13000000095 Continental Dam Inundation Report

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CONTINENTAL DAM - 1 - July 11, 2013 INUNDATION MAPPING REPORT 1.0 INTRODUCTION Deere & Ault Consultants, Inc. (D&A) has prepared this Inundation Mapping Report at the request of the Santa Maria Reservoir Company. This report documents the procedure of modeling a clear- day breach of the dam at Continental Reservoir 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 Continental Dam is located in Hinsdale County approximately 16 miles west of the town of Creede, Colorado in Section 21 of Township 42 North, Range 3 West of the New Mexico P.M. Continental Dam is an earthen compacted embankment that was constructed in the mid-1920’s. It has a height of approximately 90 feet at the dam centerline and a storage capacity of 22,678 acre-feet with the water surface at the emergency spillway crest. 2.0 DAM BREACH ANALYSIS 2.1 Breach Parameter Estimation The dam dimensions, emergency spillway crest elevation, and other relevant data were taken from the following sources which are provided in Appendix A:  1925 construction plans for Continental Dam and Reservoir, designed by Carl S. Gould. Sheets used: Revised Sheet 4 of 5, and supplemental “as-built” sheet dated 1928.  1990 “as-built” plan set: Continental Dam Rehabilitation, by Hydro-Triad. Sheet used: 3 of 7.  Capacity table for Continental Reservoir provided by SEO. The average upstream and downstream embankment slopes were estimated from Sheet 3 of 7 of the 1990 rehabilitation plans for Continental Dam. Both the upstream and downstream embankment faces consist of several varying slopes, so average slopes of 3.2:1 and 2.5:1 H:V were estimated from the plans for the upstream and downstream faces, respectively. A dam crest width of 18 feet was taken from the supplemental “as-built” sheet in the 1925 plan set. Both the 1925 and the 1990 plan sets use the same unknown vertical datum, but the capacity table lists gage height. The datums were matched up using the spillway crest elevation as a reference. A summary of the elevation data is shown in Table 1.