The following text describes terminology and methods regarding how changes in streambed elevation over time have been summarized by RNP scientists. (note: squares in text below represent the symbol delta)

The thalweg (T) is defined as the lowest point in the streambed in a cross-sectional profile. Active channel width is the channel width occupied by the effective discharge and is identified in Redwood Creek by highwater marks, vegetation breaks and breaks-in-slope. Nolan and others (1987) defined the effective discharge as the discharge that transports the majority of sediment due to its high frequency of occurrence (RI = 1.8 years on Redwood Creek or 425 m3/s or 15,000 ft3/s). 

Net change in streambed area (As) is the difference between the area of fill and area of scour across the streambed. Mean change in streambed elevation (Ec) is a normalized value that compares the relative importance of changes at cross sections of different widths and is derived by dividing the net change in streambed area (As) by the active channel width (W).

Change in Mean Streambed Elevation: Ec = As/W

Thus, a lowering of the mean streambed elevation by 0.15 m (Ec = -0.15) produces the same percent change in a 10 m wide cross section as it does in a 100 m wide cross section, even though more material has moved through the wider cross section. A change in mean streambed elevation of 0.05 m or less is within the survey measurement error and cross section changes within this range are considered to show no change.

For each survey year, the cumulative change in mean streambed elevation is calculated. The cumulative change in mean streambed elevation is plotted by year to show trends at individual cross sections over time and can depict general trends in infilling, scouring, or stability at the cross section. 

Varnum, N. and Ozaki, V. 1986. Recent channel adjustments in Redwood Creek, California. Redwood National Park Technical Report 18. U.S. Department of the Interior, National Park Service, Arcata, California. 74 pp.