The national forests were reserved from the public domain in part to "... secure favorable conditions of water flows." In the late 1800's there was great concern regarding watershed conditions on key water producing areas and the impact of sediment on channels and downstream communities. The U. S. Geological Survey (USGS) did the initial investigations to recommend which important watershed and forested lands should be reserved from the public domain. For over one-hundred years the USGS and USDA Forest Service have cooperated in the water resource arena. The opportunity for scientific cooperation is further improved by the addition of expanded biological capability in the USGS. This research cooperation is enabled by an existing cooperative agreement designed to facilitate cooperation between agency scientists on water and sediment related issues.
Characteristics of Forest StreamsThe streams draining forest lands typically have high gradients, gravel beds, and are strongly influenced by streamside vegetation and associated large woody debris. While some forested watershed areas exceed a thousand square miles, most of the management concern focuses on watersheds commonly ranging in size from less than 1 to 20 square miles. Typically, there is limited data on flow characteristics, and even less meaningful information on sediment transport. Most of the bedload sediment transport occurs at high flows. Many of these areas are inaccessible and even where accessible, measuring bedload sediment at high flows is hazardous.
Sediment BudgetsIn many forested watersheds, there are concerns about the effect of natural processes combined with past and present use activities on sediment budgets. Much of the focus is on how aquatic habitats are altered at the site level. Also, how reach level features such as pool size, pool frequency and bank cover are changed by chronic alterations in the watershed sediment regime. A better understanding of basinwide and onsite processes is essential in improving sediment models to predict the effects of activities and abatement strategies.
Transportation SystemsRoads remain one of the significant sources of sediment on forested and rangelands. Significant improvements are being made in the control of sediments from cut and fill slopes and the road tread itself. Mass erosion from slope failures, debris flows, and gullys from road drainage remain significant sources of sediment in streams draining the national forests. Work is continuing on finding better ways to reduce the impacts of the needed transportation systems.
Sediment and Aquatic HabitatMeasuring the effects of fine sediments on aquatic habitats is an important concern (USDA, 1994). It remains difficult to directly correlate measures such as cobble-embeddness to levels of annual disturbance within the tributary watersheds. Also rates of recovery in habitat measured by cobble-embeddness are poorly correlated with level of sediment control applied to upland watersheds. Work continues on better characterizing the impacts of sediment and developing methods to control impacts on channels. Understanding the role of flow regimes and related sediment in maintaining habitat features is an emerging concern. Knowledge of these relationships is vital in developing and implementing successful habitat restoration projects and in identifying needed regimes for hydropower projects and other off-channel diversions.
Riparian AreasStreamside and floodplain vegetation, referred to as riparian vegetation, is becoming recognized for the important role it plays in trapping slope sediments and controlling the rate of bank and floodplain sediment mobilization. There is currently a joint effort underway to improve rangeland riparian conditions on national forests and Bureau of Land Management administered lands. This involves applying improved livestock management strategies. Improvement activities have demonstrated that sediments can be stabilized and in many cases, former ephemeral channels now have sustained flows. These riparian areas also provide key aquatic habitat components, and water quality improvement and flood reduction benefits (Blackburn and King, 1992).
Functioning Stream ChannelsMaintaining the health and function of stream channels is an important concern. Changes in the balance between flow and sediment load can alter channel size and configuration (Meiman and Schmidt, 1992). For example, accelerated erosion and sediment from upland tributaries can result in channel aggregation. Also, significant reductions in flow, as a result of diversions, can result in channel narrowing and/or aggregation. These may affect flood damage and sediment. Increasing demand for water threatens to alter the sediment/flow relationship potentially jeopardizing the channel integrity. This may result in changes to the relationship between the channel and the floodplain and/or changes that may disrupt the sustained delivery of water to downstream users. Work is underway to determine what portions of the flow regime are vital to maintaining a healthy functioning stream channel. This process knowledge is also essential in developing successful channel restoration strategies that incorporate rather than resist geomorphic processes (National Research Council,1992).
In the Southeast better watershed management practices have reduced sediment from upland sources. Streams and rivers are now cutting through the sediments associated with historic cotton farming and exposing streambeds that were buried over a century ago. In many cases, these streams remain entrenched in the old sediments. What are the future flood, sediment and habitat consequences of this change?
Understanding flow, sediment and habitat processes are major components of needed knowledge. This information is key to developing better models for evaluating the effects of forest management activities and developing strategies to prevent or interdict sediment before it impacts channels. Previous Forest Service research studies have expanded our knowledge about effects of various forest management activities on sediment production and control. For example, how do roads and other disturbance associated with timber harvest affect sediment production. Considerable effort has been expended on improving this understanding and developing strategies and techniques to reduce impacts and to identify effective soil and water conservation practices.
Studying the relationship between flows, sediment and the condition of channels is currently receiving considerable attention. These studies have been initiated to understand the effects of sediment on aquatic habitat conditions on the national forests. Understanding these wildland streams is a challenge because most are gravel bed systems, tend toward steep gradients, represent small watersheds, have limited onsite flow data available and have received limited study to date. Management to maintain properly functioning stream channel systems requires a better understanding of flow and sediment relationships in gravel-bed streams.
Some typical current research focuses on comparing short term bedload sediment measures with long term accumulations, evaluating most effective sediment transporting flows, determining effects and requirements of riparian vegetation, understanding the role of disturbance processes, measuring the transport and impact of fine sediments, studying processes involved in stream transport of major sediment slugs, evaluating effects of altered flow regimes, and understanding habitat relations.
There are significant opportunities for continued collaboration between USGS scientists and Forest Service scientists. In the future, there is a need to focus stream gaging on more than just that data necessary to define the water supply. We need to better define flow regimes and related sediment and biologic processes; and we need to do it at significantly lower cost. Integrated studies to characterize morphology and biology of stream reaches at gaging stations should receive new emphasis. This would build on the approach suggested by Dunne and Leopold (1978). This may require changing the authorities that govern water measurement activities and will require re-engineering traditional approaches to measuring and managing data. Greater emphasis is needed on long term stations, developing bedload sediment data, relating riparian vegetation needs to flow and linking biologic, flow and sediment characteristics.
Dunne, Thomas and Leopold, Luna. 1978. Water in environmental planning. W.H. Freeman & Co., New York, NY, 818 p.
Meiman, James and Schmidt, Larry., comps. 1994. A Research Strategy for Studying Stream Processes and the Effects of Altered Streamflow Regimes. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 12 p.
National Research Council. 1992. Restoration of Aquatic Ecosystems: Science, Technology and Public Policy. National Academy Press, Washington, DC. 552 p.
United States Department of Agriculture. March, 1994. Protecting and Restoring Aquatic Ecosystems: New Directions for
Watershed and Fisheries Research in the USDA Forest Service. U.S. Department of Agriculture, Forest Service. 13 p.
AutobiographySchmidt, Larry J., USDA Forest Service, Fort Collins, CO: Current serves as Program Manager National Stream Systems Technology Center on the staff of the Rocky Mountain Forest and Range Experiment Station. The Stream Systems Technology Center seeks to provide the best available technology for meeting the mandate to achieve favorable conditions of streamflow from the National Forests. Experience during 32 years with the Forest Sevice includes assignments in Washington, DC, Southwestern and Intermountain Regions as a wildland hydrologist.