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Meridian Village WW Reuse Dam, (DAMID 080457) July 19, 2017 Jurisdictional Status Et Hazard Classification Page 3 of 9 Jurisdictional Status According to Rule 4.2.5, a jurisdictional dam must exceed one or more of the following criteria: x Reservoir storage capacity below the spillway crest elevation of 100 acre-feet, x Reservoir area at the spillway crest of 20 acres, or x Dam height of 10 feet in accordance with Rule 4.2.19. The low level outlet pipe extends through the left abutment and does not daylight near the dam; therefore it is excluded from the dam height evaluation. According to the CDG, the original ground elevation at the maximum section of the dam is 5,941.2 feet. Comparing this to the design spillway elevation of 5,948.0 feet yields a jurisdictional (hydraulic) height of 6.8 feet. As mentioned above, the reservoir area at the spillway crest elevation is approximately 15.7 acres, which is less than the minimum area criteria above. The total reservoir storage capacity below the spillway crest is 190 acre-feet, however 91 acre feet of this is excavation below the downstream toe of the embankment and is not included. Therefore, the storage capacity between the downstream toe and the spillway crest is 99 acre-feet. None of the jurisdictional dam criteria is exceeded, therefore Meridian Village WW Reuse Dam is a non-jurisdictional dam. Hazard Classification A dam breach analysis was performed using the 2D module in HEC-RAS 5.0. Topography for the analysis consisted of 0.75m resolution LiDAR gathered in Fall 2013. The elevations used for this analysis were based on the elevations found in the LiDAR topography and differ slightly from those provided by the engineer. Two breach locations were evaluated for this analysis. The first analysis evaluated a breach through the maximum embankment section, coincidentally occurring at the spillway location. This first analysis reflects the traditional approach to evaluate the hazard classification of a dam. However, the excavation for construction of both the ditch (downstream side of the dam) and the reservoir (upstream side of the dam) created a potential foundation seepage failure mode that could result in a slightly larger breach flood than would occur under the normal through-embankment sunny-day seepage failure. Therefore, a second analysis was performed to evaluate a potential foundation seepage failure into the drainage ditch immediately right of the spillway. Initial Breach Parameters The initial breach parameters were calculated using the Colorado Dam Safety empirical spreadsheets. According to the Guidelines for Dam Breach Analysis (SEO, 2010), the Montgomery Et Langridge-Monopolis with Washington State failure time (MLM-Wa) method was used for the first analysis (embankment seepage). Due to the larger reservoir volume 1313 Sherman Street, Room 821, Denver, CO 80203 P 303.866.3581 www.water.state.co.us John W. Hickenlooper, Governor I Robert Randall, DNR Executive Director I Kevin Rein, Director/State Engineer *�� �`1876�`