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I I I 'I I I I I I I I I I I I I I I I . each subbasin as well as specific locations along the major drainageway are presented in Table 4.3 . and Table 4.4. A graphical representation of the discharge profile along the major drainageway is also provided in Figures 4.1 and 4.2 for the Godding Hollow and Tri-Town Basins, respectively. Flood hydro graphs at selected locations throughout the basin are presented in Appendix B. 4.6.4 Godding Hollow Basin: Summary of Rxistinr: Drainage Problems During the 100-year flood event, storm water runoff typically exceeds the capacity of the natural channeL The limits of flooding were identified in a floodplain analysis of Godding Hollow shown on the currently effective Federal Emergency Management Agency (FEMA) flood. insurance rate maps. The regulatory floodplain information is also provided on Sheet 1 in this report. Flooding along Godding Hollow has been exacerbated where road crossings exist. It is also recognized that potential flooding problems will likely occur along several of the major tributaries to Godding Hollow, especially at the road crossings where undersized culvert and sediment accumulation limits the capacity of the crossing structures to convey stormwater runoff. A brief summary of the major problem areas noted during this master planning effort is presented in the following paragraphs. This summary is limited, however, to those locations along the major drainageway of Godding Hollow. WCR 26 Culvert The 100-year peak discharge in Godding Hollow at Weld County Road 26 is estimated to be 7,000 cfs. This flow greatly exceeds the capacity of the existing crossing structure, which is estimated to be 210 cfs. The swrmwater runoff captured by the channel will flow both east and west along Weld County Road 26 before overtopping the road. In addition, the capacity of the Godding Hollow channel is greatly exceeded by the magnitude of the 100-year peak discharge. These circumstances result in an extensive floodplain in the vicinity of the Weld County Road 26 crossing. An improved crossing structure could significantly reduce the localized flooding problems at this location. r .ast Chance Ditch Flume Low flows conveyed within Godding Hollow cross over the Last Chance Ditch in a concrete flume. During major storm events, the capacity of the existing flume is exceeded, and flooding will occur both upstream and downstream of this crossing. Stormwater flows will be captured by the Last Chance Ditch and will spill at various downstream locations. Installation of a siphon structure for the Last Chance Ditch along with channel improvements will reduce the flooding at this location. Godding HollowiRuraI Ditch r:hanneIlWastewa,v At WCR 241/2 the Godding Hollow low flow channel confluences with the Rural Ditch. The Godding Hollow channel continues northeast To' IOPENlCoweidOJ It:oweldOJ fnl rpr. wpd 4.10 Seprember8,1999