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<br />where the water surface elevation drops, other criteria should be selected <br />to limit the extent of encroachment. <br />e. Individuals developing floodway data should be alert for special <br />conditions involving the area under consideration and the criteria used <br />which may affect the application of the floodway concept. For example, <br />the resulting increase in water surface may greatly enlarge the zone <br />area affected by the selected flood an unreasonable distance beyond <br />its natural flood plain. This condition can exist when the overbank <br />area is very flat and more than an insignificant increase in the water <br />surface is permitted. <br />As shown in the Summary Printout (Appendix II), the change in <br />water surface elevation for the preliminary run was below the one <br />foot limit for the first three cross sections for both encroachment <br />profiles. Water surface elevations for the next sections were below <br />the limits for the first encroachment profile (8.4), but above for the <br />second encroachment profile (10.4). Both profiles were within the <br />limits for the last two sections. The results from the 10.4 profile are <br />probably suitable for a preliminary floodwaYi however, by combining <br />the results of the two profiles, a profile closer to the one foot <br />limit should be achievable. <br />In specifying input for a second trial, a 10.4 encroachment <br />was specified up to Section 0.34. Although the results at Section <br />0.34 were within the limit, the encroachment at this section probably <br />contributed to the excessive change at the upstream Section 0.55. For <br />Section 0.34, encroachment stations were selected between those computed <br /> <br />13 <br />