HomeMy WebLinkAboutDrainage Reports - 04/20/2015AUNITED CIVIL
Design Group LL�
March 19, 2015
Citf�rt Collins Approved Plans
Mr. Basil Harridan
Stormwater Engineering br
City of Fort Collins Utilities Department Mate:
700 Wood Street
Fort Collins, CO 80521
RE: Union Place Subdivision Second Filing
Final Drainage & Erosion Control Letter
Dear Basil,
We have prepared this letter to document the drainage design and analysis for Union
Place Subdivision Second Filing. The original report for this subdivision entitled "Union
Place Final Drainage & Erosion Control Study" was prepared by Nolte Associates, Inc. on
October 8, 2009. Addendum #i1 was prepared by United Civil Design Group on
12/31/2013 and documented the changes associated with the Minor Amendment that
was finalized on 3/12/2014.
The revisions to the site for Union Place Subdivision Second Filing include the following:
The previously planned condominiums on Lot 1 of Block 5, Lots 1 & 2 of Block 4,
and Lots 1 & 2 of Block 2 are -being changed to single family attached units.
Individual lot lines were added for each of the single family attached units which
requires a Replat and Major Amendment process.
• Revisions to utility services for the change from condominiums to single family
attached units.
• Revisions to the landscaping.
• Revisions to the lot grading for the defined single family attached units that were
previously undefined.
• Signing and Striping additions to meet fire department requirements.
A summary of the effects and changes to the site drainage is included below:
• No changes to the drainage basin boundaries.
• No changes to the impervious area calculations or runoff calculations.
• New bioretention area in Tract J. This bioretention area will work in conjunction
with pervious pavers in the private drive and the previously planned bioretention
areas on the: north side of Block 4 to provide water quality for the proposed units
in Block 4. Calculations for the bioretention areas for conformance with the
City's LID and WQCV requirements have been included with this -letter.
• New concrete sidewalk culvert in lieu of the metal sidewalk chases in Tract K.
,
a
1501 ACADEMY CT. STE 203 1 FORT COLLINS, CO 80524 1 970-530-4044 I www.unitedcivii.com
A
\UNITED CIVIL
Design Group u�
• New concrete forebay in Tract K. C
The revisions to the site and associated drainage items will improve the water quality
and conveyance,on site and will not adversely affect the stormwater runoff offsite.
Sincerely,
Samuel M. Eliason, P.E.
Principal
United Civil Design Group
Enclosures:
• Water Quality Volume and LID Calculations
,
I
5
1501 ACADEMY CT. STE 203 1 FORT COLLINS, CO 80524 1 970.530-4044 I www.unitedcivil.com
Water Quality volumes and LID calculations
0
UNITED CIVIL
Design Group
t
PROJECT NAME Union Place Subdivision Second Filing
PROJECT NUMBER U13003
CALCULATED BY SME
LID requirement
Total Replat Area (sf) 64943
Block 4, Tract I, G, H, & J Area (sf) 32884 (LID provided for this area)
51% of the new site includes LID
WQCV required
Block 4, Tract I, G, H, & J Area (sf) 32884
% Impervious 76%
Watershed (inches) 0.30
WQCV (cf)* 668
Notes:
WQCV is based on 12 hr storage for porous
landscape detention (bioretention/porous pavers)
Bioretention WQCV provided
Bottom
Top Area Area Depth Volume
Northwest bioretention 100 70 0.5 88
Northeast bioretention 220 180 0.5 217
Southeast bioretention 323 194 0.67 480
Total 785
Notes:
1. Assumes 30% void space in bioretention and gravel layers
2. Does not take into account additional water quality provided by pervious pavers that run
down the middle of Block 4 or the south side of Urban Prarie Street.
U13003-Runoff-Second Filing.xls, WQ Volumes