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Riparian cover changes associated with flow regulation and bank stabilization along the Upper Willamette River in Oregon between 1939 and 1996
This study investigates riparian cover change between 1939 and 1996 utilizing aerial
photography, bank conditions and stream gauge data. Three sites under 1.0 km2, along a 10-
km reach north of Harrisburg, Oregon, were evaluated. The cover classification scheme
included 18 classes composed of 3 canopy densities and 8 structural categories: water, bare
gravel bars, herbaceous, shrub, small trees, medium trees, closed trees, and agricultural fields.
Net cover changes and shifts between classes were analyzed for each site as a whole and as
terrestrial vs. fluvial changes. Terrestrial changes (i.e. areas unaffected by channel
movement) were discriminated from fluvial changes (i.e. areas where a channel migrated out,
in or both) by inspection of 14 air photo coverages between 1939 and 1996.
Over 75% of each site experienced net cover change between categories of water,
bare, cleared land, low vegetation, open-canopy trees, and closed-canopy trees. Water cover
composed over half the area that remained the same. Net progressive structural change (i.e.
an increase in cover maturity, e.g. bare changing to trees) exceeded or equaled net regressive
structural change at each site. Progressive structural change was only slightly favored in
fluvial areas, while terrestrial areas favored progression 4 to 1 at each site. Bare ground
decreased by 35%, 65% and 90%, while forest cover increased by 10%, 50% and 150% at the three study sites. The only areas of non-forest cover remaining in 1996 existed on land
disturbed by the channel since 1939.
The maturation of structural cover was associated with decreases in channel
dynamics and fluvial disturbance between 1939 and 1996. Channel migration affected 50%
to 70% of each study area during this period, but most shifts occurred before 1956. Sixtyeight
percent of the revetments present in 1996 were established by 1956. These revetments
hardened portions of all outer bends along the study reach, limiting lateral channel
migration. Upstream dams held 42% of the 1996 storage by 1956, which reduced peak
flows
Nuclear quadrupole resonance as a non-destructive testing tool
Nuclear pure quadrupole resonance (NQR) is a resonance technique that provides distinctly different information from that provided by nuclear magnetic resonance (NMR). In NMR the splitting of the energy levels, and therefore the frequency observed, occurs because of the interaction of the nuclear magnetic moment with an external magnetic field. Information about the system under study comes from perturbations on this magnetic interaction. These perturbations lead to a broadening of the line, or to relaxation effects on the interchange of energy between the spins and the lattice, and among the spins. In NQR the primary interaction is between the electric quadrupole moment of a nucleus and the electric field gradient at that nucleus. The field gradient is provided by internal interactions in the sample itself, arising from the chemical bonds, rather than by an external field. Anything that changes the bonding environment, such as tensile stress, will cause shifts in the quadrupole resonance frequency. All nuclei with spin greater than 1/2 have a nuclear quadrupole moment, in addition to their magnetic moment. The nucleus used as an example in this paper is 75As, which has spin 3/2
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