Pool-riffle sedimentation and surface texture trends in a gravel bed stream

A 3 year field campaign was completed to investigate spatial and temporal variability of sedimentation trends for a single pool-riffle pair located in the Santa Cruz Mountains, California. Our measurements represent a range of hydrologic conditions over 11 sediment-mobilizing events. Two different statistical methods were used to explore riffle sedimentation. Cochran's Q and McNemar's nonparametric tests (one method) indicate that riffle sediment surface texture was spatially and temporally varied at the transect level. For McNemar's test, variation was significant at p < 0: 05, with several trends evident, including strong riffle fining triggered by a 20 year flood event. A nonlinear empirical orthogonal function method known as self-organizing maps (SOMs; the second method) shows that riffle sediment surface texture is well described by two characteristic temporal signals, and one transitional signal at the sampling node level. SOM mapping to each sampling node clearly shows riffle sediment surface texture change was spatially organized over the 11 sediment-mobilizing events. Observations of pool sediment storage indicate that the pool-riffle pair exhibited a coupled sedimentation response (i.e., similar texture trends between pool and riffle) following the 20-year flood. The coupled response was characterized by a trend toward overall sedimentation conditions that were similar to those measured at the beginning of the study. The reported texture trends may be of interest to salmonid habitat studies that examine factors contributing to successful versus unsuccessful fry emergence.