9420 - Laserfiche WebLink

Home Browse Search

VS15: Utah, Washington County. The Virgin River from the confluence of the East and North Forks in T.42S. , R. lOW . , Sec. S (Salt Lake Base and Meridian) to the Quail Creek Diversion in T.41S., R.14W., Sec.36 (Salt Lake Base and Meridian). VS16: Utah, Washington County. The Virgin River from the Quail Creek Diversion in T.41S., R.12W., Sec.30 (Salt Lake Base and Meridian) to the confluence of Ash LaVerkin Creeks in T.41S., R.13W., Sec.23 (Salt Lake Base and Meridian). Virgin River Floodplain The riparian zone within the 100-year floodplain of the river reaches is proposed as critical habitat. However, only those portions of the 100-year floodplain that contain the constituent elements are considered part of critical habitat. Developed lands not considered critical habitat within the 100-year floodplain boundary include, but are not limited to: existing paved roads, bridges, parking lots, dikes, and levees; railroad tracks and trestles; residential, commercial, and industrial developments; water diversion canals outside of natural stream channels; active gravel pits; and cultivated agricultural land. These developed areas may never contain primary constituent elements or contribute to species recovery. River systems are composed not only of the mainstem channel in which water is maintained most or all of the year, but also upland habitats that are inundated during the higher water levels that are usually associated with spring flows. Studies of the major floodplain rivers of the world have documented the high value of floods bottomlands and uplands for fish production (Welcomme 1979, Hinckley and Meffe 1987). Because fishes are mobile, many species are able to take advantage of food sources made available by flooded lands. Indeed, many fishes have developed migratory strategies that allow them to utilize inundated areas as spawning, nursery, and foraging areas (Lowe-McConnel 1975, Welcomme 1979). In many cyprinid fishes, including Virgin River natives, spawning is associated with seasonal rains and flooding of rivers. It has been found that flood-related changes in the river environment not only induce spawning for many species, but these changes comprise the ultimate factors limiting the survival of eggs, larvae, or young fish (Hontela and Stacey 1990). In this context, a rich food source of terrestrial origin may enhance fish growth, fecundity, and/or survival. Use of these inundated floodplains increases the energy available for spawning and is necessary for reproductive success in some species (Finger and Stewart 1987). Seasonally flooded habitats are also major contributers to the biological productivity of the river system by providing inputs of nutrients (allochthonous energy) and making terrestrial food sources available to aquatic organisms (Hesse and Sheets 1993). Hynes (1970) reported that the presence of vegetation in a stream greatly affects the fauna and that streams with higher percentages of vegetation contained higher densities of aquatic invertebrates than streams with less vegetation. The Virgin River contains little aquatic vegetation, producing a minimum of autochthonous (indigenous) organic matter. Therefore, the fauna of the river is dependent on allochthonous energy inputs to the system to provide much of its food base, which is provided by the floodplain. 15