92 FOREST LANDS FOB THE PROTECTION OF WATERSHEDS. 



For example, in the flood of 1907, which reached its maximum at Cincinnati and 

 Pittsburg about the same time, no amount of holding back of the storm water 

 on the upper Ohio at that time would have helped the situation at Cincinnati 

 at all. 



Another important consideration in the effect of these reservoirs, as they 

 would have to be operated to prevent floods, is the great change that takes place 

 in a flood wave as it propagates itself down stream. The author is unable to 

 tell from Mr. Leighton's paper to what extent he has considered it. The paper 

 itself seems to indicate that the discharge held back by a particular reservoir 

 produces a corresponding volumetric effect (not gauge effect, of course) at all 

 points below, after making a due allowance of time for the transmission of the 

 wave. This would be an erroneous conclusion. For example, a wave that 

 might rise at Pittsburg from 100,000 cubic feet per second to 150,000 a day later 

 and to 200,000 the next day, and then fall at a corresponding rate, would not 

 at any point below produce a maximum increase of 100,000 second- feet ; and the 

 farther away the point considered the less would be the increase. At Cairo, 

 nearly 1,000 miles below, the same wave would take a much longer time in pass- 

 ing, probably not less than a week, and the maximum increase would probably 

 not be more than 25,000 second-feet. This is merely a general illustraflon, for 

 exact data on the subject are not available. The problem is of such complexity 

 that nothing but the results of long experience could establish a rule as to what 

 might be expected in any given case; but it can be stated with certainty that 

 the diminution of discharge at any considerable distance below the reservoirs 

 for a given time would never, be as great as the amount held back by the reser- 

 voirs in the same length of time, and that the quicker and the higher the flood 

 the smaller the relative effect at all points below. Tt is only when such wave 

 elimination merges into a constant quantity, continuing for a considerable time, 

 that the full effect of a reservoir would be experienced at any point below. 

 This, in fact, is what would actually happen in the contrary case of the low- 

 water season when the reservoir discharge is kept up for a long time. 



Still another feature in the high-water effect of such reservoirs is the demand 

 for water for power at all times. If there should ever result any really general 

 use for all this water, as is predicted, then the consumption for power would 

 make a considerable river in itself. Now, this much can not be shut off in any 

 case. Street cars and shops must run and houses must be lighted, whether the 

 flood is ruining the lowlands or not. An example of this occurred in 1905 on 

 the upper Mississippi, where the outflow from the upper dams was cut down to 

 a minimum to reduce the flood in the valley at Aitkin, which was then being 

 overflowed by the river. The mill at Grand Rapids, just below the reservoirs, 

 made a strenuous protest, and even threatened legal proceedings to compel the 

 release of the full normal flow of the river. 



Considering all the foregoing features of the operation of the proposed sys- 

 tem, even if every reservoir were built with the full estimated capacity, it 

 would be extremely fortunate if 75 per cent of the predicted results, either in 

 flood protection or in aid of navigation, could be realized. 



It is in the matter of cost, however, that the weak point of Mr. Leighton's 

 system appears. Judged by any reasonable .standard, his estimates are hope- 

 lessly wide of the mark. The method itself of getting at a basis of cost is inad- 

 missible. For example, in determining a unit of cost for that class of reser- 

 voirs which embrace the greater portion of the total storage, the figures for nine 

 reservoirs are taken, counting as one the whole upper Mississippi 1 system. Only 

 the Mississippi system has been built ; two others are under construction and six 

 are merely projected. In accordance with almost universal experience, and espe- 

 cially in view of the great advance in prices of all kinds since these estimates 

 were prepared, it must be expected that these works, if ever built, will cost 

 from 25 to 50 per cent more than the estimates. Three of the projected dams 

 are of the relatively cheap rock-fill construction, which would be inapplicable 

 to most of the Ohio dams from considerations of safety. 



The controlling element, however, in the unit estimate is the Mississippi 

 system, whose capacity is nearly one-third of the whole group considered and 

 whose unit cost is only about one-seventh of the average cost of the others. 

 The use of the Mississippi reservoirs in any way as a basis of estimate for the 

 Ohio system is wholly inadmissible, because of the dissimilarity of sites. The 

 Ohio sites, with one exception, are dry sites totally different from the lakes 

 of Minnesota. Even the latter reservoirs could not now be built for three 

 times what they have actually cost the Government. The flowage lands em- 

 braced about 80,000 acres, which were nearly all reserved while yet belonging 



