Urban Planning Design Considerations for Better Water Quality, Bill Hunt NC State University

Designing to Protect Water Quality

Belle Hall Study: Sprawl

Belle Hall Study: Cluster

Belle Hall Study: Results

Impacts are related to more than just imperviousness . . . We need to try and maintain

watershed hydrology

Surface Hydrology Basics

Surface Hydrology by the Numbers

Source: Center for Watershed Protection, 1996

Parameter Parking Lot MeadowCurve Number 98 58

Runoff Coefficient 0.95 0.06Time of Concentration (minutes) 4.8 14.4

Peak: 2 yr, 24 hr., CFS 4.3 0.4Volume, 1”, CFT 3450 218

Velocity, 2 yr, FT/Sec 8 1.8

Change1.6 Times More15 Times More3 Times Less

10 Times Higher15 Times More4 Times Faster

Effects on Streamflow

Flood Plain Effects

Carpenter Village

Project Partners:WW Partners Ferrell Land Dev Co.Town of CaryNC Cooperative Ext.

Funding Agencies:NC DENR - DWQ 319NC DENR - DLQ

Monitoring Design

Below

Treatment Basin

Above

Control Basin

Below

Carpenter Village

Annual Loads at Carpenter


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Loa

d (

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Clearing Building

TPTNNO3NH3



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Loa

d (

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Clearing Building

TSS

Rainfall vs. Runoff

Rainfall vs Runoff

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Ru

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fall

Clearing Building Wooded

Runoff

Cooperators and Participants NCSU School of Design Extension ProgramsDesign Research LaboratoryNCSU Water Quality Group NC Dept of Health, Shellfish Sanitation Program Duke Marine Laboratory UNC Sea Grant NCDENR Division of Water Quality 319 ProgramWetland Restoration Program Clean Water Management Trust FundCarteret Craven Electric CooperativeJumping Run Creek Watershed Citizens

Jumping Run Creek

Facts:1)Shellfish closures occurring since 1979.

2) Imperviousness less than 5%.3) Water moving through the system to shellfish bed within hours.

4) Bacterial loading has increased steadily through the years, while rainfall has stayed consistent.

J1 J2 J4 HY J1 J2 J4 HY J1 J2 J4 HY0

50

100

150

Lo

ad (

kg)

Nonstorm

Storm

Loads from 9/5/99-6/5/00

NH3 NO2+3 PO4

J1 J2 J4 HY

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oad

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Nonstorm Storm

Loads from 9/5/99-6/5/00

J1 J2 J4 HY0

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30F

ec

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Nonstorm Storm

Loads for 9/5/99-6/5/2000

Conclusions

*Impervious area not adequate indicator of water quality threat.

*Strategies to mitigate developmentneed to address hydrologic alterations.

*Bacterial source, not just location, needs to be known to properly manage.

Can Design and Planning Help?

• Competing Values, Needs, and Interests.

Planning where development occurs really can matter

• Wetlands• Headwater Streams• Link Open Space• Functioning Plant Communities• High Quality Waters• Recharge Areas• Buffers Zones

Need to plan and design development on a watershed basis

• Reliance on end-of-pipe BMP technology will not achieve the 30% reduction standard for Nitrogen.

• Development based on imperviousness alone can encourage sprawl.

• New urban scenarios while providing opportunities to implement a variety of urban land use and sensitive area protection features are high density and can be high impact.

• Source reduction approaches need to be assessed using watershed - based planning and design techniques to get the right uses in the right place.

Reduce Impervious Area:Reduce Road Widths -- Use one way streets, pull-off zones, back

alleyways for utility infrastructure and parking, alternative materials.

Reduce Parking Area -- Angled parking, narrower slots, lower allocation.

Share Driveways -- Put more houses on each drive access. Reduce Paved Sidewalk Area -- Use one side only and alternative

materials.

Contain Stormwater On-SiteUse Inverted Streets as Stormwater Collectors -- Direct to bio-filters.Invert Parking Islands to Collect Water.Direct Runoff from house gutters onto pervious areas.Reduce use of street curbing -- Use grassed or vegetative swales. Use Bioretention Areas and Rain GardensUse Green Building Techniques

Site Design Strategies

Site Design Strategies

Incorporate wetlands, bioretention areas, buffers, open space into site plan.

Share Driveways -- Put more buildings / houses on each drive access.Direct Runoff from house gutters onto pervious areas.Use on-site bioretention.Minimize footprint--use taller buildings.Collect rainwater and reuse.Use pervious materials whenever possible.

Structures-use Green Building Techniques

Carpenter Village

BuffersClusteredNarrow / Short StreetsIntegrated Open SpaceIntegrated InfrastructureAlleyway AccessVarying densityIntegrated land usesBioretention

Bioretention Case Study - Carpenter Village

• Work with Developers and Town to identify suitable locations.– Ideal -- low area, good soils, water gathering

slope form, dispersed in the watershed, part of city infrastructure.

– Reality -- got existing open space, high grades, poor soils, only two locations in the watershed, located on private property (Developers responsibility).

Case Study - Carpenter Village

• Worked with site engineers and Town staff to redesign stormwater infrastructure, streets, sidewalks, curbs.– Removed 17 storm drain inlets.

• Two new inlets, hooked to stormwater infrastructure, with proper top and bottom elevation installed in location designated for bioretention.

– Streets redesigned to direct water to swales and inyo bioretention.

• Road Grades• Sidewalk Contiguity• Flat curbs

Case Study- Carpenter Village





• Rainwater Harvesting - the collection and reuse of rainwater for non-potable applications. – Reduction in storm water runoff.– Increased opportunities for re-infiltration.– Conserve potable water.– Save money.

Case Study- Residential Demonstration





• If linked to city water and irrigation system (which increases ease of use).– Requires programmable timer.– Labeled non-potable lines.

• If not, only normal plumbing and electrical codes apply.


• Rain Garden as part of the landscape– Locate in low point of the landscape.– Grade remainder of landscape to drain to rain

garden.– Use simple plastic inlet system.– Provide overflow outlet.– Plant with facultative vegetation.







Conclusions:•Effective solutions need a “Toolbox” approach using watershed

based planning, low impact design, and green building implementation techniques.

•Wetlands and riparian buffers are essential for habitat and water quality.

•Recharge rates must be addressed by capturing storm water utilizing infiltration techniques, reapplication, and the preservation of recharge areas, open space.

Water quality protection can happen when hydrologic functionality of the watershed is maintained, pollutant load (including storm hydrology) is minimized.

More Conclusions!

• Positive results can be achieved when there cooperation between towns to develop management strategies on a watershed basis.

• Within that context, the good development work can be done if designed using multi-disciplinary teams that include architects, landscape architects, biologists, soil scientists, ecologists, botanists, and, yes, even engineers.

Environment

Urban Planning Design Considerations for Better Water Quality, Bill Hunt NC State University