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<br />. <br /> <br />. <br /> <br />. <br /> <br />When comparing the 100-year water surface shown on the flooded area maps <br /> <br />(Sheets I through 9) with the HEC-2 computer data, there are several <br /> <br /> <br />obvious discrepancies which are noticeable. These discrepancies in the <br /> <br /> <br />results are discussed below, <br /> <br />, <br /> <br />Divided Flow. There are several sections throughout the flood plain <br /> <br /> <br />where divided flow occurs, but is not delineated on the flood plain mapping. <br /> <br /> <br />The HEC-2 computer program signifies divided flow wherever the ground sur- <br /> <br /> <br />face protrudes above the computed water surface, no matter how small. There <br /> <br /> <br />are several reasons why these protrusions may not have been delineated on <br /> <br />the flood plain mapping. <br /> <br />1. Small protrusions of land (berms) only a few feet in width may not <br />show up on the topographic maps, although the computer shows a <br />divided flow situation. <br /> <br />In many places the high spots that protrude above the water surface <br /> <br /> <br />were considered insignificant and therefore not plotted. <br /> <br /> <br />tlany areas where divided flow is indicated are in regions where <br /> <br /> <br />shallow overland flooding occurs. Since this flow is not hydrau- <br /> <br /> <br />lically connected to the main channel, these high spots were inun- <br /> <br />dated and therefore not plotted. <br /> <br /> <br />In some places there are road embankments or other types of berms <br /> <br /> <br />which contain the 100-year flood but the computer shows flow on <br /> <br />both sides of the embankment, giving rise to a divided flow <br /> <br /> <br />situation. <br /> <br /> <br />5. Some areas have drainage ditches whose inverts are below the <br /> <br /> <br />100-year flood level but do not receive flow due to the nature <br /> <br /> <br />of the topography, The computer shows these areas to be divided <br /> <br /> <br />flow situations. <br /> <br />2. <br /> <br />3. <br /> <br />4, <br /> <br />Shallow Flooding Areas, Areas between stations 57+55 to 80+40 and 280+00 <br />to 300+60 are shown as regions of shallow overland flooding, These areas <br />represent sections where the flow has left the main channel and travelled <br />into overbank areas where it is not hydraul ically connected to the main <br />