You are here: Home / Research Topics / Research Highlights / Individual Highlight

Research Highlights

Individual Highlight

Do forests reduce flood risk

Photo of Snapshot : Two lines of research converged at the North Fork Caspar Creek Experimental Watershed in northwest California to address two long-standing questions in forest hydrology: to what extent does clearcut logging affect flood magnitudes and, if it does, what causes the effect For this second-growth redwood forest, peakflow magnitudes increased by an average of about 50% in fully logged subwatersheds, and the change occurred largely because about 21% less rain hits the ground under intact forest canopies in this area.

Principal Investigators(s) :
Reid, Leslie M. 
Research Location : North Fork Caspar Creek Experimental Watershed in northwest California
Research Station : Pacific Southwest Research Station (PSW)
Year : 2011
Highlight ID : 355


Flow has been monitored in subwatersheds at North Fork Caspar Creek since 1985, providing a record of peakflows before and after clearcut logging of second-growth coast redwood in 5 of 8 gaged subwatersheds. Comparison of peakflow magnitudes between the logged and forested subwatersheds showed an average increase of about 50%, a result that indicated that existing theory was inadequate to explain the mechanisms by which a forest affects storm flows. We hypothesized that rainfall interception by the forest canopy may be influencing peakflows, and began to measure rainfall both in clearings and under adjacent forest stands. Results showed that about 21% of even the largest rainstorms was trapped and evaporated by the forest canopy. The rainfall interception measurements, in combination with estimates of transpiration, then allowed calibration of rainfall-runoff models for pretreatment conditions. When the same models were applied to clearcut conditions, they closely predicted the observed response (see figure 1), and indicated that interception was responsible for about 2/3 of the effect and transpiration for about 1/3. Results of early phases of the study are already being used by the California Department of Forestry and Fire Protection to aid planning of timber harvest operations upstream of sites susceptible to flooding.

Forest Service Partners

External Partners