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Show overtopping levees as far downstream as Kansas City wats small enough to warrant their construc- tion. These levees will provide a much higher de- gree of protection in the interim period than here- tofore haad been possible. In the area downstream from iCansas City, the risk of overtopping the planned local protection works in the absence of stream reservoir control is high enough to eliminate them from consideration at this time. Local pro- tection works can be provided when properly sup- ported t>y upstream reservoirs. Conclusions Flood control projects eliminate or ameliorate damage such as the loss of crops, interruption of normal planting operations, destruction or injury to property and improvements, interruption of transportation and business activities, creation of public health hazards, and loss of life. Where pos- sible and economically feasible, location of im- provements should be so planned as to eliminate the need for elaborate flood control works. It is recommended that future construction on the flood plain be so designed. However, it is likely that many operations and activities would remain on the flood plain even without flood protection be- cause of the desirability of such locations. When flood control works are necessary, early considera- tion must be given those locations which present serious threats to life or public health. In other instances reservoirs will logically precede related flood control works. 3. Integration of Mosquito Control Measures With Other Elements of Water Programs The Problem Measures needed for the control of insect-borne diseases, associated with river basin water resources development and utilization. The Situation Cases of encephalitis in humans have been re- ported from all 10 States. The virus of the western equine and the St. Louis strains are known to in- fect humans in the Middle West. Reporting of human incidence is considered incomplete. Posi- tive clinical diagnosis is impossible, and strain iden- tification requires serological procedures. Still, scattered cases are known to occur each year, and sporadic outbreaks of epidemic proportions have been reported. In 1933 approximately 2,000 cases were reported from the 10 States, many in the St. Louis area. In 1941 an outbreak occurred in the North Central States, with 1,100 cases in North Da- kota, 669 in Minnesota, and 366 in Nebraska. Other outbreaks were reported in Kansas and Colo- rado in 1949. Incidence is believed to be much greater than these figures indicate. Equine encephalitis, a virus infection of horses, occurs in most areas of the basin. Great numbers of horses have been lost from this cause. Although it is not yet considered a public health problem, it causes considerable concern to agricultural interests. The disease in humans is believed to be trans- mitted by Culex mosquitoes, but Aedes mosquitoes have been found naturally infected and cannot be ignored as possible carriers. Both groups are com- mon to the basin. A factor common to all outbreaks of encepha- litis is water. Water determines where maximum populations of people will be found and where mosquito densities will be greatest. Encephalitis is most likely to occur in areas of high rainfall. Where encephalitis is serious, in areas of low rainfall, some other source of water, such as irrigation, is found. The construction of reservoirs and extension of irrigation will lead to increased mosquito density unless adequate precautionary measures are taken. As mosquito density increases, the incidence of encephalitis will probably also increase. It is important that water resources programs in- clude control of disease-carrying as well as pest mosquitoes. Implementation of the recommenda- tions of health agencies would do much to provide this control. Health agencies are concerned with eliminating conditions favorable to the spread of mosquito- borne diseases. These include permanent or tem- porary bodies of water suited for mosquito breeding. Such bodies are important not only when they occur near cities or towns, but also when they occur in populous farm areas or recreation centers. All projects, units, or subunits of water programs re- quire investigation and evaluation in the light of the mosquito-control problem. The major factors to be considered are: (1) Human population in the area. This in- cludes both residents and transients who use the recreation facilities. (2) The prevalence of mosquito-borne infec- tions transmissible to humans. (3) Presence of disease-carrying species. 261 |
