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~ . FLOODS OF RECORD The largest flood of record in a particular drainage basin is referred to as the "flood of record." This term applies to any flood for which there is enough reli~ble data that technical analysis is possible. Usually the term is used to identify the "maximum" flood for a specific stream. This is not to be confused with the instrumental flood of record, which is the maximum flood of record measured by stream gauges. An instrumental flood of record may not be the SJne as the historical flood of record. 134 From the data that have been collected in previous reports and for this study, it appears ~s if the 1894 flood was the historical flood of record for most of the County. A flood of record may be different for various parts of a specific stream. The largest event on the upper portion of the St. Vrain Creek basin occurred in 1941, but the flood of record on the lower portion of the basin has been identified as 1894 or 1921. This is due to the impact of localized storms. In addition, some townsites are affected by more than one creek. Longmont and its vicinity, for example, are threatened by floodwaters from both the St. Vrain and Lefthann Creeks. . By discussing the flood of record for the major towns in Boulder County, the geographic area of the County is thoroughly represented. I t should be noted, however, that the flood of record may have occurred at a time previous to those discussed in this study. The information presented represents a summary of previously published reports and this project's original research.135 But only a systematic search of all existing historic material [for example the careful examination of every Boulder County newspaper for the past century or so), combined with data from emerging paleoflood hydrology techniques,136 can more definitively answer the questions and put to rest the uncertainties associated with current information about floods of record. I n order to more fully define the possible effect Boulder County citizens and their property and chapter will discuss the floods of record as they discrepancies occur, as in the record concerning floods at Longmont, each will be discussed. of floodwaters on possessions, this stand now. When the 1894 and 1921 . The ,incorporated towns that lie within the County's boundaries will be discussed by stream basin. The basins will be examined from north to south, and within each basin the discussion will progress nownstream and focus on population centers, the areas which have the greatest damage and fatality potential. These include Lyons, Longmont, Warn, Jamestown, Nederland, Boulder, Lafayette, Louisville and Superior, Sections of Erie and Broomfield [parts of which are in f30ulder County) are affected by Boulder County creeks ann are included as well. For a conprehensive list of unincorporated towns, subdivisions and other communities in- each creek basin refer to Appendix IV.