Channel migration and beach erosion at Popham Beach, Maine
I grew up going to Popham Beach and its wilder neighbor across the outlet of the Morse River, part of the Morse Mountain Conservation Area maintained by Bates College. In late February, 2010, the Morse River became a state-wide news highlight (in the paper and on the radio) after it avulsed at its outlet during two-day storm, breaching a sand spit that been growing eastward for nearly a decade. The farther east the spit extended, the more beach there was on the Morse Mountain side (on the western bank of the river). However, just an outfielder’s throw away on the Popham side, the spit was beginning to haunt officials responsible for the state park, where erosion was threatening to undermine a new set of public toilets.
The 2010 avulsion couldn’t have been better made to order: the severed spit quickly welded onto the Popham shoreline, creating a lovely, wide beach in time for the summer high season, and also saved the toilets.
(What I love about this story is that although the Morse River has avulsed before at its outlet, as any freely meandering river will, its channel migration dynamics were not problematic until the construction of something effectively permanent on what some might describe as a poorly chosen site. Those toilets are a humble but fine example of coastal infrastructure.)
The mood of the Morse River is a regular topic of conversation among my family, especially around the holidays – if I wasn’t staying in the UK for Christmas, I’d be looking forward to a Boxing Day beach walk, en family masse. Still, I realized I’d never opened Google Earth and thumbed through the cataloged images to look at the changes at Popham for myself – so, with thanks to the folks at Google Earth, that’s what I’ve done here. The sequence begins (short of dipping into the Maine State Archives) in 1997. Note that Popham sees a mean tidal range of 2.6 m (approximately 8.5 ft) and these images don’t necessarily capture the same limb of the tide, which makes the beach in a given image appear wider or narrower.
Tidal variablity aside, the four zoomed-in images at the end of the reel show a decade of especially rapid shoreline retreat – over 5 m/yr – immediately east of Popham (note the white arrow in the zoomed-out image from 2013). Riprap – large rocks that harden or “armor” the shoreline in response to erosion – gets installed around the properties in the center of the image. For the sake of contrast, watch the group of houses near the upper right corner of the image. See their paths out to the beach in 2003? Now look at the lengths of those paths as of this past September, when the most recent image was acquired.
PS: Many thanks to Phil Payson for getting me to dig into the imagery.