Stormwater Runoff: 101

• Natural groundcover absorbs, slows and filters rainwater; pavement and rooftops do not.

• Heavier and faster runoff leads to heavier and faster stream flows, eroding sediment from stream banks and beds.

• Runoff collects oil, sediment, other pollutants as it flows over paved surfaces.

Rivanna River TMDL StudyFebruary 11, 2008

Aquatic life impairment: – 11-mile stretch where Rivanna flows around

Charlottesville

– Sedimentation is the most likely cause of the impairment

–Largest source of sediment (44%) is from streambank erosion caused by higher stream flows

Recommendations

Five categories:

1. Amend City Code provisions to reduce impervious surface.

2. Promote on-site infiltration and low impact development features.

3. Limit erosion from construction sites.

4. Update and expand City’s stormwater manual.

5. Explore new initiatives to enhance stream buffers.

Recommendations are cumulative:

individual pieces of a larger picture

1. Amend City Code provisions to reduce impervious surface

• Reduce minimum street widths for small residential streets.

• Reduce size of cul-de-sacs; require landscaped islands in the middle of larger cul-de-sacs.

• Consider reducing driveway widths.• Require 20% of spaces in larger parking

lots be “compact.”

2. Promote on-site infiltration and low-impact development features

• Parking lots:– 10% landscaping (up from 5%)

– Apply to lots of 10 or more spaces (down from 20)

– Landscaped areas designed to filter runoff

• Explore incentives:– more tree canopy

– LID features (green roofs, rainwater harvesting)

• Adopt a tree conservation ordinance.

Add picture of parking lot

3. Limit erosion from construction sites

• Time limits on re-vegetating denuded areas• Augment agreements-in-lieu-of-plans• Lower E&S threshold to 2,500 sf (from 6,000)• Topsoil guidance document

• Additional staff member(s)

Virginia’s re-vegetation regulation:

Permanent or temporary soil stabilization shall be applied to denuded areas within seven days after final grade is reached on any portion of the site.

Temporary soil stabilization shall be applied within seven days to denuded areas that may not be at final grade but will remain dormant for longer than 30 days.

Permanent stabilization shall be applied to areas that are to be left dormant for more than one year.”

4 Va. Admin. Code 50-30-40(1)

4. Update and expand the City’s stormwater guidance manual

• Develop technical guidance on:

– Periodic curb cuts

– Design of parking lot landscaped areas so they can filter some runoff

– Rainwater harvesting, utilization

5. Explore new initiatives to enhance stream buffers

• Increase number of streams protected by buffers (staff exploring this now)

• Work with local groups on education and outreach

• Encourage buffer enhancement efforts:– Provide trees, shrubs for private efforts– Apply for state grants for public efforts

• Buffers along streams in City parks