Seawall and Popham Beach Dynamics, Phippsburg, Maine

Introduction

Beach dynamics and sand movement along the shoreline at Popham Beach State Park and Seawall Beach is a continuing saga of extreme shoreline change and dune erosion. Here we look at Seawall Beach, the Morse River, and the large sand spit (bar) connected to Seawall Beach that extends seaward of Popham Beach.

In fall 2008 an enormous beach spit was connected to Seawall Beach reflecting several years of growth and easterly extension. It currently blocks the Morse River from flowing directly south to the sea and has led to severe dune erosion and loss of mature pitch pine trees in the back dune maritime forest at Popham Beach State Park. For more on the historical location of the Morse River and erosion at the park see the previous MGS web page, Tombolo Breach at Popham Beach State Park, Phippsburg, Maine.

Hiking to Seawall Beach to Visit the Morse River

Figure 1

Access to the mouth of the Morse River can be from the east via Popham Beach State Park or from the west via Seawall Beach. In order to see the new beach spit first-hand or to walk out on it when the tide is low, a hike from Route 216 will lead to the beach and the spit (Figure 1).

Seawall Beach is part of the Bates-Morse Mountain Conservation Area and has limited vehicle access. There is a small parking lot 12 miles south of Bath, Maine and 0.8 miles south of the split of routes 216 and 209 in Phippsburg and marked by a street sign labeled Morse Mountain Rd. This parking area is open during daylight hours and provides the starting point for a 2-mile hilly hike through woods and across lowlands adjacent to salt marshes. The conservation area does not allow bicycle access or pets but strollers are permitted. During hunting season it is advisable to wear orange; hunters and hikers share the area. In spring and summer prepare for insects. Note there are no restroom facilities, sources of drinking water, nor trash facilities, so please plan accordingly for a trip that could last two hours or more. For more information about the conservation area contact the Harward Center for Community Partnerships, The Nature Conservancy (Maine Branch) or the Small Point Beach Association.

On the hike to the beach you will follow a wide gravel or asphalt path that winds through the woods (Figure 2), passes a small bedrock cliff (Figure 3), crosses two salt marshes (Figure 4) with views of tidal channels and efforts at salt marsh restoration (Figure 5). Note that the marsh crossings are about at the level of the spring high tide (high salt marsh), so if tide predictions are over 10 feet (which happens only a few times a year) the path may be covered with salt water at the time of high tide. Before reaching the beach it is possible to walk up Morse Mountain on a short side trail for an overlook to see the ocean, barrier dune system, and back-barrier salt marshes of Seawall Beach and the Sprague River (Figure 6). From Morse Mountain it is even possible to see Casco Bay on a clear day. At the end of the main trail, the path crosses through mature back dunes and the frontal dune (Figure 7). The beach is important habitat for piping plovers and least terns and signs at the entrance to the beach will inform visitors of what they look like and how to avoid disturbing them in nesting season in the summer.

Seawall Beach

Seawall Beach is one of Maine's finest beaches. It is very linear and has a natural frontal dune ridge (Figure 8) and no seawalls as the name might suggest. Winter erosion can lead to dune loss and the formation of a vertical drop or scarp that runs along the frontal dune. As you approach the beach on the dune path look to the right (southwest) and note the change in dune elevations that are vegetated with American beachgrass. See if you can see signs of fresh sand washed into the dune from recent ocean storms. This process, called overwash, leads to the dunes building in elevation and being more storm resistant.

Figure 8

Figure 9

The dune scarp that forms in winter can be "repaired" naturally by wind and wave action. Waves can push sand up from the beach during high tides or periods of surf all the way to the toe of the dune. Wind can blow dried beach sand up against the dune scarp and produce what geologists call an eolian ramp (Figure 9). These processes of accumulation on the seaward edge of the dune help repair winter storm damage and also provide sand for beach grass to grow in during the summer. The beach berm or relatively flat sand accumulation in front of the dune also collects seaweed, driftwood, shells, and litter.

A walk along the beach to the east (left from the path entrance) leads to the beach spit and the Morse River. The dune gives way to a bedrock outcrop that rises directly from the beach (Figure 10). At high tide it may be necessary to get around the outcrop either by wading or climbing over its steep slopes. Along the walk you may find stranded lobster traps among other items that have been pushed ashore by surf. Along with driftwood, lobster traps act as sand traps (Figure 11 and Figure 12). At the end of the vegetated sand dune you will reach the beach spit and channel of the Morse River.

Figure 10

Figure 11

Figure 12

Morse River

The Morse River separates Seawall Beach from Popham Beach. In November 2008 the channel was located along its usual course next to a bedrock outcrop behind Seawall Beach. As it made its way to sea the river took a sharp bend to the east and flowed toward Popham Beach (Figure 13). Be cautious on the bank of the river. Sand can be soft and it is possible to slip off the bank and into the river. The Morse River flows out to sea during the ebbing (falling) tide and into the salt marsh on a flooding (rising) tide. At the mid-tide level (either ebb or flood) the currents will be the strongest and also the most dangerous.

A walk along the beach spit to the east and adjacent to the Morse River offers a chance to examine the shape (morphology) of spit accretion. In November 2008 there were several lobate deposits on the landward side of the spit that mark times of sand accumulation and buildup (Figure 14). As you walk farther out on the spit (tide permitting) you will see a general lowering of the sand elevation and a variety of sand ripples on the surface (Figure 15, Figure 16, Figure 17, Figure 18). Compare this to the hummocky and sparsely vegetated axis of the spit that rises above the tides and is affected by wind action as well as waves (Figure 19).

Popham Dune Loss

From the spit it is possible to look across the Morse River and see the loss of dunes caused by the undercutting by the river. As described in March 2008 (Dickson, 2008) the channel has scoured sand and led to shoreline migration into dunes that have existed for more than 50 years. Along Popham Beach State Parks' west beach, numerous trees are falling into the channel and across the beach (Figure 20, Figure 21, Figure 22) and entire trees are carried by the river currents elsewhere along the beach. As of November 2008, the Morse River still had a channel that ebbed easterly across the Fox Island tombolo (Figure 23).

Spit Extension Across the Morse River

Shoreline change along Popham Beach in the last few years has been nothing less than dramatic. Figure 24 shows a vertical air photograph of the Morse River inlet, sand bars, and dunes on both beaches. The extensive loss of vegetated dunes at Popham Beach State Park is shown by a June 2007 shoreline surveyed by the Maine Geological Survey. A November 2008 survey of the extent of the beach spit above a recent tide (approximately 8 feet above mean lower low water) shows how the spit has prograded into the former channel of the Morse River.

Figure 24

Figure 25

A shaded relief map (Figure 25) was generated using high-resolution topographic data (LIDAR) acquired in 2004 by the NOAA Coastal Services Center for the Maine Geological Survey. In this map the Morse River channel shows up as a flat area that is now beneath the beach spit. Easterly growth of the spit has forced the Morse River north and against the beach and dunes at Popham Beach State Park.

Future Change

Over time, the cut bank (outer bend in the channel shown in Figure 13) may erode more of the spit and allow the Morse River to cut a more direct and less sinuous path to the sea. It is hard to predict when this might happen. It may take a period of extremely high tides - and thus strong ebbing tidal currents - or a storm with flooding that covers the back-barrier salt marsh with a surplus of water that wants to exit directly to the sea on a falling tide. In any case, an extreme event may accelerate the natural cycle of channel migration.

When the day comes that the Morse River shifts its channel to a more southerly course, the beach spit will become an isolated and temporary sand bar (or if high enough a true barrier island) that is difficult to reach from either Seawall Beach or Popham Beach. As waves and tides rework the beach system, the bar should migrate ashore and "weld" onto Popham Beach State Park and lead to the end of the chronic erosion of the back dune pitch pine forest for at least a decade. As it does so, the beach at Popham Beach State Park will enlarge and the Fox Island tombolo will be wider and higher allowing better access to the islands.

References

American beachgrass, US Department of Agriculture, Natural Resources Conservation Service, PLANTS Profile.

Bates-Morse Mountain Conservation Area, The Harward Center for Community Partnerships, 161-163 Wood Street, Lewiston, Maine 04240, (207-786-6078)

Least Terns, Maine Department of Inland Fisheries and Wildlife.

Piping Plovers, Maine Department of Inland Fisheries and Wildlife.

Small Point Association, P.O. Box 7205, Portland, Maine, 04112 (207-791-7162).

The Nature Conservancy, Maine Chapter, 14 Main Street, Brunswick, Maine 04011, (207-729-5181).

Related MGS Web Sites

For other MGS coastal geology links visit our Field Localities map.

MGS Virtual Tour of Maine's Coastal Marine Geology (pdf format - 2.1 Mb)

Slovinsky, P.A. and Dickson, S. M., 2006, Impacts of Future Sea Level Rise on the Coastal Floodplain: Maine Geological Survey, Open-File Report 06-14.

Erosion and flood maps - Coastal Erosion Assessment for Maine FIRMs and Map Modernization Plan.

Seawall Beach is part of the Maine Coastal Barrier Resources System.

Bedrock Geology of the Bath 1:100,000 Quadrangle (4.9 Mb PDF file), 2002, 36" x 44" color map. Includes radiometric age dates and photos describing rock types.

Bedrock geology of the Bath 1:100,000 map sheet, coastal Maine, Bulletin 42. Describes stratified rock sequences, intrusive rocks, structural geology, and metamorphism of the Bath 1:100,000 map sheet.

Dickson, S. M., 2008, Tombolo Breach at Popham Beach State Park, Phippsburg, Maine.

Text and photos by Stephen M. Dickson.

Originally published on the web as the November 2008 Site of the Month.

Last updated on April 19, 2012