In New Durham the question isn’t only where the water goes. It’s where you’re allowed to put the pipe. On lots of ten acres or less carved out by subdivisions since 2007, the town’s Water Quality Protection Overlay keeps a vegetated buffer along wetlands, streams and small ponds — 25 feet off most wetlands, 35 off rivers, 75 off the wetlands the town calls locally significant — and digging inside it takes a conditional use permit.
Water leaves New Durham two ways. The north end drains through Merrymeeting Lake and down the Merrymeeting River, under Route 11 and through Merrymeeting Marsh, to Alton Bay and Lake Winnipesaukee. The south end is headwaters — the Cocheco and the Ela — and that water heads for the Piscataqua and the ocean at Portsmouth. A soggy yard on one side of town and a soggy yard on the other drain to different watersheds.
The overlay names the wetlands that carry the widest buffer. Cooper Cedar Woods. The wetland at the headwaters of the Ela. The wetlands along the southwest shores of Chalk Pond and March’s Pond, north of Caverly Road by Shaw’s Pond, along Davis Crossing Road and Old Bay Road, plus Beaver, Hayes, Peter and Jennings Brooks, among others. If your lot touches one of those, the buffer is 75 feet, buildings stay 100 back and septic 125.
Slope makes a buffer grow. Where the ground inside it runs 10 percent or steeper for more than ten feet, the town adds distance — 15 feet at 10 to 20 percent, 35 at 20 to 30, 55 at 30 to 40. Steep and wet is common here, so a buffer that reads 25 feet on paper can be 60 on the ground.
If a wetland or brook crosses your New Durham lot, get the buffer located before you plan any drainage. Where the pipe can end matters more than where it starts.
We find the lines before we look at the problem. Wetland edge, stream, buffer, the slope add-on — then we go see where the wet cellar or the washed-out yard really is. Most of the time the fix lives on the uphill side of the house, well clear of any buffer: an interceptor trench across the slope, perforated pipe in washed stone wrapped in fabric, carried out to daylight in the upland.
Outlets are where people get in trouble. Piping a curtain drain straight down to the brook at the bottom of the lot means trenching through the buffer, and in New Durham that’s a conditional use permit at best. We’d rather end the pipe at a stone level spreader or a small infiltration bed well up from the buffer edge and let the woods handle the last fifty feet. Cheaper, too.
Near Merrymeeting Lake, phosphorus is the word you’ll hear. Building inside the 75-foot waterfront setback takes a stormwater plan showing it won’t raise phosphorus runoff into the lake. Even the state’s own Powder Mill Fish Hatchery below the dam — the largest in New Hampshire — had phosphorus limits written into its federal discharge permit in 2020. Lawn runoff carries the same stuff. Roof water soaks in through soil. It doesn’t get piped to the shore.
Curtain and French drains in New Durham run $2,000–$8,000 depending on length, depth and how far the pipe has to travel to reach daylight outside a buffer. Regrading, swales and drip-edge trenches often come in under that. Culverts run $800 to $1,500 installed. Work that needs a conditional use permit is quoted once the plan is set.
It depends on the resource. Under the Water Quality Protection Overlay it’s 25 feet for most wetlands, seasonal streams and ponds under ten acres, 35 feet for perennial streams and rivers, 50 for vernal pools and 75 for wetlands of local significance. Steep ground inside the buffer adds another 15 to 55 feet.
It applies to lots of ten acres or less created by standard subdivisions first filed after Town Meeting 2007, and to lots and open space in open space conservation subdivisions filed since then. Older lots aren’t free of rules, though. State wetland permits and the shorefront overlay still apply wherever they reach.
Not easily. Trenching through the vegetated buffer is a disturbance the overlay doesn’t allow without a conditional use permit, and any work in the stream or wetland itself needs a state permit. Ending the pipe at a level spreader up in the upland usually solves the same problem without either.
Phosphorus feeds algae, cyanobacteria included, and it rides in on runoff from lawns, driveways and bare soil. New Durham requires a stormwater plan showing no increase in phosphorus runoff before it allows construction inside the 75-foot waterfront setback. Soaking roof and driveway water into the ground keeps most of it out of the lake.
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