USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
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Research Topics Water & Watersheds

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Caspar Creek Experimental Watershed: More than 50 years of research focusing on clean water

An aerial view of the forested mountains of the North Fork Caspar Creek watershed.
Aerial view to the east southeast across the North Fork Caspar Creek watershed in 2005.

Storms of the 1950s hit hard in northwest California forests, triggering landslides that muddied streams and altered freshwater habitat for Pacific salmon. To what extent did forest land-use activities contribute to these and other water quality impacts? We didn’t know, and to find out we would need to measure the amount of sediment produced by logging-related activities. The Forest Service and the California Department of Forestry jointly decided to study the effects of logging on the quality and quantity of water flowing from coastal watersheds.

The Caspar Creek Experimental Watersheds were formally established on Jackson Demonstration State Forest in 1962 to address this need, and research has continued there for more than a half century. Two major watershed-scale experiments have been carried out at the site: 1) the 423-ha South Fork watershed was selection-logged using tractors in 1971-73, and 2) the 474-ha North Fork was partially clearcut in 1989-1992. Comparison of rainfall, flow, and suspended sediment measurements in the treated watersheds with those in untreated control watersheds allowed the effects of logging on storm flows, dry-season flows, and sediment loads to be evaluated during each experiment.

Monitoring continues in both the North and South Fork watersheds to evaluate rates of watershed recovery, and planning for a third experiment is currently underway. The Caspar Creek Experimental Watersheds have attracted researchers in a variety of fields, and research at the site has resulted in publication of more than 175 papers and 58 technical reports and theses.

A small dam spans the width of the North Fork.
North Fork hillslope instrumented to measure hillslope soil moisture and pore pressures before and after logging. Ladders are used to prevent soil compaction during measurements (photograph taken in 1991, two years after logging).
Results of Caspar Creek watershed studies

The first experiment demonstrated that 1971-73 tractor-yarded selection logging (carried out prior to implementation of modern California Forest Practice Rules) quadrupled suspended sediment yields in the South Fork.

Sediment loads declined to near pre-treatment levels by 1985. However, loads again increased in the early 1990s due to deterioration of the old road network, and these delayed sediment inputs are now rivalling the volume introduced during the initial logging response. Monitoring also showed increased peak flows and low flows immediately after logging. Peak flows soon declined to pre-treatment levels, but low flows then dropped below pre-treatment levels, where they remained until the early 2000s.

The second experiment, carried out under the California Forest Practice Rules in effect at that time, found initial sediment increases from 1989-92 cable-yarded clearcutting to be lower than those from the first experiment, and loads had re-approached pretreatment levels by 2000. But in this case, too, sediment yields once again increased after their initial decline. Pre-commercial thinning in 2001 reactivated sediment sources, and a major 2006 landslide from a 1990 clearcut contributed a considerable volume of sediment.

Both storm flows and low flows increased after logging, and initial recovery trends were reversed by pre-commercial thinning. Much of the initial increase in sediment appears to be from in-channel erosion triggered by increased flows.

Other studies showed that nitrogen export increased after North Fork logging and algae production increased, while changes in populations of young salmon and steelhead could not be detected.

Trees, water, and sediment

A fundamental goal of Caspar Creek research is to provide the information needed to manage forests in a manner that minimizes impacts on water quality and other resources. One of the most useful kinds of information for addressing this goal is the basic understanding of how forests, water, and sediment interact. Each Caspar Creek experiment has been accompanied by a variety of more focused studies designed to better understand these interactions.

North Fork studies demonstrated a close association between increased flow and increased suspended sediment loads, and additional studies showed that logging increased runoff by reducing both transpiration and evaporation of rainfall from foliage—about a fifth of the rainfall under a 100-year-old redwood forest doesn’t reach the ground even during large storms.

These heightened flows increased the ability of small streams to carry sediment, and this contributed to in-channel erosion. Altered hillslope water budgets also likely influenced the timing of major landslides after logging: the largest landslides occurred 10 to 15 years after logging when root strength was low (roots on some logged trees had decayed while root networks for young trees were not fully developed) and within five years after pre-commercial thinning, when hillslope moisture levels had again increased.

Applications of Caspar Creek research results

Caspar Creek research results are commonly applied in one of four ways:

  1. Professional foresters, agency personnel, and landowners preparing management plans for forested areas need to describe potential effects of planned activities, and Caspar Creek results are often cited to provide these estimates. Results have been used to predict changes in peak flow, hillslope erosion, water yield, low flow, and changes in stream temperature after logging.
  2. Results have been used in the development and refinement of California Forest Practice Rules that address watershed-related topics, and have provided the information needed for state agency personnel to design strategies for controlling hydrologic changes from logging in coast redwood forests.
  3. Caspar Creek data are available on the web, and researchers from across the globe have used the data in support of their own research.
  4. Caspar Creek research has resulted in development of new methods for monitoring water quality, and the monitoring strategy developed for efficient estimation of suspended sediment loads using turbidity monitoring has now been adopted at sites as far away as Okinawa.
Caspar Creek publications

Caspar Creek research results have been described in a sequence of publications that began in the late 1960s and will continue into the future as new results are found. Many of the publications are available at the Caspar Creek website. An annotated bibliography has been prepared as a guide to published information.

More information
  • Ziemer, Robert R.; [technical coordinator] 1998. Proceedings of the conference on coastal watersheds: the Caspar Creek story. Gen. Tech. Rep. PSW GTR-168. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 149 p.