STREAM CROSSING CASE STUDIES IN A MANAGED FOREST: THE REMOVAL OF SEDIMENT THROUGH HUMBOLDT CROSSING EXCAVATION

Recent awareness of sediment impairment to anadromous fisheries has resulted in legislation requiring the mitigation and often restoration of the fisheries. Extensive impairment has resulted from ground based legacy timber harvesting. The most critical source of sediment delivery is from the construction and abandonment of road utilized for logging. The legacy roads were poorly located and poorly constructed. Roads were often located within the watercourses. Where roads crossed watercourses, the channels were often just filled with woody debris and soil (Humboldt crossing). These crossings remain today, up to 50 years in age, in varying levels of collapse. They are a chronic source of sediment input into watercourses.

Typical mitigation efforts implemented by the timber industry regarding these crossings is to excavate the remaining fill and either leave the crossing in an excavated state or replace the crossing with modern culverts. In response to laws, this process is restricted to the crossings located only on existing roads being upgraded for use. This practice is removing significant volumes of sediment that will be delivered in the future. Significant information has been learned during this process. Some lessons learned include that over excavation often can result in further sediment inputs, the removal of a few sites does not constitute a return of habitat and critical planning is necessary. We provide case studies over an approximate 5 year period of excavated, ongoing and proposed Humboldt crossing removals.