030519 Planning
Stormwater Management Plan
WINDSOR RIDGE
New Hope, MN
SVK Development, LLC
Prepared by Loucks
February 8, 2019
Loucks Project No. 18611.00
WINDSOR RIDGE
New Hope, MN
Stormwater Management Plan
I hereby certify that this plan, specification or report was prepared by me or under my
direct supervision and that I am a duly Registered Professional Engineer under the
laws of the State of Minnesota.
_____________________________
Todd McLouth, P.E.
Minnesota Registration No. 20383
February 8, 2019
Stormwater Management Plan February 8, 2019
Windsor Ridge – New Hope, MN
WINDSOR RIDGE
New Hope, MN
Stormwater Management Plan
Table of Contents
Page
Number
Introduction .................................................................................................................................. 1
Methodology ................................................................................................................................ 1
Existing Conditions ....................................................................................................................... 1
Proposed Conditions .................................................................................................................... 2
Requirements and Results………………....................................................................................... 2
Storm Sewer Design ..................................................................................................................... 4
Erosion and Sediment Control ..................................................................................................... 4
Best Management Practices ......................................................................................................... 4
Conclusion .................................................................................................................................... 4
Appendices
HydroCAD Report, Existing Conditions - 2, 10 & 100 Year Events ............................ Appendix A
HydroCAD Report, Proposed Conditions - 2, 10 & 100 Year Events .......................... Appendix B
HydroCAD Report, 2.5 Inch Event .............................................................................. Appendix C
MIDS Model – Total P & Total TSS Removal ............................................................. Appendix D
Storm Sewer Pipe Sizing ............................................................................................. Appendix E
Geotechnical Report & Double-Ring Infiltrometer Test (DRI) ..................................... Appendix F
NOAA – Atlas 14 Precipitation Frequency Data ........................................................ Appendix G
Stormwater Management Plan February 8, 2019
Windsor Ridge – New Hope, MN Page 1
Windsor Ridge
New Hope, MN
Stormwater Management Plan
Introduction
This stormwater management plan was created for the WINDSOR RIDGE development project
located along 51st Avenue between Pennsylvania Avenue and Louisiana Ave.
The project consists of a parcel approximately 8.7 acres in size. The project consists of 32
single-family residential lots with typical utilities and storm water treatment. The site is
currently a vacant lot.
Included in this Stormwater Management Plan are calculations for the existing and proposed
conditions.
Methodology
The stormwater calculations were made utilizing the stormwater-modeling program
HydroCAD 10.00. Calculations were performed for the Atlas 14-24-hour 2-year, 10-year, and
100-year rainfall events of 2.87 inches, 4.29 inches, and 7.38 inches respectively.
The Shingle Creek Watershed Management Commission (SCWMC) requires the following:
Rate Control
- Post development runoff rates shall not exceed the existing runoff rates for the 2,
10 and 100 year storm events.
Water Quality
- A permanent pool volume equal to the runoff from a 2.5 inch rainfall event.
- Remove 60% of phosphorus and 85% of total suspended solids.
Volume Abstraction
- 1.0 inches of runoff from the impervious surfaces shall be infiltrated.
Existing Conditions
The existing site is high in elevation with the majority of the site drainage flowing off-site to
the south – a Railroad right-of-way (ROW). There are several existing culverts which drain the
Railroad ROW further south. A small portion of the site drains towards the east to an existing
park (Iron Horse Park) located in the city of Crystal. This drainage eventually ends up in the
Railroad ROW further east.
There are no wetlands within the site.
The attached soil boring logs show the majority of the site consists of clayey sands while the
east and south end consists of poorly graded sands. These soils represent a soil classification
Stormwater Management Plan February 8, 2019
Windsor Ridge – New Hope, MN Page 2
of type A/B. A Double-Ring Infiltrometer (DRI) test was taken within the proposed infiltration
pond and the result was an infiltration rate of 31 inches per hour. The Geotechnical report is
included in the appendix.
Proposed Conditions
The proposed project consists of 32 single-family residential homes typical of a residential
development.
The stormwater runoff from the proposed development will follow the existing drainage area
patterns. The majority of the site drains to the stormwater retention / infiltration ponds which
outlets into the Railroad ROW. Swales and berms prevent runoff from directly flowing onto
the Railroad ROW without prior treatment and rate control. The retention pond, Pond 1,
includes the outlet control structure to the Railroad ROW.
The far westerly area drains to a depression and allowed to infiltrate. This area has an
overflow to the Railroad ROW. A small portion of the northeast corner drains to the east
where it is collected by the existing storm sewer system in 52nd Avenue located in the city of
Crystal. A remnant area drains offsite to the east into Iron Horse Park.
Pond 1 is a NURP/sedimentation/retention pond and is connect to an infiltration basin. An
outlet control structure provides rate control.
The NURP portion of the pond is designed with the following:
- Permanent pool volume equal to the 2.5 inch storm event
- A 10:1 bench at the normal water level
- A skimmer outlet structure
- An emergency overflow
An infiltration pond is proposed to provide runoff volume control. A Double-Ring Infiltrometer
(DRI) test measured the infiltration rate at 31 in/hr. The maximum rate allowed by the MN
Stormwater manual is 8.3 in/hr. This is used in the hydrology model.
Requirements and Results
Rate Control
Rate control is met for the 2, 10 and 100 year storm events by the treatment pond and the
outlet control structure. A summary table is shown below:
STORM EVENT
Existing
Conditions
Model ID
Existing
Runoff Rate
(cfs)
Proposed
Conditions
Model ID
Proposed
Runoff Rate
(cfs) ∆ (cfs)
2 3L 1.2 4L 0.3 -0.9
10 3L 6.0 4L 4.7 -1.3
100 3L 21.6 4L 15.9 -5.7
Stormwater Management Plan February 8, 2019
Windsor Ridge – New Hope, MN Page 3
Water Quality
Water quality is met by the treatment pond. The pond provides a permanent pool volume
equal to the runoff volume from a 2.5 inch rainfall event. A summary is shown below:
STORM EVENT
Proposed
Conditions
Model ID
Developed
Runoff volume
(af)
Pond Dead Storage
Volume (af)
2.5 Inch P1 & P1i 0.45 0.58
2.5 Inch P2 0.04 0.17
The pond provides treatment of phosphorus (P) and total suspended solids (TSS). A MIDS
model is used to determine the percent removals of P and TSS and the results are shown in
Appx. D. A summary of the MIDS model is shown below.
Total impervious cover (acres) 3.19
Total watershed area (acres) 10.17
Site runoff coefficient, Rv 0.40
% Impervious 31%
Development volume retention requirement (cubic feet) 12,738
Volume removed by BMPs (cubic feet) 5,613
Additional volume removal needed to meet requirement (cubic feet) 7,125
Percent volume removed 44.07%
Post-developoment annual volume (acre-ft) 9.39
Annual volume removed by BMPs (acre-ft) 7.67
Percent annual volume removed 81.74%
Post-development annual Particulate P load (lb/yr) 4.21
Annual Particulate load removed by BMPs (lb/yr) 3.86
Post-development annual Dissolved P load (lb/yr) 3.45
Annual Dissolved P load removed by BMPs (lb/yr) 2.82
Percent annual TP removed 87.13%
Post-development annual TSS load (lb/yr) 1,392
Annual TSS load removed by BMPs (lb/yr) 1,270
Percent annual TSS removed 91.22%
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Windsor Ridge – New Hope, MN Page 4
The results show the total P removed is 87%. The total TSS removed is 91%. The pond meets
the requirements for water quality.
Volume Abstraction
Volume abstraction is required to infiltrate the volume of 1.0 inch of runoff from the
impervious surface area.
The 1.0 inch runoff volume = 3.2 ac of new impervious surface X 1.0” = 11,580 cf.
The invert of the outlet is set at an elevation of 884.6 which captures 11,948 cf of runoff
allowing it to infiltrate. Using 8.3 in/hr, the time to infiltrate this volume is 8.8 hours.
11,948 cf / 8.3 in/hr / 1,947 sf infiltration area = 8.8 hrs. ≤ 48 hrs.
The volume abstraction requirement is met.
Storm Sewer Design
The storm sewer is designed for a 10 year storm event. The storm sewer system will collect all
of the runoff from the proposed development.
Erosion and Sediment Control
Erosion and sediment control measures will be constructed as shown on the plans. All areas to
be re-vegetated will be seeded and mulched. Concentrated flow areas will receive an
appropriate erosion control blanket. Silt fence perimeter sediment controls will be placed
prior to any construction activity.
Best Management Practices
Best management practices (BMP’s) will be implemented during construction per the project
Stormwater Pollution Prevention Plan (SWPPP). The final SWPPP will be prepared as part of
the construction documents as required and updated as the development occurs. Proposed
BMP’s will minimize erosion and manage sedimentation as required by the National Pollution
Discharge Elimination System (NPDES). During construction, erosion control measures will
include dust control, silt fencing, inlet protection, a temporary rock construction entrance, bio-
log rolls and a concrete wash-out area. Permanent BMP’s will include a regional treatment
pond, an infiltration basin and turf establishment of all disturbed areas.
Conclusion
The proposed Stormwater Management Plan for the WINDSOR RIDGE development project is
designed to meet City and the Watershed’s storm water requirements. The plan provides an
improved solution for the conveyance of stormwater from this site by maintaining peak runoff
rates from existing conditions and reducing runoff volume offsite.