Glendale Creek is typical of many small streams on Puget Sound that drop quickly through a steep-sided ravine before reaching the beach. The topography suggests that there may not have ever been much of an estuary, but it's likely that the stream mouth was originally deflected north by a spit (drift here is unambiguously from south to north). Building on the beach, and the placement of the stream into a pipe, greatly reduced the stream's freedom to wander and the whatever spit there was became history.
The small community of Glendale is built at the mouth of the valley and periodically gets flushed out by a gully washer (Glendale: 2009). It's pretty much like building on an alluvial fan at the mouth of a canyon - location has consequences.
The Whidbey Camano Land Trust has recently acquired property here at the beach, just south of the stream mouth. I don't know what the plans are for the site, but it seems like a wonderful opportunity to reconnect the beach with it's backshore. That won't restore the original stream mouth or the spit, but it provides access to a wonderful spot on the south Whidbey shoreline.