The California Wetlands Classification System (Ferren Jr., Capralis et al. 1987) classifies Devereux slough as a Canyon Mouth Estuary. The Devereux watershed drains down mountain canyons and gathers in an estuary before empting into the ocean.
Devereux Slough is impounded most of the year by a natural sand barrier and is influenced by tidal water two to three times annually (Ferren Jr., Capralis et al. 1987; Davis 1990). The water in the slough varies from almost completely fresh to more saline than the ocean. (See diagrams below for a visual side-view of the Slough at different times of the year).
The Devereux Watershed is the entire area that collects and funnels water into the Devereux Creek system, to the Devereux Slough and eventually out to the Pacific Ocean. Significant changes to the watershed have occurred in the last century, from the time when there was little to no development to the establishment of the University of California and the expansion of the City of Goleta.
In the 1920’s the Campbell family constructed a road to their property that bisected two fingers of the slough and permanently affected water circulation. Additionally, many non-native plant species were introduced. Much of this non-native vegetation remains today; examples include cypress and eucalyptus trees.
As the watershed has become more developed, many of the creeks that feed into the slough have been channelized with cement. Channelized creeks do not filter runoff water so more pollution and nutrient loading (eutrophication) occurs in the estuary. The increased development also caused increased runoff, which often carries pollutants into the Devereux Slough. Pavement does not allow water to permeate the ground and be filtered, so the Devereux Slough receives more water and higher pollution content than it would if the watershed were still in an undeveloped state.
In the 1960’s Ocean Meadows Golf Course was built by removing topsoil from UCSB’s South Parcel near the slough, causing erosion and a plume of sediment to accumulate in the top part of the slough. In the past, the mouth of the slough was periodically mechanically opened for drainage and the prevention of flooding. Now the slough mouth opens naturally to the ocean only 1-2 times per year. Under these conditions, the slough is a more suitable habitat for birds and fish. In recent years, the Ocean Meadows Golf Course stopped using fertilizers and the lower Devereux Creek was restored, creating important riparian habitat and removing some pollutants before runoff enters the slough and ocean.
Aerial photos of the Coal Oil Point Reserve over a seventy year period from - California Coastal Records Project
Early photographs of the area depict the mouth of Devereux Slough opening straight into the ocean. However, in the last two decades the mouth of the slough has gradually migrated west, creating a sand finger on the beach. Each year when the slough fills with rain water and the sand bar breaks, sand and mud are forcibly washed into the ocean. The breaching of the slough further erodes the west bank of the slough mouth, making the whole opening migrate westward.
The formation of a sand finger created a larger nesting area for the Western Snowy Plovers and the Globose Dune Beetles. Both species are often found in habitat formed by the over-wash of river mouths. These areas often contain small dunes and are occasionally disturbed by high tides.
The cause of the change in position of the slough mouth in the last 2 decades is unknown. One hypothesis is that the protection of the beach for the snowy plovers in 2001 allowed the dune vegetation to re-establish where it had been removed from trampling of beach goers. The dunes prevent the slough from breaking straight into the ocean by pushing the mouth westward. Other processes that might be affecting the position of the opening of the slough are patterns of sand deposition, currents, sea level, etc. It is also possible that the mouth of the slough migrates east and west in much larger cycles than we have been able to document. The presence of marsh plant species in the dune pond provide some indication that the slough mouth may have been as far west as the dune pond. Only time and more research will tell us.