A geostatistical framework for quantifying the reach-scale spatial structure of river morphology: 2. Application to restored and natural channels

摘要

Alluvial rivers are shaped by interactions between the bed topography, the flow field, and the movement of sediment. To help refine our understanding of these connections between form and process, I developed a geostatistical framework for quantifying the reach-scale spatial structure of river morphology, described in a companion paper. In this study, I applied this approach to a restored channel and three disparate reaches of a dynamic, natural stream. Repeat topographic surveys of each site were used to examine relationships between channel change and the variability and organization of the topography. For the restored river, the development of point bars increased overall morphologic diversity, primarily because of greater cross-sectional asymmetry. The three natural reaches experienced a variety of adjustments ranging from 1) gradual bar growth and bank erosion to; 2) extensive deposition followed by channel abandonment; and 3) chute cutoff and incision of a new channel. In both the restored and natural streams, geostatistical analysis, which involved variogram modeling, calculation of integral metrics, and inspection of variogram maps, provided an effective, informative summary of the observed channel changes. The use of dimensionless variables accounted for channel size, highlighted differences in spatial structure, and enabled a comparison among sites - the restored reach had not yet achieved the same degree of heterogeneity as the more pristine channels. Emphasizing variability and spatial pattern via this geostatistical framework could yield insight on form-process interactions and help to quantify geomorphic complexity and habitat heterogeneity in the applied context of river restoration.