Greeline to Greenline Width (GGW). Non vegetated Channel width. GGW. The non-vegetated distance between the greenlines on each side of the stream. Using “Greenline rules” adds precision to the measurement Consistent GGW measurements between observers validates the greenline rules.
Non vegetated Channel width
GGW approximates the scoured, or non-vegetated width of the channel.
Including islands adds width bias to the estimate.
Typically, we are estimating the width of the “active” channel which normally excludes vegetated bars and islands.
Measures Horizontal Distance (Accuracy - .01 meter)
GGW = cos D
Upstream – light impacts- 4m wide
Downstream – heavy impacts – 8 m wide
N = 125 each side
alpha = .05
Scour LineStreambank Stability
That portion of the channel cross section:
- above the scour line, and
- below the lip of the first bench.
Scour Line: The lower elevational limit of a streambank. On erosionsal banks, the scour line is the elevation of seasonal scour – often marked by undercut sod.
Scour line: On depositional banks, the scour line is the lower limit of sod-forming or perennial vegetation – or the potential lower limit of sod-forming vegetation
What is the streambank evaluated? Above the Scour Line and at the steepest angle to the water surface.
On erosional banks the measurement extends up to the bench or top of cutbank.
On bars, it extends up to the top of the depositional feature: approximately bankfull level
The first bench is the first relatively flat area above the scour line or edge of the water
Fracture: a visiblecrack is observed. The fracture has not separated into two separate components or blocks of a bank. Cracks indicate a high risk of breakdown. The fracture feature must be at least ¼ of a frame length or greater than about 13 cm of bank length.
Slump: streambank that has obviously slipped down resulting in a separate block of soil/sod separated from the bank.
Slough or “sluff soil material has fallen from and accumulated near the base of the bank. “Slough” typically occurs on banks that are steep and bare.
Eroding: applies to banks that are bare and steep (within 10 degrees of vertical), usually located on the outside curves of meander bends in the stream.
Trampling by large herbivores has caused obvious “slumping.” The slump is greater than one-fourth of the plot length and is recorded (S).
There is a hoofprint in the bank, but no slump or slough is associated with the hoofprint; therefore, there is no indicator of instability so covered (C) and absent (A) are recorded.
Top of bank associated with the hoofprint; therefore, there is no indicator of instability so covered (C) and absent (A) are recorded.
Where is the top of the bank?
Where is the scour line?
The key: whether slough enters the stream
Where is the first Bench?
In a review of the literature, Powell et al. (2000) concluded that channel characteristics, including channel width and depth, as well as bed material were often reported to be affected by livestock grazing in riparian areas.
Size distribution and Percent Fines
At 20 plot locations (200 samples)
Sampled between the greenlines
10 particles per plot (cross section) selected at heel and toe across the channel from greenline to greenline – total 200 particles
Can lay measuring rod across small streams to obtain sampling intervals
“Operator training is extremely important. When selecting particles from a predefined streambed location, or even when measuring particle sizes in a preselected sample of rocks, there is less variability between the results of experienced operators than between those obtained by novices. Field personnel need to be trained to perform procedures accurately, to avoid bias, and to use equipment that reduces operator induced error.” (Bunte and Abt (2001)