HomeMy WebLinkAbout24SITE8 - Stormwater Management ReportCLA-6314S
Page 1 of 2
CLA Engineers, Inc. | 317 Main Street, Norwich CT 06360 | 860.886.1966 | www.claengineers.com
Stormwater Report
Site Improvement Plan
Camp Oakdale – Public Works Equipment Storage Garage
176 Meeting House Lane
CLA-6314S
October 7, 2024
Narrative:
The proposed development is the construction of a 4,725-square foot equipment storage garage for
the Town Public Works Department on the 79.81-acre Camp Oakdale recreation facility. The
development will also include approximately 4,500-square feet of gravel access drive for the new
garage. Including the roof and gravel surface as impervious areas, the project will add
approximately 0.21-acres of impervious area to the park. Stormwater runoff from the new roof
and gravel parking area are design to sheet flow from the developed site easterly towards an
existing grass playing field, wooded area, and the property boundary along Meeting House Lane.
The proposed site grading has been designed to match the existing drainage patterns as closely as
possible. As a low impact development measure stormwater will sheet flow from the development
over the vegetated areas.
The site and downstream area are located within a Charlton-Chatfield (73C) soil based on NRCS
soil mapping. This soil type is a hydrologic soil group B (HSG B) soil. HSG B soil types are
characterized as having a moderate infiltration rate. There is more than 425-feet of overland flow
to the nearest downstream property line. Based on the overland travel and soil type, a majority of
the runoff from the new impervious area will infiltrate into the ground prior to leaving the property.
In our opinion the addition of 0.21-acres of impervious roof and parking on the 79.81-acre property
will have a negligible impact on peak runoff rate and will have no negative impact downstream.
Stormwater Quality:
Stormwater run-off from the proposed roof and gravel parking area will flow generally easterly
toward Meeting House Lane. The stormwater will travel via overland flow over approximately
240-feet of low gradient (±2% slope) grass athletic playing field and approximately 185-feet of
woodlands before entering Meeting House Lane. A study by Yuan et al. (2009)1 reviewed the
effectiveness of vegetated buffers on water quality and found that “the sediment trapping efficiency
was at least 80% for all buffer widths of greater than approximately 5 m.” While slope had an
impact on the sediment trapping efficiency in the studies, buffer width in excess of 15 m (49.2-ft)
produced sediment trapping efficiencies of 80% or more. As noted, stormwater runoff from the
proposed development will flow through more than 425-feet of overland flow through grass and
wooded vegetation before leaving the property. This vegetated buffer will provide more than
adequate width to treat the stormwater run-off and provide more than 8 times the buffer width
CLA Engineers, Inc.
Civil Structural Survey
317 MAIN STREET NORWICH, CT 06360 (860) 886-1966 (860) 886-9165 FAX
CLA-6314S
Page 2 of 2
CLA Engineers, Inc. | 317 Main Street, Norwich CT 06360 | 860.886.1966 | www.claengineers.com
outline in the reference study. This overland flow will provide the 90% removal of total suspended
solids in accordance with the 2024 Stormwater Quality Manual.
In our opinion, the proposed development will have no negative impact to downstream properties
or infrastructure.
CLA Engineers, Inc.
Kyle Haubert, P.E.
References
1 Yuan, Yongping, Binger, Ronald L., and Locke, Martin A., 2009, A Review if effectiveness of
vegetative buffers on sediment trapping in agricultural areas, Ecohydrology 2, 321-336 (2009)