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Lyons, to store the municipal water supply. It was not designed to store floodwater; but, during the May 1969 flood, it reduced the magni tude of the discharge that could have inundated Longment. Both the Longment Dam, located 1 mile downstream of the Button Rock Dam, and Beaver Reservoir, near the South St. Vrain Creek headwaters, have no effect on the flood discharge in Longment. Lefthand creek has been channelized along the segment from Pike Road (State Highway 22) to the mouth. The channel fram Pike Road to South Pratt Parkway is grass-lined and is designed to contain a flow of approximately 3,650 cfs. Fram South Pratt Parkway to its mouth, Lefthand Creek has been channelized; however, the overbanks remain unimproved. various structural improvements such as grass- or concrete-lined channels, detention ponds, and outfall culverts have been implemented on Spring Gulch in the segment from Ninth Avenue to Third Avenue. These improvements are inadequate to contain even the 10-year flood discharge. No flood protection measures have been taken on Dry Creek No. 1 or in Loomiller Basin, except for using Loamiller Pond as a flood-storage facility. Various properties along the streets in Loomiller Basin have low retaining walls along the street frontage to prevent yard flooding. In addition to the physical flood prevention measures mentioned, the City of Longment initiated an ordinance in May of 1973 for floodplain regulation, and has followed with floodplain management policies outlined in the St. Vrain Comprehensive Plan (Reference 5). The Town of Lyons practices non-structural floodplain management through a restrictive building code for structures located within the floodplain. No flood protection structures or measures exist or are planned along Middle Boulder Creek and North Beaver Creek within the Town of Nederland. No floodplain structures either exist or are planned within and adjacent to the Town of Superior. 3.0 ENGINEERING METHODS For the flooding sources studied by detailed methods in the community, standard hydrologic and hydraulic study methods were used to deterDdne the flood-hazard data required for this study. Flood events of a magni tude which are expected to be equaled or exceeded once on the average during any 10-, 50-, 100-, or SOO-year period (recurrence interval) have been selected as having special significance for flOOdplain management and for flood insurance rates. These events, commonly te~d the 10-, 50-, 100-, and SOO-year floods, have a 10, 2, 1, 32