logging and water yield
DESCRIPTION
Logging and Water Yield. Kim Raby GEOG 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?. - PowerPoint PPT PresentationTRANSCRIPT
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?