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GRSR296E Bottomland Site- Located at river mile 296 and six river miles downstream of the Highway 40 Jensen Bridge along the left bank, the SR Bottomland provides 283 acres of floodable acreage (this figure includes 123 acres on FT property upstream, and 5 acres of RS property, see figure 4). However, the SR bottomland, under existing conditions, does not flood until Green River flows exceed 37,000 cfs, the 100-yr flood based on post-1963 hydrology. This is due to 3-foot high (average) man-made levee road that is offset 10'-20' from the river that was built to prevent flooding. Any flooding on SR property also extends on to the FT property upstream, under existing conditions. If the levee were removed, 283 acres could be flooded two out of every three years. The area behind the levee has been used for farming and grazing purposes. If the levee were removed, existing irrigation equipment on SR property would be flooded regularly and the five buildings on site would be flooded during high flow years (over the 3-yr flood event). Irrigation pivots on FT property however would not be flooded. Proposed flooding options are discussed in chapter 4. Access to the site is good with a road connecting County Road 264 (from Jensen) to the river levee. GRSL288N Bottomland- At river mile 297, along the right bank, SL Bottomland provides up to 98 acres of floodable overbank area. It is located one mile below the Bonanza Bridge bottomland that was modified to enhance flooding in March 1997. The bottomland floods from the downstream end and extends over three properties that includes some buildings and corral structures (see Figure 5). The property is not heavily vegetated even though it has been used for farming and grazing in the past. Overbank flooding initiates when flows exceed 19,600 cfs and can flood the existing structures. A natural levee prevents flooding from initiating along the upper ends of the property (the CS and DS Tracts) more or less. Along the lower part (VR property) the bank is relatively lower. Access to the site is fair, with access roads from Highway 45 to the CS Property, and to the river. The road to the river, however, will be inundated at higher flows. Gunnison River • Two bottomland sites were surveyed on the Gunnison River during the 1997 runoff season. GUBC14S -The BC site is an excavated gravel pit located approximately one mile downstream of the Highway 141 Bridge (14 river miles upstream of the Colorado River) and Whitewater Gaging Station. The site is accessed through the Whitewater Building Materials gravel operations. The gravel pit is located downstream of a large oxbow, on the inside of a bend, before the river resumes flowing due west (see Figure 6). The Bureau of Land Management (BLM) owns Lot-4 just south of the pond. Part of the pond lies within the BLM lot, so they have been participating in easement negotiations. The site provides approximately 59 acres of floodable area that is protected by a man-make dike around the riverside of the gravel pit. The dike prevents flooding for flows up to approximately the 100-year flood event or 30,000 cfs. This site is an excellent candidate as aflow-through site. The levee can be notched at the upstream and downstream ends to increase flooding frequency to an annual event. Further discussion of the proposed site configuration can be found in Chapter 4. Dad's Flat- Located approximately 11 river miles upstream of the GUBC14S site, at river mile 25, the Dad's Flat site contains 48 acres of floodable area (see Figure 7). The site is located on the inside of a large bend and has relatively high banks. The site does not flood until flows exceed approximately 24,000 cfs, that is, the equivalent of a 25-year event. The overbank elevations are not significantly lower than the top of bank elevations, so there is no opportunity for flooding enhancement at this site. Due to limited floodability at this site, it has been dropped from consideration as a candidate for an easement and further discussion of this site is limited. 1-6