MPB & Hydrology

MPB & Hydrology
- Basic Forest Hydrology
  - Water Cycle
    - precipitation
    - interception & throughfall
    - transpiration & evaporation
    - surface flow & infiltration
    - storage & seepage
    - streamflow
  - streamflow (Q) =
    - pptn
    - - ET
    - + snow melt ("stored pptn")
    - +- storage (mitigates impact of pptn)
- Expected changes from loss of cover (fig. 2)
  - loss from ET & interception (40-70% of pptn)
    - more water for soil (storage & seepage)
    - increased water for streamflow
  - snow (interior)
    - less interception & sublimation ...
    - ... more snow accumulation on ground (more "stored water")
    - less crown cover -more solar rad'n & wind - melt quicker
    - pot'l for more surface flow (soil "full")
    - quicker melt & surface flow = quicker peak
  - more water in soil storage...
    - less rain to "exceed the bank" (i.e soil water storage is full)
    - (remember, soil water storage mitigates effect of rain on stream flow)
    - get stream peak responses more often
  - summary
    - more water
    - more quickly
    - more often
- Potential impacts
  - volume
    - more water overall (15-20%)
    - larger peaks (15-20%) ... damage pot'l
  - timing
    - peak flows sooner (2 weeks) ...
    - low flows sooner as well
  - changes in peak flows will affect
    - aquatic resources / fish habitat
    - infrastructure
    - community watersheds
    - agriculture (irrigation)
- Significance of impacts? It depends ...
  - weather
    - how much rain = volume available for flow
    - how much snow = stored volume
    - temperature in spring = energy for melt
    - warm winds = energy for melt
    - rain in spring = energy for melt
  - watershed responsiveness
    - responsiveness = time (from pptn to main stream flow)
    - soil depth and texture
    - density of streams
    - density of sidehill roads (ditches/ culverts)
  - extent of MPB attack (Pl % & mortality)
  - mgmt regime
    - no salvage
      - snags & remaining live left onsite
      - some (limited) ET is maintained
      - gradual recovery ... takes time to return to pre-epidemic state
    - salvage logging
      - removes red/grey (and green) - loss of remaining (limited) ET
      - roads ... drainage
      - but ... planting
- Recommendations
  - maintain natural drainage
    - lotsa culverts in roads
    - deactivate spur roads
    - maintain drainage structures
  - minimize activity in riparian areas (esp <10m)
    - often it's where the (green) Sx is
    - reasons
      - maintain stream temp (shading)
      - large wood in streams
  - consider harvest system
    - no salvage
      - maintain snags & remaining green
      - "maintain" (limited) interception, ET & shading
      - some snow intercepted ... less ground accum.
      - some shade ... delayed melt
      - ECA is lower (less like a CC), BUT slow recovery
    - salvage = log + plant
      - loss of remaining interception, ET & shading
      - more water to soil (storage & seepage)
      - more snow accum. on ground
      - more energy for a quicker melt
      - ECA = 100% at start, BUT quick recovery
    - logging with retention
      - is a compromise
        
        lessens short term impact of slavage
        
        and a moderate recovery rate
        
        graph of time vs. %ECA: salvage/ no salv. (fig. 4)
        
        exposure = width of curve
        
        sensitivity = ht of curve
        
        risk = area under the curve
        
        consider pot'l of large storm over time
      - other benefits to retention (wildlife, biodiversity, fisheries ...)
  - stand & landscape level
    - plan at the landscape level
      - overall retention & salvage goals
      - consider road density & drainage impact
      - consider pattern of leave/cut patches over landscape
      - determine and manage for ECA
    - execute at stand level
      - individual block retention will range: 0 - 100% retention
      - protect sensitive sites
  - communication! (industry - agencies - public)