12000000065 Fuchs Dam Inundation Report

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1.0 INTRODUCTION Deere& Ault Consultants, Inc. (D&A)has prepared this Inundation Mapping Report at the request of Fuchs Ranches, Inc. This report documents the procedure of modeling a clear-day dam breach of Fuchs Dam and the development of the resulting inundation maps downstream of the dam. The inundation maps will be used to update the existing Emergency Action Plan (EAP) and to assist those involved with emergency preparedness planning and response. The hydraulic models and inundation maps contained in this report were prepared using the NAVD 88 vertical datum. The report and all associated models have been prepared in accordance with the regulations and guidelines set forth by the Colorado Department of Natural Resources, Division of Water Resources, Office of the State Engineer(SEO). 1.1 Location and Background Fuchs Reservoir is located in the Rio Grande National Forest in Rio Grande County approximately 17 miles southwest of the town of Del Norte, Colorado in Sections 2 and 11 of Township 37 North, Range 4 East of the New Mexico P.M. Fuchs Reservoir Dam is currently classified as a Small Significant Hazard Dam, per the Rules and Regulations for Dam Safety and Dam Construction of the State of Colorado. It is an earthen compacted dam with a jurisdictional height of 25.5 feet and a normal storage capacity of approximately 241 acre-feet. 2.0 DAM BREACH ANALYSIS 2.1 Breach Parameter Estimation The dam dimensions, service spillway crest elevation, and other relevant data were taken from the following plan sets and reports: • 1938 construction plans for Fuchs Reservoir • 1985 Dam Rehabilitation Drawings by Hydro-Triad Ltd. • 2010 survey by Davis Engineering Service • 1955 capacity table for Fuchs Reservoir provided by SEO A dam site visit was also conducted by D&A in September 2011. During the site visit the condition of the dam was noted, and a tape measure was used to measure the dam crest width at several locations. Two empirical methods for predicting the average breach width and failure time were compared. The methods, which are included in Appendix A, are the Froehlich(2008) equations and the MacDonald & Langridge—Monopolis/Washington State (MLM-WA, 2007) equations (collectively referred to as the "empirical equations"). The empirical equations predict the average breach width and failure time as a function of depth of water, dam height, and volume of water stored. The MLM-WA (2007)method also takes into consideration the estimated volume of embankment eroded. A comparison of the breach parameters calculated by each of the empirical equations is shown below in Table 1. FUCHS DAM - 1 - June 15,2012 INUNDATION MAPPING REPORT