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II f I 'I I I . I I ! I I , I I I , I 1 Culvert crossings of Arkansas Avenue, Zuni Street, Clay Street, Federal Boulevard, Irving Street, Lowell Boulevard, Tennyson Street and Sheridan Boulevard all have capacity for approximately a 10- year flow. The lOa-year flows in excess of culvert capacity spill over these streets and back into the channel in very short distances. Balsam Street and Ammons Street, overflows spill across the streets and into the channel in a very narrow section, and no structures are affected. From Allison Street to Wadsworth Boulevard, Sanderson Gulch is confined in concrete pipe culverts. These culverts have approxi- mately a la-year capacity. Overflows for the lOa-year event flow onto Jewell Avenue at Allison Street and across the King Soopers' parking lot before spilling back to the gulch at Wadsworth Boule- vard (Sheet 12). The King Soopers' and adjacent buildings would be affected by sheet flows. In the reach from Sheridan Boulevard to Wadsworth Boulevard, the floodplain is primarily open space. Exceptions are the residential area around the Bit-O-Sea Reservoir and Wilson's Restaurant. The Bit-O-Sea Reservoir spillway and embankment were modified to increase flood protection for a few residential structures (Sheet 10). Planned improvements to protect Wilson's Restaurant have not been implemented. Clairefield Reservoir, a storage pond located immediately above Bit- O-Sea Reservoir, would be overtopped in the event of a lOa-year flood. Should the reservoir embankment fail, a surge of floodwaters would flow immediately into Bit-O-Sea Reservoir. This reservoir would then also overtop, realeasing a second surge of floodwaters downstream. For this analysis, it was assumed that the Clairefield Reservoir embankment would remain in place. Through Garrison Street to Kendrick Reservoir, the lOa-year dis- charge is confined within the channel (Sheet 14). The Kendrick Reservoir was improved to increase flood protection. From Kendrick Reservoir to Smith Reservoir, the lOa-year discharge is only 20 cfs and is confined to a very narrow ditch as shown on Map Sheet 15. No floodwater profile is provided for this reach. This study has not investigated the hydrology or hydraulics associated with failure of the Clairefield Reservoir embankment, and no conclusions have been drawn. The hydrOlogy used in the floodplain analysis below this reservoir assumes that the embankment will remain in place. North Sanderson Gulch. The lOa-year floodplain of North Sanderson Gulch from its confluence -"~a Sanderson Gulch to pierce Street is confined to open space aLeas (Sheet 16). No residential struc- tures are affected. From Wadsworth Boulevard to Kendrick Reservoir, the area along the gulch is largely developed, and extensive improvement have greatly reduced floodprone areas. From Jewell Park Pond to Allison Street, the lOa-year discharge is confined to the channel except at street crossings (Sheet 13). At the crossings of Cody Street, Carr Street, From pierce Street to Calahan Avenue, the improved channel and culverts have approximately the flow capacity for a la-year event. Excess flows during the lOa-year flood would spill out of the channel at Calahan Avenue and Quay Street (Sheet 17). Shallow flows would spill east along Calahan Avenue and would affect several of the residential structures that line this street. These overflows return to the gulch below pierce Street. From the Calahan Avenue crossing to Wadsworth Boulevard, lOa-year flows are confined within the channel and backyard lots of homes that border the gulch (Sheet 17). In the reach above Wadsworth (7)