Water Stewardship Information Sources
| 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. |
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| Organization | FLNRO |
| URL | https://www.for.gov.bc.ca/rco/research/hydroreports/tr022.pdf |
| 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. KEYWORDS forestry, forest harvesting, regeneration, forest management, hydrology, streams, peak flow, sediment, sediment budget, sediment production, sediment yield, Vancouver Forest Region, British Columbia 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. |
| Information Type | report |
| Regional Watershed | sunshine coast |
| Sub-watershed if known | Flume Creek |
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| Comments | |
| Project status | complete |
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