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<br />Instantaneous Failure <br /> <br />In some situations where a dam fails very rapidly, the negative wave <br /> <br /> <br />that forms in the reservoir may significantly affect the outflow from the <br /> <br /> <br />dam. In such cases, a special equation (Eq. (la)) must be used to compute <br /> <br />the maximum breach outflow. The constraint that indicates whether Eq. (Ia) <br /> <br /> <br />should be used is as follows: <br /> <br />If time of failure in min. (tf) < 0.001 <br />then: <br /> <br />* Height of dam in feet (Hd), <br /> <br />Qbmax = 3.1 Br (Iv In) Hd3/2 <br /> <br />(la) <br /> <br />where: <br /> <br />Iv = [1.0 + 0.148 (:rf (m+I) 2 _ 0.083 (:r)3 <br /> <br />3/2 <br />(m+1)5/2] <br /> <br />(3) <br /> <br />In = [1.0 - 0.5467 <br /> <br />(B ) (BBr)2 <br />Br (m+1)1/2 + 0.2989 <br /> <br />(m+l)1/4 <br /> <br />-0.1634 <br /> <br />(:rf <br /> <br />(m+l)1/8 <br /> <br />+ 0.0893 (;r) 4 <br /> <br />(m+l)1/16 <br /> <br />- 0.0486 (:rf <br /> <br />3/2 <br />(m+l)l/32] <br /> <br />(4) <br /> <br />where: Br = Breach width <br /> .. <br /> B = Valley topwidth at dam crest <br /> Hd = Height of dam <br /> m = Channel fitting coefficient <br /> <br />1-4 <br />