Technical Bulletin No. 0672: Forests as Nonpoint Sources of Pollution and Effectiveness of Best Management Practices

This report synthesizes available knowledge on the effects-of forest practices on water quality by examining six propositions:

The quality of water draining forested watersheds is normally the best in the nation whether the forests are left untouched or intensively managed. Available information supports this proposition.

Properly implemented Best Management Practices (BMPs)effectively control nonpoint sources of pollution from forestry operations under most circumstances. This proposition is generally true, but in some unstable areas conventional BMPs for road construction and forest harvest may not be sufficient to prevent adverse effects on stream channels and fish habitat.

Effects of present day management activities on water quality are usually transient and are rarely severe enough to cause significant damage to fish populations. Negative impacts of forest practices should be uncommon where conventional BMPs are used. Exceptions to this conclusion would include (a) unstable areas or areas with highly erodible soils; (b) the combination of management activities with extreme storm events and (c)possibly downstream depositional areas where there is potential for cumulative effects.

The potential for water quality impacts from forest management depends upon factors such as climate, soil types, topography, etc. Special control measures can be targeted where there is greater than normal risk for short- or long-term adverse effects (such as areas with high risk for landslides). This proposition is generally true, although we note that extreme storm events can have unavoidable effects on both managed and unmanaged landscapes and streams. The cost of special control measures may in some situations be prohibitive relative to the value of the reduced risk of water quality degradation.