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<br />changing flow is rather poor. The amount of contingency depends on the <br />consequences of exceeding target flows. If these are serious, as where <br />levees exist, the contingency allowance should be high in order to <br />avoid a preventable disaster. <br />The importance of coordinating releases to forecasted local inflows <br />at a downstream damage location depends to some extent on the relation <br />of flood control storage to release rate. Where storage is large and <br />the amount of water that can be released during the flood inflow period <br />is a small part of the design flood volume, it may not be worthwhile <br />to take an unnecessary chance of exceeding safe flows downstream. On <br />the other hand, where the release during floods is large and consti- <br />tutes a major part of the design flood volume, failure to make maximum <br />feasible releases during flood inflow periods cDuld be disastrous. <br /> <br />Section 2.02. Use of Index Flows to Forecast Local Runoff <br /> <br />Experience has demonstrated that forecasts of runoff based on <br />measured rainfall are not highly dependable and that the use of fore- <br />casted rainfall for flood operations is subject to major uncertainty. <br />Where forecasts of local runoff downstream of a reservoir must be made <br />for release scheduling, it is usually best to use river-stage reports <br />from an index location within the local tributary area as an indicator <br />of the total runoff. If index-station flows at the time of a particular <br />reservoir release correlate with local runoff that reaches the damage <br />center as late or later than the reservoir release does, a relationship <br />between index flow and total local flow can be developed, along with <br /> <br />2-03 <br />