HomeMy WebLinkAbout23SITE6 26 Platoz-Drainage Report 41823May
Engineering, LLC
Civil Engineering, Site Planning, and Consulting
1297 RT 163 Oakdale, CT 06370 Cell: 860 884-9671 Email: mayengineering@sbcglobal.net
DRAINAGE REPORT
April 18, 2023
Property Located at:
26 Platoz Drive
Uncasville, CT
Applicant:
JOHN MANDES
11 DEVONSHIRE DR
WATERFORD, CT 06385
Owner:
MANDES ARTEMIS G
11 DEVONSHIRE DR
WATERFORD, CT 06385
Prepared By:
Timothy A. May, P.E.
May Engineering, LLC
1297 Route 163
Oakdale, CT 03670
Drainage Report for 26 Platoz Dr., Uncasville, CT
May
Engineering, LLC
Civil Engineering, Site Planning, and Consulting
1297 RT 163 Oakdale, CT 06370 Cell: 860 884-9671 Email: mayengineering@sbcglobal.net
The proposed development is located at 26 Platoz Dr., Uncasville, CT. The 0.53-acre parcel has a
previously approved site plan for a multifamily unit apartment. The site was prepared and a concrete
foundation constructed but development was not completed. The concrete foundation was removed
due to the concrete being not suitable for construction. The site remained undeveloped and requires a
new site plan to develop the parcel. The parcel is located in the R-20M zone. The applicant/owner
John Mandes is proposing a plan of development for multifamily residential use; specifically proposed
is a single 64’ x 40’ 4-unit apartment building, paved parking for 8 vehicles, stormwater infiltration for
water quality volumes (WQV), and associated underground utilities.
SITE DESCRIPTION:
The site is a 0.53-acre parcel located on the northeast side of Platoz Drive, located in the Town of
Montville, CT. There are no wetlands or water courses located on this parcel. The soil type is
primarily a hydraulic soil group B consisting of Charlton-Chatfield complex fine sandy loams. The soil
types were evaluated for their permeability and have a moderate infiltration rate.
The existing stormwater drainage flow path is across the parcel in a southwesterly direction toward
Platoz Drive. No evidence of channelized flows is observed. A majority of stormwater is typically
retained onsite due to the previous construction activities.
METHODOLOGY AND RESULTS:
The Rational Method was used to determine stormwater peak runoff flows for existing and proposed
development for various storm events. The results correspond to an estimate of the amount of
expected disturbed areas to be ~1/4 acre.
The proposed developed area will include 25% grassed lawn and 28% impervious area including
roofs and pavement, with 47% remaining undisturbed wooded forest. These percentages are used to
develop the weighted Rational Runoff Coefficient (C). The existing runoff C for wood forest hydraulic
soil group B with 3-10% slope I is 0.18. The weighted C is used to model the proposed development
as low density residential (½-acre developed). The weighted C for the proposed developed parcel is
0.25.
Please note that the proposed stormwater infiltration trench with concrete galleys will remove all
stormwater runoff from the impervious portion (paved areas and roof). The impact of the stormwater
infiltration trench to remove stormwater is not included in the tabulated results, but should be
considered as a beneficial part of the Water Quality Volume (WQV) reduction and stormwater
management. The amount of stormwater water quality flow (WQF) reduction by the stormwater
infiltration trench will adequately provide stormwater storage for the Q10 storm event.
Drainage Report for 26 Platoz Dr., Uncasville, CT
May
Engineering, LLC
Civil Engineering, Site Planning, and Consulting
1297 RT 163 Oakdale, CT 06370 Cell: 860 884-9671 Email: mayengineering@sbcglobal.net
Listed are the tabulated results for the existing and proposed development conditions.
SUMMARY
The proposed site development plan is for construction of a single 4-unit apartment building, paved
parking and associated underground utilities. Stormwater runoff will be managed using BMPs that will
contain and store the 1” WQV, using the stormwater infiltration trench with 4x4 concrete galleys. The
WQF will be reduced as well. The stormwater infiltration trenches will provide pollutant and
stormwater volume reduction. The stormwater infiltration trenches will provide groundwater recharge.
Drainage Report for 26 Platoz Dr., Uncasville, CT
Rational Equation: Q=CiA
Q = Peak discharge, cfs
c = Rational method runoff coefficient Existing 0.18 Developed 0.25
i = Rainfall intensity, inch/hour
A = Drainage area, acre
soil type HSG B 2-7% slope
Storm Event (New London Co)
Acre 1 year 2 year 10 Year 25 Year 50 year 100 Year
26 Platoz Dr. 2.7 3.4 5 5.7 6.15 7.1
Drainage area 0.23
Q = Peak discharge, cfs Existing 0.11 0.14 0.21 0.24 0.25 0.29
C= wooded 0.08 & Grass Lawn 0.12 Developed 0.16 0.20 0.29 0.33 0.35 0.41
increase 0.04 0.05 0.08 0.09 0.10 0.11
wooded/bare
earth grass
Developed ½
ac
Residential