Management for Water Yield Basic treatments –Removal of woody vegetation –Weather modification...
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Transcript of Management for Water Yield Basic treatments –Removal of woody vegetation –Weather modification...
Management for Water Yield
• Basic treatments– Removal of woody
vegetation
– Weather modification
– Construction of “catchments”
Mgt. Treatments Vary by Zone• Alpine zone
– Region above tree line
• Snowpack zone– Area immediately
below alpine zone
Mgt. Treatments Vary by Zone
• Forests outside snowpack zone
• Woodland and brushy zone– Chaparral,
– Oak savanna,
– Pinon-Juniper woodland
Mgt. Treatments Vary by Zone
• Phreatophyte zone– Plants that obtain
moisture primarily from ground water or capillary fringe just above ground water.
– Occur along stream bank and in flood plain
Alpine Zone
• Characteristics of zone– Snow persists well into
summer– Summer snow fields
almost immune to net evaporation
– Major contributor to summer runoff
• Mgt. Options– Snow fences and tree
planting used to strategically place snow banks relative to sun
Snowpack Zone
• Covers largest land area
• Mostly coniferous and in western U.S., but some in East
• Mgt. Options– Clear-cut – In Arizona
this increased stream flow from equivalent of 0.6 to 13.5 inches of precipitation
Forests Outside Snowpack Zone
• Many vegetative manipulation options– Reduce woody cover
– Coweeta, NC• Increase after clearcutting
was 11 to 16 inches on north slopes, much less on south slopes
– Cascade Mt., OR • Increase after was
clearcutting 18 to 21 inches
Woodland and Brushy Zone
• Vegetative manipulation less effective– Removal increased
yield from 0 to 7 inches depending on rainfall and cover type
Oak Savanna
Phreatophyte
• Very high evapo-transpiration losses
• Manipulation studies inconclusive
• Catchment areas main tool
Low Shrub and Grassland Zone
• Drier sites• Few if any
management options• Use catchments to
retain runoff
Control of Stream Flow Regimen
• Objectives– Prevent deterioration of
regimen because of altered land uses
• Improve natural stream flow regime by management of hydrology
• Rehabilitate deteriorated watersheds
Stable banks, woody vegetation
Primary considerations• Irregular flow
– Volume of high and low flows
– Duration of high and low flows
• Capacity of structures to handle high flows• Management of aquatic ecosystems
Hyetograph
Influencing Factors and Controls
• Flow of water from disturbed areas – Route runoff into
percolation area, not directly into channel
– Reduce runoff by maintaining permeability
• Timing of runoff– Limited possibilities
– Some control of snow storage and melt
Influencing Factors and Controls
• Modify timing and amount of evaporation
• Synchronize inflows to channels by modifying watershed characteristics, e.g. catchments
Management in Alpine Zone
• Modify snow melt – concentrate drifts at higher elevations
• Control route of melt water to maximize infiltration, use earthworks to catch runoff from damaged areas
Management in Forest Snow Pack Zone
• Modify snow melt by managing forest cover, e.g. smaller openings reduce melt rate
• Route runoff to infiltration areas
• Modify synchronization of inflows to channels by varying cover among units
Forests Outside Snow Pack Zone
• Winter operations possible but soil damage likely
• Abused soil leads to rapid runoff, erosion and low summer flows
• Restoration of forest cover is usual treatment
Control of Water Quality
• Surface erosion control
• Timber harvesting• Grazing• Mining
Acid Mine Drainage, Clearfield, PA
Surface Erosion Control
• Avoid critical point in erosion –revegetation cycle
• Revegetate exposed soil as soon as possible
Timber Harvesting
• Major factor in control of water quality
• Felling, limbing and bucking – avoid riparian zones and exclude slash from channel
Timber Harvesting• Skidding and
yarding – minimize soil compaction and disturbance
• Use high lead systems in sensitive and steep areas