Given the complex array of processes influencing river networks, conceptual frameworks of rivers ... more Given the complex array of processes influencing river networks, conceptual frameworks of rivers are critical to our understanding of channel processes and response potential as well as restoration efforts. Yet despite their wide usage, many classifications are based on limited observations over homogenous landscapes, raising questions about their general applicability and quantitative thresholds. Leveraging a large, transect-based morphological field dataset across California, USA, we use data-driven methods to evaluate multivariate patterns in channel morphology and linkages with landscape properties considering a diversity of physioclimatic settings. Emergent patterns highlight the variability in channel form observed across an extensive dataset over heterogeneous but spatially linked watersheds. In general, identified dominant channel attributes and landscape properties align with established channel types defined through expert judgement, but key differences also emerge. Similar to past studies, bed sediment composition and sub-reach depth variability were discriminating channel attributes. The dominance of landscape properties associated with sediment supply or transport capacity suggests that morphological diversity largely reflects these differences as posited by prior classifications. Results also show some channel forms to be largely independent of valley confinement, with several channel bedforms and dominant grain sizes occurring across valley settings. This data analysis study demonstrates the utility of considering channel reaches and landscapes as multidimensional features to elucidate and test established geomorphic understanding over large field datasets.
Riffle-pool sequences are fundamental, ubiquitous morphological features of alluvial rivers that ... more Riffle-pool sequences are fundamental, ubiquitous morphological features of alluvial rivers that are thoroughly studied in general and commonly incorporated into river restoration projects. Most previous investigations on the effect of riffle-pool sequences on hyporheic exchanges focused on solely bed undulation, because that is widely thought to be the defining feature of riffle-pool sequences. However, riffle-pool sequences also have significant width undulations that are vital to riffle-pool sequences morphodynamics, yet relatively few studies exist on the effect of such undulations on hyporheic exchanges. Thus, in this study based on laboratory experiments and numerical simulations, we investigate the effect of bed and width undulations on hyporheic zone characteristics for various ratio of width amplitude to bed amplitude. The variation of hyporheic exchange characteristics (i.e. hyporheic exchange flux and residence time) for different riffle-pool designs were also assessed by creating prescribed topography of synthetic river valleys. The results showed that due to pressure variation along width undulations, the upwelling and downwelling patterns can also be observed for only width undulations in rivers, in the absence of bed undulations, and as width undulation amplitude decreases, the normalized hyporheic exchanges (Q*HZ) increase and normalized median residence time (RT*) decreases. Also, simultaneous channel bed and width undulations result in higher Q*HZ especially when a pool is located in an expansion (aka "oversized" crosssection) and a riffle in a constriction ("nozzle"). Our results suggest that river restoration project that artificially construct wide pools and constricted riffles will achieve maximum Q*HZ and RT*, though they will not be geomorphically self-sustainable.
Keli Mutu is a stratovolcano that has three crater lakes containing exotic fluids. This study pre... more Keli Mutu is a stratovolcano that has three crater lakes containing exotic fluids. This study presents the analytical results describing the chemistry of each lake, interprets the chemistries in terms of water-rock interactions and volcanic fluxes, and derives a physical lake model that delineates the parameter-window for volcanic crater lake existence. Geochemical investigation of the vertical and lateral compositions of the lakes on Keli Mutu required the use of a remote sampling system. Lake temperature, pH, and dissolved oxygen content were determined in the field, while the analytical chemistries of lake fluids and sediments were determined in the months after the expedition to Keli Mutu. To reconstruct the in situ chemistries of the lakes' aqueous systems, a solution equilibrium modeling program (SOLVEQ) was applied. The energy flux model that was developed assumes thermal steady state conditions to gain insight into the physical dynamics of volcanic crater lakes. This model leads to graphs of lake temperature versus volcanic gas input for lakes of different radii. Assessment of the growth and shrinking of lake volume as a function of the relative influences of endogene versus exogene forces was provided by using the additional requirement of hydrological steady state. In general, for a crater of a given radius, the temperature of the lake that exists at thermal steady state within it is a function of sulfur dioxide influx and evaporative cooling. The primary conclusion of this thesis is that the three Keli Mutu lakes are all fed by a similar volcanic gas source, but as a result of the mediated transport of that gas it yields different chemical "expressions" in each crater lake. Comparison of the individual lakes with their respective historic chemistries demonstrates that they are all approaching chemical steady state. Future studies of Keli Mutu should include a thorough investigation of volcano flank seepage outlets, as at least one such spring-fed river bears a crater lake signature and could be used to calculate element fluxes through the volcanic edifice.
Hydropeaking, a hydroelectricity generation strategy involving rapid changes to flow releases fro... more Hydropeaking, a hydroelectricity generation strategy involving rapid changes to flow releases from dams in response to fluctuations in hourly-adjusted electricity markets has been widely 10 applied due to its economic efficiency. However, these operational practices produce sub-daily 11 flow fluctuations that pose substantial hazards to riverine ecosystems and human activities. To 12 ascertain the downstream impacts of hydropeaking, features of hydropeaking have been analyzed 13 with respect to ecologically relevant hydrologic variables. However, since studies aiming to 14 characterize hydropeaking regime often require manual feature extraction, they are limited to small 15 temporal and spatial scales. Additionally, riverine ecologists have commonly treated hydropeaking 16 as a broadly similar flow-alteration pattern regardless of the complexities of the electricity market 17 and differences in the natural settings where it is applied. Therefore, this study sought to determine 18 whether significantly different hydropeaking patterns exist on a regional scale, as revealed by the variation in hydropeaking over a long temporal scale (> five years). To fulfill this goal, a new algorithm, the Hydropeaking Event Detection Algorithm (HEDA), was developed in R to automate the characterization of hydropeaking flow regimes. Clustering analyses were conducted to explore the similarities and differences of hydropeaking regimes among 33 sites in numerous hydrologic regions of California. Four distinct classes of hydropeaking flow regimes were identified and distinguished by the duration and frequency of hydropeaking. Meanwhile, rate of change, amplitude and timing of hdyropeaking played less important roles in the classification.
Global environmental changes bring unprecedented pressures to freshwater ecosystems. Interdiscipl... more Global environmental changes bring unprecedented pressures to freshwater ecosystems. Interdisciplinary approaches will be needed to face such multidimensional problems. However, crossing disciplinary boundaries presents a challenge. Ecohydraulics, an emergent field of research with a multi and interdisciplinary nature, has the potential to play an important role in the future management of freshwater ecosystems. In order to develop this field of research further, early careers on Ecohydraulics need to focus their careers in a way that crosses traditional disciplinary boundaries to ensure the true integration of ecological, physical and social values in ecohydraulics. By developing this field of research as an integrative field of research and supporting the new generations of freshwater scientists, ecohydraulics can contribute to society on local and international scales.
Urbanization results in major changes to stream morphology and hydrology with the latter often ci... more Urbanization results in major changes to stream morphology and hydrology with the latter often cited as a primary stressor of urban stream ecosystems. These modifications unequivocally alter stream hydraulics, but little is known about such impacts. Hydraulic changes due to urbanization were demonstrated using two-dimensional hydrodynamic model simulations, comparing urban and non-urban stream reaches. We investigated three ecologically relevant hydraulic characteristics; bed mobilization, retentive habitat and floodplain inundation, using hydraulic metrics bed shear stress, shallow slow-water habitat (SSWH) area, and floodplain inundation area. We hypothesized that urbanization would substantially increase bed mobilization, decrease retentive habitat and due to increased channel size would decrease floodplain inundation. Relative percent area of bed disturbance was four times higher, compared with that of the non-urban stream at bankfull discharge (Qbkf). SSWH availability rapidly diminished in the urban stream as discharge increased, with SSWH area and patch size two times smaller than the non-urban stream for a frequently occurring flow 0.7 times Qbkf. Floodplain inundation decreased in frequency and duration. These results demonstrate changes in hydraulics due to urbanization that may impact on physical habitat in streams. New "water sensitive" approaches to stormwater management could be enhanced by specification of hydraulic regimes capable of supporting healthy stream habitats. We propose that a complete management approach should include the goals of restoration and protection of natural hydraulic processes, particularly those that support ecological and geomorphic functioning of streams.
Urban streams have almost universally altered physical habitat conditions due to excess stormwate... more Urban streams have almost universally altered physical habitat conditions due to excess stormwater runoff. This includes changes to in-channel hydraulics and channel morphology. Restoration of in-channel habitat has two main levers: address the hydrology or channel morphology. Both variables impact in-stream habitat but understanding the relative role of hydrologic and morphologic change remains a challenge. This study uses two-dimensional hydraulic modelling to examine the relative roles of flow and channel morphology in setting hydraulic conditions. We investigated four test scenarios involving the combinations of urban versus natural hydrology and urban versus natural channel morphology. The analysis investigated three ecologically relevant hydraulics characteristics; bed mobilization, retentive habitat and floodplain inundation, using Shields stress, shallow slow-water habitat (SSWH) area and floodplain inundation area hydraulic metrics respectively. The results indicate substantial differences in hydraulic conditions between the two reaches. The urban reach showed increased bed mobility potential and SSWH availability plummeted as flow increased, whereas the natural channel showed a relatively stable bed with substantially more SSWH at most flows. Floodplain inundation frequency was low in the urban channel with decreased duration. Scenarios examined suggest hydraulic conditions are highly sensitive to channel morphology relative to flow regime. This suggests that once channel form has been degraded, mitigating urbanization impacts on flow regime cannot maintain 'natural' channel hydraulics. Management approaches therefore must protect channel morphology from change. Where the channel has already been fundamentally altered, opportunities for channel morphology rehabilitation needs to be considered.
Scientists and engineers design river topography for a wide variety of uses, such as experimentat... more Scientists and engineers design river topography for a wide variety of uses, such as experimentation, site remediation, dam mitigation, flood management, and river restoration. A recent advancement has been the notion of topographical design to yield specific fluvial mechanisms in conjunction with natural or environmental flow releases. For example, the flow convergence routing mechanism, whereby shear stress and spatially convergent flow migrate or jump from the topographic high (riffle) to the low point (pool) from low to high discharge, is thought to be a key process able to maintain undular relief in gravel bedded rivers. This paper develops an approach to creating riffle-pool topography with a form-process linkage to the flow convergence routing mechanism using an adjustable, quasi equilibrium synthetic channel model. The link from form to process is made through conceptualizing form-process relationships for riffle-pool couplets into geomorphic covariance structures (GCSs) tha...
Transect-based hydraulic geometry is well established but depends on a complex set of subjective ... more Transect-based hydraulic geometry is well established but depends on a complex set of subjective fieldwork and computational decisions that sometimes go unexplained. As a result, it is ripe for reenvisioning in light of the emergence of meterscale, spatially explicit data and algorithmic geospatial analysis. This study developed and evaluated a new spatially explicit method for analyzing discharge-dependent hydraulics coined 'hydraulic topography' that not only increases accuracy but also eliminates several sample-and assumption-based inconsistencies. Using data and hydrodynamic simulations from the regulated, gravel-cobble-bed lower Yuba River in California, power functions were fitted to discharge-dependent average width, depth, and depth-weighted velocity for three spatial scales and then their corresponding exponents and coefficients were compared across scales and against ones computed using traditional approaches. Average hydraulic values from cross sections at the segment scale spanned up to 1.5 orders of magnitude for a given discharge. Transectdetermined exponents for reach-scale depth and velocity relations were consistently over-and underestimated, respectively, relative to the hydraulic topography benchmark. Overall, 73% of cross-sectional power regression parameters assessed fell between 10 and 50 absolute percent error with respect to the spatially explicit hydraulic topography baseline. Although traditional transect-based sampling may be viable for certain uses, percent errors of this magnitude could compromise engineering applications in river management and training works.
The dynamics of fish stranding have not been academically investigated within the context of phys... more The dynamics of fish stranding have not been academically investigated within the context of physical adjustments to rivers for habitat enhancement purposes. River projects may aim to help fish populations but instead may function as attractive nuisances reducing populations because of unaccounted-for stranding risk. This study applies a novel algorithm to predict spatially explicit, meter-resolution fish stranding risk at a river rehabilitation site in California to address three scientific questions. Post-project disconnected wetted area predictions were validated against water surface elevation measurements and time lapse photography of flow reductions and stranding events. Comparison of pre-project, final design, and postproject topographies revealed that occurrence and severity of stranding events is highly sensitive to side-channel topographic structure and post-project morphodynamic change. Even with moderate flows, side channel exits tend to close off by bars built across them via bedload transport. Implications for river management practices and river rehabilitation project design are discussed.
Advances in remote sensing, informatics, software and microprocessors enable meterresolution two-... more Advances in remote sensing, informatics, software and microprocessors enable meterresolution two-dimensional (2D) hydrodynamic models that produce nearly a census of ecohydraulic conditions over long river segments with 10 5 to 10 8 computational elements. It is difficult to test statistical and spatial model performance at such scope using fixedpoint velocity measurements, because field methods are so expensive, laborious, slow, and restricted by safety factors. This study evaluated low-cost water surface particle tracking by kayak with real time kinematic GPS for 2D model validation using 7.2 km of the lower Yuba River in California. Observed flows were between 15 to 140 m 3 /s, which were inchannel up to and including bankfull conditions. The coefficients of determination between 5780 observations and 2D model predictions were 0.79 and 0.80 for velocity magnitude and direction, respectively. When surface speed was downscaled and compared to modeled depth-averaged velocity, median unsigned difference was 15.5%. Standard hydrological model performance metrics affirmed satisfactory validation. Surface tracking provided the novel benefit of enabling validation of velocity direction, and that testing found satisfactory performance using all metrics. Having 10 to 1000 times more data enables robust statistical testing and spatial analysis of both speed and direction, which outweighs the loss of depthaveraged data. Both fixed-point and kayak particle tracking methods are useful tools to help evaluate 2D model performance.
Microhabitat suitability models are commonly used to estimate salmonid habitat abundance and qual... more Microhabitat suitability models are commonly used to estimate salmonid habitat abundance and quality with unknown accuracy or reliability. When tested, the metrics used to evaluate these models are often limited by the methods used to develop them. More generalized bioverification strategies that transcend methodology are therefore needed in ecohydraulics. This study further developed and applied such a generalized bioverification framework to four approximately 1-m-resolution rearing salmonid microhabitat suitability models. Water depth and velocity habitat suitability criteria (HSC) functions were developed for two size classes of rearing Oncorhynchus tshawytscha and O. mykiss using snorkel survey data collected over three years at seven sites along the lower Yuba River in California, USA. An expert-based cover HSC function was modified from previous studies. HSC functions were applied to previously validated, approximately 1-m-resolution two-dimensional hydrodynamic models and cover maps of the river. Mann-Whitney U tests confirmed that suitability values were significantly higher at utilized locations compared to randomly-generated, non-utilized locations for all four models. Bootstrapped forage ratios demonstrated that microhabitat suitability models accurately predicted both preferred and avoided habitat beyond the 95% confidence level. This generalized bioverification framework is recommended for evaluating and comparing the accuracy and reliability of ecohydraulic models used in habitat management worldwide.
16 17 Reach-scale morphological channel classifications are underpinned by the theory that 18 eac... more 16 17 Reach-scale morphological channel classifications are underpinned by the theory that 18 each channel type is related to an assemblage of reach-and catchment-scale 19 hydrological, topographic, and sediment supply drivers. However, the relative 20 importance of each driver on reach morphology is unclear, as is the possibility that 21 different driver assemblages yield the same reach morphology. Reach-scale 22 classifications have never needed to be predicated on hydrology, yet hydrology controls 23 discharge and thus sediment transport capacity. Scientifically, the novel question is
Past river classifications use incommensurate typologies at each spatial scale and do not capture... more 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.
The extent and timing of many river ecosystem functions is controlled by the interplay of streamf... more The extent and timing of many river ecosystem functions is controlled by the interplay of streamflow dynamics with the river corridor shape and structure. However, most river management studies evaluate the role of either flow or form without regard to their dynamic interactions. This study develops an integrated modeling approach to assess changes in ecosystem functions resulting from different river flow and form configurations. Moreover, it investigates the role of temporal variability in such flow-form-function tradeoffs. The use of synthetic, archetypal channel forms in lieu of high-resolution topographic data reduces time and financial requirements, overcomes site-specific topographic features, and allows for evaluation of any morphological structure of interest. In an application to California's Mediterranean-montane streams, the interacting roles of channel form, water year type, and hydrologic impairment were evaluated across a suite of ecosystem functions related to hydrogeomorphic processes and aquatic habitat. Channel form acted as the dominant control on hydrogeomorphic processes, while water year type controlled salmonid habitat functions. Streamflow alteration for hydropower increased redd dewatering risk and altered aquatic habitat availability. Study results highlight critical tradeoffs in ecosystem function performance and emphasize the significance of spatiotemporal diversity of flow and form at multiple scales for maintaining river ecosystem integrity. The proposed approach is broadly applicable and extensible to other systems and ecosystem functions, where findings can be used to inform river management and design testing.
Given the complex array of processes influencing river networks, conceptual frameworks of rivers ... more Given the complex array of processes influencing river networks, conceptual frameworks of rivers are critical to our understanding of channel processes and response potential as well as restoration efforts. Yet despite their wide usage, many classifications are based on limited observations over homogenous landscapes, raising questions about their general applicability and quantitative thresholds. Leveraging a large, transect-based morphological field dataset across California, USA, we use data-driven methods to evaluate multivariate patterns in channel morphology and linkages with landscape properties considering a diversity of physioclimatic settings. Emergent patterns highlight the variability in channel form observed across an extensive dataset over heterogeneous but spatially linked watersheds. In general, identified dominant channel attributes and landscape properties align with established channel types defined through expert judgement, but key differences also emerge. Similar to past studies, bed sediment composition and sub-reach depth variability were discriminating channel attributes. The dominance of landscape properties associated with sediment supply or transport capacity suggests that morphological diversity largely reflects these differences as posited by prior classifications. Results also show some channel forms to be largely independent of valley confinement, with several channel bedforms and dominant grain sizes occurring across valley settings. This data analysis study demonstrates the utility of considering channel reaches and landscapes as multidimensional features to elucidate and test established geomorphic understanding over large field datasets.
Riffle-pool sequences are fundamental, ubiquitous morphological features of alluvial rivers that ... more Riffle-pool sequences are fundamental, ubiquitous morphological features of alluvial rivers that are thoroughly studied in general and commonly incorporated into river restoration projects. Most previous investigations on the effect of riffle-pool sequences on hyporheic exchanges focused on solely bed undulation, because that is widely thought to be the defining feature of riffle-pool sequences. However, riffle-pool sequences also have significant width undulations that are vital to riffle-pool sequences morphodynamics, yet relatively few studies exist on the effect of such undulations on hyporheic exchanges. Thus, in this study based on laboratory experiments and numerical simulations, we investigate the effect of bed and width undulations on hyporheic zone characteristics for various ratio of width amplitude to bed amplitude. The variation of hyporheic exchange characteristics (i.e. hyporheic exchange flux and residence time) for different riffle-pool designs were also assessed by creating prescribed topography of synthetic river valleys. The results showed that due to pressure variation along width undulations, the upwelling and downwelling patterns can also be observed for only width undulations in rivers, in the absence of bed undulations, and as width undulation amplitude decreases, the normalized hyporheic exchanges (Q*HZ) increase and normalized median residence time (RT*) decreases. Also, simultaneous channel bed and width undulations result in higher Q*HZ especially when a pool is located in an expansion (aka "oversized" crosssection) and a riffle in a constriction ("nozzle"). Our results suggest that river restoration project that artificially construct wide pools and constricted riffles will achieve maximum Q*HZ and RT*, though they will not be geomorphically self-sustainable.
Keli Mutu is a stratovolcano that has three crater lakes containing exotic fluids. This study pre... more Keli Mutu is a stratovolcano that has three crater lakes containing exotic fluids. This study presents the analytical results describing the chemistry of each lake, interprets the chemistries in terms of water-rock interactions and volcanic fluxes, and derives a physical lake model that delineates the parameter-window for volcanic crater lake existence. Geochemical investigation of the vertical and lateral compositions of the lakes on Keli Mutu required the use of a remote sampling system. Lake temperature, pH, and dissolved oxygen content were determined in the field, while the analytical chemistries of lake fluids and sediments were determined in the months after the expedition to Keli Mutu. To reconstruct the in situ chemistries of the lakes' aqueous systems, a solution equilibrium modeling program (SOLVEQ) was applied. The energy flux model that was developed assumes thermal steady state conditions to gain insight into the physical dynamics of volcanic crater lakes. This model leads to graphs of lake temperature versus volcanic gas input for lakes of different radii. Assessment of the growth and shrinking of lake volume as a function of the relative influences of endogene versus exogene forces was provided by using the additional requirement of hydrological steady state. In general, for a crater of a given radius, the temperature of the lake that exists at thermal steady state within it is a function of sulfur dioxide influx and evaporative cooling. The primary conclusion of this thesis is that the three Keli Mutu lakes are all fed by a similar volcanic gas source, but as a result of the mediated transport of that gas it yields different chemical "expressions" in each crater lake. Comparison of the individual lakes with their respective historic chemistries demonstrates that they are all approaching chemical steady state. Future studies of Keli Mutu should include a thorough investigation of volcano flank seepage outlets, as at least one such spring-fed river bears a crater lake signature and could be used to calculate element fluxes through the volcanic edifice.
Hydropeaking, a hydroelectricity generation strategy involving rapid changes to flow releases fro... more Hydropeaking, a hydroelectricity generation strategy involving rapid changes to flow releases from dams in response to fluctuations in hourly-adjusted electricity markets has been widely 10 applied due to its economic efficiency. However, these operational practices produce sub-daily 11 flow fluctuations that pose substantial hazards to riverine ecosystems and human activities. To 12 ascertain the downstream impacts of hydropeaking, features of hydropeaking have been analyzed 13 with respect to ecologically relevant hydrologic variables. However, since studies aiming to 14 characterize hydropeaking regime often require manual feature extraction, they are limited to small 15 temporal and spatial scales. Additionally, riverine ecologists have commonly treated hydropeaking 16 as a broadly similar flow-alteration pattern regardless of the complexities of the electricity market 17 and differences in the natural settings where it is applied. Therefore, this study sought to determine 18 whether significantly different hydropeaking patterns exist on a regional scale, as revealed by the variation in hydropeaking over a long temporal scale (> five years). To fulfill this goal, a new algorithm, the Hydropeaking Event Detection Algorithm (HEDA), was developed in R to automate the characterization of hydropeaking flow regimes. Clustering analyses were conducted to explore the similarities and differences of hydropeaking regimes among 33 sites in numerous hydrologic regions of California. Four distinct classes of hydropeaking flow regimes were identified and distinguished by the duration and frequency of hydropeaking. Meanwhile, rate of change, amplitude and timing of hdyropeaking played less important roles in the classification.
Global environmental changes bring unprecedented pressures to freshwater ecosystems. Interdiscipl... more Global environmental changes bring unprecedented pressures to freshwater ecosystems. Interdisciplinary approaches will be needed to face such multidimensional problems. However, crossing disciplinary boundaries presents a challenge. Ecohydraulics, an emergent field of research with a multi and interdisciplinary nature, has the potential to play an important role in the future management of freshwater ecosystems. In order to develop this field of research further, early careers on Ecohydraulics need to focus their careers in a way that crosses traditional disciplinary boundaries to ensure the true integration of ecological, physical and social values in ecohydraulics. By developing this field of research as an integrative field of research and supporting the new generations of freshwater scientists, ecohydraulics can contribute to society on local and international scales.
Urbanization results in major changes to stream morphology and hydrology with the latter often ci... more Urbanization results in major changes to stream morphology and hydrology with the latter often cited as a primary stressor of urban stream ecosystems. These modifications unequivocally alter stream hydraulics, but little is known about such impacts. Hydraulic changes due to urbanization were demonstrated using two-dimensional hydrodynamic model simulations, comparing urban and non-urban stream reaches. We investigated three ecologically relevant hydraulic characteristics; bed mobilization, retentive habitat and floodplain inundation, using hydraulic metrics bed shear stress, shallow slow-water habitat (SSWH) area, and floodplain inundation area. We hypothesized that urbanization would substantially increase bed mobilization, decrease retentive habitat and due to increased channel size would decrease floodplain inundation. Relative percent area of bed disturbance was four times higher, compared with that of the non-urban stream at bankfull discharge (Qbkf). SSWH availability rapidly diminished in the urban stream as discharge increased, with SSWH area and patch size two times smaller than the non-urban stream for a frequently occurring flow 0.7 times Qbkf. Floodplain inundation decreased in frequency and duration. These results demonstrate changes in hydraulics due to urbanization that may impact on physical habitat in streams. New "water sensitive" approaches to stormwater management could be enhanced by specification of hydraulic regimes capable of supporting healthy stream habitats. We propose that a complete management approach should include the goals of restoration and protection of natural hydraulic processes, particularly those that support ecological and geomorphic functioning of streams.
Urban streams have almost universally altered physical habitat conditions due to excess stormwate... more Urban streams have almost universally altered physical habitat conditions due to excess stormwater runoff. This includes changes to in-channel hydraulics and channel morphology. Restoration of in-channel habitat has two main levers: address the hydrology or channel morphology. Both variables impact in-stream habitat but understanding the relative role of hydrologic and morphologic change remains a challenge. This study uses two-dimensional hydraulic modelling to examine the relative roles of flow and channel morphology in setting hydraulic conditions. We investigated four test scenarios involving the combinations of urban versus natural hydrology and urban versus natural channel morphology. The analysis investigated three ecologically relevant hydraulics characteristics; bed mobilization, retentive habitat and floodplain inundation, using Shields stress, shallow slow-water habitat (SSWH) area and floodplain inundation area hydraulic metrics respectively. The results indicate substantial differences in hydraulic conditions between the two reaches. The urban reach showed increased bed mobility potential and SSWH availability plummeted as flow increased, whereas the natural channel showed a relatively stable bed with substantially more SSWH at most flows. Floodplain inundation frequency was low in the urban channel with decreased duration. Scenarios examined suggest hydraulic conditions are highly sensitive to channel morphology relative to flow regime. This suggests that once channel form has been degraded, mitigating urbanization impacts on flow regime cannot maintain 'natural' channel hydraulics. Management approaches therefore must protect channel morphology from change. Where the channel has already been fundamentally altered, opportunities for channel morphology rehabilitation needs to be considered.
Scientists and engineers design river topography for a wide variety of uses, such as experimentat... more Scientists and engineers design river topography for a wide variety of uses, such as experimentation, site remediation, dam mitigation, flood management, and river restoration. A recent advancement has been the notion of topographical design to yield specific fluvial mechanisms in conjunction with natural or environmental flow releases. For example, the flow convergence routing mechanism, whereby shear stress and spatially convergent flow migrate or jump from the topographic high (riffle) to the low point (pool) from low to high discharge, is thought to be a key process able to maintain undular relief in gravel bedded rivers. This paper develops an approach to creating riffle-pool topography with a form-process linkage to the flow convergence routing mechanism using an adjustable, quasi equilibrium synthetic channel model. The link from form to process is made through conceptualizing form-process relationships for riffle-pool couplets into geomorphic covariance structures (GCSs) tha...
Transect-based hydraulic geometry is well established but depends on a complex set of subjective ... more Transect-based hydraulic geometry is well established but depends on a complex set of subjective fieldwork and computational decisions that sometimes go unexplained. As a result, it is ripe for reenvisioning in light of the emergence of meterscale, spatially explicit data and algorithmic geospatial analysis. This study developed and evaluated a new spatially explicit method for analyzing discharge-dependent hydraulics coined 'hydraulic topography' that not only increases accuracy but also eliminates several sample-and assumption-based inconsistencies. Using data and hydrodynamic simulations from the regulated, gravel-cobble-bed lower Yuba River in California, power functions were fitted to discharge-dependent average width, depth, and depth-weighted velocity for three spatial scales and then their corresponding exponents and coefficients were compared across scales and against ones computed using traditional approaches. Average hydraulic values from cross sections at the segment scale spanned up to 1.5 orders of magnitude for a given discharge. Transectdetermined exponents for reach-scale depth and velocity relations were consistently over-and underestimated, respectively, relative to the hydraulic topography benchmark. Overall, 73% of cross-sectional power regression parameters assessed fell between 10 and 50 absolute percent error with respect to the spatially explicit hydraulic topography baseline. Although traditional transect-based sampling may be viable for certain uses, percent errors of this magnitude could compromise engineering applications in river management and training works.
The dynamics of fish stranding have not been academically investigated within the context of phys... more The dynamics of fish stranding have not been academically investigated within the context of physical adjustments to rivers for habitat enhancement purposes. River projects may aim to help fish populations but instead may function as attractive nuisances reducing populations because of unaccounted-for stranding risk. This study applies a novel algorithm to predict spatially explicit, meter-resolution fish stranding risk at a river rehabilitation site in California to address three scientific questions. Post-project disconnected wetted area predictions were validated against water surface elevation measurements and time lapse photography of flow reductions and stranding events. Comparison of pre-project, final design, and postproject topographies revealed that occurrence and severity of stranding events is highly sensitive to side-channel topographic structure and post-project morphodynamic change. Even with moderate flows, side channel exits tend to close off by bars built across them via bedload transport. Implications for river management practices and river rehabilitation project design are discussed.
Advances in remote sensing, informatics, software and microprocessors enable meterresolution two-... more Advances in remote sensing, informatics, software and microprocessors enable meterresolution two-dimensional (2D) hydrodynamic models that produce nearly a census of ecohydraulic conditions over long river segments with 10 5 to 10 8 computational elements. It is difficult to test statistical and spatial model performance at such scope using fixedpoint velocity measurements, because field methods are so expensive, laborious, slow, and restricted by safety factors. This study evaluated low-cost water surface particle tracking by kayak with real time kinematic GPS for 2D model validation using 7.2 km of the lower Yuba River in California. Observed flows were between 15 to 140 m 3 /s, which were inchannel up to and including bankfull conditions. The coefficients of determination between 5780 observations and 2D model predictions were 0.79 and 0.80 for velocity magnitude and direction, respectively. When surface speed was downscaled and compared to modeled depth-averaged velocity, median unsigned difference was 15.5%. Standard hydrological model performance metrics affirmed satisfactory validation. Surface tracking provided the novel benefit of enabling validation of velocity direction, and that testing found satisfactory performance using all metrics. Having 10 to 1000 times more data enables robust statistical testing and spatial analysis of both speed and direction, which outweighs the loss of depthaveraged data. Both fixed-point and kayak particle tracking methods are useful tools to help evaluate 2D model performance.
Microhabitat suitability models are commonly used to estimate salmonid habitat abundance and qual... more Microhabitat suitability models are commonly used to estimate salmonid habitat abundance and quality with unknown accuracy or reliability. When tested, the metrics used to evaluate these models are often limited by the methods used to develop them. More generalized bioverification strategies that transcend methodology are therefore needed in ecohydraulics. This study further developed and applied such a generalized bioverification framework to four approximately 1-m-resolution rearing salmonid microhabitat suitability models. Water depth and velocity habitat suitability criteria (HSC) functions were developed for two size classes of rearing Oncorhynchus tshawytscha and O. mykiss using snorkel survey data collected over three years at seven sites along the lower Yuba River in California, USA. An expert-based cover HSC function was modified from previous studies. HSC functions were applied to previously validated, approximately 1-m-resolution two-dimensional hydrodynamic models and cover maps of the river. Mann-Whitney U tests confirmed that suitability values were significantly higher at utilized locations compared to randomly-generated, non-utilized locations for all four models. Bootstrapped forage ratios demonstrated that microhabitat suitability models accurately predicted both preferred and avoided habitat beyond the 95% confidence level. This generalized bioverification framework is recommended for evaluating and comparing the accuracy and reliability of ecohydraulic models used in habitat management worldwide.
16 17 Reach-scale morphological channel classifications are underpinned by the theory that 18 eac... more 16 17 Reach-scale morphological channel classifications are underpinned by the theory that 18 each channel type is related to an assemblage of reach-and catchment-scale 19 hydrological, topographic, and sediment supply drivers. However, the relative 20 importance of each driver on reach morphology is unclear, as is the possibility that 21 different driver assemblages yield the same reach morphology. Reach-scale 22 classifications have never needed to be predicated on hydrology, yet hydrology controls 23 discharge and thus sediment transport capacity. Scientifically, the novel question is
Past river classifications use incommensurate typologies at each spatial scale and do not capture... more 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.
The extent and timing of many river ecosystem functions is controlled by the interplay of streamf... more The extent and timing of many river ecosystem functions is controlled by the interplay of streamflow dynamics with the river corridor shape and structure. However, most river management studies evaluate the role of either flow or form without regard to their dynamic interactions. This study develops an integrated modeling approach to assess changes in ecosystem functions resulting from different river flow and form configurations. Moreover, it investigates the role of temporal variability in such flow-form-function tradeoffs. The use of synthetic, archetypal channel forms in lieu of high-resolution topographic data reduces time and financial requirements, overcomes site-specific topographic features, and allows for evaluation of any morphological structure of interest. In an application to California's Mediterranean-montane streams, the interacting roles of channel form, water year type, and hydrologic impairment were evaluated across a suite of ecosystem functions related to hydrogeomorphic processes and aquatic habitat. Channel form acted as the dominant control on hydrogeomorphic processes, while water year type controlled salmonid habitat functions. Streamflow alteration for hydropower increased redd dewatering risk and altered aquatic habitat availability. Study results highlight critical tradeoffs in ecosystem function performance and emphasize the significance of spatiotemporal diversity of flow and form at multiple scales for maintaining river ecosystem integrity. The proposed approach is broadly applicable and extensible to other systems and ecosystem functions, where findings can be used to inform river management and design testing.
Keli Mutu is a stratovolcano that has three crater lakes containing exotic fluids. This study pre... more Keli Mutu is a stratovolcano that has three crater lakes containing exotic fluids. This study presents the analytical results describing the chemistry of each lake, interprets the chemistries in terms of water-rock interactions and volcanic fluxes, and derives a physical lake model that delineates the parameter-window for volcanic crater lake existence. Geochemical investigation of the vertical and lateral compositions of the lakes on Keli Mutu required the use of a remote sampling system. Lake temperature, pH, and dissolved oxygen content were determined in the field, while the analytical chemistries of lake fluids and sediments were determined in the months after the expedition to Keli Mutu. To reconstruct the in situ chemistries of the lakes' aqueous systems, a solution equilibrium modeling program (SOLVEQ) was applied. The energy flux model that was developed assumes thermal steady state conditions to gain insight into the physical dynamics of volcanic crater lakes. This model leads to graphs of lake temperature versus volcanic gas input for lakes of different radii. Assessment of the growth and shrinking of lake volume as a function of the relative influences of endogene versus exogene forces was provided by using the additional requirement of hydrological steady state. In general, for a crater of a given radius, the temperature of the lake that exists at thermal steady state within it is a function of sulfur dioxide influx and evaporative cooling. The primary conclusion of this thesis is that the three Keli Mutu lakes are all fed by a similar volcanic gas source, but as a result of the mediated transport of that gas it yields different chemical "expressions" in each crater lake. Comparison of the individual lakes with their respective historic chemistries demonstrates that they are all approaching chemical steady state. Future studies of Keli Mutu should include a thorough investigation of volcano flank seepage outlets, as at least one such spring-fed river bears a crater lake signature and could be used to calculate element fluxes through the volcanic edifice.
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Papers by Gregory B Pasternack