Once and future salt marshes: A tutorial

Fri, 09/27/2019 - 8:00am

Depending on where you start counting, our earth satellite has just finished its year’s travel around the sun; and now, we start a new year with autumn. Some or our favorite summer activities are enhanced and made sublime by fall weather. A walk in October light and cooler air is delightful compared to summer walks in blazing sun and sweat. A September swim in water the same temperature as August waters, seems warmer against the day’s cooler air. And, a walk at Andy’s Way — or any mud flat — is more precious in fall when the Spartina is in seed, when the blue crabs are large and scuttling, when bare feet on the wet sand is soothing, and, when the specter of winter wind, cold and ice is in the offing.

Salt marshes are amazing. They are more than a thing of beauty and a place to walk and observe the wonders found at the edge of sea and land. Salt marshes are a specialized ecosystem of plants and animals adapted to various amounts of marine and fresh water in a landscape that slowly progresses uphill. Salt marshes provide important buffers as they absorb encroaching high water caused by tide, surf, or rising sea levels. Where the topography of the land abutting marshlands – and shorelines in general — is low or gently sloping upwards, the marshes will be able to migrate inland to accommodate encroaching waters. However, where the abutting land to the marsh or shoreline is steep or lined with structures – think roads, houses, bulkheads, seawalls — flooding and erosion are the only processes available for the incoming water; in these cases, salt marshes will drown in place.

Marsh migrations, flooding and erosion — resulting from tidal and storm surges compounded by the rising sea level of our era — will increasingly be a phenomenon to which we must accept, endure, and adapt.

The photo of Andy’s Way (seen above) shows the area at a three foot high tide. Rhode Island’s Coastal Resources Management Council (CRMC) predicts that sea level rise in this area will reach three feet by 2050 (30 years from now!) So, the photo is an illustration of where the sea water will be during low tide in 30 years. Unless the Andy’s Way salt marsh migrates inland, this area may be good for tonging for clams from a skiff in 2050, but October walks on the mudflats will no longer be an option here.

Of course, no one really knows exactly what changes will occur along our island’s shores in the next 30 to 80 years. But glimpses of the possibilities can be seen during high water events such as storm surges, and occasional super high tides. By observing, and documenting, water levels at these times we may get insights into where we humans should work to: accommodate marsh migrations, relocate needed infrastructure, or to plan community growth/retreat.

Get ready for a King Tide, and participate in your future

On Monday, Sept. 30, at about 9:30 a.m., the island will be inundated by one of the highest high tides of the year — a king tide. King tide is loosely defined as a tide that is higher (or lower) than normal because of the effect of the extra pull of the moon on the earth’s oceans during full and new phases. (See sidenote at end.) Taking photos of where high water is during a king tide is an excellent way to peer into the future — and, of course, there is an app for that. The app MyCoast (hosted by CRMC) is free and easy to use, and is a great way we, as community members, can collect data about where, and how high, tidal waters will reach.

By observing these high-water events we may be able to witness potential new areas for salt marsh development, not just trouble spots of damage and loss. And, by participating in the MyCoast project we can help build a data-rich resource upon which local and state-wide planning can occur. As sea level rises, and climate is disrupted with increases of temperature, extreme and changing weather patterns, each of us can participate in understanding and preparing for life in our little places of paradise.

Join me for a MyCoast Tutorial and a walk along the rocky shoreline on Monday, Sept. 30 at 9:30 a.m., at the beach end of West Beach Road. The walk will include practicing with MyCoast (bring a phone or traditional camera if you have one), discussing sea level rise and the effects on our coastline, imagining what change (good and bad) might look like, and developing a plan for how we might all help document the changes we see over the next year. And, of course, we’ll marvel at the quality of autumn light as it reflects off the ocean while spending morning time along a rocky shoreline ecosystem.


I’ll spare you all the science about this, but here are the main points: the sun’s gravitational pull on the earth effects our tides; tides are more greatly affected by the gravitational pull of the moon as it is closer than the sun; the effect of the force is greater during full and new moon phases (because the earth, moon and sun are aligned); and, the moon’s orbit around the earth is in the shape of an ellipse, which means that sometimes the moon is closer to the earth than at other times, and thus has a greater pull on the oceans during those times. So, yes, there are lots of variation in the height and depth of tides depending on the alignment and relative positions of sun, earth, and moon.