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Show lence to be on the north shore in Clarendon County-near the Potato Creek Wildlife Refuge. Here 38.7 percent of the 470 blood films examined were positive for malaria parasites. Under the con- ditions created by lack of malaria-prevention meas- ures, malaria assumed epidemic proportions on the margin of Santee Reservoir. Surveys conducted during the epidemic period indicated that the uncleared portions of the Santee- Cooper Reservoir were the most important source of malaria mosquitoes, with the wildlife refuges the next most serious. Flight range studies showed that mosquitoes were flying as far as 3.6 miles from their breeding places. Mosquito-breeding areas include large and small artificial lakes, natural sloughs, marshes, and old river channels. There are eight major water im- poundments in the Alabama-Coosa Basin. In addi- tion to these large artificial lakes, many small stock and fish ponds have been constructed. The rivers and creeks are bordered by meanders whose edges were vegetated and surfaces partially covered with aquatic plants. Climatic conditions over most of the basin favor production of mosquitoes, including those which transmit malaria. Alabama, Georgia, and Tennessee-the States in- volved in this river basin-require mosquito-preven- tive measures as a part of water impoundment proj- ects. In 1921 Alabama, through its board of health, became the first State to issue regulations governing the impoundment of water. Since that time the State has carried on an effective antimosquito pro- gram in water impoundment areas. This board has achieved marked success in carrying on a well- rounded mosquito control program on stock and fish ponds, and in draining borrow pits, natural sloughs, and ponds near thickly settled communities. The major mosquito and mosquito-borne disease problems and control activities have been in the Alabama part of the basin. However, Georgia and Tennessee have definite mosquito-control programs. Study of the situation was made at Allatoona Reser- voir and measures were taken to insure that no health hazards developed. Post impoundment in- vestigations are being continued to determine the effectiveness of mosquito-control measures. Conclusions It is important that project planning in the basin include measures for mosquito control. Experience shows that preventive measures regarding mosquito control in relation to water impoundments are more economical than corrective or remedial measures. 911610-51- -37 5. Flood Plain Zoning The Problem Extent to which flood plain zoning can be used to avoid flood damages. The Situation The purpose of flood plain zoning is (1) to dis- courage encroachment on river flood plains where flooding may be expected to cause losses to residents and damage to installations and structures; and (2) to reduce costs of flood protection. Zoning is a function of the police power dele- gated by a State to a political subdivision under which local authorities, acting in the public interest, exercise reasonable control over privately owned lands without compensation to the land owners. Accordingly, if flood plain zoning is to be associated with Federal flood control improvement, it must be administered by a county or city voluntarily or in compliance with a condition of local cooperation imposed as a prerequisite to the improvement. The initial cost of flood plain zoning is low com- pared with the cost of positive measures for provid- ing flood protection. However, the exclusion of more intensive uses from flood plains may cause some economic losses even after allowing for oc- casional damage or destruction by floods since these uses may yield a greater return than the most profitable use under zoning restrictions. These factors may be evaluated and the decision to pre- vent flood damages by flood plain zoning or by the construction of flood protection works may be made on the basis of the relative economic advantages of the two methods with due regard for the related intangible considerations. Zoning restricts future uses of the zoned property and will be more readily accepted by land owners in relatively unsettled areas were land is not in- tensively used. Such is the case throughout most of the Alabama-Coosa Basin. Most flooded lands adjacent to the rivers are low-lying agricultural, timber, or swamp areas. It is unlikely that dense settlement will occur in these areas. In the case of urban areas, flood plain zoning would cause hardship if the flood plain is the only area into which the growing business and industrial section of the town can expand. However, this is seldom the case in the basin and flood plain zoning is a means which could be used to discourage urban expansion in areas where flood hazards normally exist. Where flood plain zoning is not invoked, a 555 |