Forest Investment Account (FIA) - Forest Science Program
FIA Project Y073273

    Tsitika River sediment budget project
 
Project lead: Hudson, Rob (BC Ministry of Forests and Range)
Imprint: [BC]:,2007
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
The Tsitika River sediment budget project was initiated in 1991 to conduct sediment budget research to determine the role of man-made sediment sources in delivering sediment to the channel system. The original intent was to construct a sediment budget for the whole Tsitika River watershed, which drains an area of 370 km2 at the gauging site. The project met with limited success in the early stage; it became apparent that the task of constructing a sediment budget at that scale was not possible with the resources that were available. This led to the decision to concentrate the study within a sub-basin of the Tsitika River in order to study sediment production and transport processes at a smaller scale. Russell Creek was chosen for this task for the following reasons: Monitoring of streamflow, suspended sediment concentration (SSC) and precipitation / temperature began in 1991, providing a historic data set on which to build. Russell Creek contains a variety of terrain types, 2 contrasting lithologies, a history of harvesting with ongoing activity, and its hydrology is the result of a combination of rainfall, rain-on-snow (ROS) and snowmelt processes At 31-km2 Russell Creek is an order of magnitude smaller than the Tsitika River watershed. The variety of sediment source and terrain types and the mix of hydrologic processes provide reasonably good representation of the sediment production and transport characteristics of coastal watersheds. The watershed area is sufficiently small to design a field data collection program that is both comprehensive and manageable. The task of building up a suitable network of nested stream-gauging sites and meteorological stations began in 1994. In 1996, funding was obtained from FRBC to conduct sediment budget research at Russell Creek in order to provide answers to the original research questions as outlined above. The success of this program has been well documented (Hudson 2002, 2001a, b, c). The nested study design is a key element in the success of the sediment budget work because it allows the watershed area to be compartmentalized into smaller units that are relatively uniform in terms of selected attributes. This has allowed the smaller units to be studied at a level of detail required to understand how the sediment budget works, and how the governing processes differ between units. The success can also be attributed in part to the fact that a modeling approach was used to develop the sediment budget. The sediment budget model estimates the total mass of sediment that is produced during storm events from three main sediment source groups: gullies, road crossings and landslides. Within each group, regression equations were developed to predict the sediment yield based on attributes of the source and storm rainfall parameters. The model then calculates the sediment budget of sub-basins of Russell Creek by routing the flow and sediment through valley flat areas where appropriate, and finally adds the components together to give the overall sediment yield, broken down by type. Current focus of the sediment budget research has been to develop the sediment budget model as a road deactivation effectiveness-monitoring tool, and to validate and/or adjust the model under a broader range of storm conditions. Results obtained so far have yielded a road source yield model that suggests road deactivation measures that may reduce sediment yield from crossings. Potential road deactivation techniques range from water management to divert water away from crossings, to reduction of exposed sediment area in cut and fill slopes and stabilization of fill slopes. These techniques are being tested on selected active roads in Russell Creek, in conjunction with ongoing monitoring in order to test their effects on the sediment budget. The relative cost of these techniques, compared to their effectiveness at reducing unwanted sediment input to streams, will help form the basis of best management practices to manage sediment yield due to forestry activities. It has also been recognized that a better understanding of the processes that govern streamflow is essential to further develop the sediment budget model, since sediment production and transport is intrinsically linked to streamflow. At the same time it is also apparent that streamflow has been significantly altered by forest harvesting and subsequent regeneration (Hudson, 2002) and that this change in streamflow has resulted in a change in sediment transport in Russell Creek (Hudson, 2001c). The effects of forest roads on streamflow must also be included to fully understand the sediment budget. At some sites there is reason to believe that ditches divert large volumes of water into the crossing under high flow conditions. Persistent patterns of sediment production at these sites indicate that dilution may be occurring as a result of inflows from ditches. These developments have led us to undertake a road drainage study that involves combined field work and model development. We have undertaken to develop the DHSVM hydrology simulator as a platform for developing a physically based model to integrate the effects of forest management practices and sediment production and transport processes. This model will ultimately form a powerful tool to forecast the effects of management practices on streamflow and sediment budgets. We will convert existing empirical models (hydrologic recovery and sediment budget) into physically based models that have much greater ability to be extended to other areas due to being firmly rooted in hydrologic and geomorphic processes.
Contact: Floyd, Bill, (250) 751-7051, william.floyd@gov.bc.ca

Updated April 29, 2011 

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