|Citation||Hudson, R. 2002. Effects of forest harvesting and regeneration on peak streamflow in a coastal watershed. Forest Research Technical Report TR-022. Vancouver Forest Region.|
|Abstract/Description or Keywords||The issue of whether or not forest harvesting affects peak
streamflows in Coastal British Columbia watersheds has been
the subject of recent debate in the literature. In British Columbia,
we use equivalent clearcut area (ECA) as an estimate of
the potential for existing forest harvesting and regeneration to
affect peak streamflow, but the link between ECA and peak
streamflow has not yet been developed. This report works towards
establishing that link, and also suggests the geomporphic
significance of the changes in peak flow.
At Russell Creek, a fourth-order tributary sub-basin of the
Tsitika River on northeastern Vancouver Island, a model of
peak flow based on rainfall intensity was developed and used
to demonstrate a decline in peak flows concurrent with a decline
in ECA. The model divides up the 10-year data record
into three distinct time periods with significantly different peak
flow responses, such that the changes in peak flow can be assessed
as a logarithmic function of a relative change in ECA.
The mean response to a change in ECA of 10% was a change
in peak flow of about 50%.
A specific gauge analysis reveals a major shift in gauge height
consistent with channel scour that occurred at the time of two
large peak flow events of 43 and 42.4 m3
/s. The model predicts
that at an ECA of 17.5%, these flows were increased by
70% compared to the unharvested state. The estimated effect
of ECA conditions on flow frequencies suggests that channel
forming events of 12-year return interval have been increased
in both frequency and magnitude by about 70%. This effect
has been substantiated by other studies at Russell Creek where
significant changes in sediment transport have been attributed
to declining ECA.
forestry, forest harvesting, regeneration, forest management, hydrology,
streams, peak flow, sediment, sediment budget, sediment
production, sediment yield, Vancouver Forest Region,
DISCLAIMER - - https://www.for.gov.bc.ca/rco/research/Hydroreports/tr022_disclaimer.pdf The results presented in this paper represent a first step towards the interpretation of ECA
in its effect on peak streamflow. Very substantial changes in peak flow were documented
for relatively small changes in ECA at Russell Creek. While the research has been judged
sound under critical review, the method (meteorological control) used to assess these
changes is not the standard method and has yet to be accepted by the scientific
community at large. Furthermore, the method has been applied to one watershed under a
limited range of ECA conditions. Therefore the results of this analysis are not ready for
general application. The following steps must be taken:
• The meteorological control method must be evaluated alongside the standard paired
watershed method to validate its utility at assessing changes in peak flow. This must
be done in an experimental watershed that has both a control watershed and the
appropriate meteorological data.
• The product of the above analysis will be submitted to a refereed journal (Water
Resources Research) for publication.
• Once accepted the meteorological control method can be applied to other logged
watersheds with a range of morphological characteristics.
• Once the above steps have been taken, then a general model of the relationship
between ECA and peak streamflow will begin to emerge.
|Regional Watershed||sunshine coast|
|Sub-watershed if known||Flume Creek|