Gar Creek in Huntersville
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Transcript of Gar Creek in Huntersville
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Gar Creek in Huntersville
LID Requirements in Mecklenburg County
What Is The Goal?
Why Is It Necessary?
Where Is It Required?
How Does It Work?
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Town Limits = 38.9 square miles ETJ = 22 square miles Total Area = 60.9 sqaure miles
Huntersville JurisdictionEffective February 2003
Stream Miles = 40
Impaired Stream Miles = 25 @ 63%
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Increased Development Results in Declining Water Increased Development Results in Declining Water Quality ConditionsQuality Conditions
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Storm Water Runoff Pollutants
Bacteria
Sediment
Heavy Metals
Pesticides
Fertilizers
Petroleum Products
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Channel erosion due to storm water runoff volumes and rates.
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McDowell Creek, Huntersville
Mountain Island Lake
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McDowell Creek Water Quality Model
Developed by Tetra Tech, Inc. – Private consulting firm
Objectives of the Modeling Effort:
Quantify the negative impacts
Identify causes
Predict future impacts
Develop solutions
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116.9
205.4
0
50
100
150
200
250
ton
s/ye
ar
Existing FutureTN
75.7 % Increase
Total Nitrogen
Existing Future
10.17
18.93
0
2
4
6
8
10
12
14
16
18
20
ton
s/ye
ar
Existing FutureTP
86.1 % Increase
Total Phosphorus
Existing Future
1.8
13.5
0
2
4
6
8
10
12
14
Tim
es/
yea
r
Existing FutureBankfull Return Interval
650 % Increase
Bank Full Conditions
Existing Future
Modeling Results
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The conventional methods alone do not work effectively.
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To establish storm water management requirements and controls to prevent surface water degradation by controlling discharges of pollutants
as well as runoff volumes and rates.
Goal Established by Elected Officials
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Performance Criteria:
6 Basic Elements Need to be addressed:1. 85% TSS removal.2. Using LID treat the runoff from the first 1 inch of
rainfall.3. Use LID in combination with conventional practices
to treat the difference in runoff from pre versus post conditions for the 2 year 24 hour storm.
4. Any temporary water quality storage pools must drawdown in 48 to 120 hours.
5. Peak storm water runoff rates shall be controlled for development above 12% impervious
6. No one BMP shall receive runoff from an area greater than 5 acres.
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Rain Gardens
Dry Ponds
Wet Ponds
Grassed Swales
LID Conventional
Use a combination of conventional and Low Impact Development (LID) techniques to mimic, to the extent practicable, the natural hydrology of a site by:
• infiltrating,
• storing,
• retaining, and
• detaining
storm water.
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BMPs for Use in Huntersville (Tables 6.1 and 6.2, Pages 48 and 49)
BMP Applicable Zoning Districts(1)
Applicable Performance Criteria
(2)
Design Function(3)
Function(4)(WQ, VC, PC)
Strategic Clearing & Grading U, T, R 3(a) WQ, VC, PC
Reduce Impervious Surfaces U, T, R 3(a) WQ, VC, PC
Bioretention (Rain Garden) U, T, R 3(a), 3(b) Section 4.0 WQ, VC, PC
Infiltration Trench U, T, R 3(a), 3(b) Section 8.0 WQ, VC, PC
Infiltration Swale U, T, R 3(a), 3(b) Section 8.0 WQ, VC, PC
Swales U, T, R 3(a) Section 5.0 WQ, VC
Swales with Outlet Control T, R 3(a), 3(a) Section 5.0 WQ, VC, PC
Vegetative Filter Strips & Buffers U, T, R 3(a) Section 7.0 WQ, PC
Dry Well, Cistern & Rainbarrel U, T, R 3(b) WQ, VC, PC
Porous Paving U, T, R 3(b) WQ, VC
Curb & Gutter Elimination R 3(b) WQ, PC
Rooftop Storage U, T, R 3(b) VC, PC
Wet Pond U, T, R 3(b), 3(d) Section 1.0 WQ, VC, PC
Extended Dry Pond T, R 3(b), 3(d) Section 6.0 VC, PC
Storm Water Wetlands T, R 3(b) Section 2.0 WQ, VC, PC
Sand Filter T, R 3(a) Section 3.0 WQ, VC, PC
(1) Applicable Zoning Districts: These are the Zoning Districts where the BMP can be used including U = Urban; T = Transitional; R = Rural.(2) Applicable Performance Criteria: These are the Performance Criteria Section numbers (see Section 3) that the BMP can be used to satisfy.(3) Design Function: All BMP designs are contained in the N.C. Department of Environment & Natural Resources, Storm Water Best Management Pratices, April 1999(4) Functions: These are the dominate functions that the BMPs perform including WQ = Water Quality; VC = Volume Control, PC = Peak Control.
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Site Data SheetArea (ft2) % of Site Area (ft2) % of Site
Pervious AreasRow Crops
PastureForest
WetlandMeadow
LawnImpervious Areas
Residential & Light IndustrialRooftops
Driveways & Parking LotsOther Impervious Area
RoadSidewalk
Commercial & Heavy IndustrialRooftops
Parking LotOther Impervious Area
RoadSidewalk
Storm Water Management FacilitiesPond/Wetland Surface AreaSwales/Channels/Infiltration
Site Totals: 0 0.0% 0 0.0%
Total Site Impervious Cover1
Impervious Cover within Developed Area2
Existing Land Use Proposed Land UseLand Use/Cover Data
N/AN/A
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BMPsProject Unassigned Drainage Areas (DA) associated with BMP sets.
Areas (ft2) Area (ft2) DA1 DA2 DA3Pervious Areas
Row Crops 0 0Pasture 0 0Forest 0 0
Wetland 0 0Meadow 0 0
Lawn 0 0Impervious Areas
Residential & Light IndustrialRooftops 0 0
Driveways & Parking Lots 0 0Other Impervious Area 0 0
Road 0 0Sidewalk 0 0
Commercial & Heavy IndustrialRooftops 0 0
Parking Lot 0 0Other Impervious Area 0 0
Road 0 0Sidewalk 0 0
Storm Water Management FacilitiesPond/Wetland Surface Area 0 0Swales/Channels/Infiltration 0 0
Total Area 0 0
Proposed Land Use/ Cover Data by DA
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BMPsBMPs Applied to DA DA1 DA2 DA3Wet PondDry PondWetlandSurface Sand FilterBioretentionWater Quality Dry SwaleGrass ChannelsInfiltrationUser-defined BMP (Sequential with other assigned BMPs)
Stream BufferEnter Buffer Width for each DA with Stream Buffer (feet): 50Percent of DA within treatment zone (150' + buffer width) 56.0%
Storage volume for 2 yr, 24 hr storm (acre-ft) 1.376
Net Reductions DA1 DA2 DA3Flow converted to infiltration by BMPs 35.0% 0.0% 5.6%Total Nitrogen 67.8% 25.0% 17.3%Total Phosphorus 80.6% 19.0% 21.5%TSS 93.1% 47.0% 34.6%Fecal Coliform 97.8% 78.0% 2.8%
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Model Output – Pollutant Loading
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Davidson
Goose, Duck & Stevens Creek Watersheds in
Mint Hill
Other Areas of Mecklenburg County where LID is being Considered
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