A wall of limited height, however, is really desirable, at least along certain parts of the river. While reservoir control would result in reclaiming considerable areas of land, a wall would provide means for adding to the amount and greatly improve the appearance and usefulness of the banks. The handling of cargoes, to and from river boats would be greatly facilitated by means of modern devices. Sheds could be constructed along the wall and close to the boats which would lie alongside. Such arrangement would make feasible the bringing directly of river and rail transportation with the great advantage of through rates and routes, a condition which is now lacking at practically all points on American rivers.
FLOOD PREVENTION.
In the treatment of the flood problem, prevention, by the use of storage reservoirs, for the purpose of holding back the damaging part of the flood water, is the rational and comprehensive method, as it goes to the source of the trouble, and extends its benefits throughout the entire river valleys, not only in the form of flood relief, but by improvement of the low-water flow, due to the release of the impounded flood waters during the dry season.
Forest cover is beneficial to some extent in retarding the run-off and in improvement of low-water flow, and the attitude of the Flood Commission is to support such National and State legislation as will tend to preserve and increase the present forest cover. The Commission, however, recommends the use of the storage reservoir system, supplemented by other means where necessary, for the reason that such a system could be speedily brought about. The use of storage reservoirs for flood control is not a new idea in this country and this method is now successfully employed in European countries.
The exhaustive surveys and studies for flood prevention disclosed the fact that forty-three reservoir sites are available in the Allegheny and Monongahela drainage basins above Pittsburgh, and that while not needed for present purposes additional sites are feasible. The forty-three projects would have a total capacity of 80,500,000,000 cubic feet, would cost $34,000,000, and would control about sixty-two per cent. of the total drainage area above the city. After a careful analysis it was found that a less number of reservoirs was practically as effective, under proper manipulation, and a selection was made of the most favorable ones, seventeen in number. These would have a total capacity of 59,500,000,000 cubic feet, would cost $21,700,000, or about $364 per million cubic feet of storage capacity, and would control fifty-four per cent. of the total drainage area.
As a basis, eleven of the principal floods, occurring within recent years, were exhaustively studied and it was found that the seventeen selected reservoir projects would reduce all of them, with one exception, to below danger line. Investigation showed that a low wall built at comparatively small cost along a few parts of the low-lying river fronts could be used in combination with the seventeen reservoirs to prevent overflow by the highest known floods. This combination was therefore recommended, the total cost being estimated at $22,350,000.
Some of the benefits to be derived by preventative methods and stream regulation and development, may be summarized as follows:
1. Reducing or doing away with floods and flood damages and their constant menace, thereby encouraging and making possible for present and future generations full development of affected areas.
2. (a) Improving of navigation, by permanently increased stream-flow in slackwatered rivers, where dry weather flow is frequently inadequate to furnish desired draft, thus providing uninterrupted transportation not only for present business but for future demands. (If the reservoirs were brought up to maximum capacity, that is, above flood control requirements, the low-water flow of the Ohio, at Wheeling, ninety miles below Pittsburgh, would be nearly six times the present minimum, giving an increase in stage of 3.7 feet. One of the largest floods would have been reduced over thirteen feet.)
(b) Making possible slack water on certain rivers, worthy of attention, but now unimproved largely on account of absolute lack of sufficient water.