In a previous post I discussed how it is something of a misconception that many of our swamp rivers in the Carolinas are not actively migrating laterally. The post mentioned several indicators of growth (lateral extension) of fully vegetated point bars: shoaling, recent vegetation colonization, and a younger-to-older vegetation gradient from the water’s edge inward.
I recently paddled the section of the Waccamaw River, S.C. shown below (for those familiar with the area, this is from Red Bluff and Star Bluff upstream). You can see the river’s high sinuosity here, and some oxbows and sloughs indicating past lateral channel changes. However, except at the left side of the photo at Star Bluff, you don’t see any sandy channel-margin or point bars, suggesting lateral stability.
Portion of the Waccamaw River in Horry County, S.C. Flow is toward the left; area shown is roughly 1.5 X 2 km (Google EarthTM image). Note: Highway 31E shown is Old Highway 31, not the Carolina Bays Parkway highway 31.
On the river, however, it’s a different story. The indicators of point bar accretion mentioned above are present to varying extents on most bends, which also have indicators of bank erosion (erosion scarps, undercut trees, exposed roots) on the outer bend. Point bar growth plus cutbank erosion equals lateral migration.
At least two generations of recent cypress trees on a bend interior and other recent vegetation, with older trees further in.
It was particularly encouraging to see new bald cypress (Taxodium distichum) recruitment. The growing point bars potentially offer just the right conditions—exposed to sunlight, wet, and a good spot for the water-dispersed cypress seeds to land. Even better is that many of the bars show several generations of new cypress, indicating that the recruitment is, at least in the recent past, ongoing.
Recently established cypress on point bars.
Several “recruiting classes” of young cypress.
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