Logging and Water Yield

Kim RabyGEOG 3511

Denver Post, 11/10/02

Coon Creek, WY

4,100 acre demonstration project illustrates patch cuts in lodgepole pine forest

1990s research says clearcut increased spring runoff by 17 percent

Is this the right decision for Colorado?

What’s happening:

Snow collects in clearings instead of being intercepted and evaporating before it can become overland flow, yielding more runoff

Can it work? Is it worth it?

Interception• Sublimation is greater from vegetation

than from groundHigher temperature on leaf surfaceGreater surface areaTrees radiate longwave radiationHigher air temperature surrounding snowIncrease in SVP

• Cut trees to decrease interceptionIncrease snowpack volumeIncrease water yield

Source: Meiman 1987

Summary of 50 years of clearcutting and thinning experiments at small scale Fraser Experimental Forest

The more area removed, the greater the SWE increase

If 100 percent of basal area is removed, ~35 percent increase in water yield

Yields have been long-lived but clearcuts must be maintained

Summary

Source: Troendle et al. 2001

Control: Upper East Fork

Treatment: Coon Creek

Maximum mean daily discharge comparison

Daily mean flow increased 11% with treatment

Goal of the Coon Creek Water Yield Augmentation Pilot Project: to test whether results demonstrated at small scale experimental basins (like Fraser Experimental Forest) can be duplicated to operational/large watershed scale

Large-Scale Replication

Source: Troendle and Stednick 1999

24% increase

91% increase

Control: North Fork of Dry Creek

Treatment: Brownie Creek

Slopes are significantly different (p=0.0001)

Flow during the two periods is significantly different

~70 percent increase in water yield relative to control after harvesting 25 percent of Brownie Creek

Increased Water Yield

Source: Meiman 1987

Fraser Experimental Forest

Increased accumulation after plot cut averaged 5.8 inches of water or 45 percent more than upwind plot

No significant difference between upwind and downwind forest plots

Peak SWE Increases

Source: Troendle and Meiman 1984

How large should the clearcut be?•Very site-dependent•This representation is for the Fraser Experimental Forest (maximum snow depth at 5H (5x the canopy height))•As the size of the opening increases, its efficiency in trapping snow decreases to the point (approximately 15H) where there is a net loss

Loss is associated with increased wind scour and sublimation losses

Area of Clearcut

Source: Golding and Swanson 1986

clearing

James River site, Alberta, Canada

SWE is greatest on the leeward side of a clearing

SWE is least on the windward side of a clearing

Second peak occurs because right before the snow hits the far side of the forest, decrease in wind speed results in additional snow accumulation

wind direction

second peakfirst peak

Influence of Wind

Source: Gary 1974

Fraser Experimental Forest

Similar results

Increased snow accumulation and SWE at leeward edge of forest

clearing

wind direction

SWE Increases

Source: Troendle and Olsen 1994

Fraser Experimental Forest, Fool Creek Watershed

Total seasonal flow increased by 40 percent (longer duration of high flows)Peak flow increased by 20 percentMost of the detectable change occurred in May

Hydrograph

Source: Troendle and Stednick 1999

Increases in peak discharge mean more erosion and flooding

Results in a need for additional reservoirs to store water for low flows

Generally, flows increased most during wet years as opposed to during droughts

During drought (low antecedent moisture), snowmelt infiltrates and recharges groundwater, does not go to discharge NEED RESERVOIRS

Hydrograph

Source: Swank et al. 2001

Appalachian catchment

Logging-related activities (including road construction activities) increase erosion and sedimentation

Sediment yield increased considerably as a result of road building and logging activities

Sedimentation

Source: Swank et al. 2001

Appalachian catchment

Logging activities increase nutrient loading, DOC, conductivity (ion concentrations)

Sustained increases in nitrate concentrations after clearing and logging due to:•Reduction in nutrient uptake due to vegetation mortality•Nutrient release from decomposition of trees and logging residue•Increased soil N transformations

Nutrient Loading

Wildfire mitigation?• Proponents herald logging to increase

water yield as a “forest health effort”• Say it will serve a dual purpose

• Increase water yield• Reduce fire risk

• However, logging trees at high elevation catchments will not reduce fire in high risk areas (at lower elevations)• Logging in high elevation areas could

mean less money to spend on thinning fire-prone areas

Other considerations for CO• Cutting lodgepole pine stands would remove habitat for

federally threatened lynx and other interior forest species

• High cost, maintenance required to maintain yields• Difficult to replicate Fraser results in other parts of

Colorado• Study of runoff changes as a result of cutting ski runs at Eldora

(Gaudagno) deep snow collected in spruce-fir stands open runs scoured almost bare by high winds didn’t produce same results as Fraser experiments

• Other environmental costs• Erosion and sedimentation can stifle habitat for fish and aquatic

insects• Amount of water flowing off trees increases as they

mature• Colorado’s middle-aged forests will soon become old-growth and

capture more snowfall• Shift focus from increasing supply reducing demand?