HomeMy WebLinkAboutFile Documents.ASPEN MOUNTAIN RD.0023.2018 (10).ACBK
DRAINAGE REPORT FOR
ASPEN MOUNTAIN BOOSTER STATION
ASPEN, CO
I hereby affirm that this report for the analysis of proposed booster pump station on Aspen
Mountain in Aspen, Colorado was prepared by me for the owners thereof in accordance with
the provisions of the City of Aspen Urban Runoff Management Plan. I understand that it is
the policy of the City of Aspen that the City of Aspen does not and will not assume liability
for drainage facilities designed by others.
February, 2018
Prepared by
118 West Sixth Street, Suite 200
Glenwood Springs, CO 81601
970.945.1004
970.945.5948 fax
02/28/18
3/04/2018
Reviewed by Engineering
03/30/2018 9:25:50 AM
"It should be known that this review shall not
relieve the applicant of their responsibility to
comply with the requirements of the City of
Aspen. The review and approval by the City is
offered only to assist the applicant's
understanding of the applicable Engineering
requirements." The issuance of a permit based
on construction documents and other data shall
not prevent the City of Aspen from requiring the
correction of errors in the construction
documents and other data.
Drainage Report
This report discusses the proposed Aspen Mountain booster station and its effect on
local drainage. The proposed booster pump station is located on Aspen Mountain near the
existing City of Aspen water tank and Aspen Skiing Company pump station with a latitude of
39.184296° and longitude of -106.819784°. The site is over 300’ from the nearest paved
road and an exhibit of the proposed site can be seen in Appendix A. The existing site is
mostly grass with some bare ground and is currently used for storing Aspen Skiing
Company equipment.
The only surface improvement included in this project is the 386 square foot booster
pump building. The existing area drains north to a grated manhole. The outfall of this
manhole is an 8” pvc pipe that daylights to the north onto areas of native vegetation. After
the project is constructed, the rainfall will run off of the proposed building roof and sheet flow
across the native grass area to the existing manhole.
The manhole subbasin is composed of hydraulic soil group type C, as specified by
the City of Aspen Urban Runoff Management Plan. The existing impervious area for the
manhole subbasin is 550 square feet and is made up of part of the existing Aspen Skiing
Company primary pumphouse and surrounding transformer pads. The existing impervious
area was not included in the historical peak flow calculations. The total proposed impervious
area for this subbasin is 936 square feet. The longest distance traveled in the subbasin is
200’ and will not change.
The rational method calculations in the table below show that the proposed runoff will
increase to 1.09 cfs from a historical runoff of 1.05 cfs. Because of the vegetation between
the manhole outfall and the nearest property line, we do not expect this new peak flow to be
carried onto adjacent properties.
Historical Proposed
C10 0.26 0.28
C100 0.51 0.53
I10 (in/hr) 3.43 3.43
I100 (in/hr) 5.47 5.47
A (ac) 0.38 0.38
Q10 (cfs) 0.33 0.36
Q100 (cfs) 1.05 1.09
Rational Method Calculation Table
The 27 linear feet of native grass between the proposed building and the existing
manhole will provide an excellent grass buffer for water quality treatment. Two 4” drain lines
are shown in the drainage exhibit below, the foundation drain and the emergency overflow
drain. Both of these drains will discharge into the existing manhole. The emergency overflow
drain is connected to a trench drain inside of the building in case of a pump failure. Neither
of these drains will carry storm runoff.
The proposed impervious area is very small, disconnected from adjacent properties,
and near the bottom of the Aspen Mountain Basin. Because of these reasons, as well as
those described in further detail above, I believe that this project meets the City of Aspen
Urban Runoff Management Plan requirements and most importantly the goals of the City of
Aspen Engineering Department.
3/04/2018
Drainage Report
Appendix A
Drainage Exhibit
3/04/2018
3/04/2018