SILVICULTURE


POTENTIAL WATER QUALITY PROBLEMS

Timber harvest and related road construction activities can cause water quality problems by increasing sediment and nutrient concentrations.  Also, timber harvest in riparian areas may result in increased water temperatures if shade vegetation is removed.  In addition, if herbicides/pesticides have been applied to facilitate growth, these substances may enter waterways more readily with the increased runoff that is likely after timber harvest.  Finally, increased runoff after vegetation removal can scour channels and erode streambanks.  If not properly managed, harvest impacts can be long term until vegetation is re-established.

Increased sediment concentrations in waterbodies can impact fisheries and other aquatic life. This may include less successful spawning activity, a change in the macro-invertebrate populations, and a change in the aquatic plant community.  

Increased nutrient concentrations can cause over fertilization of waterbodies creating a condition known as eutrophication.  This situation, which is often more serious in lakes than streams, results in excessive algal growth.  When the algae die and decompose, oxygen is depleted.  Depending on the extent of the oxygen depletion, a fish kill may result.  Increased nutrient levels can also impact water supplies that are used for human consumption. Elevated nitrate levels can interfere with the blood's ability to carry oxygen.  This can be a serious problem for infants and the elderly.  

Increased herbicide/pesticide concentrations can impact aquatic life.  Depending on the type of herbicide/pesticide, a number of human health problems are possible.

CRITICAL AREAS AND ISSUES

The closer the timber harvest activity or road construction activity is to a surface waterbody or ground water source, the greater the chance for a water quality impact.  While this is a general rule of thumb, it is possible that areas close to water may not have an impact and areas removed from water may have a significant impact.  

When identifying critical areas, it is important to consider: soil type; topography; drainage patterns; road systems; and precipitation patterns.  It is especially important to examine road systems.  Whether constructed for harvest, or other purposes, they are often a major contributor of sediment leaving a forested watershed.  Situations that are likely to have a negative impact on water quality include: clear cutting large areas on steep slopes; removal/destruction of vegetation in riparian areas; and road construction without proper layout, shoulder stabilization, culverts and bridges. 

A number of management tools can be used to protect water quality.  They are outlined in the 'Making Improvements' section below.   However, before improvements can be planned existing conditions should be assessed.

ASSESSING EXISTING CONDITIONS

If a timber harvest is being considered, there is a potential for a negative impact on water quality if any of the following exist:

  • The area has surface waterbodies located within its boundaries, or drainage patterns carry runoff from the area to nearby surface waterbodies.
  • The area has moderate to steep topography.
  • A harvest system such as clearcutting is being considered that removes the majority of vegetation.
  • There will be a need to operate equipment in riparian areas.
  • There is noticeable sheet, rill or gully erosion prior to harvest.
  • There is noticeable streambank erosion prior to harvest.
  • Additional roads will need to be constructed.

MAKING IMPROVEMENTS

Improvements, often called Best Management Practices (BMPs), fall into two broad categories: structural or management. Good planning often requires both types of BMPs.

There are many kinds of structural BMPs including: access roads; culverts; bridges; rip-rap; straw bale dikes; sediment traps; etc. Depending on complexity, a structural BMP may require a detailed engineering drawing.  In other cases, existing drawings can be utilized or modified to fit a given situation. 

Management BMPs include: selective removal of vegetation; leaving buffer strips along riparian areas; limited stream crossings; slash disposal practices; etc.     

Excellent sources of information for planning specific BMPs include:

Preplanning the timber harvest to reduce water quality impacts is very important. The following will generally be included in a good plan:

  • Use existing roads whenever possible to minimize the total amount of construction necessary.
  • Construct new roads a safe distance from a waterbody.
  • Minimize the number of stream crossings.
  • Fit new roads to the topography.
  • Design the road system to minimize total mileage.
  • Carefully design roads with bridges, culverts, waterbars, stabilized slopes, etc.
  • Construct bridges during periods when streamflow is low. 
  • Route road runoff to a filter strip and not directly into a waterbody.
  • Provide energy dissipaters (bales, rocks, logs, etc.) to reduce the erosion force of runoff.
  • Carefully locate, and properly reclaim, borrow pits and gravel sources for road construction.
  • Complete road construction prior to the main runoff season to minimize exposure of unfinished roads to heavy runoff. 
  • Carefully locate skid trails and landing locations on stable soils and avoid steep gradients.
  • Minimize elongated exposure of soils up and down slopes.
  • Don't destroy all vegetation in the harvest area. Leave small trees and brush when possible. 
  • Leave a filter strip along riparian areas.
  • Don't drive in or through the riparian area more than necessary.
  • Lift the front end of logs when dragging to minimize soil and vegetation disturbance.
  • Skid logs perpendicular to the slope.
  • Establish vegetative cover on heavily disturbed areas.
  • Don't dispose of slash in a riparian area.
  • When re-seeding, operate equipment parallel to the slope to discourage erosion.
  • Protect re-seeded area with mulch, grazing control, etc.

FUNDING AND TECHNICAL ASSISTANCE

Section 319 funds are available from DEQ to assist with conservation practices on private forest land.  Applicants for these funds must show that a water quality problem exists and that the proposed practices will improve the problem. Interested parties should apply through their local conservation district.  The Wyoming Game and Fish Department has funds for practices that benefit fisheries.

Technical assistance is available from the National Forest Service and the Wyoming Division of Forestry.  The Internet also contains a wealth of information including the following sites:

 

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