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Show the ancient Egyptians from the Nile. And it would similarly require adjustment of our ways in these alluvial valleys to adapt them to occa- sional flooding of the land. In other words, it would then be necessary to look upon the natural flood plain of a river as its rightful floodway. It would be reserved as such. No new permanent development or structures would be permitted to be put in this flood plain unless adapted to the exigencies of floods. This would, of course, be considered only in the case of certain valleys, where the sediments have not been leached of their fertility. There are three general applications of flood plain zoning: 1. Prohibition of encroachment upon an es- tablished floodway to insure that the capacity of the floodway is not reduced by obstructions and to prevent or minimize future flood damage in the unprotected area of the floodway. 2. Restrictions on development in the pro- tected or unprotected flood plain areas where maintenance of the flow capacity is not a con- trolling consideration. The purpose here is to prevent or minimize future flood damage, partic- ularly landward of levees which provide only partial protection, or to eliminate works which provide full or partial protection. 3. Restriction of developments in areas sub- ject to inundation by impounded water in con- nection with reservoirs or sumps necessary for the proper functioning of interior drainage fa- cilities landward of levees. As for the first, it is the practice of the Army Engineers to recommend as a condition precedent to Federal participation in the accomplishment of floodway works, a requirement that local in- terests maintain the floodway free of encroach- ments. As for the second, the Engineers' practice is to provide a 3-foot freeboard for federally improved levees protecting agricultural lands above design floods. This provides protection generally against all floods except a record flood, say once in 100 years. That degree of protection is not undertaken unless the cost will be fully amortized by the flood damage savings generally within 50 years. The Commission has reviewed the possible util- ity of flood plain zoning in its survey of the typical river basins. In the case of the Rio Grande it appears that zoning in certain areas may be con- sidered and, as a minimum, appropriate posting to apprise all concerned of the flood hazard. In the case of the Missouri, zoning as a means of precluding excessive flood damages has defi- nite possibilities and should be encouraged wher- ever possible. Other than in connection with public land purchase and evacuation of an area, however, its use would be principally to limit fur- ther development of areas subject to flooding. The proposal for or possibility of obtaining flood protection deters serious consideration by local people of utilizing zoning restrictions. In the Alabama-Coosa Basin, local flood pro- tection works in connection with which flood plain zoning might be invoked are of two kinds: (1) Levees, flood walls, and appurtenant instal- lations for the protection of urban areas, such as those already installed at Rome, Ga., and now being considered in separate reports for Gadsden, Montgomery, and Selma, Ala., and (2) channel clearing and rectification in rural areas, such as the four such projects now included in the ap- proved basin-wide plan of the Army Engineers. In the second case, a plan could be developed for zoning of the flood plain with a view to future possible developments to prevent ill-advised en- croachments. Now bordering flooded lands are low agricultural, timber, or swamp areas upon which no structures will in any event encroach. In the case of the urban areas, prevention of en- croachment onto the flood plain would in some cases work real hardship because it is the only area in which the growing business and indus- trial section of the town can economically expand. The basin, however, offers the possibility of a comprehensive flood control plan to include zon- ing and levee protection as well as conservation storage reservoirs. In general, flood plain zoning is a function of the police power of the States, which may be delegated to the local subdivisions. Therefore, if it is to be done at all in connection with a Fed- eral flood control improvement, it must be either as the result of voluntary cooperative effort be- tween counties or cities and the United States, 145 |
