Forest Investment Account (FIA) - Forest Science Program
FIA Project Y092214

    Cotton Creek Phase II: Multi-scale, spatially explicit studies of Mountain Pine Beetle impacts on watershed function
Project lead: Moore, Dan (University of British Columbia)
Contributing Authors: Jost, Georg; Moore, R. Dan; Weiler, Markus; Gluns, David R.; Alila, Younes
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
The Cotton Creek Experimental Watershed (CCEW) has been monitored intensively for three years, and is yielding valuable information on watershed function and the effects of forest management. The 17.4 km2 watershed lies 17 km south of Cranbrook. Elevations range from 1050 m to over 2000 m. Snow accumulation and melt dominate the hydrology as is typical in southeast BC.

Over 50% of the watershed is covered by lodgepole pine and CCEW is thus rated as a high risk watershed for Mountain Pine Beetle (MPB) infestation. Outbreaks of MPB in the watershed in the 1980s and 1990s resulted in salvage logging (see Fig. 1). MPB are currently infesting neighbouring catchments, and are beginning to establish within CCEW. There is a reasonable likelihood that MPB infestation will further expand over the next three years to the point that further salvage logging may be warranted. Should this occur, CCEW would provide a unique opportunity to document the effects of MPB-related tree death and salvage logging on watershed processes and aquatic habitat.

CCEW is one of the only medium-sized watersheds that has detailed and dense field monitoring of hydrological processes, micro-meteorological processes, channel morphology, water quality and riparian processes. In contrast to long-term monitoring of streamflow and water quality at individual sites, as conducted in paired catchment experiments, we simultaneously monitor the variability and changes of streamflow and channel geomorphology in multiple, nested basins, and employ a stratified sampling approach to study snow accumulation, snow melt and runoff generation. The existing infrastructure involves a nested network of 12 gauges along the main channel measuring stream discharge, stream temperature and electrical conductivity. This network documents the effect of riparian zone management on water temperature and the effect of road density on surface runoff using hydrograph separation techniques. Climate stations at different elevations and aspects record air temperature, humidity, wind speed and direction, precipitation, incoming solar radiation and snow depth (Fig 2). A network of 60 groundwater wells monitors subsurface flow and the occurrence of surface saturation (Fig 3). Soil moisture is also monitored at all groundwater wells.

Channel morphology and bedload transport are measured with 2 bedload pillow systems (developed for this watershed and installed in 2005). In additional, several bedload traps were installed along the main channel and in several tributaries to record the spatial variability of annual bedload transport.

A GIS database was established based on available GIS data sources, but also includes additional data collected in the watershed. For example, a detailed terrain analysis was undertaken in 2005 and digitized to be used in a GIS. The GIS database also includes a high resolution DEM (10 m), terrain indices (e.g. slope, wetness index), longitudinal stream profiles, updated road network, GPS corrected road culvert locations and drainage direction, and 50 soil profile observations.

We propose to continue the CCEW study for the next three years (and beyond), during which time MPB should affect a substantial portion of the watershed (the area dominated by Pinus contorta is at high risk of MPB attack or is already under attack as red attack has been observed this summer at some plots). Because we have already collected extensive baseline date during the last 3 years, CCEW provides a unique opportunity to monitor changes in watershed processes prior to and during MPB infestation and following salvage logging. We do not expect salvage logging to occur in the watershed during the next 3 years (but probably afterwards), but since some extensive areas in the northern part of the watershed have already been salvage logged, the cumulative effect of disturbance varies among the subwatersheds and hence allows a spatial comparison of watershed function across a range of disturbance intensities.

The spatially distributed measurements of snow accumulation and melt, soil moisture and groundwater levels will allow site-scale impacts on surface and subsurface hydrology to be quantified, and the nested stream gauging network will capture the cumulative catchment-scale hydrologic effects. This study will address well-recognized knowledge gaps. For example, site-scale studies near Prince George indicate that dead stands accumulate almost as much snow as a clearcut, but have melt rates closer to those under a forest canopy (Sarah Boon, UNBC, pers. comm.). However, it is unclear whether these results are more broadly transferable, especially to mountainous catchments with diverse slopes and aspects. It is also unclear how those stand-scale processes will integrate up to influence hillslope runoff and streamflow patterns. There is also the potential for increased nutrient export in streams, which could have implications for aquatic communities. There is also uncertainty concerning how channel stability and morphology and habitat characteristics will respond, particularly in relation to the effects of wood loading

The proposed work will focus on two components: (1) runoff dynamics and the influences of forest disturbance and management; and (2) processes governing the downstream transport and distribution of water, nutrients, heat, sediment and woody debris. Component (1) will improve our knowledge of the fundamental hydrologic processes as influenced by forest disturbance and management, particularly the propagation of impacts from hillslope to channel. If MPB continue to spread within CCEW, we will have an excellent opportunity to observe the effects of tree death and, ultimately, management response at both site and catchment scales. Furthermore, the data collected will contribute to the ongoing testing of spatially distributed, physically based models such as Distributed Hydrology-Soil-Vegetation Model (DHSVM) and the Sensitive Area Mapping Model (SAMM) (see linkages section for details). Component (2) will involve two sub-components: (a) a study of the spatial patterns of channel processes and morphology in relation to catchment scale and governing geomorphic processes; and (b) a study of hyporheic exchange at the channel unit, channel reach and channel network scales, particularly in relation to channel and basin morphology. Component (2) will provide a basis for understanding and predicting the propagation of disturbance effects in the headwaters to downstream reaches, i.e., cumulative effects.

Research will be conducted by 3 PhD students supervised by the co-applicants. The project will continue to be a partnership between UBC and BC MoFR (via Dave Gluns), and the industrial partners in Phase I (Tembec, Kalesnikoff and Apex Geoscience) will continue to be partners in Phase II should the proposal proceed beyond the LOI.
Related projects:  FSP_Y081214FSP_Y103214

Improvement on snow melt model
Executive summary (16Kb)

Updated August 16, 2010 

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