farm families.

CHAPTER II. THE FLOOD PROBLEM

ORIGIN OF FLOODS

The origin of all floods in the uplands is storm rainfall. All general types of storms common to the region; i. e., tropical hurricanes, thunder storms, and frontal storms, are the source of rainfall causing flood run-off. The rainfall of tropical hurricanes and thunderstorms is usually more intense and occurs generally during the growing season, April to November. Flood damage from these storms is greater in the aggregate than that caused by frontal storms normally which are of longer duration and are characterized by low to medium rainfall intensities. Furthermore, the frontal storms usually occur in the winter or spring seasons when damageable values are relatively low; principally they damage property and lower agricultural yields by delaying planting. Most of the major floods occur when storms of long duration or unusually high intensities blanket extensive portions of the watershed. Thus, in the frontal storm of January 17-23, 1935, on the Coldwater Basin, approximately 12 inches of rain fell, of which 10 inches immediately ran off and caused severe flooding in the bottom lands.

Detailed investigations in the Yazoo Basin show conclusively that the depleted condition of the watershed cover is a major cause of floods, principally because this condition lowers the capacity of the soil mantle to absorb water. The result is an abnormal volume of surface run-off from compacted or nearly impervious surface soils and from eroded subsoils. On the smaller watersheds less than 1 inch of rain has caused damaging floods, partly because the run-off was high and partly because the capacity of the stream channels was inadequate. The stream channels contain sediment and debris which have reduced their capacity to convey water to a rate so low that overbank flows may occur 10 to 15 times a year.

NATURE OF FLOODS

The volume of water causing floods comes from surface run-off. As a result the stream discharges rise rapidly to a crest and descend slightly less rapidly to produce a sharp crested hydrograph. This type of flood is accompanied by severe erosion and later deposition of sediment on the flood plain. Because floods are of this type they can be reduced significantly by measures designed to decrease surface run-off and store the increased infiltrate in the soil reservoir. With increased infiltration, much less erosion will take place.

The flood plains of this basin are wide and flat so that large areas of land are inundated by flows only slightly in excess of bankfull stream capacity. Furthermore the drainage of the flood plains after flooding is slow; prolonged inundation results.

Because all types of storms can cause flooding in this watershed, overflows are not confined to certain seasons but occur throughout

the year. Records reveal that of 305 floods occurring on the Coldwater River from 1929 to 1941, inclusive, 161 floods or 53 percent occurred during late winter or spring whereas fewer and smaller floods occurred in the late summer or fall.

Between 1905 and 1943, several floods of sufficient magnitude to command national interest have occurred throughout the uplands, 14 of which flooded the Yazoo delta. During this same period there were many times this number of smaller floods, the aggregate damage. from which is much greater than that from the major occurrences.

A flood-sequence study indicates that during the period 1929 to 1941, inclusive, the number of floods on various tributaries ranged from 4 to 24 annually varying with land-use conditions and streamchannel characteristics. A medium-size flood having a frequency of approximately once in 2 years during the growing season is caused by a rainfall of about 4 inches lasting from 2 to 6 days. It inundates approximately 330,000 acres and causes a damage of about $850,000. Such a flood would cause a maximum discharge of 8,250 cubic feet per second on the main stream of the Yalobusha River at Grenada, whereas the normal flow of water at this point is only about 100 cubic feet per second. An average flood of this magnitude causes damage to more than 20,000 farms thus directly affecting the income of about 65 percent of the population.

Damage from floodwater.

DAMAGE FROM FLOODS

More than three-fourths of the bottom lands in the upland portion of the watershed have been cleared and developed for agriculture. At present, approximately 30 percent is in corn, 20 percent in cotton or other row crops, 8 percent in hay or close-grown crops, 4 percent in pasture, 2 percent idle, and the remaining 36 percent in woods or other uses. Major flood damage to these agricultural interests occurs during the growing season and varies according to the condition of the crop, the duration of flooding, and weather conditions following inundation.

In the early spring, flood damage may occur when there is a forced delay in planting operations or when, as a result of flooding, crops must be replanted (pl. 5). After the crops are growing and well advanced, a flood may cause a complete kill or merely a reduction in yield. During the late fall months, a flood may cause complete loss of harvestable crops or a partial loss depending on the depth and duration of the flood.

The duration of a flood is a most important factor influencing damage. In this watershed floods may last from a few hours to several days. The damage depends on depth of inundation or length of the storm period. Another important factor is the weather which follows receding water. A cool, cloudy period following s flood sometimes permits almost complete recovery of the crop. whereas sunshine associated with warm, clear weather will ofter scald the plants even though the duration and depth of flooding is of minor character.

Based on a gage height of 35 feet and over at Greenwood, Miss. This stage has been exceeded in esch of the following years: 1911, 1912, 1913, 1917, 1920, 1921, 1922, 1927, 1931, 1932, 1933, 1935, 1937, and 1939. Refer to appendix, exhibit E, not printed.

In the Yazoo delta, two types of flooding and damage have been appraised other than those occasioned by Mississippi River backwaters. The greater damage occurs where hill streams enter the delta. Here, a decrease in velocity causes silt-laden waters to drop part of their load thus building up extensive alluvial fans. The other type of overflow occurs along main streams in the delta proper. In the past this has been extremely severe. If the present Army Engineer flood-control program is carried out, complete flood protection will be afforded to all of the delta area except to a few lowlying predominantly wooded sections that will be afforded some degree of protection. Only on those areas where partial protection will be afforded are damages here recognized."

PLATE 5.-A June flood on cotton. This flood was caused by a local thunderstorm and lasted less than an hour. The owner replanted to corn but could expect only low yields.

The agricultural damage (to crops, pasture, and woods) from floodwater originating in the upland portion of the watershed amounts annually to $1,077,786 in the five upland drainage units, $461,066 in the alluvial fans, and $25,616 in the delta main stream areas, a total of $1,564,468. Approximately 98 percent of the damage is to cotton, corn, and hay (pl. 5). This damage represents a reduction in net income of those depending on agriculture for a livelihood. If agricultural floodwater damages in the hill areas were equally distributed, each family there would suffer an annual loss of approximately $50. Flood damage to property in the Yazoo watershed is primarily damage to roads and bridges (pl. 7). Railroads and fences and other farm property sustain a small amount of damage. Very few buildings are located in the flood plain and damage to such structures is usually inconsequential. Occasional losses of livestock are incurred, but farm animals are generally removed from danger areas before flooding.

Those delta areas that will be afforded only partial flood protection are adjacent to the main streams from Greenwood to Marks.