HomeMy WebLinkAbout605 E. PLUM ST., DUPLEX - BASIC DEVELOPMENT REVIEW - BDR180009 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE RELATED DOCUMENTMay 14, 2018
Mr. Dan Mogen
City of Fort Collins Engineering Department
700 Wood Street
Fort Collins, Colorado 80521
RE: Drainage Memo – 605 E. Plum Street Parking Addition
605 E. Plum Street, Fort Collins, Colorado 80524
Project No. 2474.00
Mr. Mogen:
The purpose of this letter is to address drainage impacts to the existing 0.22-acre property, located at 605
E. Plum Street, due to the addition of a proposed recycled asphalt parking area. The site is situated in
Lot 7, Block 178, FTC, City of Fort Collins, County of Larimer, State of Colorado. Specifically, the
property is located between Smith Street and Stover Street and bound by East Plum Street to the north
and a common alley access-way to the south. The subject property is surrounded by residential
properties to the west, east, across the alley to south, as well as across Plum Street to the north.
The existing property currently consists of a house, concrete sidewalks, detached garage, and mature
landscaping. Historically, the northern third of the site drains north to the curb and gutter of E. Plum
Street. The remaining portion of the site drains south to the existing alley. The proposed improvements
include the addition of two (2) 9’ x 19’ recycled asphalt parking spaces along the southern property line.
The proposed parking spots are to be perpendicular to the existing alley and constructed to existing
grade.
The proposed improvements will not alter the historic drainage patterns. Due to the small scope of the
improvements, no water quality or on-site detention is being proposed. The addition of approximately
350 ft2 of recycled asphalt to the existing site will have a negligible effect on the amount of runoff
generated. The Rational Method was used to calculate the runoff for the area south of the detached
garage for the existing and proposed site conditions. Assuming the minimum time of concentration of
five minutes, the addition of the proposed recycled asphalt parking spaces causes an increase of 0.03 cfs
during the 100-year storm event.
The proposed site improvements should not cause adverse impacts to the adjacent properties.
Page 2
If you have any questions or require additional information, please call Coffey Engineering at (970) 622-
2095.
Sincerely,
COFFEY ENGINEERING & SUEVWYING, LLC
Reviewed By:
Ramsey Pickard Troy Campbell, PE
Engineering Designer Project Manager
Attachments –
-Vicinity Map
-Rational Method Calculations
Composite C Values
605 E Plum
Total Area Minor (2-YR) Major (100-YR)
(acres) Runoff Coefficent Runoff Coefficent
Existing 0.00 0.00 0.00 0.02 0.08 0.10 0.24 0.58
Proposed 0.00 0.00 0.01 0.02 0.07 0.10 0.31 0.61
Composite C values obtained from Table RO-11
Basin(s) Asphalt Area (acres) Concrete Area (acres)
Recycled
Asphalt (acres)
Roofs (acres) Lawns (acres)
RJP Plum Rational Method Flow Calculations.xlsx 5/11/2018
Individual Basin Flow Calculations
605 E Plum
Area Minor Major
(acres)
Composite
"C"
Composite
"C"
Length
(ft)
Slope
(%)
Minor tov
(min)a
Major tov
(min)a
Length
(ft)
Slope
(%)
Channel
Type
Velocity
(fps)c
tt (min)
Minor TC
(min)
Major TC (min) 2-yr 10-yr 100-yr 2-yr 10-yr 100-yr
Existing 0.10 0.24 0.58 75 2.00 10.70 6.47 0 0.70 PA 1.67 0.00 5.00 5.00 2.85 4.87 9.95 0.07 0.12 0.58
Proposed 0.10 0.31 0.61 75 5.00 7.26 4.50 0 0.50 GW 1.06 0.0000 5.00 5.00 2.85 4.87 9.95 0.09 0.15 0.61
Equation RO-3
Initial/Overland Time Final TC Intensity (in/hr) Basin Flows (cfs)
Basin (s)
Travel Time
RJP Plum Rational Method Flow Calculations.xlsx 5/11/2018