Browsing by Author "Bledsoe, Brian P., advisor"
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Item Open Access Eco-hydraulic evaluation of whitewater parks as fish passage barriers(Colorado State University. Libraries, 2013) Fox, Brian, author; Bledsoe, Brian P., advisor; Myrick, Christopher A., committee member; Venayagamoorthy, Subhas Karen, committee memberWhitewater parks (WWPs) have become a popular recreational amenity in cities across the United States with Colorado being the epicenter of WWP design and construction. Whitewater parks consist of one or more in-stream structures that create a hydraulic wave for recreational purposes. A wave is typically created by constricting flow into a steep chute creating a hydraulic jump as it flows into a large downstream pool. Concerns have been raised that high velocities, resulting from the constricted flow at these structures, may be inhibiting movement of certain fish species at different times of year. I completed a field evaluation of the effects of WWPs on upstream fish passage by concurrently monitoring fish movement and hydraulic conditions at three WWP structures and three adjacent natural control (CR) pools. Fish movement was evaluated using a network of Passive Integrated Transponder (PIT) antennas installed at the study sites for a period of 14 months. 1,639 individual fishes including brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), longnose sucker (Catostomus catostomus), and longnose dace (Rhinichthys cataractae) were tagged and released within the WWP and CR study sites. Detailed hydraulic conditions occurring during the study period were evaluated by developing a fully three-dimensional hydraulic model using FLOW-3D®. Results show that this WWP is not a complete barrier to upstream movement, but differences in passage efficiency from release location range from 29 to 44% in WWP sites and 37 to 63% for control sites indicating a suppression of movement within WWPs. Further, this suppression of movement appears to be related to fish body length. Results from the hydraulic models indicate that these are not likely burst swimming barriers to salmonids despite flow velocities greater than 10 ft/s within each of the WWP structures. Hydraulic model results provided insight in identifying other possible causes of the suppressed movement and guidance for future research efforts.Item Open Access Ecologically-focused calibration of hydrological models for environmental flow applications(Colorado State University. Libraries, 2015) Adams, Stephen K., author; Bledsoe, Brian P., advisor; Poff, N. LeRoy, committee member; Stein, Eric D., committee memberHydrologic alteration resulting from watershed urbanization is a common cause of aquatic ecosystem degradation. Developing environmental flow criteria for managing the effects of urbanization and other human influences requires quantitative flow-ecology relationships that link biological responses to streamflow alteration. To the extent possible, gaged flow data are used; however, bioassessment sites are frequently ungaged and hydrological models must be used to characterize flow alteration. Physically-based rainfall-runoff models typically utilize a "best overall fit" calibration criterion, such as the Nash-Sutcliffe Efficiency (NSE), that does not focus on specific aspects of the flow regime relevant to biotic endpoints. This study aims to identify how accurately coastal southern California rainfall-runoff models can be calibrated using specific elements of the flow regime known a priori to be critical to benthic macroinvertebrates (ecologically-focused) versus a traditional best overall fit criterion. Additionally, this study seeks to assess the utility of ecologically-focused calibrated models by comparing flow metric accuracy and the strength of flow-ecology relationships among different calibration approaches versus gage data. For this study, continuous HEC-HMS 4.0 models were created for 19 coastal southern California watersheds and calibrated to USGS streamflow gages with nearby bioassessment sites using one best overall fit and three ecologically-focused criteria: NSE, Richards-Baker Flashiness Index (RBI), percent of time when the flow is < 28 L/s (< 1 cfs), and a Combined Calibration (RBI and < 1 cfs), respectively. Ecologically-focused criteria were selected based on preliminary statistical flow-ecology relationships at gaged bioassessment sites. Calibrated models were compared using flow metric accuracy relative to gage data and the strength of flow-ecology relationships. Models were highly accurately calibrated to ecologically-focused criteria, with calibration median percent errors less than 1.5% and only a single model with a percent error greater than 10%, and NSE criteria, with a median value of 0.634. Regardless of high calibration accuracy for ecologically-focused models, additional flow metrics not explicitly calibrated, especially those describing magnitude or rise and fall rates at aggregated daily time scales, were not consistently reproduced by models. Despite inaccuracies across a full suite of 71 flow metrics, low flow and flashiness metrics relevant to biotic endpoints were modeled accurately (< 20% error) and often provided stronger flow-ecology relationships than best overall fit criteria in terms of adjusted R2 in multiple regression analyses and variance explained in random forest modeling. This was especially true when two ecologically-focused criteria were combined, suggesting the importance of multiple calibration criteria. Flow metrics from the Combined Calibration provided the strongest flow-ecology models in correlation and regression analyses compared to the other three calibration approaches, and perform similarly in random forest models. This study demonstrates that if ecologically relevant flow metrics can be identified using published literature or preliminary statistical analyses of gaged bioassessment sites prior to developing a hydrologic foundation, they can be incorporated as calibration criteria and provide stronger modeled flow-ecology relationships than exclusive use of a best overall fit criterion.Item Open Access Effects of hydraulic structures on fish passage: an evaluation of 2D vs 3D hydraulic analysis methods(Colorado State University. Libraries, 2015) Ryan, Erin R., author; Bledsoe, Brian P., advisor; Myrick, Christopher A., committee member; Nelson, Peter A., committee memberChannel-spanning hydraulic structures can act as barriers to upstream fish movement. Negative consequences associated with this disruption of longitudinal habitat connectivity highlight the need for accurate and practicable assessment techniques. Three-dimensional evaluation methods have been shown to resolve the complex flow at in-stream structures and accurately predict fish movement; yet three-dimensional modeling can be impractical due to time and resource requirements. This study investigates using a two-dimensional computational fluid dynamics model and statistical analyses to describe the hydraulic conditions at a whitewater park structure in Lyons, Colorado. Fish movement observations are paired with the resulting hydraulic variables along spatially explicit, continuous paths which represent potential swimming routes. Logistic regression analyses indicate that flow depth and velocity are strongly associated with fish passage; a combined depth and velocity variable accurately predicts 92% of rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) movement observations at this hydraulic structure. The results of this study suggest that two-dimensional analysis methods can provide a cost-effective approach to assessing the effects of similar hydraulic structures on fish passage when three-dimensional analysis in not feasible. Further, conclusions from this study can be used to guide management and design decisions for both trout and fishes with comparatively lower swimming performance.Item Open Access Effects of urbanization on the hydrologic regimes and geomorphic stability of small streams in southern California(Colorado State University. Libraries, 2009) Hawley, Robert Jeffrey, author; Bledsoe, Brian P., advisor; Stein, Eric D., committee member; Wohl, Ellen E., 1962-, committee member; Watson, Chester C., committee memberIn southern California streams, altered hydrologic and sediment regimes associated with urbanization (hydromodification) have induced significant morphologic responses such as incision, widening, and planform shifts from single-thread to braided with far-reaching effects to adjacent land and throughout drainage networks. The overarching objective of this dissertation is to improve process-based understanding of these changes such that the risk of future degradation may be mitigated through improved management. Three chapters follow from this fundamental flow of logic: changes in land cover beget changes in flow regimes, leading to increased erosive energy and sediment-transport potential, which, dependent on the relative resistance of the setting, can culminate into substantial changes in channel form. The purpose of Chapter 1 was to understand the first step in this sequence: how urbanization affects the flow regime. Duration Density Functions (DDFs) were developed as histogram-style cumulative duration curves that represent the full range of geomorphically-significant flows as simple power functions. Using long-term data from 52 U. S. Geological Survey (USGS) gauges, empirical models were fit to both peak flows and DDF parameters (i.e., magnitude and shape) as multivariate functions of statistically-significant spatial variables including total impervious area. With little flow control at the subdivision scale to date, total impervious area became an effective hydrologic iv surrogate for urbanization, demonstrating an exponential effect on peak flows, particularly the 1-, 1.5-, and 2-yr events, and increased durations of all sediment-transporting flows. For example, watersheds with ~10% imperviousness typically exhibit a ~5-fold increase in Q1.5 and 2 to 3 times as many days of sediment-transporting flows relative to an undeveloped setting. The models developed in Chapter 1 directly informed the hydrologic components of the subsequent chapters, where impervious area was not found to be a significant predictor of geomorphic response when considered independent of setting or sediment transport. The focus of Chapter 2 was to understand the relative susceptibilities of regional channel types to hydromodification in the context of a 'Screening Tool' that is being developed to help managers assess risk across geomorphic settings. Specifically, Chapter 2 is focused on 1) the general framework of a pre-final version of the susceptibility screening tool, and 2) the development of risk-based analyses of geomorphic thresholds, a central component of key decision nodes in the screening tool. Geomorphic thresholds are real and of great concern in stream management, such that any susceptibility-assessment scheme should account for the proximity to such threshold-based responses. Logistic-regression analyses of braiding, incision, and bank stability directly and probabilistically assess proximity to geomorphic thresholds, and offer a framework for assessing risk that goes beyond expert judgment. Calibrated with local data that were collected in an extensive field campaign, the logistic models were highly significant (i.e., p < 0.005 to p < 0.0001) and correctly classified unstable states in ~90% of the cases using simple but powerful predictor variables that can be measured at the screening/reconnaissance level. A screening tool that incorporates objective probabilistic-based components is novel relative to previous and more subjective classification v schemes, such that regionally-diverse agencies and staff can quantitatively assess channel susceptibility with less variable results. With the objective of developing a process-based understanding of observed channel changes, Chapter 3 presents models that predict relative magnitudes, directions, and risks of channel responses as functions of cumulative sediment-transport capacity ratios (Lr) that contrast 25-yr DDF simulations of urbanized versus undeveloped conditions. Lr was a highly significant term in quantifying channel 'enlargement', whereas logistic regression of Lr in combination with d50 suggested that fine-grained systems (i.e., especially d50 ≤ 16 mm) have little capacity to absorb any increases in sediment-transport potential. A regional Channel Evolution Model (CEM) that includes departures from the original CEM of Schumm et al. (1984) is also presented along with a modified dimensionless stability diagram (sensu Watson et al. (1988)) that provides a conceptual framework for assessing relative departure from equilibrium/reference form for both lateral and vertical channel responses. The overarching conclusion of this dissertation is that urbanization markedly affects the flow regimes of streams in southern California and that the corresponding imbalances in sediment-transport capacity result in substantial geomorphic instabilities across most stream settings. Consequently, mitigation strategies should be tailored to specific stream types and incorporate process-based objectives such as maintaining sediment continuity via duration standards rather than traditional regulations focused exclusively on flow magnitude.Item Open Access Effects of whitewater parks on fish passage: a spatially explicit hydraulic analysis(Colorado State University. Libraries, 2014) Stephens, Timothy A., author; Bledsoe, Brian P., advisor; Myrick, Christopher A., committee member; Nelson, Peter A., committee memberWhitewater parks (WWPs) provide a valuable recreational and economic resource that is rapidly growing in popularity throughout the United States. WWPs were originally thought to enhance aquatic habitat; however, recent studies have shown that the hydraulic conditions required to meet recreational needs can act as a partial barrier to upstream migrating trout and that WWP pools may contain lower densities of fish compared to natural pools. There is limited knowledge of the direct effects of WWPs on fish passage. Managers and policy makers are forced to review WWP designs and make permit decisions without sound scientific evidence. It is also difficult to make design recommendations for future WWPs and possibly retrofitting existing WWPs to allow for successful fish passage without improved understanding of the factors contributing to suppression of movement in WWPs. We describe novel approaches combining fish movement data and hydraulic results from a three-dimensional computational fluid dynamics model to examine the physical processes that limit upstream movement of trout in an actual WWP in Lyons, Colorado. These methods provide a continuous and spatially explicit description of velocity, depth, vorticity, and turbulent kinetic energy (TKE) along potential fish swimming paths in the flow field. Variation in the magnitude and distribution of velocity and depth relative to fish swimming ability is reflective of variation in passage success among WWP structures and size classes of fish. Logistic regression analyses indicate a significant influence of velocity and depth on limiting passage success and accurately predict > 86 percent observed fish movements. Relationships emerge at individual WWP structures that highlight unique hydraulic characteristics and their effect on passage success. The methods described in this study provide a powerful approach to quantify hydraulic conditions at a scale meaningful to a fish and mechanistically evaluate the effects of hydraulic structures on fish passage. The results of these analyses can be used for management and design guidance, have implications for fishes with lesser swimming abilities, and demonstrate the need to assess additional WWPs of various sizes.Item Open Access Flow duration curves and sediment yield estimation for urbanizing watersheds(Colorado State University. Libraries, 2015) Rosburg, Tyler Thomas, author; Nelson, Peter A., advisor; Bledsoe, Brian P., advisor; Wohl, Ellen E., committee memberLand use change associated with urbanization can alter natural flow regimes, typically resulting in larger peak flows for a given precipitation event than in a pre-urbanized watershed condition. The overall influence of urbanization on how flows of different frequencies might change over time, while important in hydrologic design, remains poorly understood. In this study, we first investigate the effects of urbanization on flow duration curves (FDCs) and flow variability through a case study of several watersheds in the Puget Sound Region of Washington State. A FDC is a graphical representation of the frequency, or fraction of time, that a discharge magnitude is equaled or exceeded. Using different time windows of the flow record, we analyzed stream discharge, precipitation, and watershed urbanization for a minimum of 25 years between 1960 and 2010 to quantify how key FDC percentiles changed with time in response to urbanization in small watersheds (less than 200 km²) with land uses ranging from highly urban to primarily rural. In the urban watersheds, the 95th-99th percentile of the daily-mean flow series increased by 0-94% with an average increase of 35%. The magnitude of small discharges (10th percentile) in the urban watersheds also increased by up to 34% with an average increase of 15%. The rapidity and magnitude of changes in streamflow, commonly known as “flashiness,” was also observed to increase over the period analyzed for both urban and rural watersheds. Flashiness increased by 46% on average in urban watersheds, a result likely caused by increases in population density and impervious surfaces. Rural watersheds were found to have lesser increases in flashiness, 14% on average, attributed to baseflow reductions and increasing precipitation intensity and variability. As watersheds become flashier, the decision to use either daily-averaged or sub-daily streamflow records has the potential to impact the calculation of sediment transport metrics. To investigate, we calculated the effective discharge, sediment yield, and half-load discharge using sediment rating curves over long time periods with both daily-averaged and sub-daily streamflow records, in the second part of this study. The pool of sites in the analysis included 39 sites with bedload measurements and 99 sites with suspended load measurements from several regions of the United States. Results of this analysis were compared to site-specific metrics such as stream flashiness and bed sediment size. A comparison of sediment transport metrics calculated with both daily-average and sub-daily stream flow data at each site showed that daily-averaged flow data were unable to adequately represent the magnitude of high streamflows at flashy sites. This caused an underestimation of sediment transport and sediment yield at flashy sites, the degree of which was controlled by the magnitude of the best-fit exponent of the sediment rating curve. Regression equations are provided for estimating this bias as a function of stream flashiness and sediment rating curve parameters. No relationship between flow data resolution and effective discharge was found. The results of this analysis help inform the use of FDCs and sediment yield estimation in urbanizing watersheds. This analysis demonstrates the magnitude of change that urbanization may cause in a FDC. Additionally, this analysis illustrates the importance of using sub-daily flow data in the calculation of sediment yield in urbanizing or otherwise flashy watersheds.Item Open Access Flow resistance prediction in high-gradient streams(Colorado State University. Libraries, 2010) Yochum, Steven Edward, author; Bledsoe, Brian P., advisor; Rathburn, Sara L., 1962-, committee member; Watson, Chester C., committee member; Wohl, Ellen E., 1962-, committee memberFlow resistance measurements were collected on high-gradient streams in the Fraser Experimental Forest, Colorado, for bankfull through low flows using Rhodamine WT dye tracing, ground-based LiDAR scans, and laser theodolite surveying of longitudinal profiles and below-water features. A dataset of 59 resistance measurements was collected on fifteen reaches with instream wood present in varying densities. Values of Manning's n ranged from 0.05 to 0.52, and Darcy-Weisbach ƒ varied from 0.28 to 56. All measurements indicated subcritical reach-average conditions, with Froude numbers ranging from 0.15 to 0.78. Relative grain submergence (R/D84) was a poor predictor of flow resistance while relative bedform submergence, defined as the ratio of depth or hydraulic radius to the standard deviation of the residuals of a bed profile regression (hm/σz, R σz), explained up to 76 and 80 percent of the variance of n and ƒ, respectively. Both clasts and instream wood contribute to bed variability; steps are heightened by wood lodging among the clast steps. Hence relative bedform submergence captures the combined influence of wood and clasts, which contribute both form and spill resistance. Relative bedform submergence is less effective for prediction in reaches with substantial non-step-forming instream wood and in steep channels. In the steepest reaches, with slopes over about 18 percent, the data indicate a shift towards a skimming regime with a partial submergence of bedforms and a threshold reduction in flow resistance. Three-dimensional measures of geometric variability were explored, to assess the correlation of flow resistance with higher-order spatial variation due to composite effects of bedforms, large clasts, and instream wood. With the exclusion of bank effects, a normalized variable (ha3/σz3) explained 77 and 81 percent of the variance of n and ƒ, respectively. Multivariate regression models with variables describing bedforms, bankforms, and instream wood explained 87 percent of the variance of n and ƒ. On average, flow resistance due to bedforms (form and spill) are the greatest contributor to overall flow resistance in these high-gradient streams, followed by form resistance generated by bankforms, and lastly, by form resistance induced by non-step instream wood.Item Open Access Full spectrum analytical channel design with the capacity/supply ratio (CSR)(Colorado State University. Libraries, 2017) Stroth, Travis R., author; Bledsoe, Brian P., advisor; Nelson, Peter A., committee member; Rathburn, Sara L., committee memberAnalytical channel design tools have not advanced appreciably in the last decades, and continue to produce designs based upon a single representative discharge that may not lead to sediment continuity. It is beneficial for designers to know when a simplified design may be problematic and to efficiently produce alternative designs that approximate sediment balance over the entire flow regime. The Capacity/Supply Ratio (CSR) approach, an extension of the Copeland method of analytical channel design for sand channels, balances the sediment transport capacity of a design reach with the sediment supply of a stable upstream reach over the entire flow duration curve (FDC) rather than just a single discharge. Although CSR has a stronger physical basis than previous analytical channel design approaches, it has not been adopted in practice because it can be a cumbersome and time-consuming iterative analysis without the use of software. I present a novel design tool that was developed using the Visual Basic for Applications (VBA) programming language in Excel® and produces stable channel slope/width combinations based on the CSR methodology for both sand- and gravel-bed streams. The CSR Stable Channel Design Tool's (CSR Tool) code structure was based on Copeland's method in SAM and HEC-RAS (Hydrologic Engineering Center – River Analysis System) and was tested with a single discharge to verify outputs. Eighteen sand-bed rivers were investigated with the tool in a comparison of designs based on the CSR approach and five single-discharge metrics: the effective discharge (Qeff) or discharge that transports the most sediment over time, the 1.5-year recurrence interval discharge (Q1.5), bankfull discharge (Qbf), and the discharges associated with 50th (Qs50) and 75th (Qs75) percentiles of the cumulative sediment yield curve. The Qs50 and Qs75 single-discharge designs match the CSR output most closely followed by the Qbf and Qeff. The Qeff proved to be the most inconsistent design metric because it can be highly dependent on the binning procedure used in the effectiveness analysis. Furthermore, I found that the more rigorous physical basis of the CSR analysis is potentially most important in designing "labile' channels with highly erodible substrate, high perennial flow "flashiness', low width-to-depth ratio, and high incoming sediment load. The CSR Tool provides a resource for river-restoration practitioners to utilize process-based design techniques that can promote more reliable and sustainable designs for dynamic fluvial systems.Item Open Access Improving hydrologic modeling of ungaged basins to support environmental flow management in a heterogeneous region(Colorado State University. Libraries, 2021) Adams, Stephen K., author; Bledsoe, Brian P., advisor; Poff, N. LeRoy, committee member; Niemann, Jeffrey D., committee member; Stein, Eric D., committee memberEnvironmental streamflow management can sustain aquatic ecosystems and the services they provide by reestablishing elements of the natural flow regime that are necessary for ecological health. One of the more difficult challenges with developing environmental flow criteria is estimating streamflow at locations without gage data; however, this challenge is not unique to environmental flows. Streamflow prediction in ungaged basins is a very common problem in hydrology and engineering with no clear solution, but it is particularly difficult to model environmental streamflow metrics across heterogeneous regions with highly diverse land uses, geologic settings, and hydroclimatological processes. In this dissertation, I create a new regionalization framework, "Streamflow Regionalization with Hydrologic Model-based Classification" (SR-HMC), for modeling challenging flow metrics in ungaged basins across a heterogeneous region. I also test the efficacy of the new framework for developing environmental streamflow criteria. In Chapter 2, I explore different approaches for classifying streams with similar flow regimes and develop a novel classification technique for prioritizing regional accuracy of hydrologic models. As the precursor to SR-HMC, this "Hydrologic Model-based Classification" (HMC) groups hydrologically similar streams by determining the degree of reciprocity of calibrated parameters between a regional catalog of rainfall-runoff models as quantified through jackknife resampling. Results show that HMC complements traditional classifications based on streamflow metrics and watershed characteristics, and offer advantages over these traditional classifications when used to regionalize ungaged basins. Next, Chapter 3 describes implementation of ensemble modeling to optimize HMC into a regionalization framework for producing time series of streamflow at ungaged sites. For gaged locations, hydrologic model parameters that cannot be calculated directly can be calibrated using observed flows; however, these same model parameters are much more uncertain and difficult to estimate at ungaged locations. SR-HMC uses geographically-weighted model output averaging with regionally-calibrated parameter sets to reduce parameter uncertainty in models of ungaged basins. This new framework is tested at five sites across a large and diverse region. Results were improved using SR-HMC over standard nearest-neighbor regionalization approaches. Finally, I turn to management applications of these novel methods in ungaged basins by analyzing the statistical relationships between streamflow alteration and ecological integrity. In Chapter 4, I compare the explanatory power of simple flow-ecology relationships produced by different methods for regionalizing ungaged basins and different metrics of flow alteration. Results highlight robust modeling practices amenable to management. Development of environmental streamflow recommendations based on prediction in ungaged basins is an ongoing challenge; however, this research demonstrates how novel approaches to classification and model extrapolation can improve streamflow estimation at ungaged locations in heterogeneous regions, and thereby bolster the scientific basis of environmental flow management.Item Open Access Investigating nitrate uptake and transient storage in headwater streams among gradients of geomorphic complexity, land use, and restoration techniques(Colorado State University. Libraries, 2010) Mueller Price, Jennifer Suzanne, author; Bledsoe, Brian P., advisor; Gooseff, Michael Nikolai, committee member; Loftis, Jim C., committee member; Wohl, Ellen E., 1962-, committee memberHeadwater streams are a crucial component of nutrient processing in watersheds, owing to high surface-to-volume ratios that favor nitrate uptake and to the large percentage of headwater stream length in the total length of a river system. In this study, I explore how geomorphic characteristics may influence transient storage and nitrate uptake of streams across a gradient of land use and restoration practices. To examine linkages among geomorphic complexity, transient storage, and nitrate uptake in streams, I investigated an urban stream and two agricultural streams. Study reaches representing distinct geomorphic settings with varying substrate size, sinuosity, bed slope, and styles of restoration and management were chosen within each stream. I performed detailed physical characterizations and multiple nutrient injections of bromide and nitrate to estimate transient storage and nitrate uptake in each reach. Comprehensive data sets, including pebble counts, longitudinal profiles, cross-section surveys, hydraulic measurements, and benthic organic matter (fine and coarse), were collected to characterize physical complexity along each reach. To estimate parameters of transient storage and nitrate uptake, the OTIS model was run through UCODE for optimization of parameter estimates. Regression models were developed to relate attributes of flow and geomorphic complexity with transient storage and nitrate uptake parameters. The models showed associations among nitrate uptake velocity and length (vf, Sw) and transient storage parameters (Fmed200), which were influenced by key factors of geomorphic complexity (longitudinal roughness), flow (Reynolds number), and substrate condition (median grain size and fine benthic organic matter). There were no conclusive patterns showing that in-channel structures and natural revegetation of riparian areas promoted nitrate uptake in the study streams. For example, a reach with instream wood but without restoration structures exhibited more transient storage and comparable nitrate uptake when compared to a paired reach with extensive J-hook vane structures. Finally, an investigation of the urban stream before and after a high flow event indicated that transient storage and nitrate uptake are highly context-specific and mediated by interactions between geomorphic setting and flow variability.Item Open Access Land use effects on physical habitat and nitrate uptake in small streams of the central Rocky Mountain region(Colorado State University. Libraries, 2009) Baker, Daniel Wayne, author; Bledsoe, Brian P., advisorWatershed land use alteration and flow extraction influence the physical habitat and geochemical functions of small streams. In two associated studies, I explore stream physical habitat characteristics and nutrient uptake across a range of land use influences (flow extraction, agriculture, and urbanization). In the first study, I examined the effects of flow diversion to fine sediment deposition in a detailed field analysis pairing reaches above and below diversion dams on 13 mountain streams throughout north-central Colorado and southern Wyoming. Diversions are ubiquitous across the American West, yet previous studies on the impact of flow extraction have yielded mixed results. Through application of strict site selection criteria, multiple fine sediment measures, and an intensive sampling scheme, this study found that channels downstream of diversions contained significantly more fine sediment and slow flowing habitat as compared to upstream control reaches. Susceptibility to fine sediment accumulation was associated with decreasing basin size, bankfull depth, and d84, and appears to be magnified in streams of less than 3% slope. In the second study, I investigate physical and hydraulic influences on transient storage and nutrient uptake in small agricultural and urban streams across a gradient of channel conditions and management modifications. Three geomorphically distinct segments on each of two streams were studied in the summer of 2007: one in a Colorado Front Range urban setting and the other in a mountainous agricultural region in north-central Colorado. The urban stream exhibits various levels of stabilization and planform alteration, and the agricultural stream has been subject to historically variable cattle-grazing practices. Reach-scale geomorphic complexity was characterized using highly detailed surveys of channel morphology, substrate, hydraulics, and habitat units. Injections of conservative bromide (Br-) and non-conservative nitrate (NO3-) tracers were used to characterize channel processes. Geomorphic characteristics, specifically increased longitudinal roughness and flow depth, were strongly associated with both nutrient uptake and transient storage. Collectively, the studies underscore the primary influence of flow regime on habitat response and nutrient spiraling functions in the context of human influences.Item Open Access Modeling in a three-dimensional world: whitewater park hydraulics and their impact on aquatic habitat in Colorado(Colorado State University. Libraries, 2013) Kolden, Eleanor, author; Bledsoe, Brian P., advisor; Wohl, Ellen, committee member; Grigg, Neil S., committee memberWhitewater parks (WWPs) are becoming more popular in Colorado rivers and streams, but the effects of WWPs on aquatic habitat and fish passage are poorly understood. This study investigated the use of a three-dimensional (3-D) hydrodynamic model (FLOW-3D®) for assessing effects of WWPs on aquatic habitat. The objective of this study was to compare modeled habitat quality to actual fish biomass and to examine the utility of 3-D modeling (vs. two-dimensional (2-D) modeling) in this hydraulically-complex system. Two sections of a small river in Colorado were modeled: one natural section, and one section containing a WWP with three engineered drop structures. A 2-D habitat suitability analysis for juvenile and adult brown and rainbow trout, longnose dace, and longnose sucker predicted higher habitat quality in the WWPs than the natural reaches for adult brown and rainbow trout at some flow rates, while in-stream surveys showed higher fish biomass per volume in the natural pools. All hydraulic metrics (depth, depth-averaged velocity, turbulent kinetic energy (TKE), 2-D vorticity, and 3-D vorticity) had higher magnitudes in the WWP pools than in the natural pools. In the WWP pools, 2-D model results did not describe the spatial distribution of flow characteristics or the magnitude of variables as well as 3-D results. This thesis supports the use of 3-D modeling for complex flow found in WWPs, but other projects should be evaluated case-by-case to determine if the simplified 2-D rendering of flow characteristics is acceptable. For 3-D modeling to be widely useful, improved understanding of linkages between 3-D aquatic habitat quality and hydraulic descriptors such as TKE, vorticity, and velocity is needed.Item Open Access Modeling stream evolution and its consequences for watershed scale pollutant loading(Colorado State University. Libraries, 2018) Lammers, Roderick W., author; Bledsoe, Brian P., advisor; Arabi, Mazdak, committee member; Nelson, Peter, committee member; Rathburn, Sara, committee memberThroughout the world, streams are degraded due to impaired water quality and erosion and sedimentation caused by hydrologic and sediment imbalances. These two issues are linked. Channel erosion not only damages stream habitat but can be a significant source of fine sediment and nutrient pollution in watersheds. Phosphorus in particular is common in streambanks and when these soils are mobilized – for example during amplified high flows in urban streams – they can contribute to eutrophication of downstream water bodies. Understanding these dynamics is important for reversing these impairments and sustainably managing our water resources. In this dissertation, I provide a new tool to quantify the magnitude of channel erosion as a pollutant source. First, I put this issue in context by reviewing recent literature on stream restoration and its ability to either reduce nutrient loading or enhance natural nutrient removal processes. Results suggest that stream restoration can help reduce nutrient pollution, but quantifying these benefits remains challenging. Despite the rapid growth of the stream restoration industry, there is still insufficient monitoring and assessment of project success. Perhaps this is due to a lack of standardized tools and methodologies. The remainder of this dissertation attempts to fill part of this gap --- providing a new tool to predict watershed sediment and phosphorus loading from channel erosion. I develop a new model to simulate stream channel evolution at the watershed scale. This model is built around specific stream power, a variable that is straightforward to calculate using easily quantified parameters: discharge, slope, and width. I first develop new sediment transport equations based on specific stream power. These are used by the model to simulate channel bed aggradation and degradation. I link these processes with a simplified version of a bank erosion model to account for lateral channel adjustment. Model simulations match physical understanding of channel evolution in response to disturbance as well as field datasets of rivers adjusting to both human and natural perturbations. Importantly, the model is structured to quantify uncertainty in model projections. This is essential for understanding both model limitations and more generally for simulating complex systems in a stochastic world. Finally, I apply this new model to estimate sediment and phosphorus loading from bank erosion in two watersheds: Big Dry Creek, Colorado and Lick Creek, North Carolina. Despite their many differences and their unique simulated responses to disturbance, results for both watersheds suggest that channel erosion may be responsible for nearly all of the suspended sediment pollution, but very little of the phosphorus. This new model has a number of applications in both the scientific and management communities --- exploring river behavior in more detail while also answering relevant management questions as we try to more effectively steward our water resources.Item Open Access On the development of flow-ecology relationships for streams in coastal watersheds of southern California(Colorado State University. Libraries, 2014) Eberhart, Sarah R., author; Bledsoe, Brian P., advisor; Poff, N. LeRoy, committee member; Stein, Eric D., committee memberLinking hydrologic alteration to the biotic responses of streams is essential for understanding and managing the effects of land use changes and other human influences on aquatic ecosystems. This study develops flow-ecology relationships for wadeable streams in coastal watersheds of southern California to understand the ecological effects of urbanization and other sources of hydromodification. Streams in this region are predominately flashy, seasonally intermittent, and fine grained; hence, the inherently harsh disturbance regime is a major determinant of biotic composition. I match biological and geomorphic data with proximate U. S. Geological Survey streamflow gages to examine flow-ecology relationships between benthic macroinvertebrates and the hydrologic and hydraulic regimes of 32 biomonitoring sites spanning a gradient of watershed urbanization. Associations between landscape, streamflow, and biotic metrics indicate that flow permanence and urbanization are overarching and interacting influences on benthic macroinvertebrate assemblages in this region. In particular, flow intermittency and flashiness are significant predictors of both taxonomic and traits-based measures of biotic composition. Urban land cover and road density are significantly correlated with higher flow flashiness and decreasing measures of biotic integrity. Hydraulic metrics describing streambed mobility are strongly positively associated with measures of biotic integrity as a result of high intercorrelation with flow permanence. Thus, it appears that benthic macroinvertebrate assemblages are fundamentally influenced by flow intermittency and urban-induced flashiness in this region. Use of daily discharge data analyzed 3 yrs prior to biological sampling events appears to result in little to no loss of resolution in flow-ecology relationships compared to sub-daily (15-min) and long-term (decadal) flow records. Results also underscore the utility of traits-based analyses and stratification of sites by flow permanence and dominant substrate in revealing mechanistic relationships between flow and biotic metrics. By using gaged sites to identify the flow metrics best describe biological variation, this study provides insight into which elements of the flow regime are most important to model accurately in future efforts to develop a regional hydrologic foundation that will allow the inclusion of ungaged biomonitoring sites in refining flow-ecology relationships.Item Open Access On the nature and mechanics of floodplain response and stability in the semi-arid environment of southern California(Colorado State University. Libraries, 2009) Dust, David Walter, author; Bledsoe, Brian P., advisor; Grigg, Neil S., committee member; Watson, Chester C., committee member; Wohl, Ellen E., 1962-, committee memberThe core research questions motivating this dissertation are: (1) How can we assess the existing stability state of a floodplain? ; and (2) How can we estimate the trend and magnitude of the change in floodplain geometry due to urbanization? Field investigations conducted early in this research indicated that it was essential to build a basic framework of understanding for the fluvial systems in the semi-arid environment of southern California, prior to addressing the core research questions. To build this framework, various classification systems and conceptual models have been developed to characterize the nature and form of floodplains at multiple spatial scales. A reach-scale classification system and conceptual model were created to synthesize the observed floodplain forms into three basic floodplain continuums (armored, non-armored, and active-regional alluvial fan), where each of these continuums are comprised of three to five alluvial floodplain forms (cascade, step-pool, plane-coarse-bed, plane-mixed-bed, plane-fine-bed, pool-riffle, braided, and dune-ripple). A catchment-scale conceptual model was created to describe the interrelationship between the three basic floodplain continuums in terms of climatic and geologic metrics. This conceptual model provided the basis to develop a practical GIS-based technique for predicting the floodplain continuum type within a catchment. For the non-armored and armored floodplain continuums, floodplain state plots have been generated to quantitatively describe the natural downstream progression of floodplain forms, using specific stream power and the width-to-depth ratio as the state and shape metrics. These floodplain state plots provided the bases to create conceptual models for intra-catchment processes and to develop techniques for assessing the stability state of a floodplain. Using the series of conceptual models as a framework, regime-type modeling tools have been developed for estimating the trend and magnitude of the change in floodplain geometry due to changes in water and sediment supply. At the core of these tools are the basic flow relationships of continuity, flow resistance, and sediment transport for floodplains with trapezoidal geometry. To factor in bank erosional resistance and stability characteristics, the basic flow relationships are coupled with floodplain response and stability constraints developed from the conceptual models for intra-catchment processes.Item Open Access Uncertainty and sensitivity in a bank stability model: implications for estimating phosphorus loading(Colorado State University. Libraries, 2015) Lammers, Roderick William, author; Bledsoe, Brian P., advisor; Baker, Daniel, committee member; Wohl, Ellen, committee memberEutrophication of aquatic ecosystems is one of the most pressing water quality concerns in the U.S. and around the world. Bank erosion has been largely overlooked as a source of nutrient loading, despite field studies demonstrating that this source can account for the majority of the total phosphorus budget of a watershed. Substantial effort has been made to develop mechanistic models to predict bank erosion and instability in stream systems; however, these models do not account for inherent natural variability in input values. Providing only single output values with no quantification of associated uncertainty can complicate management decisions focused on reducing bank erosion and nutrient loading to streams. To address this issue, uncertainty and sensitivity analyses were performed on the Bank Stability and Toe Erosion Model (BSTEM), a mechanistic model developed by the USDA-ARS that simulates both mass wasting (stability) and fluvial erosion of streambanks. Sensitivity analysis results indicate that variable influence on model output can vary depending on assumed input distributions. Generally, bank height, soil cohesion, and plant species were found to be most influential in determining stability of clay (cohesive) banks. In addition to these three inputs, groundwater elevation, stream stage, and bank angle were also identified as important in sand (non-cohesive) banks. Slope and bank height are the dominant variables in fluvial erosion modeling, while erodibility and critical shear stress are relatively unimportant. However, the threshold effect of critical shear stress (determining whether erosion occurs) was not explicitly accounted for, possibly explaining the relatively low sensitivity indices for this variable. Model output distributions of sediment and phosphorus loading rates corresponded well to ranges published in the literature, helping validate both model performance and selected ranges of input values. In addition, a probabilistic modeling approach was applied to data from a watershed-scale sediment and phosphorus loading study on the Missisquoi River, Vermont to quantify uncertainty associated with these published results. While our estimates indicated that bank erosion was likely a significant source of sediment and phosphorus to the watershed in question, the uncertainty associated with these predictions indicates that they should probably be considered order of magnitude estimates only.