Simulated Effects of Beetle Attacks and Salvage on Water Yield

The purpose of this paper is to estimate plausible hydrologic effects of mountain pine beetle attacks and subsequent salvage efforts on annual water yield and peak flows from affected watersheds. I use the WinWrnsHyd program, based on the WRENNS (USEPA 1980) procedure to estimate annual water yield and peak flow changes. The WinWrnsHyd program is used to simulate attack by mountain pine beetles under four scenarios: a) No salvage, b) immediate salvage of all merchantable timber, and c) 1-5 year delay of salvage. In each case I impose two wind regimes, 1) winter wind speeds 15-20 km/h and 2) winter wind speeds less than 4-7 km/h. Salvage clear-cuts are 20 ha blocks. The 'no salvage' and 5-year delayed salvage scenarios produce the greatest increase in water yield and peak flows. Both results are attributed to the standing dead trees which form a barrier to wind penetration to the snow surface to minimize the effect of wind on winter snow loss. The 'immediate salvage' scenario produces varying results depending upon winter wind speeds and the size of salvaged areas. The snow in 20 ha clear-cuts is susceptible to wind-driven erosion and sublimation losses. With 20 km/h winds, the snow pack can be completely depleted until the height of regrowth (about 20 years after initial beetle attack in this case) is sufficiently high to protect the snow surface from erosion and sublimation