Fencing near the Wissahickon, Sandy Run and Tookany: floodplains, Ida and what’s allowed

How high do these creeks actually get?

The Wissahickon watershed covers about 64 square miles. Its headwaters are in the Lansdale and Montgomery Township area, and it takes in North Wales, Ambler, Upper Dublin, Whitemarsh and about a dozen other municipalities before the creek reaches Philadelphia. The USGS gauge at Fort Washington State Park (01473900) is the number everyone along the creek watches. The creek leaves its banks at about 12 ft on that gauge, and roads start flooding at 12.9 ft.

Wissahickon Trails, reporting the USGS Fort Washington gauge.

County officials put Ida’s rainfall at 8.25 in on average across Montgomery County. On that kind of day a backyard fence near the creek isn’t a privacy screen. It’s something in the current.

Sandy Run

Sandy Run rises in Dresher and Roslyn and runs about 6 miles through Abington, Upper Dublin, Springfield and Whitemarsh before joining the Wissahickon at Fort Washington State Park. After Ida, Upper Dublin’s township manager credited two dams built on Sandy Run about eight years earlier with likely preventing significant property loss. Downstream, Fort Washington Office Park is low enough to need vehicle rescues in floods; a $500,000 state grant in 2022 paid to replace the Bodenstein Channel culvert under Commerce Drive, which drains to Sandy Run.

Tookany Creek

Tookany Creek flows through Cheltenham into Philadelphia, and the township has a long history of flooding along it. A 2015 Army Corps of Engineers report blamed urbanization for more runoff and less creek capacity. Some Elkins Park residents built stone walls after repeated floods.

Can I put a fence in the floodplain? Township by township

Floodplain rules are written into each municipality’s zoning code, and they differ. Here is what we found for the creekside municipalities we serve:

Checked October 2026 from the codes listed under Sources. Floodplain maps and ordinances change; the zoning officer decides whether your lot is in the district.

Two practical points follow from that table. First, being near a creek isn’t the same as being in the floodplain district. The district boundary comes from the township’s flood maps, and the zoning officer can tell you whether your lot is in it. Second, swale and stormwater rules reach well beyond the creeks. In Cheltenham, Upper Moreland and Montgomery Township, a fence that blocks the drainage swale behind a row of houses can be a violation even if the nearest creek is half a mile away.

Lower Gwynedd’s 20 ft stream buffer

Lower Gwynedd deserves its own note because its larger, wooded lots along the Wissahickon and its tributaries often have a stream running through them. The township bars removing trees or vegetation within 20 ft of a stream bank, and work within 50 ft of the top of bank needs a DEP permit. Clearing brush to run a fence line down to the water is exactly what that rule stops. If the fence has to cross the property, we plan it to stay out of the buffer and work with the existing tree line.

If a fence is allowed near water, what kind?

Where the township does allow a fence in a flood-prone area, or where your yard sits just above the line and still takes water in big storms, the design should let water through instead of holding it back.

• Open styles. Split rail, post-and-rail and aluminum picket fences pass floodwater and give debris fewer places to snag. A solid board or vinyl privacy fence acts like a dam: leaves, branches and trash pile against it, the water pushes harder, and posts fail.
• Run it with the flow, not across it. A fence parallel to the creek catches less than one strung across the low point of the yard.
• Keep the bottom open. A gap under the fence lets sheet flow pass during ordinary storms.
• Plan for repair. Near water, choose a fence you can repair in sections. Rails and aluminum panels can be replaced one bay at a time.

The soil matters too. A post that sits in saturated ground for days loses its grip, especially in the clay and shale soils on the north side of our area. Concrete footings that are crowned at the top to shed water, set to at least the 36 in frost benchmark Montgomery Township uses for footings, hold up better than shallow posts.

A checklist for creekside yards

1. Ask the zoning office whether your lot is in the floodplain, floodway or a riparian overlay.
2. Find the swales and easements on your plot plan or deed; Towamencin, Cheltenham and Upper Moreland all restrict fences in them.
3. Walk the yard after a heavy rain and note where water actually runs.
4. Choose an open fence style if any part of the line crosses a low spot.
5. Leave the stream-bank vegetation alone, especially in Lower Gwynedd.
6. Call PA One Call (811) at least 3 business days before digging. Creekside yards often have sewer and storm lines.

Creekside lots are where we most want to see the yard in person before quoting. Bring up the creek when you book the free estimate and we’ll check the township’s floodplain rules for your address first.

Common questions