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1.3 Base Information Regulatory 100-year flood water surface elevations are found in the PIS (FEMA, 1995). Copies of the regulatory hydraulic models were obtained from the City. Because of the much greater resolution of topographic information used for the current studies compared to the regulatory Flood Insurance Study (FIS), and because the spill from Fourmile Canyon Creek to Wonderland Creek substantially changes flood peak discharges for the 50-, 100-, and 500-year flood events along a substantial portion of both Creeks, flood elevations in the regulatory model cannot be directly compared to the current study. We have provided a "Tie" hydraulic model in this submittal package to document to FEMA that our Fourmile Canyon Creek study ties both upstream and downstream; however, the model for which we are requesting a LOMR did not actually extend as far up the Fourmile Basin as the tie model. Topographic information required for the study was obtained from aerial topographic maps at a scale of 1 in = 12,000 ft, I-foot contours prepared by Merrick & Company and flown during 2003. LIDAR was captured in January 2004 in the floodplain area. Field survey data was obtained by Flatirons Surveying during 2003, by Arrow Land Surveying, Inc., in 2001 and by Geosurv and by the City of Boulder as a part of this study. Additionally, Robert Sayre, PLS provided several field surveyed cross sections for one property Fourmile Canyon Creek to clarify an individual property's actual site elevations and this information was incorporated into the studies. The hydraulic analyses of the study reach for both streams utilized HEC-RAS ver. 3.1.1 developed by the US Army Corps of Engineers (US ACE, 2003). 2.0 STUDY AREA 2.1 Scope of Study The LOMR encompasses Fourmile Canyon Creek and Wonderland Creek. The LOMR uses new field surveyed cross sections and new aerial topography to update the hydraulic analyses of the floodplain for both of these streams. NGVD 1929 vertical datum in the FIS has been updated to NA VD 1988 in the LOMR. The study is located in part of Sections 12 and 13, Township 1 North, Range 71 West, and Sections 15, 16, 17,18,21, and 22 Township 1 North, Range 70 West. 2.1.1 Fourmile Canyon Creek Flood peaks for the 10-, 50-, and 100-year events reported in the FIS were calculated using flood peaks obtained using the Colorado Unit Hydrograph Procedure (CUHP) written by UDFCD and routed using HEC-l. UDFCD no longer supports HEC-l for hydrograph routing, and the updated hydrology uses UDFCD supported Urban Storm Water Management Model (UDSWM) to route the CUHP hydrographs. The most recent update to the CUHP was used and parameters were updated to reflect current conditions -4-