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and losses ~llong Fourmile Canyon Creek have generally been low, because the nrea is primarily undeveloped. Significant flooding 4long Goose Creek occurred in August 1951 and July 1954. The 1954 event damaged an addition to the Community Hospital, which was under construction. :0 These floods are just a few that have occurred in the area. Major, area-wide floods also occurred in 1904, 1909, 1914, 1921, and 1923. During May 1973, flooding caused an estimated $70,000 worth of damage. No estimates of the recurrence intervals of the historic floods have been made. There has been little documentation of flooding on Wonderland, EImers Twomile, and Skunk Creeks. ~ There is a history of debris blockage and flow diversions throughout Boulder. 2.4 Flood Protection Measures Past urbanization in the City of Boulder has encroached drainage- ways and reduced stream storage, thereby increasing runoff peaks and volumes" Undersized cuI verts and channels exi st throughout the city. A few measures have been taken to alleviate these problems on some of the study streams and are discussed below. This discussion excludes drainage improvements constructed to provide protection from erosion. The degree to which the flood- control measures discussed protect from return interval floods is unknown at this time. ::.. Flood-protection measures along Wonderland Creek consist of Wonderland Lake (Reference 5); the ponding area between Wonderland Lake and Broadway; the channelization projects along the Winding Trail Vi llage and Aspen Grove developments, located between the Longmont Diagonal and 26th Street (Reference 6); the recently constructed 26th Avenue Crossing culvert and drop inlet (Reference 6); and the detention pond east of 47th Street (Reference 7). Wonderland Lake, while not designed to provide flood protection, will attenuate the 100-year peak floodflow from 400 to 100 cubic feet per second (cfs). For the routing analysis, Wonderland Lake will be considered filled to the spillway crest at the time of storm runoff routing. The area between Wonderland Lake and Broadway creates an unplanned flood-control structure, because the culvert at Broadway will convey very little flow and a considerable ponding volume is available. This unplanned flood reservoir was not included in the hydrologic analysis. Divers ion flow from Fourmile Canyon Creek to the north will also reach Wonderland Creek at this location. The 26th Avenue Crossing culvert constructed and are designed to (Reference 4). The pond east of effect on the 100-year peak flow. and drop structure have been contain the 100-year floodflow 47th Street will have little 9 j