Discharge and instantaneous sediment concentration may not have a stationary relation during a single storm flow. The tendency for sediment concentration to have different values at identical stream discharges (a "hysteresis" effect) is the primary drawback to application of transport curves during storm flow. Two examples of hysteresis are shown in figure 19 . Sediment sample data are plotted for the storm flows of December 3-4, 1982, and December 9-10, 1987, at the North Fork Toutle River at Kid Valley. The 1982 data are instantaneous sediment concentrations of cross-section samples, and the 1987 data are adjusted automatic pumping samples. The arrows indicate the sequence of sample collection for sediment concentration.
