A Case Study · 2004. 12. 13. · A Case Study Post-Construction Stormwater Management Workshops NOVEMBER - DECEMBER 2004 A Presentation Nick Vande Hey, P.E. McMAHON ... Ma Manawa

A Case StudyA Case Study

Post-Construction StormwaterManagement Workshops

NOVEMBER - DECEMBER 2004

A Presentation

Nick Nick Vande Vande Hey, P.E.Hey, P.E.McMAHON ASSOCIATES, INC.

Sponsored by:Sponsored by:

...From Planning...From PlanningThrough DesignThrough Design

Prepared by:Prepared by:

Land acquisition: 87.9 acresSite gently slopes from northwestto southeastCurrent land uses:

Agriculture / Pasture 87.2 %Woodland 7.0 %Farm Homestead 4.5 %Rural Residential 1.3 %

Total: 100.0 %

Development Site:

2

Mixed land use: Commercial,Residential, and ParkPublic sanitary sewer and water alongCounty HighwayPark dedication required within portionof woodsDriveway access restrictions alongCounty Highway

Developer’s Concept Plan:

3

Site topography and slopesElevation difference 24 ftAverage slope 0.8%Maximum slope 17%

No remediation sites within 500 ft of siteNo endangered species habitatFEMA 100-year floodplain mapDNR Wisconsin Wetland Inventory map

Initial Site Screening:

4

NRCS Soil Survey Information

Ce Casco L B No >20 >6 ft. >60 in.Ma Manawa SICL C Inc. 0.06-0.2 1-3 ft. >60 in.Nn Nenno L C Inc. 0.6-2.0 1-3 ft. >60 in.Pu Poygan SICL D Yes 0.06-0.2 0-1 ft. >60 in.

Initial Site Screening:

MAPSYMBOL

SOILNAME

USDASURFAC

ETEXTUR

E

HYDROSOIL

GROUPHYDRIC

SOIL

PERMEABILITY@5 FT DEPTH

(IN/HR)

WATERTABLEDEPTH

BEDROCKDEPTH

5

Topographic survey (1 foot contours)Wetland delineationActual FEMA 100-year floodplain limitsNo karst features

Field Verification of Initial Screening:

6

Redevelopment areasPrivate wells within 100 feet of site perimeterNo public wells


7

On-site soil texturesNo bedrock encountered

Field Verification ofInitial Screening:

8

Hydrologic Soil Groups (HSG)On-site surface soil textures determine actual HSGActual HSG limits different than NRCS Soil Survey


9

Depth to Seasonally High GroundwaterField Verification of Initial Screening:

10

Infiltration Exclusions and Exemptions: SoilsIdentifying Optimal Infiltration Areas:

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Post-Construction Storm Water Management Workshops

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Identifying OptimalIdentifying OptimalInfiltration AreasInfiltration Areas

Infiltration Exclusions and Exemptions:Groundwater

Residential areas with less than 3 feet from bottomof infiltration system to high groundwater.Infiltration of roof runoff is not prohibited.

Commercial areas with less than 5 feet from bottomof infiltration system to high groundwater.

Infiltration Exclusions and Exemptions:Groundwater

Residential areas with less than 3 feet from bottomof infiltration system to high groundwater.Infiltration of roof runoff is not prohibited.

Commercial areas with less than 5 feet from bottomof infiltration system to high groundwater.

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Infiltration Exclusions and Exemptions: GroundwaterIdentifying Optimal Infiltration Areas:

13

Design Infiltration RatesIdentifying Optimal Infiltration Areas:

14

Initial Ranking of Potential Infiltration AreasIdentifying Optimal Infiltration Areas:

15


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Local OrdinancesLocal OrdinancesTotal Suspended Solids:

Same as NR 151.12(5)(a)

Peak Discharge:New and redevelopment sitesReduce post-development peak flows to pre-development peak flowsfor 2, 10, and 100-year, 24-hour storms.Maximum pre-development curve number based on “meadow”

Hydrologic Soil Group A B C DRunoff Curve Number 30 58 71 78

Infiltration:Same as NR 151.12(5)(c)

Protective Areas:Same as NR 151.12(5)(d)

Fueling and Vehicle Maintenance Areas:Same as NR 151.12(5)(e)

Total Suspended Solids:Same as NR 151.12(5)(a)

Peak Discharge:New and redevelopment sitesReduce post-development peak flows to pre-development peak flowsfor 2, 10, and 100-year, 24-hour storms.Maximum pre-development curve number based on “meadow”


Infiltration:Same as NR 151.12(5)(c)

Protective Areas:Same as NR 151.12(5)(d)

Fueling and Vehicle Maintenance Areas:Same as NR 151.12(5)(e)

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Southwest Corner of SiteProtective Areas:

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Protective Areas:

18

Preliminary Development Plan:

19

Preliminary Development Plan:

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Final Development PlanFinal Development PlanModifications to Preliminary Development Plan:

Conserve larger wooded areaPreserve permeable soilsReduce imperviousness, particularly within permeable soilsDisconnect residential roof drains (Compared to DNR standard land use files)Benefits of modifications include: Reduced runoff volume, peak flows, TSS load,and required infiltration volume

Modifications to Preliminary Development Plan:Conserve larger wooded areaPreserve permeable soilsReduce imperviousness, particularly within permeable soilsDisconnect residential roof drains (Compared to DNR standard land use files)Benefits of modifications include: Reduced runoff volume, peak flows, TSS load,and required infiltration volume

SOIL TYPE BCN DIFF

SOIL TYPE CCN DIFF

SOIL TYPE DCN DIFF

TR-55 LAND USES

• Meadow 58 71 78• Park Open Space 61 5% 74 4% 80 2%• Residential (1/4 ac) 75 29% 83 17% 87 12%• Commercial 92 59% 94 32% 95 22%

Curve Number Comparison: Post vs. Pre-Development

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Final Development Plan:22

Limits of Land Disturbance:

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InfiltrationInfiltrationResidential Development

Post-development infiltration volumes shall be at least 90%of pre-development infiltration volumesMax. 1 % of project site required for effective infiltration area

Non-Residential DevelopmentPost-development infiltration volumes shall be at least 60%of pre-development infiltration volumesMax. 2 % of project site required for effective infiltration area

Redevelopment areas are exempt from infiltration

Residential DevelopmentPost-development infiltration volumes shall be at least 90%of pre-development infiltration volumesMax. 1 % of project site required for effective infiltration area

Non-Residential DevelopmentPost-development infiltration volumes shall be at least 60%of pre-development infiltration volumesMax. 2 % of project site required for effective infiltration area

Redevelopment areas are exempt from infiltration

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Infiltration:

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InfiltrationInfiltrationSLAMM “Undeveloped” source area for pre-developedPre-development SLAMM results are as follows:SLAMM “Undeveloped” source area for pre-developedPre-development SLAMM results are as follows:

NEWDEVELOPMENT

AREAS ONLY

• Non-Residential• Residential• Residential

Total

AREA(acres)

SLAMMSOILTYPE

AVERAGEANNUAL

RAINFALLVOLUME

(cu.ft.)

RUNOFFVOLUME

(cu.ft.)

INFILTRATIONVOLUME

(cu.ft.)

0.2014.9555.1570.30

SiltSilt

Clay

16,4291,228,0964,530,4025,774,927

54340,610

213,542254,695

15,8861,187,4864,316,8605,520,232

PRE-DEVELOPMENT

26


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InfiltrationInfiltration

Determine minimum required post-development infiltration volumeDetermine minimum required post-development infiltration volume

NEWDEVELOPMENT

AREAS ONLY


Total

AREA(acres)

SLAMMSOILTYPE

PRE-DEVELOPINFILTRATION

VOLUME(cu.ft.)

NR 151INFILTRATION

REQUIRED

MINIMUMREQUIRED

POST-DEVELOP

INFILTRATIONVOLUME

(cu.ft.)

0.2014.9555.1570.30

SiltSilt

Clay

15,8861,187,4864,316,8605,520,232

60%90%90%

9,5321,068,7373,885,1744,963,443

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Post-development SLAMM results are as follows:Post-development SLAMM results are as follows:

NEWDEVELOPMENT

AREAS ONLY


Total

AREA(acres)

SLAMMSOILTYPE

0.2014.9555.1570.30

SiltSilt

Clay

5,9411,060,8913,702,9344,769,766

16,4291,228,0964,530,4025,774,927

10,448167,205827,468

1,005,161

AVERAGEANNUAL

RAINFALLVOLUME

(cu.ft.)

RUNOFFVOLUME

(cu.ft.)

INFILTRATIONVOLUME

(cu.ft.)

POST-DEVELOPMENT

28


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Determine required post-development runoff volume to be infiltrated:Determine required post-development runoff volume to be infiltrated:

NEWDEVELOPMENT

AREAS ONLY


Total

AREA(acres)

SLAMMSOILTYPE

0.2014.9555.1570.30

SiltSilt

Clay

3,5917,846

182,240193,677

9,5321,068,7373,885,1744,963,443

5,9411,060,8913,702,9344,769,766

MINIMUMREQUIRED

(cu.ft.)

PROVIDEDNo BMP’s

(cu.ft.)

REQUIREDFOR BMP’s

(cu.ft.)

POST-DEVELOPMENTINFILTRATION VOLUME

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InfiltrationInfiltrationPreliminary evaluation of infiltration requirement

Runoff volume from silt soils is 177,693 cu.ft.Infiltrate 15,984 cu.ft. or more runoff volume from clay soils to satisfy the193,677 cu.ft. infiltration requirementClay soil designation only represents the uppermost soil texture

Preliminary evaluation of infiltration requirementRunoff volume from silt soils is 177,693 cu.ft.Infiltrate 15,984 cu.ft. or more runoff volume from clay soils to satisfy the193,677 cu.ft. infiltration requirementClay soil designation only represents the uppermost soil texture

NEWDEVELOPMENT

AREAS ONLY


Total

AREA(acres)

SLAMMSOILTYPE

0.2014.9555.1570.30

SiltSilt

Clay

3,5917,846

182,240193,677

10,488167,205827,468

1,005,161

RUNOFFVOLUME

(cu.ft.)

BMPINFILTRATION

VOLUMEREQUIRED

(cu.ft.)

POST-DEVELOPMENT

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Infiltration Considerations:Infiltration Grass Swales (Code 1005):

Highest permeable soil is not at ground surfaceDeveloper dislikes rural streets with culvertsRural streets may have sidewalk challenges

Infiltration Basin (Code 1003):Residential pretreatment: 60% TSS removalHighest permeable soil is not at ground surfaceGroundwater mounding considerations

Bioretention (Code 1004):Engineered soil (3 ft) replaces low permeable soilsBioretention device fits within a residential lotProvides equivalent protection if < 20% fines

Infiltration Considerations:Infiltration Grass Swales (Code 1005):

Highest permeable soil is not at ground surfaceDeveloper dislikes rural streets with culvertsRural streets may have sidewalk challenges

Infiltration Basin (Code 1003):Residential pretreatment: 60% TSS removalHighest permeable soil is not at ground surfaceGroundwater mounding considerations

Bioretention (Code 1004):Engineered soil (3 ft) replaces low permeable soilsBioretention device fits within a residential lotProvides equivalent protection if < 20% fines

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Infiltration ConsiderationsInfiltration:

32

Proposed Bioretention DevicesInfiltration:

33

Proposed Residential Bioretention DevicesInfiltration:

34


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Peak DischargePeak Discharge

Local Ordinance more restrictive than NR 151:New and redeveloped sitesReduce post-development peak flows to pre-development peakflows for the 2, 10, and 100-year, 24-hour stormsMaximum pre-development curve number based on “meadow”


Local Ordinance more restrictive than NR 151:New and redeveloped sitesReduce post-development peak flows to pre-development peakflows for the 2, 10, and 100-year, 24-hour stormsMaximum pre-development curve number based on “meadow”


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Predevelopment Peak FlowsPeak Discharge:

36

Post-development peakflows without any detention

Peak Discharge:

B

37

Post-development peakflows with wet pondsand bioretention

Peak Discharge:

B

AUNCAPTURED

38

Comparison of pre-developmentand post-development peak flows

Peak Discharge:

B

AUNCAPTURED

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Total Suspended Solids (TSS)Total Suspended Solids (TSS)

New Development: Reduce TSS load by 80% minimum ascompared to no runoff management / BMP controls.

Redevelopment: Reduce TSS load by 40% minimum ascompared to no runoff management / BMP controls.

New Development: Reduce TSS load by 80% minimum ascompared to no runoff management / BMP controls.

Redevelopment: Reduce TSS load by 40% minimum ascompared to no runoff management / BMP controls.

40

Total Suspended Solids Removal RequiredTotal Suspended Solids (TSS):

41

Total Suspended Solids Removal ProvidedTotal Suspended Solids (TSS):

WET POND B1

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Documents

A Case Study · 2004. 12. 13. · A Case Study Post-Construction Stormwater Management Workshops NOVEMBER - DECEMBER 2004 A Presentation Nick Vande Hey, P.E. McMAHON ... Ma Manawa