River restoration practices aiming to sustain wild salmonid populations have received considerable attention in the Unites States and abroad, as cumulative anthropogenic impacts have caused fish population declines. An accurate representation of local depth and velocity in designs of spatially complex riffle-pool units is paramount for evaluating such practices, because these two variables constitute key instream habitat requirements and they can be used to predict channel stability. In this study, three models for predicting channel hydraulics-1D analytical, 1D numerical and 2D numerical-were compared for two theoretical spawning habitat rehabilitation (SHR) designs at two discharges to constrain the utility of these models for use in river restoration design evaluation. Hydraulic predictions from each method were used in the same physical habitat quality and sediment transport regime equations to determine how deviations propagated through those highly nonlinear functions to influence site assessments. The results showed that riffle-pool hydraulics, sediment transport regime and physical habitat quality were very poorly estimated using the 1D analytical method. The 1D and 2D numerical models did capture characteristic longitudinal profiles in cross-sectionally averaged variables. The deviation of both 1D approaches from the spatially distributed 2D model was found to be greatest at the low discharge for an oblique riffle crest with converging cross-stream flow vectors. As decision making for river rehabilitation is dependent on methods used to evaluate designs, this analysis provides managers with an awareness of the limitations used in developing designs and recommendations using the tested methods.

24In efforts to rehabilitate regulated rivers for ecological benefits, the flow regime has been one of 25 the primary focal points of management strategies. However, channel engineering can impact 26 channel geometry such that hydraulic and geomorphic responses to flow reregulation do not 27 yield the sought for benefits. To illustrate and assess the impacts of structural channel controls 28 and flow reregulation on channel processes and fish habitat quality in multiple life stages, a 29 highly detailed digital elevation model was collected and analyzed for a river reach right below a 30 dam using a suite of hydrologic, hydraulic, geomorphic, and ecological methods.

Past river classifications use incommensurate typologies at each spatial scale and do not capture the pivotal role of topographic variability at each scale in driving the morphodynamics responsible for evolving hierarchically nested fluvial landforms. This study developed a new way to create geomorphic classifications using metrics diagnostic of individual processes the same way at every spatial scale and spanning a wide range of scales. We tested the approach on flow convergence routing, a geomorphically and ecologically important process with different morphodynamic states of erosion, routing, and deposition depending on the structure of nondimensional topographic variability. Five nondimensional landform types with unique functionality represent this process at any flow; they are nozzle, wide bar, normal channel, constricted pool, and oversized. These landforms are then nested within themselves by considering their longitudinal sequencing at key flows representing geomorphically important stages. A data analysis framework was developed to answer questions about the stage‐dependent spatial structure of topographic variability. Nesting permutations constrain and reveal how flow convergence routing morphodynamics functions in any river the framework is applied to. The methodology may also be used with other physical and biological datasets to evaluate the extent to which the patterning in that data is influenced by flow convergence routing. Copyright © 2018 John Wiley & Sons, Ltd.

20The relationships between flow hydrology, topography, and channel change in mountain 21 rivers is important to understanding landscape evolution, the structure and persistence of aquatic 22 habitat, and also the physiochemical cycling of upstream derived organic and inorganic 23 materials. There is a paucity of detailed studies that analyze the joint roles of hydrology and 24 topography in controlling multiple mechanisms of channel change in mountain rivers. In this 25 study, gravel and cobble channel change in a bedrock river canyon were analyzed in light of a 26 controlled yet natural experiment where 4,491 metric tonnes of rounded gravel and cobble was 27 augmented below a sediment-barrier dam in a 1,200 m long mountain river reach that had no 28 prior sources of rounded gravel or cobble and still experiences floods above the bankfull 29 discharge. The overall study goal was to investigate how flow hydrology can modulate multiple 30 channel change processes depending on the topographic features engaged by the flow. Channel 31 change was assessed via differencing of high resolution repeat topographic and bathymetric 32 surveys, along with cm-scale aerial photography post injection. Statistical tests used to implicate 33 topographic feature-specific mechanisms of channel change that vary with discharge included 34 analyzing geomorphic covariance structures of flow dependent width, bed elevation, and channel 35 change as well as autocorrelation of flow width spatial series. Stage dependent topographic 36 steering was inferred from associations of erosion and deposition with changes in 2D model 37 derived flow directions at multiple discharges. A variety of mechanisms of channel change were 38 qualitatively and quantitatively confirmed including particle hiding, topographic steering, 39 eddying, and flow convergence. No single mechanism explained the observed patterns of 40 channel change but rather it is thought that process-blending occurs, as modulated by the 41 interactions of flow hydrology with complex topography. Results from this study suggest that 42 both existing channel boundary variability and input hydrologic variability work together to 43 create hydrodynamic spatial patterns that control the fate and transport of sediments in mountain 44 rivers and ultimately their spatial structure. 45 46

River corridors exhibit landforms nested within landforms repeatedly down spatial scales. In Pasternack et al. (), a new, scale‐independent, hierarchical river classification was developed that uses five landform types to map the domains of a single fluvial process – flow convergence routing – at each of three–five spatial scales. Given those methods, this study investigated the details of how flow convergence routing organizes nested landform sequences. The method involved analyzing landform abundance, sequencing, and hierarchical nesting along the 35 km gravel/cobble lower Yuba River in California. Independent testing of flow convergence routing found that hydraulic patterns at every flow matched the essential predictions from classification, substantiating the process–morphology link. River width and bed elevation sequences exhibit large, nonrandom, and linked oscillations structured to preferentially yield wide bars and constricted pools at base flow and bankfull flow. At a flow of 8.44 times bankfull, there is still an abundance of wide bar and constricted pool landforms, but larger topographic drivers also yield an abundance of nozzle and oversized landforms. The nested structure of flow convergence routing landforms reveals that base flow and bankfull landforms are nested together within specific floodprone valley landform types, and these landform types control channel morphodynamics during moderate to large floods. As a result, this study calls into question the prevailing theory that the bankfull channel of a gravel/cobble river is controlled by in‐channel, bankfull, and/or small flood flows. Such flows may initiate sediment transport, but they are too small to control landform organization in a gravel/cobble river with topographic complexity. Copyright © 2018 John Wiley & Sons, Ltd.