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I I I I I I I I I I I I I I I I I I I The impact of filling into the main channel was measured by calculating the rise in the floodway water surface for the 1986 cross section condition with the FIS floodway limits. The 1986 condition profile was compared to the before encroachment model (1976 condition) to measure the relative rise resulting from encroachment. The current FIS base flood profile and floodway limits remain as the regulatory elevations and limits. The profiles computed herein are only for relative comparison. The total river reach would need to be evaluated with the new cross sections, to determine new base flood and floodway profiles. This analysis approach has been discussed with FEMA representatives from Region 8. They have commented that the approach is acceptable to address the concerns they have expressed to the City. Flow Profiles Fi gure 4 shows the FI S base fl ood and fl oodway profi 1 es (profil es A and B), taken from the December, 1976, FIS. Also, the figure shows the computed fl oodway profil es wi th the new hydraul i c model for the before (C) and after (D) encroachment condition. The floodway profile calculated by the new model is approximately 0.5-feet higher than the same profile tabulated in the FIS. The FIS thalweg and surveyed thalweg are also plotted. Table 1, Floodway Elevation Data, shows the comparative elevations through the study reach. The filling along the south bank has resulted in an identifiable rise in the new floodway profile (D), over the FIS condition (C). The calculated rise ranges from approximately O.l-feet at section 28.4 to a maximum of approximately 0.5-feet at section 29.5. The effect of the fill is also seen at Section 30.0, where the calculated profile ri se is 0.3- feet. The impact of the fi 11 on the profil e ri se may -9-