HomeMy WebLinkAboutFile Documents.629 W Smuggler St.0173.2017 (2).ARBK
DRAINAGE REPORT
11/07/2017
Reviewed by Engineering
11/15/2017 7:41:20 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.
I. GENERAL LOCATION AND DESCRIPTION
A. Location
The 629 Smuggler site is located on the northwest side of Aspen a couple blocks north of
highway 82. At the corner of North 6th Street and West Smuggler St. City of Aspen, County of
Pitkin, State of Colorado. The proposed site changes are located along east side of North 6th
Street and west side of the residence, approximately 1077 feet northeast of the Main Street.
B. Description of Existing Property
The site is approximately 4,500 square feet (0.1033 acres). The existing lot consists of a home,
patios, walkways, a shed, landscaping and trees. The site is bordered by a private property to
the east, West Smuggler to the north, North 6th to the west and the Smuggler-Francis alley to the
south. The driveway drains from the southeast to the north/northwest and offsite at the corner of
North 6th Street and West Smuggler Street. No offsite basins drain on to the site. Grades range
from approximately 2-percent to 4-percent.
C. Soils Description
Within the area of study, there is one soil type as designated by the United States Department of
Agriculture Soil Conservation Service in cooperation with Colorado Agricultural Experiment
Station. The soil type that encompasses the site is designated as soil 107, Uracca, Moist-Mergel
Complex, having 1%-6% slopes. The Soil Conservation Service describes the soil as deep and
well drained with moderate to moderately rapid permeability, and a low water capacity. The soil
is defined as hydrologic group ‘B’. A site specific soil study was completed by CTL Thompson
on January 9, 2006 (project no. GS04537-120) for a prior construction project, and found the
subsurface conditions to consist of 1 foot of sandy clay topsoil underlain by slightly silty gravel
with sand, cobbles and boulders to the depth of exploration.
II. PROPOSED IMPROVEMENTS
A. Description
The proposed project includes the expansion of an existing patio located west of the residence
and the extension of a walkway and driveway to North 6th Street. The improved driveway and
walk will drain away from North 6th Street.
B. Drainage
The improvements present no drainage issues and marginally alter the existing drainage pattern.
Previously, a portion of the patio drained to the grassy area within the right-of-way (ROW)
located west of the patio. With the proposed patio improvements, runoff will be directed to
prevent flow discharging into the ROW. After water quality treatment, runoff will ultimately
flow into the City of Aspen’s drainage system, as it did before the proposed project. The flow
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path of stormwater discharging to the city system can be found on the Grading and Drainage
Plan attached to this report.
III. DRAINAGE DESIGN
A. Criteria
This drainage study was prepared in conformance with the City of Aspen, Colorado Urban
Runoff Management Plan (URMP), dated April of 2010 and the revised sections dated thereafter.
Less than 1,000 square feet of area will be disturbed with the proposed construction; therefore
the site is viewed as a Minor Project per the URMP, and water quality for the proposed
improvements will be necessary.
Water Quality Capture Volume (WQCV) will be determined for the site that will undergo site
grading as per the URMP standards. The WQCV is defined as the treatment for up to the 80th
percentile runoff event, corresponding to between a 6-month to 1-year event. The WQCV was
determined for the proposed site using the runoff reduction and conveyance methodology
provided by the City of Aspen URMP to drain to green space, as required for minor design.
B. Basins
Delineation for water quality design has been separated into two sections undergoing the
proposed improvements, the driveway area and the patio area. With the proposed grading and
increase in impervious surfaces, each area will drain to a separate green space for water quality
treatment.
C. Low Impact Site Design.
The driveway and walkway west of the residence will drain away from North 6th Street into
green space in the form of a grassed swale, to provide treatment and conveyance into the city
drainage system. The patio will drain into a planter surrounded by edging that will spread runoff
to be uniformly distributed over a grass buffer. The grass buffer location will not need to be
disturbed as the existing area consists of dense grass with gradual slopes. The grass buffer occurs
along a low ridge that will continue to evenly distribute flow northeast/northwest past the grass
buffer for runoff not infiltrated into the soil during large storm events.
D. Water Quality System Design
Water quality treatment methods and values were determined by the previously mentioned
process from the City of Aspen URMP. All improvements have been designed to drain to green
space, as required for minor grading projects. The grass buffer area for the patio improvements
was determined using a 1:1 ratio of the impervious area, as shown in the attached Grading and
Drainage Plan. The small lawn within the patio area has a slight depression sloped to act as a
swale leading runoff into a channel that will convey stormwater to the existing planter and grass
buffer. The channel will have a grate to capture additional runoff from the patio. Calculations for
the small-sized drain have been attached to this report.
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IV. CONCLUSION
No drainage issues are anticipated with the proposed project. Site drainage has been improved
with the proposed design by conveying ROW runoff through a grassed swale, as well as
directing the patio runoff to a green space within property lines. Following water quality
treatment, stormwater runoff will enter the City of Aspen drainage system flowing east down
West Smuggler Street before entering the curb and gutter of North 5th Street that discharges into
the inlet at the Gillespie Avenue/North 5th Street intersection.
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Rainfall Intenstity Chart Patio
Basin I P1-2yr P1-10yr P1-100yr Td
PR-1 2.42 0.47 5.0
PR-1 3.96 0.77 5.0
PR-1 6.33 1.23 5.0
REACH
Tc
TC
Tc
2 YEAR INTENSITY
10 YEAR INTENSITY
100 YEAR INTENSITYOVERLAND FLOWFLOW VELOCITY, V (FIGURE *RO-1 UDFCD) (fps.)
FLOW LENGTH, L (ft.)TRAVEL TIMESURFACE DESCRIPTION
FLOW LENGTH, L (TOTAL <300 FT.) (ft.)
LAND SLOPE, S (ft./ft.)
BASIN
MINIMUM 5 MINUTES
6.33
PATIO
3.96
2.42
PATIO
46.2
RATIONAL COEFFICIENT. C (FIGURE 3.2 OF URMP) 0.73
AREA IDENTIFIER
FLOW SLOPE, S (ft./ft.)
(MIN)
TRAVEL TIME = L/(60V) (min.)
URBAN CHECK = 10+L/180
0.0
0.025
10.3
To (MIN)
5.0
1
0.025
3.4
3.4
0.0
CALCULATED BY: BDB STANDARD FORM SF-3
DATE: 10-10-2017 STORM DRAINAGE SYSTEM DESIGN
CHECKED BY: RDN (RATIONAL METHOD PROCEDURE)
Contributing Area
AREA (AC)RUNOFF COEFF.Tc (MIN)C * A (AC)I (IN/HR)Q (CFS)Tc (MIN)SUM (C*A) (AC)I (IN/HR)Q (CFS)SLOPE (%)STREET FLOW (CFS)DESIGN FLOW (CFS)SLOPE (%)PIPE SIZE (INCHES)LENGTH (FT)VELOCITY (FPS)Tt (MIN)(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22)
0.09 Design Point 1
TRAVEL TIME
REMARKS
1 PATIO 0.018 0.81 5.00 0.01 6.33
JOB NO. 2171027.00
PROJECT: 629 SMUGGLER STREET
DESIGN STORM: PROPOSED 100 YEAR
STRUCTURE NO.DESIGN POINTDIRECT RUNOFF TOTAL RUNOFF STREET PIPE
ADDRESS: 629 SMUGGLER ST.
DRAINAGE REPORT
BY: BDB
CHECKED BY: RDN
DATE: 10-10-17
PATIO 785.0 0.018 709.8 90.4 216.2 216.400 0.71 0.73 0.75 0.81
Type B Soils
BASIN AREA (S.F.) AREA (ACRE)
IMPERVIOUS AREA
(SF)
PERCENT
IMPERVIOUS
2 YR RUNOFF
COEFFICIENT
10 YR RUNOFF
COEFFICIENT
100 YR RUNOFF
COEFFICIENT
AREA OF GREEN
SPACE PROVIDED
5 YR RUNOFF
COEFFICIENT
PROPOSED
IMPERVIOUS AREA (SF)
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Channel Report
Hydraflow Express Extension for Autodesk® AutoCAD® Civil 3D® by Autodesk, Inc.Monday, Oct 9 2017
PATIO DRAIN 100YR
Rectangular
Bottom Width (ft) = 0.25
Total Depth (ft) = 0.17
Invert Elev (ft) = 0.17
Slope (%)= 1.00
N-Value = 0.011
Calculations
Compute by:Known Q
Known Q (cfs) = 0.09
Highlighted
Depth (ft)= 0.16
Q (cfs)= 0.090
Area (sqft)= 0.04
Velocity (ft/s)= 2.25
Wetted Perim (ft) = 0.57
Crit Depth, Yc (ft) = 0.16
Top Width (ft)= 0.25
EGL (ft)= 0.24
0 .1 .2 .3 .4 .5
Elev (ft)Depth (ft)Section
-0.25 -0.42
0.00 -0.17
0.25 0.08
0.50 0.33
0.75 0.58
1.00 0.83
Reach (ft)
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