68 BULLETIN 1017, U. S. DEPARTMENT OF AGRICULTURE. 



of the mean year. The maximum storage under these conditions 

 is seen to be 5.9 billion cubic feet, at water elevation 979.1. The 

 reservoir in this case would be empty by October 1. 



In diagram C, figure 20, the run-off curve was made up of the 

 spring run-off of the mean year (January- June) and the maximum 

 summer and fall run-off (July-December). Maximum storage here 

 is shown to be 7.2 billion cubic feet, at elevation 980.5. The reservoir 

 would be empty by the middle of December. 



In diagram D, figure 20, the most extreme conditions that may 

 be expected are shown. The run-off plotted here is for the hypo- 

 thetical maximum year as stated on page 64. This diagram shows 

 that the maximum storage required in the most extreme case (that of 

 closing the reservoir during the last 15 days of August) would be 

 12.1 billion cubic feet, if the rate of outflow were 1,000 second-feet 

 continuously after May 1. However, before the water surface 

 reached elevation 985.1 required for this amount of storage, the spill- 

 way alone would be discharging at a much greater rate than 1,000 

 second- feet, so that this stage would not be reached under these con- 

 ditions and there would be a minimum freeboard on the dam of more 

 than 3 feet. By regulating the outflow during September at 2,000 

 second- feet, which could be taken care of by the outlet channel if 

 necessary, the storage could be reduced to 7.8 billion feet by October 

 1, and with a flow of 1,000 second-feet from then on the reservoir 

 would be emptied by early in January. If the heavy July run-off 

 were to occur in June, with that of June transferred to July, the 

 maximum storage would be 10.6 billion cubic feet. If in addition to 

 closing the reservoir for 15 clays at one time it should become neces- 

 sary, on account of some great storm, to close it at another time for a. 

 short period, say 4 clays, an increase in the rate of outflow to 1,400 

 second- feet would in 10 days bring the storage back to normal. In 

 all cases the reservoir would be empty before the heavy spring run- 

 off of the following year begins. These conditions are extreme and in 

 all probability never will occur ; but should such a combination .of 

 run-off come, it can be controlled without damage to the reservoir 

 and with less damage from flooding in the lower valley than would 

 result from the unhampered flow of such run-off. 



Should even worse conditions prevail than have here been con- 

 sidered, the reservoir would still be safe from destruction. The spill- 

 way and culvert together would be capable of discharging more 

 than 4,000 second-feet when the water reaches elevation 985.0 in the 

 reservoir. Before the water could rise high enough to overtop the 

 reservoir the discharge through sluiceway and spillway would be 

 more than doubled. To raise the reservoir to a height that would 

 involve this rate of discharge would require a rate of run-off very 

 much higher than has ever been recorded in the Bed River watershed 



