Stormwater Management

We are the Stormwater Experts

HW is recognized as one of the most experienced stormwater management design, assessment, planning, policy, and training consultants in New England. Our philosophy is to mimic the natural hydrologic water balance as we design systems that are easy to construct and maintain. Our designs seek to enhance property values and improve aesthetic appeal using natural systems to meet stormwater management objectives and regulatory requirements. We have developed stormwater design manuals and Low Impact Development guidelines nationally and in the Pacific Islands.

What is the problem with stormwater runoff?

When it rains, stormwater runoff picks up oil, excess fertilizer and other pollutants from hard surfaces and carries them via storm drains to our beaches, ponds, and even to groundwater. Stormwater can be a significant source of pollution to your local waters. Stormwater management refers to methods used to collect, clean, and infiltrate runoff to prevent pollution and flooding problems.

How can you help?

Stormwater from typical residential lots flows quickly from roof to driveway to street, picking up pollutants. You can break the impervious cycle by adding rain barrels (photo), building rain gardens (photo), or by planning more native trees and shrubs in your yard.

How do you build a rain garden?

Rain gardens are landscaped depressions designed to absorb stormwater runoff from rooftops, driveways, roads, parking lots, and compacted lawn areas. This runoff can carry pollutants, cause flooding and erosion, damage infrastructure, and affect aquatic ecosystems. Rain gardens use soils and plants to filter pollutants, promote recharge to groundwater, and encourage evapotranspiration. Rain gardens are NOT wet features; they should be dry less than 24 hours after a rain event.

Site Selection

Walk your property
Determine existing flow paths
Avoid wet areas
Maintain setbacks from structures, trees, and septic systems
Find flat areas for easiest installation

Design

Estimate impervious areas draining to your rain garden (rooftops, driveways, patios, etc.)
Size rain garden to hold 1 inch of rain (P=o.o8 ft) Use equation below or Table 1 for reference
Typical rain gardens are 6 inches deep (D=0.5 ft) – go shallower for clayey soils
Use the UCONN Rain Garden App to help you!

Installation

Call Town to determine if you need a permit and call Dig Safe before you dig
Mark out footprint of garden with string or spray paint
Dig to desired ponding depth plus the depth of mulch and any soil amendments
Make sure garden is level
Install inlets and overflows
Plant and mulch

Maintenance

Weed and prune
Stabilize eroding slopes and inlets
Amend soils if garden stays wet
View Hingham Rain Garden Video

2010 Rhode Island Stormwater Design Manual and Municipal LID Site Planning and Design Handbook
CNMI and Guam Stormwater Management Criteria and Guidance Manual
Roadway Drainage Improvements and Stormwater Treatment
Plymouth, MA
Stormwater Design, Billington Street Park, Plymouth, MA
Assessment and Design of Stormwater Management Measures at Bare Hill Pond, Harvard, MA
Stormwater Master Plan, Retrofits, Wetland Restoration, and Flood Management for Peabody, MA

Contact Rich Claytor, PE, LEED AP, Principal Engineer, at rclaytor@horsleywitten.com for more information about our stormwater management services.