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SECTION 3 - HYDROLOGY Irriqation Canals 3.1 Introduction Four irrigation canals cross the Spring creek lIasin ilnd channel. The Pleasant Valley ilnd Lake Canal crosses Spring Creek south of Drake Road and west of Taft Hill Iload. The New Mercer Canal and the Larimer County Canal No. 2 cross Spring Creek in Rolland Moore Park north of Drake Road between Shields Street and Taft Hill Road. Arthur's DitCh crosses Spring Creek between Drake Road and Prospect street west of the Burlington Northern Railroad and COllege Avenue. The hydrologic analysis consisted of determination of the 2-, 10-, 2S-, 50-, 100-, and so a-year discharg"" at lOCations throughout the basin for both existing basin conditions and projected fully-developed basin conditions. 'rhe analysis was conducted utilizing the Stor~ Water Management MOdel (SWMM) data developed in the study "Spring Creek Major Drainageway Plan," by Gingery Associates, Inc., August, 1980. Modifications to this model were made to more accurately reflect existing conditions ~nd changes in anticipated development. 'rhese modifications are discussed in detail in the Technical Addendum. 3.2 Basin Characteristics Development Conditions All of the canals intercept storm water runoff. with the exception of the Pleasant Valley and Lake Canal, each canal has a structure at its intersection with Spring Creek which allows exCess storrnwater to spill past the canal. Typically, these structures consist of a manually operated gate for control of low flows and an emergency side overflow weir for larger flows. The Basin is nearly fully developed from the confluence with the Cache La Poudre River to Taft Hill Hoad. [)(~velol',"ent is primarily residential. but also im;llldes "'om" indu1,triat development near the confluence with the powlt-e River, heaVY commercial development along College Avenue, and scattered commercial developments throughout the basin at intersections of major arterial streets. The City of Fort Collins has developed a plan for importation of storm water into the Spring Creek Basin from the Canal Importation Basin (immediately north of the Spring Creek Basin). The_ plan calls for a serles of detention areas and channel improvements to safely convey runoff into the Spring Creek Basin. Releases from the Canal Importation Basin for events less freqllent than the la-year event will not exceed the IO-year rclea~e rate. The effects of the Canal Importation Basin releases were accounted for in this plan by including the la-year developed conditions hydrographs in the Spring Creek SWMM data f;f't,,, tor both existng dnd developed conditions. The area south of Drake Road and west of '!'aft Hill Road is undeveloped, with the exception of a mobile ho,"" pd!:"k <\I,d o;omf) scattered residences. According to City ilnd County Pli1nnill(j personnel, future land Use within this are-a ul-' to the 5200 foot elevation will be limited to light residenti"l. Above ~200 feet it will be limited to 1.7 units per ,,~'rp. j..ocal D<'!tentio!l '" Off-stream detention ponds are located throughout the ~pring Creek Basin. In most cases, these ponds were designed to contrOl 10c<>1 runoff, and, in general, "ppeilr Lo h,1\10 little effect on "