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,. but there is only limited flow capacity on the north side of Vine. Th~ channel slope, and therefore flow, is parallel to the flow south of Vine. TO model this situation, preliminary ru!'lS ~~re made letting the program create a vertical bank along the centerline of Vine. The approximate limits of overtopping along Vine and the channel capacity prior to overtopping were then determined. Two driveways (control sections) exist north of Vine which were in line with established cross- sections south of Vine. These cross-sections were extended to include the driveways and the program rerun, allowing overtopping for a pair of discharges. The output was analyzed and an over- bank discharge somewhere between the two control section overbank disch~rges waS selected. A ~in channel discharge versus side chQnnel discharge graph was developed and used for intermediate values. Reach R The overbank situQtion along Reach R, peudre High School, required a marc ~o~~licatcd analysis procedure. The bankfull capacity of the main channel is a factor of ten less than the 100 year developed storm flow, and the overbank is essentially flat and has no existing levee or mound at the channel bank. In sllch a situation realistic overbank backwater effects are difficult to model. A maintenance building which divides the overbank flow adds to the problem by creating three different discharge points. The primary prOblem in this situation was establishing downstream control at the poinls of d.Lversion. Downstreare control was establiShed by first dividing the reach into 3 subn,ache>l .sh,,~ing comnon cross-s!'ctions hased on diversion points. A startLng water surface elevation was then established by using the slope area program to compute the friction slope - and, hence, stage from tho uniform flow ('guations based on the geo~etric mean of cross-section conveyances in the subreach. With this water surface elevation, the HEC-2 program calculated the flow distribution between overbank and main channel flow. The ~in Channel flow in the downstream cross-section of the upstream subr~ach was used to repeat the procedure for the next downstream subreach. This procedure gave only marginal agreement in water surface elevation of cross-sections common to two sub- rC<lches. However, better procedure could not be developed using tho HEC-2 computer model. V.D. Results The final results of the hydraulic analysis are presented On the 100 year floodplain naps, Fig~res 6 through 10, and On the water surface profiles, Figures 11 through 16; and in ~able 4. The 9"n"ralizution", and qualifi<';<lt:Luns b",low '''ill did interpretation of the flood intensity and degree of certaintr in each reach. In general, the flood waters were found to be wide, shallow and slow moving. Excluding reach A where a channel exists, the flood waters rarely exceeded two feet in depth or four feet per second in average velocity. Ponded water depths much greater than this were encountered in b~rkw~~~r~ hehind raised roadways and other man-made features in the drainagoway. The floodplains plotted On the accompanying drawings were derived from the start station and end station output par<lmeters of the HEC-2 computer runs. In cases of divided flow the cross-section output .....as reviewed and the siz", and height above flood water of the remaining island was considered. In most -32- -33-