In logging this EarthCache, you will learn first-hand how the inter-tidal areas of the Minas Basin have been changing, and still are today. By examining evidence onsite, consisting of the remains of a 200-year old dyke and a modern dyke, you will learn about these changes. This cache listing also has information on how the Acadian & Planter settlers built dykes to keep the ocean out of intertidal areas, allowing them to be converted to cropland.
Much of this information is from the book "Sods, Soil, and Spades: The Acadians at Grand Pre and Their Dykeland Legacy" by J. Sherman Bleakney.
To gather the information necessary to log your find, you'll need to visit the posted coordinates, and a waypoint along the way. The waypoint is atop the modern "Wickwire Dyke" which was constructed in the 1960s using modern construction equipment. In contrast, the listed coordinates are at the end of the remains of the "Planter Dyke", constructed by hand in 1806 and abandoned in 1931. This was part of a dyke that used to go further north, and turn east towards Grand-Pré.
Rising wetlands:
Since the planter dyke was built in 1806, the marshland has risen 5-6 feet through the continued accumulation of soil. There are several indications of this continued accumulation:
- As you stand at the listed coordinates, you are on top of what was the Planter Dyke. It's now not much more than a hummock of 1 to 2 feet height.
- If you walk north along the dyke, to the edge of the river, and look down, you will see the boards that would have been at the base of the dyke when it was constructed. The base of the dyke would have been built on top of the marshland in 1806. Based on this evidence and evidence from other sites in the area, Bleakney hypothesizes that the soil is accumulating on top of the marshland at a rate of 3 feet per century.
- Further evidence is part of question #1 below also.
The accumulation described above comes from silt that the tides erodes continually from the shoreline. This silt is carried by the tide, and deposited on the tidal meadows, as a mixture of silt, sand, clay and water. Looking at the water, you'll see it is quite brown, a bit like chocolate milk. This is the silt which will eventually be deposited where you are standing. You will have experienced the mud firsthand on your way to the posted coordinates!
Rising tides:
The tides have been rising at the same rates as the wetlands. There is evidence of the rising tides, although you'll be hard pressed to see some of it onsite:
- Where you're standing now, on the top of the Planter Dyke, is knee-deep in water several times during the year. Government of Canada tidal predictions are available at this link
- In contrast, the nearby Wickwire dyke, built by mechanical excavators in 1960, is 2 metres higher than the abandoned planter dyke.
- The high tide level fluctuates cyclically, from month to month and over the years. Once every 18 years there's an exceptionally high tide. The famous Saxby Gale hit in October 1869 during one such high point. During the Saxby Gale, waves topped the dykes by 3-6 feet and 3,000 acres were flooded. It was 3 years before the cropland was usable again.
How to build a dyke: The marshlands and tides were an ideal combination for the Acadians to perfect the art of building a dyke.
One might think that during dyke construction, the two daily high tides would interrupt the process. But the range from low to high tide varies cyclically, and most high tides did not cover the intertidal area. Tides are influenced by the positions of both the sun and the moon, and the "high tide" can be low enough for up to 3 weeks (a "neap tide" period) that the salt marsh stays dry. This provides a team of workers with sufficient time to construct a dyke, provided they could identify these cycles and time the project.
To build the dyke, Acadians would cut sods from the surrounding grassland, and stack them to make the dyke. The sods were dense with a root matrix, giving them strength to hold together and become a living wall. An experienced "cutter" could use the special dykeland spade to cut, lift and toss a sod in one smooth motion. "Imagine the skill required to step onto a grassy marsh, lean on your spade, and produce hundreds of identical sods... This was done at a rate of one sod every 10 to 15 seconds."
The streams that drained out from what would be the interior farmland needed special attention when building a dyke. A special tunnel with a one-way drain, called an "aboiteau" needed to be constructed. Hollowed out trees or planks were used for the drain. The lower stream bed required additional work to build the wall. Typically the aboiteau area was built first without the regular dyke on either side, allowing higher tides to simply move around the aboiteau as it was being built. Then afterwards the remainder of the dyke could be added and tied in to the aboiteau.
The dyked area was gradually extended to eventually span all the salt marsh between Grand Pre, Wolfville and Long Island. A sequence of dykeland enclosures was built up over time, eventually connecting Long Island to the mainland. Although dykes on the interior became redundant, they were left as a guard against breaches in the outermost dykes. Bleakney comments that "the west dyke was 1.8 miles long... the east dyke was 2.2 miles long... To achieve this the Acadians had built at least 17.5 miles of dykes..."
To log this geocache, send me the answers to the following questions:
- Standing on the modern dyke, compare the level of the salt marsh on the "ocean" side with the level of the farmland on the interior. Which is higher? How much higher?
- What does this difference in height indicate is happening to the salt marsh?
- Walk to the very end of the planter dyke and look down over the edge at the mud. What man-made thing do you see in the mud? This was part of the dyke that you're standing on.
- Name one way in which the construction of modern dykes differs from the methods described above.
- In your "found it" log, include a picture of yourself or a personal object at the posted coordinates (ie at the northern tip of the salt marsh).
If you're interested in learning more, I recommend the book "Sod, Soil, and Spades: The Acadians at Grand Pre and Their Dykeland Legacy" by J. Sherman Bleakney. It provides a lot of interesting information, and was what brought me to this spot originally.