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14 the gates IllUst be rdsed when the flood level reaches their top. Then the power storage can run out too, and thus the structure can actually produce a bigger flood crest below the d8Jn than would have taken place if the multi-purpose dam were not there. Chart X shows a true dry reservoir flood control dam with the same gross flood control space (416,000 acre feet) as the multi- purpose project built at the same site. The basin is formed by a simple dam equipped with an outlet or slot of the proper size without gates or any other artific1&l means of controlling the flow. The rich farm lands remain in cultintion. Farm buildings are located above the flood line, out of harms way. Chart II shows how the dry :retarding basin works during floods. During the few days when the water is backed up behind the dam, there is no current, and hence no scouring takes place. Instead the lends are enriched by the silt deposited in the still water. Most floods occur before the growing season and there is 11 ttle, if' any, crop damage. Much less land is involved. The town is high and dry. Chart XII shows graphically one of the reasons why it is that a true flood control d8Jn is so much less expensive than a multi-purpose dam. Another example of an actual multi-purpose dam is shown by Chart XIII. This one is built and in service, and has been tested by a big flood. On January 4, 1939, Major Genere.J. J L Schley, Chief of Engineers, U S J.rrv, in recoJMI..nning the construction of this reservoir, (which is the first of three of the series on the river) said: "I believe, however, that the need for controlling flood flows ... makes it advisable to construct one of the reservoirs at an early date. Installation of power features would be deferred and the entire storage capacity utilized for flood control until ... construction of the third reser- voir."