Stormwater Management & Green Infrastructure

Going Green: Innovations in Stormwater Management

By Karen Firehock, Green Infrastructure Center, March 2016

The Green Infrastructure Center

creates landscape models to

help communities conserve and

restore their natural assets in

rural and urban areas.

We help communities create

plans and strategies to

conserve or expand their green

infrastructure.

See examples of our work at:

www.gicinc.org

New! A national ‘how-to’

book, with statistics to make

the case for green

infrastructure from

landscapes to sites,

expanded focus on urban

forest conservation, case

examples from other regions

and instructions for building a

model for any state.

http://islandpress.org/book/str

ategic-green-infrastructure-

planning

What is stormwater?

Water generated from storms (by frequency

e.g. 2 year storm, 10 year storm, 50

year storm).

Most systems designed to treat the two year storm.

Excessive stormwater is eroding the soil from these trees

Imperviousness is a problem in developed

areas. One acre of pavement releases 36

times more runoff than a forest.

During a rainfall event of one inch, one

acre of forest will release 750 gallons of

runoff, while a parking lot will release

27,000 gallons (PennState Extension).

This parking lot could be retrofitted so we get less runoff, less flooding, less pollution.

Consequences of high flows = public safety concerns

High stormwater flow can lead to hazards, such as flooding.

A key stormwater solution: think green infrastructure!

But, what is green infrastructure?

At left, a city’s grey infrastructure including buildings and roads.

Classified high-resolution satellite imagery (right) adds a green

infrastructure data layer (trees and other vegetation) .

Origin of Term

“Green

Infrastructure” 1994: Florida coined the term

“Green Infrastructure” in a

report to the governor on land

conservation strategies. It

was intended to reflect the

notion that natural systems

are important components of

our “infrastructure.”

They built a model to find the

best quality green

infrastructure network to

strategically protect it.

When Did Green Infrastructure Definition Expand?2006: EPA begins calling integrated best management practices

(previously referred to as Low Impact Development strategies)

“Green Infrastructure.” This led to confusion!

The key is right order thinking!

1) Protect your natural assets on site and across landscape.

2) Build in the least impactful manner and then,

3) Mitigate your impacts with LID.

So think, first conservation, then mitigation.

Rain gardens Permeable pavers No mow zones

Traditional

DevelopmentGreen Infrastructure

Based-Development

Plan for grey

infrastructure first (roads,

stormwater pipes)

First, assess natural

features and functions

and protect them.

Green spaces in

leftover lands (e.g. steep

slopes and floodplains)

Plan for parks, trails,

habitat connections

before siting buildings.

Work within confines of

parcel = pocket parks,

inner trails, gated

systems

Connect land and water

habitats to region and

across ownerships

Trees – the original green infrastructure!

Trees give us cleaner air, shade,

beauty and stormwater benefits at

a cost that is far cheaper than

engineered systems!

Remember too that the water a

typical street tree can intercept in

its crown, ranges from 760 gallons

to 3000 gallons per tree per year,

depending on species. That means

less flooding!

For example, in Suffolk, Norfolk, Hampton we are considering how much tree canopy do we have now? How much canopy could we add? How much stormwater could be mitigated with trees?

Approaches to stormwater managementusing constructed solutions …

Best -- Utilize smaller scale

biofiltration throughout

development.

Good -- Detention Pond

works in areas where you

have room to maneuver. Better -- Improve pollution

removal by adding wetland

benches and plants to

existing ponds.

“Retrofit”

Source: Encarta Dictionary

to install newly developed parts or devices into a machine or building, that were not available when the machine or building was made

Retrofit with Low Impact Development

Low Impact Development is a design strategy with a goal of maintaining or replicating the pre-development hydrologic regime through the use of design techniques to create a functionally equivalent hydrologic site design.

Source: Low Impact Development

DRAFT Technical Bulletin

Filterra Box

Green

Rooftops

Parking lot biofilter

Downspout filtration

Rain

Barrel

Porous pavers

Urban Impacts = Need for Mitigation Using Low Impact Development

LID methods

Primarily to counter human induced changes to the environment.

Not a license to develop anywhere.

Not No Impact Development!

PLAC 5860/LAR 5280

So why is LID innovative? Includes water quality treatment

too (not just quantity).

Considers and enhances aesthetics.

Often combines natural processes (plant and soil decomposition) with engineered approaches (swales, holding tanks etc.)

Can be fit (retrofit) within small space – even vertically!

Costs less than traditional methods due to less piping and maintenance.

Myth -- Stormwater is only an urban problem.

Oh really? What is happening to these creeks?

Five Basic Steps of LID Design*

1) Conservation – avoid disturbance

2) Minimization of land cover changes

3) Predevelopment Time of Concentration – more time for interaction, filtration

4) Redevelopment curve and runoff volume – mimic predevelopment

5) Pollution prevention – ensure best practices

* Steps from France, Handbook of Water Sensitive Planning and Design, 2002

Lots of hardscape so find alternate ways to infiltrate …

Green roof on part of the Norfolk library here…

Commercial: Water

Storage – Detain and

Hold (temporarily)

Image courtesy of: Arlington CountyWater storage as sculpture …

Residential

Need to Make LID Easy to UseE.g. Fairfax County, Va. Public Facilities Manual List LID Standards:

6-1300 Retention, detention, and LID development facilities

6-1302 Rooftop Storage

6-1303 Percolation Trenches

6-1304 Porous Pervious Pavement

6-1305 Retention and Detention Ponds

6-1306 Maintenance Design Considerations

6-1307 Bioretention Filters and Basins

6-1308 Vegetated Swales

6-1309 Tree Box Filters

6-1310 Vegetated Roofs

6-1311 Reforestation

Example of provided guidance

6-1310.3 Design of Vegetated Roofs.6-1310.3A Extensive vegetated roof systems shallhave a minimum growth media depth of 3 inches and a max growth media depth of 6 inches. Director may approve growth media depths less than 3 inches for systems constructed on existing buildings when necessary because the structural design of the roof is not sufficient to carry thegreater loads. 6-1310.3B Intensive vegetated roof systems shall have a minimum growth media depth of 6 inches. A maximum growth media depth is not specified for intensive vegetated roof systems. Unless needed to accommodate small trees or large shrubs, the growth media depth should not be greater than 12 inches (300 mm). Intensive vegetated roof systems may include subareas with different growthmedia depths to accommodate different types of plants.

As applied to ecosystems, or to an integrated system of people and the

natural environment, resiliency has three defining characteristics:

1) The amount of change the system can undergo and still retain the

same controls on structure and function.

2) The degree to which the system is capable of self organization.

3) The ability to build and increase the capacity for learning and

adaptation.

First identify natural assets and consider how to protect them.

Natural systems are our first line of defense from storm surge and for

infiltrating water. So, look for risks and address gaps – where do we need

more?

Resiliency

Re-building resiliency by restoring

native shorelines in Norfolk.

SLR is a great challenge

Once assets are

mapped, we look at

risks to those assets

and most importantly:

what should we do

about it?

Many ways to look at

risk

• Water impairments

• Runoff/flooding

• Incompatible zoning

• Loss of property and

habitat through sea

level rise

Risk + Opportunity Assessment

Spatial information is

important for addressing

questions such as:• What populations will be most

affected?

• How much green space/urban

tree canopy will be lost, and

can it be replaced in other

areas?

• What types of land uses will be

most affected?

• What is the capacity of

shorelines to retreat naturally?

Sea level rise scenario (VIMS 2100

Accelerated Scenario) shown for

illustrative purposes only.

Add back in natural functions to absorb water – i.d. where coastal habitat is impaired, insufficient,

disconnected… and restore!

Tips for successMake sure you utilize natural features and functions as the first line of defense – restore tree canopy, wetlands, daylight creeks. It’s cheaper and provides multiple benefits!

Reduce problems closest to the source; eliminate excessive pavement first rather than starting with treatment.

Investigate conflicts in your locality’s codes – are you asking for LID while simultaneously requiring more parking?

Establish relationships with suppliers to make it easy to get LID materials (e.g. Luckstone can make a biofilter soil, sedums for green rooftops may be grown at local nursery etc.)

Most of your landscape is likely residential so take a yard-by-yard approach (e.g. Elizabeth River’s River Star Homes).

If using incentives, make sure developers will use them. Ask them!

End…www.gicinc.org