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HomeMy WebLinkAboutDRB140562_Lot 10 Hazard Report_1418427780.pdfArthur I. Mears, P.E., Inc. Natural Hazards Consultants 555 County Roan 16 Gunnison, CO 81230 Cell: (970) 275-1548 November 14, 2014 Ms. Lisa Morris 9281 Egret Ridge Nelmont, NC 28012 c/o Mr. Michael Suman RE: Avalanche Hazard at 4842 Meadow Lane, Vail, Colorado Dear Ms. Clark: At the request of Michael Suman I completed a site visit to the above-referenced property on November 5, 2014. The purpose of my site visit was to assess the rockfall and avalanche hazards at your proposed house and to recommend mitigation if this is needed. Your property is shown as a rockfall area on Town of Vail hazard maps however I conclude that rockfall hazard does not exist and mitigation for rockfall is not needed. I have reached this conclusion because there is no evidence of rockfall at your property and source areas for rockfall that would reach it do not exist. Snow Avalanche Hazard Slopes above and below the existing house are sufficiently steep in places (30º to 40º) to produce small “snow slides” (technically avalanches according to Vail hazard regulations). These snow slides could reach the back wall of the existing house after falling approximately 30 feet vertically. Snow slides could also start below this existing house, fall approximately 50 feet and reach the back walls at the location of your proposed house. The sketch below (Figure 1) shows schematically the relationship between the existing house, the proposed house and the direction of snow slides (blue arrows) that can impact either structure. This schematic also shows a proposed “impact wall” as a black line at the back of the lower, proposed house. This wall is discussed further under “avalanche mitigation.” After the existing house is removed the bench where the old house was located will be reached by and stop the small slides starting on the upper slope. This will not affect the hazard on the lower slope. Avalanche Mitigation The snow slides (small avalanches) can be mitigated at the new house by building a reinforced impact surface 8 feet high at part of the back walls. The impact walls are required on surfaces facing the slope. The impact pressure on the walls is a maximum of 80 lbs/ft² at the base of the wall and will decrease linearly to zero at a height of 8 feet. This means the impact pressure at a height of 4 feet will be 40 lbs/ft². Windows and doors are acceptable within this surface if they satisfy these loads. Activities or facilities (e.g. hot tubs, etc.) that encourage use in the avalanche-exposed areas behind the house are discouraged. Reduction of avalanche hazard below house The proposed avalanche mitigation will not deflect avalanches toward adjacent public or private property. Furthermore, if designed according to the standards provided in this letter, it will protect the occupants of the proposed house and all areas below this house. SIncerely, Arthur I. Mears, P.E. Proposed House Reinforced lower wall Existing House Figure 1. Schematic cross section showing house, impact walls and avalanche direction.