Forest Investment Account (FIA) - Forest Science Program
FIA Project Y082031

    Hydrogeomorphic response to forest disturbance: Fishtrap Creek
 
Project lead: Eaton, Brett (University of British Columbia)
Contributing Authors: Eaton, Brett C.; Phillips, Jeffrey C.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
This project is focused on impacts following an intense forest fire in 2003 that burnt much of the Fishtrap Creek watershed. We will document the resulting geomorphic changes, and compare them to a numerical model. W will also conduct research on stream temperature changes following the fire. The results from both aspects of the study will give us insight into how streams impacted by the mountain pine beetle are likely to be affected, and will help to improve our management strategies. In summer 2003, the McLure fire near Kamloops caused severe disturbance to approximately half of the Fishtrap Creek catchment area. Large portions of the burned areas have now been salvage logged. In the lower valley, the fire killed almost all of the trees in the riparian zone adjacent to the channel mainstem. Numerical models of stream channel morphology suggest that the reduction in bank strength due to the death of the riparian vegetation will result in a shift from the current stable single thread channel morphology to a braided channel with on average about four individual channels: the associated transport capacity for the current median sediment size on the bed is predicted to drop by at least one order of magnitude, suggesting that significant changes in the sediment routing will occur as well. This case presents a unique opportunity to study disturbance effects on watershed hydrology, sediment dynamics and channel morphology due to the availability of data and easy year-round access to the stream’s lower reach. This research will help us answer the basic question, ‘what are the types of watershed response and their magnitude that can be expected following a large, intense disturbance such as a forest fire or Mountain Pine Beetle infestation?’ The research is the first phase of a longer term commitment by researchers at the University of British Columbia to study the processes and rates of watershed disturbance and recovery. Fishtrap Creek is an ideal study site since it has been gauged by Water Survey of Canada (WSC) since 1971. In addition, our research team has collected data on water chemistry, suspended sediment dynamics, water temperature, and channel morphology and dynamics since the fire, so we have a good baseline dataset. Streamflow and water quality measurements are also being made on nearby Jamieson Creek, which was not disturbed by recent wildfire. Fieldwork conducted during the initial phase of this FSP project indicates that these changes are already in progress, and we have already presented the preliminary results at two conferences and the work to-date forms the basis for one MSc degree. The work planned for 2007/2008 will lead to the completion of at least two more MSc projects (J. Leach and C. Andrews), to additional conference presentations and to the publication of several peer-reviewed journal articles. Response from colleagues in the US Forest Service is that this is some of the most important and relevant work on environmental change and stream channel response being conducted anywhere. During the first post-fire freshet, suspended sediment concentrations at Fishtrap Creek did not exceed typical values for undisturbed catchments, as documented by pre- and post-fire monitoring (Petticrew and Owens, in press), indicating that significant channel changes did not occur during this peak flow event. However, during 2005, measured SSC peaked at almost 700 mg/L, several times the peak value for Jamieson Creek. Observations from the freshet in 2006 indicate that the channel upstream of the monitoring site is beginning to widen and aggrade, and there are signs that the channel may become braided, possibly over the course of the next few years. These changes are occurring as a result of loss of root strength due to the fire, but changes in the large woody debris (LWD) input rates to the stream channel also seems to have had significant effects on the instream geomorphic processes. It is expected that the rate of channel change will continue to accelerate over the next few years as the root structure continues to decay. The dataset that we will collect on the resulting channel changes will be unique, and will help complete the calibration of the channel dynamics model published by Eaton (2006), which is used to separate channel changes related to increases (or decreases) in peak stream discharge from those associated with changes in vegetation-related dynamics. This tool will help managers assess potential responses in other impacted watersheds. Large-scale disturbances associated with wildfire and insect infestations can produce dramatic vegetation changes in the riparian zone, as has been observed at Fishtrap Creek. Loss of foliage from dead trees will reduce stream shading and should result in summertime stream warming due to increased solar radiation. However, the standing dead trees continue to cast some shade, similar to a leafless deciduous forest. In the short to medium term, stream widening, aggradation and a shift to a braiding habit may decrease the amount of shading and result in shallower flows, both of which would tend to increase stream temperatures. In the longer term, recovery of riparian forest should increase shade. While many studies have studied stream temperature response to forest harvesting with and without riparian buffers (Moore et al., 2005), and some have documented longer term thermal recovery, fewer studies have examined stream temperature response to natural disturbances (Nitschke, 2005), and none has attempted to quantify the amount of shade cast by standing dead trees or document longer-term post-fire thermal changes. Fishtrap Creek presents an excellent opportunity to document stream temperature response to changes in riparian vegetation over a range of time scales.
Related projects:  FSP_Y071031

    Deliverables:

Final Technical Report (0.2Mb)
UBCRM User’s Manual (0.3Mb)
Post-Fire Dynamics of a Gravel Bed Stream (Thesis) (1.8Mb)
Data (30Kb)

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Updated August 16, 2010 

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