Sunday, November 29, 2015

Ala Spit

Here's my most recent update from Ala Spit from a visit a week and a half ago.

In 2011, rock was pulled from the neck of the spit and the berm was reshaped, with hopes of restoring both the original spit and the processes that maintained it (see link to previous posts below). But once those processes were restored, they went to work reshaping the spit in ways that weren't exactly planned. A few quick storms eroded through the restored berm, spreading gravel into a broad deposit on the back side and leaving the berm crest low enough that high tides regularly washed over it. Unfortunately, the geometry of the site and the volume of available sediment have been inadequate to allow the berm to rebuild in the intervening years.


Earlier this fall, the County took another swing at it. The groin to the south has been partly dismantled. Essentially, the central portion of the groin was removed, a compromise that restores some sediment movement while also trying to maintain the wider beach that had built up on the southern (updrift) side of the structure. I suspect some of the structure may also have been left simply because a few of the rocks were enormous and would have been very difficult to remove.

The concrete bulkhead that ran from the groin to base of the spit is also gone, except for a short section in front of the parking lot. Whether erosion will be a problem at all in this area remains to be seen, but if nothing else, the remnant wall will provide a reference against which to compare future changes.

The big change is that the berm along the neck has been rebuilt. Right now it's still a little raw and looks more like a gravel causeway than a spit, but hopefully time and vegetation will help the site heal. My guess is that there is more than sufficient height and volume to make overwash unlikely. Ironically, one of the original processes to be restored was overwash, but finding a balance between too much and not enough is difficult.

It's been hard to write about Ala Spit, since there are strong opinions and much at stake. And because the more I watch it, the more I realize I don't understand. I'm one of those folks who thinks if the answer is simple or elegant, it is probably wrong!

Previous posts mentioning Ala Spit - most from Ala, but some from other places, too.

My attraction to Ala Spit has been that it illustrates some of the challenges of restoring dynamic geomorphic environments (not that we shouldn't keep trying). For example, different processes play out at different timescales. High tides and waves can wash over a berm in a single storm. The movement of sediment from updrift (south) occurs over seasons or years.  And significant changes to the shallow bars offshore of the spit may take many decades.

Ala Spit may have been changing rapidly, even in the absence of 20th-century human modifications. The morphology of the spit is probably influenced by the building or shifting of those bars offshore, which influence sediment availability to the spit itself and which modify the wave environment along the base of the spit. And just to complicate things, Skagit Bay is subject to changes in currents as the Skagit Delta presses towards North Whidbey Island and is subject to potential elevation changes related to nearby faults with Holocene activity, both of which would have ramifications for the morphology of Ala Spit over longer time scales.