Every year since 2013 I've been able to get out and collect shoreline profile data on Dungeness Spit, along roughly 35 cross-shore oriented transect lines spread out evenly along the length of the spit:
Dungeness Spit is an awesome place to study the dynamics of spit morphology - its long and largely un-modified, with un-modified bluffs to the west that presumably supply sediment for its on-going growth. And grow it has. Schwartz et al. (1987) estimated an average annual rate of progradation of the spit of 4.4. m/yr, based on an analysis of 4 data-sets (either survey maps or aerial photos) collected between 1855 and 1985. I walked into this effort thinking that what I would learn about spit progradation would be how much that average rate of positive growth varied annually. Indeed, after my first year of surveying (2013) I could see that the end of the spit grew by roughly 5 meters or so based on a comparison to an aerial LiDAR dataset collected in 2012:
|Intertidal profile data along a transect bisecting the very tip of Dungeness Spit for 2012, 2013 and 2014. 2012 data are from aerial LiDAR, 2013 and 2014 are from topographic GNSS surveys.|
Exactly as expected. Since then, though...things have been a little different, with an average annualized erosion rate on the end of the spit of roughly 8 meters/yr. That is ~25 feet per year of erosion on average:
Same location and data as are shown above, but for 2013-2020, all GNSS surveys.
Its worth noting that this erosion at the very end of the spit is NOT representative of the spit as a whole. Largely the rest of the spit, especially the long skinny "strand" connected to land, is astonishingly stable. I started out this study hypothesizing that I might see a very slow rate of migration of this part of the spit, associated with storm-driven overwash. But I don't. Year after year the beach and crest are in an almost identical position despite being regularly battered in the winter:
|GNSS survey-based profile data along a transect at roughly mile 2.5 on Dungeness Spit. |
Any other ideas out there?