1986-12-18_REVISION - M1981302 - Laserfiche WebLink

Home Browse Search

Mr. Bill DeGroot December 18, 1996 Page 3 could have occurred prior to mining and construction of the laves. If this levee was to be removed or breached, 1C0-year spills from South Boulder Creek above Highway 36 would increase from about 2700 cfs to arcurd 4000 cis, potentially creating significant liabilities that are not easily remedied. We believe that potential liabilities exist for the past and current owners of the Flatirons Property and for the Colorado Department of Transportation ICDO71, and recommend that a legal opinion be sought regarding existing conditions and various future scenarios. CONCLUSIONS Based upon our analysis, we have reached the following gerierai conclusions perraining to issues posed oy -he scope of work: 1. The G&O hydraulic model should be refined and expended to include the South Boulder Creek spill zones ;dantlfied by Love. Since the Love study was limited to a short sac-ion of South Boulder Creek and was formulated to determine a conservative, high water surface, their models cannot be used directly to determine regulatory ftoodplaine. 2. Furher surveying, hydrology, and hydraulic inveatigetiori-are necessary to refine and update the South Boulder Creek floodplain mapping, particularly to evaluate the impacts of spills leaving the creek in the area of the Flatirons property downstream to where these spills rejoin the main creek. 3. The realistic 100-year flows leaving South Boulder Creek upstream of the Highway 36 Bridge, with the upper and middle Flatirons Levee in place, are about 2380 cubic feet per second tcfsl. An additional 310 cis flows adjacent to the Flat:rons Levee, resulting in a total of 2690 cfs flowing to the northwest from South Boulder Crack along the south side of Highway 36. The comparable amount of flow diverted to the northwest if the levee were breached or removed would increase to approximately 4000 cfs. Two hundred and twenty cis Cross Highway 38 at the Dry Creek Ditch No. 2 culvert. This results in a flow of 2470 cfs to the Foothills Interchange from South Boulder Crack. A. The Vlele culvert across Highway 36 returns about 840 cfs to South Boulder Creek via the rower Viele Channel. B. According to hydrology from the Corps' model, the Upper Viola Orsinege would probshly discharge about 380 cfs at the peak of the South Sculder Creek 100-year flood, which wcL.ld join the spill to the northwest and not go to South Boulder Creek directly. Subtracting the 840 cfs (Lower Vielel and adding the 380 cfs (Upper Viola) results in flow of 2010 cfa to the northwest from the Foothills Interchange.