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<br />002113 <br /> <br />I' <br />J <br /> <br />2.2.1 Anderson Subdivision Levee <br /> <br />Concern: <br /> <br />Undercutting and erosion of this part of the levee <br />system occurred on !(;e evening of June 10, 1985. A new "levee" <br />was hastily built n~f ~aturat~materiaj.?Jduring the flood. <br />The elevation of the "levee" may not be high enough to prevent <br />overflow into the town during the next flood. <br /> <br />Findings: <br /> <br />A site inspection indicated that the unprotected "levee" <br />would probably dissolve during a major flood. It currently <br />pretends to protect an undeveloped portion of a subdivision in <br />northwest Alamosa, The top of the "levee" appeared to be at or <br />only slightly higher than what the river bank would actually <br />be. If homes were allowed to be constructed in the subdivided <br />lots behind, the levee without additional fill, they would <br />suffer serious damage in the next flood, <br /> <br />A ground survey along the top of the south bank levee <br />and along Leroy Street was performed by the City at the request <br />of the Damage Survey Team. Comparison of the levee elevations <br />with the flood profiles published in the Flood Insurance Study <br />indicated that there are definitely at least two points in the <br />"levee" below the 100-year flood and there was, an average, <br />only about one foot of freeboard above a SOO-year flood. At <br />least, 3.0 feet of freeboard above the lOO-year level is the <br />current accepted design standard. Additional surveys along the <br />entire crest of the Alamosa levees on both sides of the river <br />would be a good idea, <br /> <br />Examination of old maps raises a question about whether <br />the so called "levee" actually existed in this reach prior to <br />about 1982. Certainly the Anderson or Riverwoood Estates <br />Subdivision does not appear on the Flood Insurance Study maps <br />published in 1977 for the city and 1978 for the county, <br /> <br />Furthermore, the entire Alamosa levee system above the <br />North bridge is shown to be within the floodway on the county <br />f'lood Insurance Study map. The floodway is where high <br />velocities will cause severe erosion. <br /> <br />Since the flood insurance maps were published, the city <br />has annexed areas on both sides of the river which are within <br />the floodplain. <br /> <br />To compound the <br />the Riverwood Estates <br />of the river, and 19 <br />floodway, <br /> <br />problem, a dozen of the plotted lots in <br />subdivision I-- extend to the center to <br />lots are partially or wholly in the <br /> <br />/ <br /> <br />61 <br />