Research Projects

Landscape Dynamics and Ecologic Restoration in the Middle Ranch Hayfields Region, Catalina Island, California: A Soil-Geomorphic Approach to Understanding Landscape Responses to Restoration Activities

PI: Tom Bullard
Co-PI: Eric McDonald

Project Period: 2002 - 2003

Funding: Catalina Island Conservancy and CALEM

Keywords: soil-geomorphology, fluvial geomorphology, erosion, revegetation, Catalina, scrub oak

Project Description

Following more than 150 years of environmental modification to support grazing, the Middle Ranch Hayfields area near Middle Canyon on Catalina Island was decommissioned and designated for restoration in 1998. Several critical geomorphic questions have arisen regarding a restoration plan developed by the Ecological Restoration Division (ERD) of the Catalina Island Conservancy. Issues of concern include the following:

• Revegetating the valley floor and riparian corridor
• Removing the existing bridge near the east end of the valley and realigning the stream
• Relocating an access road from the north to the south side of the valley
• Reintegrating side tributary drainages with the main channel
• Recontouring the valley floor through the addition of silt

The scope of the DRI assessment included developing a preliminary geomorphic history of the study area, combining this geomorphic history with analysis of the drainage basin to characterize surface hydrology in the watershed, and analyzing a relatively undisturbed area (Bulrush Canyon) as a natural analog to the behavior of Middle Canyon. Specific methods included geologic and geomorphic mapping using aerial photographs, field verification of mapping units, field examination of stratigraphy and soils (Figure 1), analysis of the geomorphology and drainage of the watershed, and reconnaissance-level mapping of Bulrush Canyon. Key findings of the DRI assessment include the following: (1) erosional remnants of ancient (>10,000 years old) fluvial terraces indicate long periods of down cutting by stream systems punctuated by periods of stability during which time the terraces formed, (2) most old fill sediment was removed from the canyons more than 4,000 years ago, (3) most of the alluvium in the valley floors is very young (several hundred to a few thousand years old) and has accumulated episodically, (4) stream deposition of sediments has been limited during historic (1850 to the present) time periods, and (5) hillslopes are relatively stable at present. Based on these and other findings, this study concluded that (1) revegetation of the valley floor and riparian corridors will likely have a stabilizing effect on Middle Canyon, (2) efforts to remove the bridge and realign the stream to control downstream erosion will likely be met with mixed results, (3) relocating the road may provide a short-term solution to the road degradation that now occurs but could have undesirable long-term implications, (4) integrating small tributaries with the main channel could adversely effect restoration activities, (5) and recontouring the valley floor through the addition of silt could result in increased incision of the valley floor, reintroduction of silt to the stream, and return of silt to the reservoir. This preliminary assessment supports the view that restoration efforts should carefully consider the geomorphic history of the area and behavior of system components while indicating the need for future study (e.g., effects of grazing on erosion, assessment of soil-geomorphic variables related to revegetation) to develop the most effective restoration strategies.

Figure 1. (a) Stratigraphy exposed in Middle Canyon (site M-12a) upstream from the Middle Ranch Hayfields, showing recognizable buried soils (slightly darkened horizon) and indicating at least four discrete depositional cycles punctuated by stability and soil formation as well as minor erosion of upper parts of soil profiles prior to deposition of overlying sediments. (b) Sketch of the stratigraphy at M12-a showing units representing discrete depositional and erosional events. Soils are depicted by the short vertical lines and represent periods of stability and soil development. The truncation of soils and stratigraphic units represents downcutting by the Middle Canyon channel following filling events. In this sketch, Unit 1 is the oldest, perhaps several thousand years, and Unit 6 is the youngest unit, perhaps a few decades to a few hundred years old.

Return to Projects List