Sunday, January 13, 2008

Battle Point

Also from November. Battle Point is a neat little cuspate spit and lagoon on the western side of Bainbridge Island. The inlet is on the south shore, while the northern limb shows some signs of continued accretion. Note the newer berm in the upper photo. Erosion of the inlet exposes peat from an earlier incarnation of the lagoon and marsh.

Point Monroe

Point Monroe, at the northeastern tip of Bainbridge Island, is a poster child of a developed barrier beach. It looks more like a causeway than the recurved spit that it is. One need only show an aerial photo and say "sea level rise" and everyone gets the point. It is the northernmost end of a larger barrier that begins a mile south and that includes Fay Bainbridge State Park.

Point Monroe was hammered by the back-to-back northerlies of December 1990. I suppose it will be hammered again - much more frequently when sea level is a foot higher.

Ala Spit

After Friday's site visits were postponed, I decided it was time to post a few retrospectives from earlier in the fall. Sadly, I haven't been getting to the beach much the last few months. This is from October 11th, taking the long route back from teaching a Beach Watchers class on Whidbey.

The rock and concrete on the spit suggest a complicated history - like other spits, large and small (Ediz, Semiahmoo, Shaw's Cove), concern about breaching leads to armoring of the narrowest part of the spit, which may only make things worse. Spits are typically most vulnerable near their bases. Unlike the distal ends, where sediment accumulates to form broad berms, these narrow approaches are just transport corridors and are susceptible to big storms and small changes in sediment supply. Most are probably migrating. Armoring just forces the beach to become narrower and prevents overwash from maintaining the backbone of the spit. Pull the rock off the spit, add some gravel to compensate for decades of neglect, and allow the spit to shift north a little bit.

Ala Spit (sometimes called Ben Ure Spit) is probably not helped by the seawall, fill, and rock groin immediately south, which muck up sediment transport and may simply be encouraging growth of a gravelbars at the expense of the current spit.