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Principal Flood Problems and History Fort Collins is vulnerable to flooding :from several different sources. Flood sources include; 1) the rivers and streams in Fort Collins which include the Cache La Poudre River, Spring Creek, Dry Creek, Fossil Creek, Cooper Slough, and Boxelder Creek; 2) potential dam failure, and; 3) urban flash flooding from intense rainfall on smaller drainage basins. The main cause of floods in the Fort Collins area is intense rainfall, which normally occurs in the period of May through September. Of all the floodplains within the City, Dry Creek is the most developed with regard to the number of structures and people at risk. The majority of development within the Dry Creek. floodplain is "pre-FIRM", meaning that it was developed prior to the City and County entering the National Flood Insurance Program (NFIP) in 1979, and therefore, the majority of structures do not meet the minimum design and construction criteria established by the Federal Insurance Administration (FIA) and the Federal Emergency Management Agency (FEMA) which are intended to reduce flood damages and losses. In addition, most of the pre-FIRM commercial and residential properties do not carry flood insurance unless they have been "substantially improved" as defmed by FEMA. Dry Creek has not had serious flooding downstream of the Larimer and Weld Canal (Eaton Ditch) since the early 1950's. This absence of even minor flooding is generally attributed to the network of irrigation canals that have some capacity for intercepting small to moderate Dry Creek flows up to about the 5-year event. Flood history prior to this time is unclear. Before significant development occurred in the area, flows could often be ignored because little damage was incurred. The flood of 1904 is documented in a newspaper account which stated that "the Water Supply and Storage company got a lot of water from Dry Creek, storing in the Rocky Ridge reservoir at the rate of nearly 500 feet per second". One death :from the 1904 flood is documented. John Parkinson, a 7-year old boy, drowned. The family lived near the Eaton Ditch, which overflowed above their house after they had gone to bed. Flooding also occurred in 1924 with flows several feet deep in the vicinity of College Avenue and Hickory Street. It is unclear as to whether this was actually due to overflows :from the Poudre River. Dry Creek has several lakes and storage reservoirs which reduce the contributing drainage area by approximately 13 percent, although they were not constructed for flood control purposes. Douglas Lake, located about 3 miles north of the current Fort Collins corporate limits is also an irrigation reservoir that provides about 15%-20% flood flow attenuation for the IOO-year event. 2