Maynard Road Stream Restoration and Nitrogen Removal BMP Project

Download or view a printer-friendly version of the presentation:

Background (2.08MB)

Benefits & Issues (1.94MB)

Map (564KB)

Background

§ Town of Cary decides to widen Maynard Road

§ Stantec is retained to design widening of road

§ Road widening will impact 200 linear feet of stream

§ Clean Water Act requires mitigation for impact to stream (stream restoration)

Watershed

§ The watershed (all land that drains to this stream) is very urbanized

§ It includes part of downtown Cary, churches, an elementary school, a shopping center, apartments, and other residential areas

§ Development has increased flows in the stream

§ Increased flows have degraded the stream

Degraded Stream

§ Bank erosion

§ Loss of trees

§ Debris jams

§ Increased sediment load

§ Loss of habitat

§ Reduced water quality

§ Eroding

Stream Restoration

§ Restoration means creating a stable pattern, dimension and profile

§ Stop bank erosion

§ Improve habitat

§ Town hired Stantec to design stream restoration

§ Design was completed in 2005 and was to be built when Maynard was widened

Town Property

§ To mitigate for impacts, the Town needed to restore 300 feet of the degraded stream channel

§ Town decided to restore as much additional stream channel as possible (~2000 feet)

§ Credit from extra 1700 feet will be banked by the Town for future use

Nitrogen Removal

§ In 2005, Town learned that NCEEP had a program to fund Nitrogen removal projects

§ Town applied for and received a grant for $400,000 to install Nitrogen removal Best Management Practices (BMPs) in association with the stream restoration project

§ Town hired Stantec to evaluate options for nitrogen removal including bioretention, detentions ponds, retention ponds, and stormwater wetlands

§ Wetlands represent the best option to remove nitrogen and improve water quality

§ Natural wetlands exist along the stream channel

§ Stormwater wetlands will complement the existing wetlands and increase nitrogen removal in the watershed

Nitrogen Removal Wetlands

§ Wetlands would be designed to intercept runoff flowing through stormwater channels

§ Wetlands retain water and remove nitrogen using natural treatment processes

§ Wetlands would be built in conjunction with the stream restoration and the road widening

§ All wetlands would be located on Town property

Project Benefits

Stream Restoration credits allow the Town to avoid paying an impact fee of $200 per linear foot.

Other benefits:

§ Water quality improvement

§ Reduced flooding

§ Removal of invasive species

§ Bridge stabilization

§ Greenway improvements

§ Sewer stabilization

Project Benefits - Water Quality Improvement

§ Reduce nitrogen

§ Reduce sediment

§ Improve habitat

§ Protect endangered species downstream (i.e., dwarf wedge mussel)

Project Benefits – Reduced Flooding

§ Size of culvert will be increased

§ Capacity of new stream channel will be increased by addition of floodplains

§ Debris jams will be removed

Project Benefits – Removal of Invasive Species

§ The valley has been overrun by a number of invasive species (e.g., multi-flora rose, ivy, privet, Japanese honeysuckle)

§ Invasive species will be removed within project area

Project Benefits – Bridge Stabilization

§ Existing bridge is at risk

§ Will install structures in the stream above and below the bridge to protect it

Project Benefits – Greenway Improvements

§ The existing trail currently has drainage problems

§ Tropical Storm Alberto damaged the trail even more

§ Trail will be rebuilt to a higher standard

§ Some portions of the trail will be relocated to accommodate the nitrogen removal wetlands

Project Benefits – Sewer Stabilization

§ The degrading stream channel has exposed a sewer line and created some risk of a break

§ The sewer line will be stabilized during the construction of the new stream channel

Issues – Tree Removal

§ The project will require the removal of some trees to facilitate construction of the new stream channel and wetlands

§ Trees will also be removed to reduce the risk of flooding and debris jams

§ All trees were surveyed to ensure that trees are preserved wherever possible

§ The trees removed will be used in the stream restoration project

Issues – Mosquitoes

A common misconception is that wetlands cause an increase in mosquito populations. A well functioning wetland will provide habitat for various species that prey on mosquitoes, such as dragonflies. NC State University has done studies on stormwater wetlands and has shown that, if done properly, they will not lead to increased mosquito populations.

Issues – Public Safety

§ The nitrogen removal wetlands will be shallow (about 18 inches)

§ Grading of wetland slopes will be gradual

§ There will be no steep embankments along the stream or wetlands

Questions?

Contact:

Tom Ellis
Town of Cary Engineering Department
P.O. Box 8005
Cary, NC 27512-8005
(919) 469-4333
tom.ellis@townofcary.org