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Floods occurred on Spring Creek in 1902, 1904, 1938, 1949, and 1951, prior to the completion of the Horsetooth Reservoir, which cuts off the upper portion of the Spring Creek Drainage basin. The Horsetooth Reservoir was completed in the early 1950s and has helped reduce flooding problems by reducing drainage area. Floods occurred in 1975 and 1977, causing flooding in several basements, but there are no recorded discharges or damage estimates available. A flood occurred on June 25, 1983, that produced 1.9 inches of rainfall over 2 hours. The storm sewer that carries Spring Creek under the mobile home park surcharged and water ponded to a depth of several feet. Property damage was estimated in the $5,000 to $10,000 range (Reference 54). A devastating flash flood occurred on July 28, 1997, on Spring Creek. Over 14.5 inches of rain fell between 4:00 PM on July 27th and 11 :00 PM on July 28th, with over 10 inches of that amount occurring during a six hour time period on July 28th. There were five deaths and over $200 million in property damage. The discharge was estimated at 8,250 cfs going into the detention pond behind the Burlington Northern Railroad just west of College Avenue. This event was greater than a 0.2-percent annual chance flood event (Reference 73). 2.4 Flood Protection Measures There are no structures along the Big Thompson River or its tributaries that provide a major reduction in flood flows. Numerous levees along the river will contain a high frequency flood (10- and 4-percent annual chance) but provide little protection against the I-percent annual chance flood. The SCS has constructed four detention structures in the watersheds above the Town of Wellington to reduce the flood discharges of Boxelder Creek and Coal Creek. The reservoirs retain runoff from a combined area of 175.5 square miles or 70 percent of the drainage basin. The level of flood protection decreases, however, as the distance below the structures increases. There are no flood-control structures located in the Cooper Slough basin (Reference 9). Although they are not actual flood-control structures, Dry Creek has several lakes and storage reservoirs that reduce the contributing drainage area by approximately 13 percent. The network of irrigation canals in the Dry Creek basin has some capacity for intercepting Dry Creek flows (Reference 1). Douglas Lake, also aD irrigation reservoir, significantly reduces peak discharges. Numerous irrigation canals cross the Dry Creek channel and directly intercept drainage flows, as mentioned previously. Several of these canals, including the Larimer and Weld Canal Eaton Ditch), the Larimer County Canal, the Terry Inlet, the Poudre Valley Canal, and the North Poudre Ditch, have large enough flow capacity to significantly affect flood magnitudes on Dry Creek. For the more frequent flood events, the Larimer and Weld Canal (Eaton Ditch), the Larimer County Canal, and the Terry Inlet were assumed to intercept all Dry Creek flows reaching their channels (Reference 1). As development within the basin continues, these canals will intercept greater flows on a more frequent 17