NRWA organized a tour of the University of New Hampshire’s Stormwater Center

Protecting our Water through Stormwater Management and Low Impact Development

In the 1960’s, the Nashua River, along with many other rivers and streams in the United States, was overwhelmed by industrial pollutants and human wastewater that was directly discharged to the rivers via pipes. The Clean Water Act and other federal environmental laws now prohibit such direct discharges, or point source pollution. Today the water quality in our rivers and streams is threatened most by non-point source pollution, a pollution source which cannot be traced back to a single source such as a pipe. A major source of non-point source pollution is stormwater runoff. Stormwater runoff includes precipitation running off hard surfaces such as roads and parking lots carrying pollutants like road salt, oil, greases, and lubricants. It also includes water running off cleared lands with exposed soils enabling erosion, which allows bacteria and soil particles into our waterways. Older municipal storm drainage systems may allow runoff to be discharged into water bodies without proper wastewater treatment. All of these forms of untreated stormwater runoff threaten our water quality and negatively impact aquatic ecosystems and recreation, such as boating and swimming.

Siltation of streambed caused be erosion from storm runoff - Photo from Townsend Conservation CommissionStormwater Management and Low Impact Development are two means of controlling runoff through good site planning and creation of systems to slow runoff thus preventing non-point source pollution from reaching our rivers and streams. NRWA has been actively assisting our communities with stormwater management and promoting low impact development.

With grant funding provided by the ENVIRON Foundation, the NRWA prepared An Introduction to Water Resource Protection in Massachusetts and New Hampshire. This introductory guide to protecting water resources includes chapters on wetland protection, river and shoreland protection, stormwater management, low-impact development, aquifer and wellhead protection, erosion control and the protection of steep slopes. These are the most important water resource related topics that Conservation Commissioners and Planning Board members should be aware of in reviewing development proposals and in appraising the effectiveness of their zoning bylaws and regulations. The guide complements our work with municipal boards to develop bylaws and regulations that are in keeping with the latest practices to manage runoff.

Our water monitoring program helps to identify river stretches that are being negatively impacted by runoff. As part of our work to track sources of bacterial contamination, NRWA organized volunteers in Fitchburg to stencil storm drains to alert communities that what goes into the storm drain flows to the river. Our Monoosnoc Brook Greenway Project has worked with Leominster schools to teach children about non-point source pollution and help them to create rain gardens on school properties. We’re also partnering with the Massachusetts Watershed Coalition in its Billion Gallons per Year Initiative which has a goal of cleansing a billion gallons of stormwater before it reaches our local waterways.

Our adult education programs offer presentations on sustainable landscaping and creation of rain gardens, while our professional workshops help to inform developers, engineers, and municipal boards about topics like the NH Shoreland Protection Act and new techniques in erosion and sediment control.

More on Stormwater Management

Stormwater is worsened by hardened or impervious surfaces, which prevent runoff from soaking into the ground (infiltration) or being taken up by plants. In fact, several studies, such as that conducted by the Center for Watershed Protection, show that the health of a stream or water body is directly proportional to the amount of impervious surfaces in its contributing watershed. When the percentage of impervious cover is less than or equal to 10% of the watershed, stream quality is generally safeguarded. When the percentage of impervious surfaces increases to 10 – 25%, the ecosystem functions of streams are increasingly impacted.

Stream banks often show more erosion due to the more widely fluctuating water levels after storm events, and biological diversity begins to decrease. When the percentage of impervious surfaces increases to more than 25%, the stream is severely impacted and may become non-supportive of native plant and animal species. Such streams are often classified as urban streams, and are in essence drainage channels more than natural streams.

Source: The Center for Watershed Protection

The United States Environmental Protection Agency (USEPA) developed an approach to addressing non-point source pollution called the National Pollutant Discharge Elimination System. Under Phase I of this program, which was enacted in 1990, stormwater discharges into medium to large municipal storm sewer systems were addressed.

These were defined as communities serving a population of at least 100,000 people, as well as stormwater discharges from eleven categories of industrial activities. Construction activities disturbing five or more acres of land are one category of such industrial activity.

In 2003, the USEPA published the standards for Phase II of their stormwater program. This program is aimed at municipal separate storm sewer systems, or ‘MS4’s’ for short. It covers all urbanized areas as identified in the 2000 US Census.

Even when a small town is not subject to the USEPA’s Phase II stormwater program, choosing to address stormwater in a comprehensive manner is one of the best steps a town can take to safeguard its water resources. Small towns can adopt bylaws / ordinances and accompanying regulations addressing stormwater runoff from construction sites and from illicit discharges.

As previously mentioned, most new construction activities require removal of vegetation and moving dirt around a site. Doing so exposes soil that was previously held in place by vegetation to the erosive effects of rainwater and dispersal by wind. In order to minimize such effects, practices can be adopted that minimize the amount of soil exposed at any one time and that prevent soil particles and other pollutants from leaving the site in runoff. Such practices can be spelled out in bylaws, ordinances, and regulations.

Typically, such regulatory provisions apply to construction activities above a certain threshold, such as a half acre or acre of land disturbance. Some of these regulatory approaches also place limits on the amount of impervious surfaces that can be created, either as a percentage of total lot area or a maximum amount of square footage. The environmental agencies of both Massachusetts and New Hampshire have developed model stormwater bylaws, ordinances and regulations that address the impacts of construction activities.

Illicit discharges refer to unpermitted or illegal discharges of stormwater or wastes into a sewer, drainage system or water bodies such as streams, rivers, lakes and ponds. The sources of illicit discharges are many and include but are not limited to industrial discharges and untreated sewage. Illicit discharge bylaws / ordinances and regulations usually require an agent of the town to be on the lookout for such discharges. In most cases this is an employee of the local Department of Public Works or the Highway Department.

Most illicit discharge bylaws / ordinances exempt residential land-uses from regulation, including the washing of individual cars, waterline flushing, discharges from lawn irrigation and water from foundation drains and sump pumps. Though residential uses such as those listed above are often exempt from formal regulation, homeowners and renters can still follow common sense best management practices in undertaking such activities.

More on Low-Impact Development

Low Impact Development (LID) is a term that has been applied to several development practices that minimize human impacts to the environment at the site and local level. LID can refer to everything from open space (cluster) style development to small scale ‘green’ stormwater systems. The term LID most often refers to practices that reduce both the amount and impacts of stormwater runoff. LID often first seeks to minimize the amount of impervious surfaces being created, because, as was seen in the stormwater discussion, the amount of impervious surfaces is directly correlated with water quality. LID also seeks to treat stormwater as close to its source as possible, in contrast to standard stormwater practices that often discharge stormwater far from where it originates.

The Massachusetts Coastal Smart Growth program of the Executive Office of Energy and Environmental Affairs (EOEEA) describes the benefits of LID as follows: “In conventional sprawl development, destruction of natural features and introduction of large impervious surfaces reduces infiltration of water into the ground and necessitates large structural stormwater controls such as catch basins, pipes and detention ponds. LID, in contrast, seeks to preserve natural features and relies on thoughtful site planning and the use of a broad range of design techniques, such as clustering, permeable paving, and bioretention to reduce the level of impervious cover and address the quantity and quality of stormwater drainage. Natural drainage pathways and open space are preserved, and the overall impact from development is significantly reduced.” The Practice of Low Impact Development 

Rain garden bio-retention system plan and elevation views - Graphic by Stella LensingAt the site development level, LID typically consists of a series of small-scale stormwater best management practices that preserve and work with the natural features of the land as opposed to large-scale conventional methods of collecting, conveying, and piping away runoff such as large detention basins. LID attempts to mimic the natural flow of water (hydrology) on a site, and as such seeks to allow as much rainwater falling on a site to recharge the groundwater in the same location. Prior to widespread adoption of LID, best management practices often consisted of collecting the stormwater from a wide area and recharging it either far from where it was collected or in a different drainage basin altogether. This practice altered the natural drainage patterns and water balance of many locations, and often resulted in the depletion of local aquifers. Therefore, LID can be thought of as smaller scale, decentralized and predominantly vegetation-based stormwater management techniques that seek to mimic the natural flow of water on and underneath a site or area.

Typical LID stormwater practices include rain gardens (otherwise called ‘bioretention’), which use specific plant materials and soils to handle and treat stormwater, shallow road side swales, green infiltration strips within commercial parking lots, and porous pavement.

LID has been demonstrated to be economical, effective, flexible and attractive. Like well designed stormwater management systems, LID can reduce peak flows during flooding, remove sediments and pollutants from stormwater, provide health protection by removing bacteria, and improve property values due to the attractiveness of techniques such as rain gardens.

For more information about Stormwater Management and Low Impact Development, please contact Mark Archambault, NRWA Smart Growth Circuit Rider, at (978) 448-0299, or This email address is being protected from spambots. You need JavaScript enabled to view it. .

Stormwater Management and LID Resources

NRWA—An Introduction to Water Resource Protection in Massachusetts and New Hampshire 

Massachusetts Stormwater Handbook

New Hampshire Stormwater Manual (available online and in hard copy)

Innovative Land Use Planning Techniques: A Handbook for Sustainable Development 

Stormwater Magazine, Forester Media, Inc., 2946 De La Vina Street, Santa Barbara, CA 93105

Organizations and their websites: