Abstract:
I documented reach scale changes in the physical structure of 12 stream channels in the
summer months of 2006, comparing four small streams draining forested catchments with eight
streams from developed watersheds of similar catchment size. Study sites in four of the urban
streams are within recently implemented natural channel design restoration projects. To assess
whether restoration projects increase stream habitat and flow heterogeneity and increase water
exchange with floodplain and hyporheic sediments I compared reach-scale geomorphic (e.g.
slope, cross section, degree of incision, variation in water depth) and hydrologic (e.g. transient
storage volume (TS), surface-water groundwater exchange, fine scale variation in velocity)
features of each stream. I used ArcGIS to compile watershed maps and to produce detailed maps
of reach habitat for each stream, and the hydrologic model OTIS-P to estimate transient storage
from field rhodamine releases. Minimally impacted reaches were found to have shallower
average depths with a greater variation in depth than urban or restored stream reaches. Streams
restored to provide habitat had the lowest flow habitat heterogeneity of the three stream classes.
Channel incision was the only physical channel feature for which the urban restored streams
were more similar to the forested streams than the urban degraded condition. Surprisingly, I was
unable to detect significant differences in transient storage volume or hyporheic exchange
between our three stream classes. My results suggest that restoration designs are placing
inadequate attention on recreating the physical template seen in less degraded streams.
