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Study results

Last updated on January 23, 2023

The research data from the slash in stream studies show which variables are the best predictors of channel disturbance.

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Results

The Nitinat Lake study included 99 stream reaches and the Anderson River study included 42 stream reaches. The graphs below show the characteristics of the streams for each variable included in the studies.

Click on images to enlarge.

Graph showing the location of streams, most were in a gully or open slope. Click to enlarge.

Graph showing the depth of the streams. Over half the Anderson streams were 0.1 to < 0.3 metres and over half the Nitinat were 0.2 to < 0.4 metres deep. Click to enlarge.

Graph showing the size of woody debris moving in the streams. Most streams had small woody debris, and few had logs. Click to enlarge.

Graph showing the gradient of streams, most were between 10 and 30 percent. Click to enlarge.

Graph showing the extent of stream bank erosion, most showed no erosion. Click to enlarge.

Graph showing the average jam volume in cubic metres. Most jams in Nitinat were 0.1 to 10 and most in Anderson were 0 to 1 cubic metres. Click to enlarge.

Graph showing width of streams. Almost half the Nitinat streams were 2 to < 3 metres, and half the Anderson streams were 1 to < 2 metres wide. Click to enlarge.

Graph showing the extent of bed erosion in the streams. The majority had no erosion. Click to enlarge.

Graph showing the average sediment wedge volume in cubic metres. Almost half in Anderson were 0.1 to 1 while 40 in Nitinat had no volume and a third had 0.1 to 1 cubic metres. Click to enlarge.

Predictors of channel disturbance

Based on the data collected during the studies, the following variables are significant predictors of channel disturbance:

  • Channel width, depth, and area; width is best predictor
  • Size of sediment transported in the stream
Channel width and size of woody debris moved
Woody debris size moved Channel width (m)
Anderson Nitinat
Minimum Median Maximum Minimum Median Maximum
Small woody debris (SWD) 1.1 1.6 2.8 0.8 2 3.3
Large woody debris (LWD) 2.2 2.9 5.7 1.9 3 4.6
Logs   4.9   3.1 4.1 5.8

Jam volume and width for Anderson
Graph showing average jam volume and channel width for Anderson. Click to enlarge.

Click on image to enlarge.

Jam volume and width for Nitinat
Graph showing average jam width volume and channel width for Nitinat. Click to enlarge.

Click on image to enlarge.

 

Sediment size and woody debris size moving
Woody debris size moved Sediment size moved (mm)
Anderson Nitinat
Minimum Median Maximum Minimum Median Maximum
Small woody debris 1 100 120 2 90 280
Large woody debris 110 200 310 45 150 360
Logs   340   140 210 360

Jam volume and sediment size for Anderson
Graph showing average jam volume and maximum sediment size moved in channels in Anderson study. ​Click to enlarge.

​Click on image to enlarge.

Jam volume and sediment size for Nitinat
Graph showing average jam volume and maximum sediment size moved in channels in Nitinat study. ​Click to enlarge.

​Click on image to enlarge.

What about gradient?

  • Gradient has no real effect
  • Steeper streams have more channel roughness
  • Lower gradient streams are more able to float woody debris

Useful predictors of water transport potential:

  • Channel width (could also use channel area, but no better as a predictor)
  • Size of sediment moving in channel
  • In these two studies, the size of woody debris moving in the channel was used as a response variable, but can also be used as a predictor prior to harvesting

Water transport assessment and cleaning strategies

The research led to recommended cleaning strategies based on water transport potential in streams. 

Water transport assessment
Water transport potential Low Moderate High
Bank full channel width (m) ≤  2 > 2 to ≤  3.5 > 3.5
Size of water transported woody debris SWD LWD Logs
Largest sediment transported (mm) ≤ 100 > 100 to  ≤ 200 > 200

Cleaning strategy
Water transport potential Cleaning strategy
Low Do not clean
Moderate Clean all introduced SWD and most LWD
High Clean all logging debris except larger logs