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6, Existing structure no. 10 is a 30-inch eMf crossing Bennett Avenue at C Street. This structure is adequutelysized but should be cleaned and a grate installed on the inlet end oflhe pipe to eliminate futuredugging. 7, Existing slruClI.lre no. 8 is an IS-inch eMP crosslng Teller County One. Although this structure is adequately sized to convey the lO-year design storm runoff,flowscxceedinglhe lO-year ctesignslOrm runoff will not cross Teller County One at this location increasing the potential [or flooding problems on downstream properties. It is recommended that this structure be replaced with a 3o-inch eMP with a minimum headwater of three feet. B, Thurlow Avenue Tributary The Thurlow Avenue drainageway oollects runoff from a relatively small basin with minor dcveJnpment in the snutherly portion of the city's corporate limits. Runoff from tbis basin is conveyed hy a poorly developed channel to Cripple Creek at a pnint directly north of the city's wa.\tewater treatment racility. Several small culverts presently exist within the Thurlow Avenue drainage basin. These culverts primarily exiSI to convey flows through road crossings. Two improvements are presently recommended within Ihis basin but a., futun: development occurs, channel improvements and confinement of flood walers may be warranted. The recommended improvements are as follows. 1. Existing structure no. 29 (IS-inch CMP with 18 inches of headwater) is too small to cunvey even the Io-year design storm runoff. This culvert should be replaced with a 24-inch CMP with a minimum of 3 feel of headwater thus increa..;ing culvert capacity to meet lhe IO-yeardesignstorm ruooff condition. 2. Existing structure no. 31 (existing 24-inch CMP) is not capable of conveying runufffromthc lo-year design storm. Design SlOrm runoff at this point is VI-5 32 CFS for the IO-year storm and 109 CFS for the Ioo-ycar storm. Although f1uoding potential at the present time is minimal, it is recommended that this slructurebe replaced with astfllcture capable of conveying runoff from the tOO-year de~;jgn storm due to the potential for development within this area. A 48-inch RCP culvert with a minimum of 5 feet of headwater should hc in~tal1ed at this location. The installation should include a headwall at each end of the culvert. c, SeeondStreetTributary The Second Street tributary is comprised of three drainage ba.<dnswhich produce and convey runoff from the centra] portion of the city's corporate limits to Cripple Creek. The Second Street tributary is generally bounded on the north and south by the city's corporale limits, on the west by the alley between A Street and B Street and on the east by Third Street. Existing structures within this area include numerous eulvert.\ at Toad crossings and a portion of the Bennett Avenue ~torm sewer system. Numerous structures within the Second Streel tributary are severely un dersizedand have created some of the roost intense and frequcnl flooding problems within the city's corporate limits. This flooding occurs even though the actual design storm runoff in this tributary is relatively small compared to flows in Pony Gulch and Cripple Creek. Existing culverts used for road crossings in outlying areas appear, for the m{)~t part, 10 b<l adequate but as flows approach the bu~iness district, undcrsizing of existing stfllctures becomes acute as can bcscen by the frequent floo ding which occurs at the inten;eclionofSecond Street and Bennett Avenue. Some of the reconum:ndations for illlprOVemCnls within the Second Street tributary address replacement of road crossing culverts in outlying areas. The majority of recommendations revolve around installation of a storm sewer system within Bennett Avenue and a storm sewer outfa\! line in Second Street from Eaton AVCllLl<: 10 Warren Avenne. The intent of this system is to intereepl as much runoff as possihle VI-6