Ringing in the New Year with NCOS Rainstorms

Tue, 01/10/2023 - 09:36 -- jeremiahbender

The intermittently tidal nature of the NCOS wetland system has been on full display during the past two weeks. For most of the year, there is a sandbar at the beach that blocks the connection between Devereux Slough and the ocean. This sandbar is breached and partially washed away when water levels in the slough exceed the height of the sandbar that sits at about 9.5 feet above sea level. When the breach occurs, the system becomes tidal until the sandbar is rebuilt by wave action depositing sand on the beach. The breaching of the sandbar results in dramatically changing water levels as water rushes out of the wetland system into the ocean, creating a widening channel at the breach site, as seen in the photos below.

Devereux Slough breach following the rain on New Year's Eve Day. Photo by Ann Bishop, taken on 1/01/23.

The storm complex that started on December 31 deposited 1.74 inches of rainfall on the Devereux Slough watershed which led to a breach of the sand bar at 11:30 pm on new year's eve: out with the old and in with the new. The slough was tidal for several days until large waves eroded the Dunes at Sand's beach significantly and redeposited sand in the recently opened mouth, which led to water being impounded up to 7.8 ft elevation (about 3.5 feet deep at Venoco bridge). But not for long!

The sand berm at the mouth of Devereux Slough rapidly reformed to an elevation of 7.8 feet during heavy surf. Image taken 1/06/23.

Yet another heavy storm system on January 9-10 deposited 4.74 inches of rain, which breached the reformed sand berm and resulted in a water level of 5.5 feet elevation (about 1.2 feet deep at Venoco Bridge) as of January 10th. This storm illustrated the impressive flood capacity of the NCOS wetland system, as displayed by the video footage from 1/09/23 below. The design of the system, with seasonal ponds and shallow slopes, allows the water to be retained to support groundwater recharge and wildlife habitat.

Devereux Slough breach during rainstorm - click image to access video.


Devereux Slough breach during rainstorm - click image to access video. 


Phelps Creek - click image to access video. 


View from Phelps Bridge - click image to access video. 


Long-billed Curlews foraging in the midst of the Devereux Creek floodwaters - click image to access video. 


Devereux Creek flowing into the NCOS channel - click image to access video. 


Western Ponds - click image to access video. 


West arm and overflowing Devereux Creek - click image to access video. 

Tuesday, January 10, 2023 - 09:15