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Mr. Roger Schmidt <br /> September 2, 2016 <br /> Page 6 <br /> Year I Description of Conditions / Events <br /> Time Frame <br /> 2016 (January) • Construction completed for sheet pile installation along bike path. <br /> 2016 (August) • Construction nearly complete for the breach repair work. <br /> REGULATORY FLOODPLAIN MAPPING <br /> At the time the Al Pit permitting occurred starting in 1992 through its construction in the 2001 <br /> time frame,the effective floodplain mapping was the Flood Insurance Rate Map (FIRM)Panel <br /> Number 080266 0609C, dated September 28, 1982 (see Figure 2). For the purpose of this <br /> evaluation,this 1982 FIRM was obtained from the Federal Emergency Management Agency <br /> (FEMA)to understand the extent of the regulatory floodplain at the F Street agricultural field and <br /> the surrounding area at the time of the Al Pit construction. The field owned by the City of <br /> -- Greeley, adjacent to the area where the Boyd-Freeman Ditch was relocated along the west side of <br /> _ the Al Pit, is mapped as"Zone AO," indicating that the area is subject to shallow flooding during <br /> a 100-year flood event. The estimated depth of this shallow flooding is approximately 2 feet. <br /> The FIRM panel dated September 28, 1982 indicates that the area where the Boyd-Freeman <br /> Ditch was realigned was in the regulatory floodplain prior to the date when the ditch was <br /> relocated. The Iverson/Martin Marietta Pit is also located within Zone AO on the FIRM dated <br /> September 28, 1982. <br /> The FEMA FIRM for this area was subsequently updated, with new FIRM panels issued <br /> effective January 20, 2016. The updated FIRM, Panel Numbers 08123CI510E (Figure 3a) and <br /> 08123C 1528E (Figure 3b), show the original location of the Boyd-Freeman Ditch to be primarily <br /> outside (to the south) of the 100-year floodplain boundary. In contrast, the F Street agricultural <br /> field and the relocated Boyd-Freeman Ditch on the west side of the Al Pit are both located within <br /> the 100-year floodplain defined in the updated mapping, as is the Iverson/Martin Marietta Pit. <br /> For reference, the 100-year flow rate for the Cache La Poudre River, per the Flood Insurance <br /> Study(FIS), effective January 20, 2016, is estimated to be 10,700 cubic feet per second (cfs)just <br /> downstream of 8th Avenue in Greeley (at Eaton Draw), approximately 4.3 miles downstream <br /> from the F Street agricultural field. Further discussion of flood hydrology is provided below. <br /> HYDROLOGY <br /> Flow records for the Cache La Poudre River were analyzed to evaluate the approximate flow <br /> rates in the river, and the associated recurrence intervals of those flow rates, at the times of <br /> different runoff events when the BIC facilities were damaged, as described in the chronology of <br /> events. The nearest gage available with flow record is located at the City of Greeley Waste <br /> Water Treatment Plant (WWTP), slightly less than 6 miles downstream on the Cache La Poudre <br /> River from the location of the breach at the Boyd-Freeman Ditch. The gage at the WWTP <br />