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001796 STUDY SUMMARY I I t Based on the findings of the reconnaissance study, the City of Alamosa and Alamosa County should take steps to fund a major improvement program to upgrade the levee system along the Rio Grande, so as to provide for the health, safety and welfare of the citizens and property of Alamosa, East Alamosa and the immediate surrounding areas. Floods have occurred in the past and will occur in the future. The 1985 flood was of a 10-year magnitude. A 100-year flood would be of a flow magnitude approximately 2.5 times the 1985 flood. As years 90 by without high water in the river, the chances for a major flood event become larger and more certain. Currently, the area experiences an annual flood risk or cost of $900,000 to $1,000,000. This represents an annualized cost of flood damages over a lOO-year period, assuming the current status of development and flood protection. This cost represents past and future damage to private and public property. Improving the levee system to federal criteria would result in average annual risks being reduced to approximately $50,000 to $75,000. Hydraulic evaluations show that a cleared river system will pass the 100-year flood at a profile approximately 2-feet lower than the comparab 1 e flood profil e with the ri ver choked with vegetation and large accumulations of river sediment. Clearing the river channel on a regular basis will provide significant economic benefits to the community in terms of maintaining the levee system capacity. Improvements to the levee system have been identified that, if implemented, would upgrade the integrity and capacity of the system to federal standards and criteri a. Improvements i ncl ude rai si ng and widening the levees, providing riprap armour protection, reducing seepage under and through the levees, providing access control along the top of the levees and constructing new tieback levees northwest of the City for right and left bank levee systems. The details of the improvements should be evaluated and finalized during the design phase, prior to construction. Initial estimates of construction costs for the conceptual improvements totals approximately $4.0 million, including construct ion, cont i ngenci es and engi neeri ng. Cost s may decrease or increase th rough the fi na 1 desi gn phase, dependi ng upon the opportunity for economy in scope and materials or the need for more extensive improvements than currently envisioned. Based upon the cost estimates of flood damages and constructing the improvements, as reported in this report, the improvements are -4-