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<br />INTRODUCTION TO GENERAL PROCEDURE <br /> <br />The procedure for approximate dam-failure floodplain mapping consists of the <br />following steps: <br /> <br />~ <br /> <br />1. Compute the peak discharqe hvdroqraph at the dam site. due to failure <br />of the dam. The peak of the hydrograph is designated Qp. and the hydrograph <br />is asswned to be of triangular shape. The method for computation of Qp was <br />developed by the Colorado state engineers' office.l It consists of an <br />empirical formula. derived from r~9ression analysis of actual dam failures. <br />considering physical dimensions d( the dam and reservoir as well as the <br />relative erosiveness of the embankment soils. <br /> <br />2. Route the dam failure hvdroqraph (OP peak value) downstream to <br />typical section(s) of the stream. where the peak of the routed hydrograph is <br />designated Qri. Calculate the depth of flow (Di) at these typical section(s). <br />using Qri and the physical characteristics of the channel. The method of <br />successive averages2 has been adopted for routing. since it allows easy <br />calculation of downstream flood" peaks (Qri) without the necessity to develop <br />the entire routed hydrograph. <br /> <br />3. Draw the Floodplain Inundation Map using flow depths Di calculated <br />for typical sections. The mapping technique allows the use of standard U.S. <br />geological survey quadrangle maps and requires no special tools.3 <br /> <br />This general procedure is designed to allow development of a floodplain <br />inundation map. which reasonably predicts the extent of flooding due to <br />failure of a dam. It is not designed to consider all the dynamics of a flood <br />traveling down the stream. overtopping and .then washing out roads. scouring <br />deep ravines in one location and depositing ~hick layers of alluviwn in <br />others. However. the procedure is valuable to emergency planners who want to <br />know where the flood is going. about how long it will take to get there. and <br />an estimate of the limits of flooding. <br /> <br />The entire procedure can be performed without special tools or equipment using <br />the worksheets in the appendix. The calculations for Qp and Qri can be <br />completed rapidly using the basic language program (HAZARD2) listed in <br />appendix 3. <br /> <br />A detailed discussion of each step of the procedure is covered in the text and <br />illustrated by an example. <br /> <br />1. 2. 3 -- See references at end of text. <br /> <br />1 <br />