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Home My WebLink AboutDRB140097 Rockfall Hazard report Arthur L Mears, P.E., Inc. Natural Hazards Consultants 555 County Road 16 Gunnison, CO 81230 Ce1L• (970)275-1548 Tel/Fax: (970)641-3236 April 11, 2014 Michael Suman Suman Architects 141 E. Meadow Dr., Suite 211 Vail, CO 81657 RE: Elk Meadows Subdivision Dear Mr. Suman: As requested, I evaluated the rockfall hazard to 3 lots (lots 2,3 and 5) in the Elk Meadows Subdivision of Vail.They are identified on the "partial topographic map" by PLC dated "09/15/13." Changes to lot locations may invalidate the results of this study.These lots were designated 'high severity" rockfall hazard on Town of Vail hazard maps produced in 1984. We recommend removing these lots from rockfall hazard designation for the reasons discussed in this report. 1. Evidence of previous rockfall activitv on the slopes was not found. The 30°to 35°slope directly north of the subdivision was investigated by me on site on April 9, 2014. Snow cover had melted and vegetation had not leafed out, consequently visibility was good.The slope from Buffehr Creek Road 8,300')to a possible source outcrop at 8,950 feet was investigated. Rockfall boulders were not found on the slope above the 3 lots. 2. Evidence for rockfall in the valley. Extensive grading and construction has taken place in the valley adjacent to Buffehr Creek Road in the past 30 years. Construction and grading would have obscured evidence of rockfall deposits at the base of the slope. However, additional high- quality U.S. Forest Service photos dated "10-12-50," more than 2 decades before construction, also shows no evidence of rockfall deposits at the base of the slope. , . 3. Rockfall source area characteristics. The '�:, '� � primary source for rockfall is a light grey, fine- �°n.,� � �� f i,- grained sandstone member of the Minturn � �, ` Formation (Figure 1). The bedding planes of rock � '� '' x '- units dip to the north at approximately 20°. Joints �� - � :. a�,�' at spacings of 2—5 feet are parallel to the beds. �. , '` ��+�, `,'�-� 1 _ � � Some rocks, which tend to be tabular in shape, ' �,"��r� �"� � . �ti' �; ; have fallen to the base of the slope and stopped ` " '' ' ,°�1l (see figure 2). Rocks of this typical shape are not �.,5�� y -�t�',�..�� n7r�''� it� 3.:'.. . s� < � #, ;�; � �, likely to roll or bounce down the slope as rockfall. °�� `' ��A��' ¢��'�� ` Sections of the cliff do not a ear in dan er of � >'•`� `�� pp g ,�s,t� toppling onto the steep slope and descending as rockfa I I. �.. - �- 4. Buffehr Creek Road. The road is �'�` _ � - °��: �;,- ��. :: �a'' �. �� t , . �, _� ',4 approximately 30 feet wide above �� " �- a ". �� k the subdivision would serve to `� �' ' ' �y `;�#� �� , ' t��f �� , ,�: stop and/or dissipate rockfall ��q'= . � .=� �1 "� �.�'� 'i energy if the very improbable ` � k"'�� "� �� ° �'�; (referto points 1, 2 and 3 above) �$f � ` ��' 'r � ' 4� _ . ;� .. x� �" ,"'' .�k � � rockfall event reached the road. - : . 't� .�" r� �,_ f� . �,,r � �.P '�`#� ;'!t °� -`. It is not possible to state that the rockfall .�� 4 -.� � �:. �' ,,,�„� � hazard and risk is zero below this or any }�'�� ' ��;��' "� `"�"�*' '� �� ..�� r., " a�� ., t: other sandstone outcropping. However, "` .' '�� Y� ' S• � `�� : based on my experience in Vail during the -'�,� �F ,,, °`�'�:ry ��"�`"�'""�a"' � � �� , �. � ' past 40 years and my experience with �� ` ';�� w}"� ��." 't �,�-"°�` ' °4''� '� „ . �° y `y ,. , - _ . :, ��: .,.� �, .� _-0 ..k�_,� : rockfall hazard analysis, mapping and mitigation at numerous sites in Colorado, I believe the hazard is minimal at the proposed building locations evaluated in this study. As a result, I do not recommend mitigation for rockfall hazard at lots 2, 3 and 5 of the Elk Meadows Subdivision. Limitation and disclaimer You as my client should know that while our company can and does attempt to uphold the highest professional standards,the state of scientific and engineering knowledge is incomplete, and does not always permit certainty.The complex phenomena involved in rockfall cannot be perfectly evaluated and predicted, and methods used to predict rockfall behavior change as new research becomes available. While we can and will offer our best professional judgment,we cannot and do not offer any warranty or guarantee of results. Sincerely, �;�L ��'Lw1�� J�L��.�,.� Arthur I. Mears, P.E.