Testing and improving predictions of scour and fill depths in a northern California coastal stream

Seasonal scour and fill from bankfull flows were measured in Freshwater Creek, a gravel-bed coastal stream of northern California, to test a previously developed approach predicting the reach-average and distribution of scour or fill depths based on Shields stress and the exponential function. Predictions of reach-average scour and fill depths were within 4-60% of measured depths. Three of the four predicted distributions of scour and fill depths were statistically different (P < 0.05) from measured distributions. Differences between predicted and measured values were likely due to scour and fill patterns in Freshwater Creek that were influenced by sediment supply and location within the channel network, channel form roughness, and possibly multiple peak flows. Consequently, the predictive approach may be better suited for individual peak flows on straight reaches that are in equilibrium between sediment supply and transport, and with form roughness similar to the creeks where the approach was developed. Improved predictions of scour and fill are possible with adjustments for aggrading reaches and form roughness. Copyright (c) 2005 John Wiley & Sons, Ltd.