Applications of Turbidity Monitoring to Forest Management in California

Abstract

Many California streams have been adversely affected by sedimentation caused by historic and current land uses, including timber harvesting. The impacts of timber harvesting and logging transportation systems on erosion and sediment delivery can be directly measured, modeled, or inferred from water quality measurements. California regulatory agencies, researchers, and land owners have adopted turbidity monitoring to determine effects of forest management practices on suspended sediment loads and water quality at watershed, project, and site scales. Watershed-scale trends in sediment discharge and responses to current forest practices may be estimated from data collected at automated sampling stations that measure turbidity, stream flow, suspended sediment concentrations, and other water quality parameters. Future results from these studies will provide a basis for assessing the effectiveness of modern forest practice regulations in protecting water quality. At the project scale, manual sampling of water column turbidity during high stream flow events within and downstream from active timber harvest plans can identify emerging sediment sources. Remedial actions can then be taken by managers to prevent or mitigate water quality impacts. At the site scale, manual turbidity sampling during storms or high stream flow events at sites located upstream and downstream from new, upgraded, or decommissioned stream crossings has proven to be a valuable way to determine whether measures taken to prevent post-construction erosion and sediment production are effective. Turbidity monitoring at the project and site scales is therefore an important tool for adaptive management. Uncertainty regarding the effects of current forest practices must be resolved through watershed-scale experiments. In the short term, this uncertainty will stimulate increased use of project and site-scale monitoring.

Logging and turbidity in the coastal watersheds of northern California

“…The use of turbidity to assess the water quality impacts of forestry operations has increased in California and is used at various scales (Harris et al, 2007). Long-term turbidity monitoring programs, some limited to grab sampling, have been used to detect recovery trends in Washington (Reiter et al, 2009).…”

A guide to forest–water management

“…These types of impact can alter the seasonal timing of flows. Monitoring is essential for ensuring that management practices are not causing negative impacts on water timing (Harris et al, 2007).…”

Temporal and Spatial Turbidity Patterns Over 30 Years in a Managed Forest of Western Washington1

“…We used turbidity as a surrogate for suspended sediment because our turbidity record is more complete than that for suspended sediment concentration (SSC). While turbidity is not a direct measurement of suspended sediment (e.g., Anderson and Potts, 1987) and can be influenced by colloidal material (both organic and inorganic), water color and sediment particle size distribution (e.g., Hudson, 2001; Madej et al ., 2002), it still provides an easy‐to‐obtain indication of the relative concentration of suspended material in stream water (Beschta, 1980; Davies‐Colley and Smith, 2001;Harris et al ., 2007; Minella et al ., 2007). Although there is uncertainty associated with using turbidity values to represent SSCs, the relationship between the two parameters is generally strong enough that turbidity is a more reliable index of SSC than flow (e.g., Beschta, 1980; Lewis, 1996; Christensen et al ., 2002).…”