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<br />CHAPTER 4. REGULATION OF EXPECTED FLOODS <br /> <br />The degree of flood protection provided by a reservoir may vary <br />seasonally or stochastically with varying hydrologic conditions. For <br />example, when flood control requirements conflict seriously with other <br />project functions, it may be advisable to compromise and reduce the <br />degree of flood protection during certain periods of the year. As <br />another example, an extended period of drought could result in substan- <br />tial empty space within the conservation pool at the start of a major <br />flood, in which case a higher degree of protection than usual would be <br />provided. In order to evaluate any plan of operation, it is necessary <br />to integrate the effects of all combinations of conditions and potential <br />flood ~agnitudes that can prevail. <br />A complete evaluation of a plan of operation could theoretically <br />be made if the operation of the reservoir were studied in detail under <br />conditions prevailing during hundreds of years, presuming that all of <br />the important combinations of initial conditions. downstream conditions <br />and inflow conditions would be adequately represented in such a long <br />period of time. However, it is not ordinarily feasible to perform such <br />extensive computations, and some means must therefore be employed for <br />approximating the results that would be obtained. <br />The most common method of evaluation is to route all major histori- <br />cal floods througp the reservoir for one or more conditions of initial <br />storage. One assumed condition might be that the reservoir flood space <br />is empty at the beginning of the flood. Another procedure would be to <br /> <br />4-01 <br />