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? . . path ofa 1,660 cubic feet per second (cfs) split flow at U.S. 36. This split flow represents approximately 30% of the 6,000 cfs 100'year storm volume and is significant enough that it should not have been neglected. As a result ofthis omission, the study did not identifY the existing flooding potential in the developed residential neighborhoods within the City north of U.S. 36 on the west and east sides ofFoothiIIs Parkway. Instead of providing a detailed analysis of the split flow at U.S. 36, the G&O study stated on page 9 that, "The split flow returns to the main channel just downstream of U.S. Highway 36 near South Boulder Road." In addition to this statement, notes reflected on the detailed floodplain mapping sheets indicate no potential for flooding into the City neighborhoods north ofD.S. 36. The note on Sheet 9A of31 states, "Overflow Into Viele Channel," which suggests that all split flows are intercepted by an existing 900 cfs drainageway serving a smaller flood basin west of South Boulder Creek. Another note on Sheet 10 oDl states, "All Flow Assumed to Remain in Basin," and provides a flow arrow on the map that suggests that the split flow passes across U.S. 36 east of the City limits. The floodplain zone delineations reflected on the 1988, 1990, and 1995 FIRMs also reflect no 100,year flooding potential in the developed City neighborhoods north of U.S. 36, based on the adoption of the G&O study. However, a note on these FIRMs that states, "Limit of Detailed Study," on the west side of the South Boulder Creek floodplain at U.S. 36 should additionally indicate that the G&O study was incomplete in fully studying the split flow flood path. 2. Man-Made Berm was Inaccnrately Assumed to be Natural Ground: Upstream of U.S. 36, a narrow earthen berm averaging three feet in height is reflected in the G&O mapping (Sheet 11 of31) around an area identified as an "Existing Gravel Mining Area." This earthen berm is a man,made feature that was constructed by the mining operator, Flatiron Companies, in about 1980 and was a physical change impacting the floodplain that was not addressed in the G&O study. According to the Boulder County Special Permit issued to the mining operator for placement of fill in the floodplain, the berm was intended to protect the mining operation from flooding but was not intended, or legally permitted, to be a flood protection levee for protection of downstream neighborhoods or development activities on undeveloped land, The G&O study failed to identifY the earthen berm as a man,made feature and physical change in the floodplain, and further failed to recognize this feature as an uncertified levee that did not comply with FEMA levee standards. Instead G&O considered the berm as a permanent land form that caused the South Boulder Creek floodplain to narrow upstream ofD.S. 36, and prevented flooding west of the berm inside the main mining operation. G&O states on page 10 of the study, "Areas landward of the embankment were assumed ineffective for flow conveyance." Based on this, the G&O detailed mapping removed the mining area from the floodplain, and this revision should have been noted as a significant change from the previous 1979 FIRM. With such a significant change occurring in the South Boulder Creek floodplain, G&O should have included an