Unintended consequences of restoration: Loss of riffles and gravel substrates following weir installation

a b s t r a c t We used pre-and post-restoration channel surveys of the Donner und Blitzen River, Oregon, to evaluate the effects of grade-control structures on channel morphology and baseflow habitat conditions for native redband trout and other aquatic biota. Six years after installation, we found that the channel had a smaller proportion of riffles and pools and less gravel substrate, combined with an increase in the proportion of flat waters and consolidated clay on the bed surface. Both local scour downstream from weirs and backwater effects upstream from weirs appear to have caused the general flattening and fining of the channel. A direct-step backwater calculation indicates that backwaters extended to the upstream weir at both low and high flows, creating long sections of flat water separated by short, steep drops. Despite backwater effects, a comparison of longitudinal profiles before and six years after weir installation showed bed erosion downstream of nearly all weirs, likely a consequence of the cohesive clay material that dominates the channel bed and banks. A deep inner channel reflects the cohesive nature of the clay and the mechanisms of abrasion, and indicates that sediment load is low relative to the transport capacity of the flow. Unfortunately, weirs were problematic in this system because of the cohesive clay substrate, limited sediment supply, and low channel gradient. Although deeper flows due to backwaters might be more favorable for resident trout, less gravel and fewer riffles are likely to negatively impact trout spawning habitat, macroinvertebrate communities, and biofilm productivity. Our results demonstrate the potential limitations of a single-feature approach to restoration that may be ineffective for a given geomorphic context and may overlook other aspects of the ecosystem. We highlight the need to incorporate geomorphic characteristics of a system into project design and predictions of system response

Tapping Environmental History to Recreate America’s Colonial Hydrology

To properly remediate, improve, or predict how hydrological systems behave, it is vital to establish their histories. However, modern-style records, assembled from instrumental data and remote sensing platforms, hardly exist back more than a few decades. As centuries of data is preferable given multidecadal fluxes of both meteorology/climatology and demographics, building such a history requires resources traditionally considered only useful in the social sciences and humanities. In this Feature, Pastore et al. discuss how they have undertaken the synthesis of historical records and modern techniques to understand the hydrology of the Northeastern U.S. from Colonial times to modern day. Such approaches could aid studies in other regions that may require heavier reliance on qualitative narratives. Further, a better insight as to how historical changes unfolded could provide a “past is prologue” methodology to increase the accuracy of predictive environmental models

Imperfect Realities: Practical Strategies for Monitoring Geomorphic and Ecological Responses to Trout Habitat Restoration

Pre- and post-project monitoring are essential components of any restoration strategy. Monitoring programs must be thoughtfully designed and implemented to avoid unnecessary expense and produce informative results that can aid adaptive management and future restoration. A design must incorporate which response variables to measure, the scales (temporal and spatial) of observation, clearly identified performance goals, the condition of reference sites, and the type of analysis desired. However, the realities of project implementation, natural variability, and management objectives often complicate monitoring design. Two years of pre- and post-project monitoring on the Strawberry River, Utah - a site of ongoing instream restoration aimed at cutthroat trout recovery - have generated important insights into both the effectiveness and complications of a comprehensive monitoring program. We evaluate the lessons learned from four commonly-used metrics - percent bed fines, fish population density, habitat complexity, and bank erosion rate - by categorizing monitoring techniques, measurement scales, response scales, observed short-term responses, and expected long-term responses for each variable. From this assessment, we identify which variables and what scales of observation yielded the most information about the system response (or lack thereof) to restoration and which will be most useful for long-term assessments. We also address complicating factors that can skew analyses or invalidate certain indicators, including natural variability in reference sites, lack of adequate pre-restoration data, and external interference with response variables. In light of these lessons, we propose strategies for restoration and monitoring that will enhance our ability to learn from our efforts. We recommend greater integration of monitoring design into pre-project planning and implementation, such as experimentally-designed restoration, time and funds for pre-project assessments, and the establishment and maintenance of suitable reference site

Some physical and biological factors influencing the fate of fine clastic particles in flowing water

An experimental flume study was conducted to assess the influence of several physical and biological factors on the movement and deposition of fine particles (< 125 µm) in flowing water. Mechanisms of particle movement were elucidated from measurements of flow hydraulics, particle concentrations, surface deposition, and subsurface infiltration for varying flow rates, bed sand fractions, particle densities, initial concentrations, and periphyton structures. Results showed that low flows slowed total deposition, an unexpected result given the lower near-bed Reynolds stresses and velocities of this condition. Similarly, a bed with a high sand fraction also slowed total deposition despite having lower near-bed Reynolds stresses. A higher amount of surface deposition to the high sand bed was offset by limited subsurface deposition, likely due to the clogging of pore spaces by fine sand and reduced advective transport. Particle density also significantly altered deposition rate but had no effect on particle infiltration or flow hydraulics. Along a gradient of low to high initial concentrations, deposition rate and infiltration increased, due to greater particle availability and an increase in particle interactions. A comparison of theoretical and measured concentration profiles showed that for fine particles the Rouse equation, using a depth-integrated particle size, performed as well as or better than more complex models. All models under-predicted concentrations of low-density plastic particles, over-predicted at low concentrations, and performed better with a high sand bed. Periphyton had a significant effect on hydraulics and deposition for a range of structures, densities and spatial scales. High density, closed periphyton patches compacted under high flows resulted in higher velocities and lower near-bed Reynolds stresses by constricting the flow depth and smoothing the bed surface. Lower density patches increased bed roughness, reducing near-bed velocities and transferring turbulent shear upward. Mucilaginous diatoms at low to moderate biomasses increased deposition rate and surface deposition by reducing near-bed Reynolds stress and enhancing particle adhesion. However, at high biomasses, diatom assemblages clogged interstitial spaces and reduced the amount of subsurface deposition thus slowing total deposition. In contrast, deposition occurred more slowly for most growth stages of filamentous algae, possibly due to partial clogging of the bed and a lack of surface adhesion. However, later algal growth stages increased Reynolds stress and advective transport, in turn increasing the amount of subsurface deposition and thus total deposition rate.Arts, Faculty ofGeography, Department ofGraduat