| Summary: | It is common for mountain riverbeds to exhibit a repetitive pattern of topographic lows and
highs known respectively as pools and riffles. Pool-riffle structures are ecologically important
because salmon rely on them for birth, growth and regeneration, and they are physically important because pool-riffles are observed across diverse landscape settings. A common physical characteristic of pool-riffles is that pool spacing is proportional to channel width, for longitudinal bed slopes that vary by two-orders of magnitude. Furthermore, field, numerical
and laboratory based studies observe that pools are colocated with points of channel narrowing,
and riffles with points of widening. What is not known, however, is how downstream
changes of channel width give rise to, and maintain pool-riffles. The goal of my thesis is to
address this knowledge gap, and to specifically build physical understanding for the observed
spatial correlation between channel width and pool-riffle architecture. I use field work, laboratory
experiments and theory to address this goal. In Chapter 2 I apply non-parametric
statistics and self-organizing maps to understand the spatial and temporal character of riffle
bed surface texture spanning 11 different sediment mobilizing floods, and conclude that
frequent texture adjustment is part of the maintenance process for pool-riffles which exhibit
topographic stationarity. I build from this finding in Chapters 3, 4 and 5 with laboratory experiments designed to investigate how pool-riffles form and evolve along variable width channel reaches. In Chapter 4 I conclude that pool-riffle formation is physically driven by two competing timescales which reflect the tendency to build riverbed topography through sediment
deposition, vs. the tendency to destroy topography through net particle entrainment. I capture
these timescales in a mathematical model I develop using theory with physical scaling.
In Chapter 5 I show that the (dis)equilibrium state of pool-riffle evolution is quantitatively described by a competition between two rates which reflect the temporal adjustment of riverbed
topography and riverbed surface texture. I conclude that equilibrium, or comparability between
the rates of topographic and sediment texture adjustment, is most likely to occur when
overall sediment mobility and grain size sorting are relatively high. === Arts, Faculty of === Geography, Department of === Graduate
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