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I I I I I I I I I I I I I I I I I I I Drainageway Reach A4-A2 B-D/J ~F ~G ~l J-K J-North Potential Flood Damage Problem Areas Flood water accumulation peak of tributary flews from adjacent Sub-basins A, A2, A3 and A5 occurring at the intersection of 17th and Bryant approximately 40 minutes later and of greater magnitude than the peak runoff from the local Mile High Stadium - McNichols Sports Arena area (Sub-basin A4). The Rocky Mountain Irrigation Ditch presents another potential problem in that it currently intercepts flood flews from portions of Sub-basins G, L and I, as well as other tributary areas. The ditch will store and convey flood waters until the point when the banks begin to overtop. It is not possible, within the scope of this project, to determine where ditch overtopping will occur. Flood water accumulation could occur below the irrigation ditch, particularly near delineated flood plains. Another ditch related concern voiced by the residents of the area not specifically addressed in this project is the possibility that the ditch would be aban- doned and, through maintenance neglect or future changes in land use development, render the ditch useless to intercept any storm water run- off. This drainage planning study assumed that no change would occur to the operation, maintenance and topographic appearance of this ditch in the future totally developed Basin. It was also assumed, that the ditch would not significantly alter stormwater flows in the basin on the premis that the ditch would fill and overtop during periods of flooding allowing the stormwater to pass on through. Flood water accumulation from local runoff and Sloans lake overflew into the local topographic depression along 20th Avenue between Quitman and Newton Streets at the northeast lakeshore area. Flood water accumulation from drainageway overflew at the commercial area near 18th and Sheridan, the apartment com- plex between Depew and Harlan Streets, and the residential area between Harlan and Ingalls Streets. Flood water contribution to adjacent downstream Sub-basin D and local accumulation through the residential area along 20th Avenue between Wadsworth Boulevard and Teller Street. Flood water contribution to adjacent Sub-basin D and local accumulation through the residential area between Teller and Pierce Streets near 25th Avenue. Flood Plain and Floodway Data Flood water accumulation from drainageway overflow into the commercial area near 24th Avenue and Sheridan and through the residential area from 24th to 26th Avenues, between Chase and Gray Streets. Flood water contribution to adjacent Sub-basin J and local accumulation through the residential area from 29th to 30th Avenue between Ingalls and Kendall Streets. The limits of future flooding are outl ined on the attached drawings and tabulated in Table C-l In Appendix C, Flood Plain and Floodway Reference Data. The table lists the potential flood elevations, flooding widths and channel bottom elevation at each cross section for the drainage reaches studied. The flood profile, channel bottom profile and flood plain width at any point on the streams is graphically shown on the drawings. Floodways have also been computed for each stream. A floodway represents that part of the flood plain which is required to pass a IOO-year flood event without raising the flood profile more than an acceptable amount and which represents hazards to personal safety and welfare. In this study, the 11