Mountain Scholar :: Browsing by Author "Morrison, Ryan, advisor"

Browsing by Author "Morrison, Ryan, advisor"

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Open Access
Experimental flume and numerical studies into the influence of floodplain vegetation on river-corridor hydrodynamic processes
(Colorado State University. Libraries, 2023) White, Daniel C., author; Morrison, Ryan, advisor; Nelson, Peter, advisor; Thornton, Chris, committee member; Rathburn, Sara, committee member
The active channel has historically been the primary focus of river hydrodynamic process studies and river engineering. However, increased global flood risk and awareness of ecosystem services provided by floodplains has encouraged managers to broaden their perspective beyond the banks. As water exits and reenters the channel during floods, water, nutrients, and sediment are exchanged with the floodplain. This flux is heavily influenced by both channel-floodplain hydrologic connectivity, or the ability of water to access the floodplain, and by floodplain land cover types. River and hydrologic modifications that result in disconnected floodplains include channel planform and cross-section geometry alterations, diversions and dams, levees, land cover change, and river sediment mining. As river managers, land-use managers, and landowners acknowledge the benefits of functional, laterally connected river corridors, more river restoration projects are undertaken with a primary goal of reconnecting a river channel to the adjacent floodplain. A major component of large river restoration and river engineering projects includes designing for and predicting future flow scenarios using hydraulic models and other analytical methods. Developing a hydraulic model for river restoration design relies on the theory and science of fluvial morphodynamic processes as well as the parameterization of hydraulic roughness coefficients. Because of the historical emphasis on in-channel processes, the scientific literature related to channel-floodplain hydrodynamics and floodplain roughness parameterization is sparse. Specifically, there are limited studies investigating the influence of vegetation on channel-floodplain exchange flow, lateral connectivity, and resulting channel topography. To address this knowledge gap, I conducted a series of physical and numerical modeling experiments where floodplain vegetation and flow parameters were varied. In Chapters 2 and 3, I present the results of flume experiments where I measured bedform topography and the flow field under varied floodplain vegetation conditions at two overbank flow depths. The experiments were conducted in a 1-m wide meandering compound channel inset in a 15.4-m long, 4.9-m wide basin. The channel bed was a mobile sand-and-gravel mixture with a median sediment size of 3.3 mm, and sediment transport occurred only within the channel. I tested bare and vegetated floodplain conditions with 2.7-cm diameter rigid emergent vegetation elements at spacings of 3.0 units m-2 and 12.1 units m-2. My observations of the flow field indicate that high density vegetation enhances secondary circular flow through the meander bend and reduces momentum exchange at the channel-floodplain interface. At a low relative depth, flow through high density vegetation was deflected away from the down-valley direction and forced to reenter the channel at a steep angle with respect to the channel centerline. However, at a high relative depth, dense vegetation steered in-channel surface flows more closely following the channel centerline. These observations shed light on the hydrodynamic processes leading to flood wave attenuation, enhanced nutrient cycling, and channel altering stresses, and these results may inform river restoration riparian management best practices. To investigate bedform response, I performed a moving-window analysis of topographic surface metrics including skewness, coefficient of variation, and standard deviation, as well as topographic patch analysis of area and contagion to measure changes in bedform heterogeneity as flow depth and vegetation density were varied. My results show that both greater density vegetation and larger flows can increase bedform topographic heterogeneity. These findings suggest that floodplain vegetation and natural hydrologic regimes that include overbank flows can enhance stream habitat complexity. Designing for the effects of established vegetation conditions and prioritizing floodplain vegetation planting may be useful for river managers striving to achieve successful biomic river restoration. Expanding on the observations made in the flume, I explored the ability of a 2D hydraulic model to predict the effects of vegetation on meandering channel flow dynamics. I used the TreeLS point cloud processing tool to automatically extract woody floodplain vegetation characteristics and estimate Manning's roughness coefficients for vegetation from aerial LiDAR. I investigated the influence of varied vegetation densities on channel-floodplain exchange flows in HEC-RAS 2D. I developed hydraulic models for three reaches along the Butokamabetsu River in the Hokkaido University Uryu Experimental Forest in Northern Japan where each reach had distinct biogeomorphic characteristics including channel width, slope, sinuosity, and floodplain vegetation density. I found that in the lower gradient, higher sinuosity reaches, floodplain vegetation density had more influence on channel-floodplain exchange flow attenuation. These results highlight the importance of planning for the presence and density of vegetation in river restoration projects particularly in lower gradient, more sinuous stretches of river. The results and analysis presented in this dissertation suggest that biological drivers such as rigid emergent floodplain vegetation play an important role in river form and function particularly in conjunction with floods that occasionally access the floodplain. These detailed observations of flow, sediment, and resulting bed morphology as well as analysis of innovative remote sensing techniques provide a basis for an improved understanding of morphodynamic processes in meandering rivers.
Open Access
Hydrodynamics in meandering compound channels with varied emergent floodplain vegetation densities: a 3D numerical modeling study
(Colorado State University. Libraries, 2021) Brouillard, Nicolas P., author; Morrison, Ryan, advisor; Nelson, Peter, advisor; Wohl, Ellen, committee member
Emergent floodplain vegetation can influence the hydrodynamic interactions between floodplain and main channel flows during floods in meandering compound channels. These interactions impact the flow and boundary shear stress fields in the main channel, which govern sediment transport, channel morphodynamics, and the capacity to convey flood flows. These processes are important to sustaining aquatic habitats, understanding geomorphic change, and predicting flood severity. However, the effects of emergent floodplain vegetation density on flow phenomena in meandering compound channels are poorly understood. Therefore, this study had three objectives: 1) accurately numerically model three-dimensional (3D) flows at different relative depths (ratio of floodplain to main channel flow depths) in a meandering compound channel with a fixed rectangular main channel cross section and a smooth floodplain using data from published physical experiments, 2) use the numerical model to simulate varied emergent floodplain vegetation density conditions, and 3) analyze the effects of different emergent floodplain vegetation densities on the main channel and floodplain hydrodynamics. Specifically, the effects of floodplain vegetation conditions on primary flows, secondary flows, and boundary shear stresses in the main channel were explored. This study also looked at how floodplain vegetation density affected total discharge capacity as well as inbank and overbank layer-averaged flow patterns. Smooth floodplain, low floodplain vegetation density, and high floodplain vegetation density scenarios were modeled with uniform arrays of emergent cylinders with non-dimensional vegetation densities (portion of the control volume occupied by vegetation) of 0, 0.00946, and 0.0368, respectively, based on natural floodplain forests. These scenarios were modeled for eleven relative depths ranging from 0 to 0.80. Previous research in meandering compound channels with smooth and roughened floodplains has shown that minimum average streamwise velocities and boundary shear stresses in the main channel occur at a given threshold value of overbank relative depth. Therefore, a major focus of this research was to examine the relationships between vegetation densities, overbank relative depths, and minima in average main channel streamwise velocities and boundary shear stresses. The 3D numerical model accurately replicated the results of previously published physical experiments (objective 1) based on calibrated error metrics comparing free surface elevations and main channel streamwise velocities. Results from the calibrated numerical model show that as floodplain vegetation density increased, the initial minimum values of average main channel streamwise velocities and boundary shear stresses were lower in magnitude and occurred at greater relative depths and discharges (objectives 2 and 3). Unlike in the smooth and low vegetation density floodplain scenarios, these average main channel values generally did not increase with relative depth and discharge above the initial minimum case for the high vegetation density scenario. Furthermore, the main channel boundary shear stress field had strong gradients and had greater variations in magnitude in the vegetated floodplain scenarios compared with the smooth floodplain scenario. Additionally, increasing floodplain vegetation density greatly reduced the discharge capacity as well as the average main channel streamwise velocities and boundary shear stresses above the lowest relative depths. Finally, the character of the main channel primary and secondary flow structures as well as the inbank and overbank layer-averaged flows were also affected by floodplain vegetation density. As vegetation density increased, floodplain flows deviated further from the valley-wise direction and plunged more steeply into the main channel below the bankfull level, thus increasing interactions between inbank and overbank flow layers. The strength of separation between inbank and overbank flow layers at an imaginary bankfull level horizontal plane is believed to influence energy losses in the flow, which helps to explain trends in the flow velocity and boundary shear stress fields. In conclusion, this study illustrates why river scientists and engineers should consider the effects of floodplain vegetation density on main channel hydrodynamic processes in similar meandering compound channel systems.
Open Access
Improving hydrologic modeling of runoff processes using data-driven models
(Colorado State University. Libraries, 2021) Han, Heechan, author; Morrison, Ryan, advisor; Grigg, Neil S., committee member; Bailey, Ryan T., committee member; Kampf, Stephanie, committee member
Accurate rainfall–runoff simulation is essential for responding to natural disasters, such as floods and droughts, and for proper water resources management in a wide variety of fields, including hydrology, agriculture, and environmental studies. A hydrologic model aims to analyze the nonlinear and complex relationship between rainfall and runoff based on empirical equations and multiple parameters. To obtain reliable results of runoff simulations, it is necessary to consider three tasks, namely, reasonably diagnosing the modeling performance, managing the uncertainties in the modeling outcome, and simulating runoff considering various conditions. Recently, with the advancement of computing systems, technology, resources, and information, data-driven models are widely used in various fields such as language translation, image classification, and time-series analysis. In addition, as spatial and temporal resolutions of observations are improved, the applicability of data-driven models, which require massive amounts of datasets, is rapidly increasing. In hydrology, rainfall–runoff simulation requires various datasets including meteorological, topographical, and soil properties with multiple time steps from sub-hourly to monthly. This research investigates whether data-driven approaches can be effectively applied for runoff analysis. In particular, this research aims to explore if data-driven models can 1) reasonably evaluate hydrologic models, 2) improve the modeling performance, and 3) predict hourly runoff using distributed forcing datasets. The details of these three research aspects are as follows: First, this research developed a hydrologic assessment tool using a hybrid framework, which combines two data-driven models, to evaluate the performance of a hydrologic model for runoff simulation. The National Water Model, which is a fully distributed hydrologic model, was used as the physical-based model. The developed assessment tool aims to provide easy-to-understand performance ratings for the simulated hydrograph components, namely, the rising and recession limbs, as well as for the entire hydrograph, against observed runoff data. In this research, four performance ratings were used. This is the first research that tries to apply data-driven models for evaluating the performance of the National Water Model and the results are expected to reasonably diagnose the model's ability for runoff simulations based on a short-term time step. Second, correction of errors inherent in the predicted runoff is essential for efficient water management. Hydrologic models include various parameters that cannot be measured directly, but they can be adjusted to improve the predictive performance. However, even a calibrated model still has obvious errors in predicting runoff. In this research, a data-driven model was applied to correct errors in the predicted runoff from the National Water Model and improve its predictive performance. The proposed method uses historic errors in runoff to predict new errors as a post-processor. This research shows that data-driven models, which can build algorithms based on the relationships between datasets, have strong potential for correcting errors and improving the predictive performance of hydrologic models. Finally, to simulate rainfall-runoff accurately, it is essential to consider various factors such as precipitation, soil property, and runoff coming from upstream regions. With improvements in observation systems and resources, various types of forcing datasets, including remote-sensing based data and data-assimilation system products, are available for hydrologic analysis. In this research, various data-driven models with distributed forcing datasets were applied to perform hourly runoff predictions. The forcing datasets included different hydrologic factors such as soil moisture, precipitation, land surface temperature, and base flow, which were obtained from a data assimilation system. The predicted results were evaluated in terms of seasonal and event-based performances and compared with those of the National Water Model. The results demonstrated that data-driven models for hourly runoff forecasting are effective and useful for short-term runoff prediction and developing flood warning system during wet season.
Open Access
Non-perennial streamflow & geomorphic patterns in a semi-arid rangeland slated for development
(Colorado State University. Libraries, 2023) Poteet, Dixie L., author; Bhaskar, Aditi, advisor; Morrison, Ryan, advisor; Kampf, Stephanie, committee member; Grigg, Neil, committee member
Urbanization has widely recognizable impacts on stream morphology and flow patterns. Predicting and quantifying these impacts can be difficult, especially for non-perennial streams in semi-arid rangelands. Non-perennial streams tend to lack a historical baseline with complete records of streamflow presence and absence. A historical pre-development baseline allows for better consideration when making development and infrastructure decisions as well as post-development comparison to quantify urbanization-driven impacts. This project focuses on a non-perennial stream channel in West Stroh Gulch, located in Parker, Colorado south of Denver, U.S.A. A historically semi-arid rangeland area slated to undergo housing development in the next few years, West Stroh Gulch is a unique opportunity to establish a historical baseline for a non-perennial stream. Streamflow presence and absence was recorded at multiple locations along the stream network with time-lapse photography. Photo observations and precipitation data were reviewed to determine what storm events did, or did not, trigger a flow response. After over two years of stream channel monitoring, one precipitation event with a total depth of 92-mm and maximum 60-minute intensity of 50-mm per hour triggered streamflow. Additionally, a hydrodynamic model was built in SRH-2D to compare the impacts of predicted flows through a reach of interest. Topographic pre-development data and Storm Water Management Model (SWMM) generated peak flows were used to simulate impacts of different sized storms. Peak flows varied both by storm and development scenario: existing undeveloped, traditional centralized post-development detention, and post-development distributed detention. Boundary shear stresses were used to compare the different simulations. Overall, the pre-development existing scenario had the lowest flows shear stresses for the two smallest storm scenarios (water quality capture volume and 2-year storms). For the 5-, 10-, 50-, and 100-year storms, the proposed post-development scenarios that incorporated distributed detention had the lowest flows and shear stresses. The traditional centralized detention post-development stormwater strategy had the highest flows, shear stresses, velocities, and water depths for all storm sizes. The simulation results indicate that the post-development distributed detention strategy will be effective at reducing stream channel stresses and erosion for larger storm events.
Open Access
Quantifying floodplain health in the contiguous United States using an index of integrity
(Colorado State University. Libraries, 2022) Simonson, Kira, author; Morrison, Ryan, advisor; Nelson, Peter, committee member; Wohl, Ellen, committee member
Despite the numerous hydrological, geological, and ecological benefits produced by floodplain landscapes, floodplains continue to be degraded by human activities at a much higher rate than other landscape types. Although this large-scale landscape modification has been widely observed, a comprehensive, national dataset quantifying the degree to which human activities are responsible for this degradation has not previously been evaluated. Floodplain integrity can be defined as the ability of a floodplain to support essential environmental functions that sustain diversity and ecosystem services through geomorphic, hydrologic, and ecological dynamics. In this research, I seek to analyze floodplain integrity at a national scale for the United States by spatially quantifying the impact of anthropogenic stressors on essential floodplain functions. I assess the prevalence of human modifications through widely available geospatial datasets, which I then use to quantify indicators of floodplain health for five essential floodplain functions. The five essential floodplain functions include flood attenuation, groundwater storage, habitat provision, sediment regulation, and organics and solute regulation. Rather than focusing solely on the ecological health within the floodplain, I develop a more comprehensive integrity evaluation by assessing both the biological and hydrogeomorphic functioning ability of the floodplain. I extend a previously established methodology for quantifying floodplain integrity to better understand the impact that human development has had on floodplain health and critical floodplain functions at the national scale. Additionally, I apply this methodology using land use change data for a 60-year period to analyze how land use has impacted floodplain integrity over time. Quantifying the health of spatially explicit floodplain elements will allow for restoration efforts to be targeted to the areas in most desperate need of preservation.
Open Access
Quantitative assessment of floodplain functionality in Colorado using an index of integrity
(Colorado State University. Libraries, 2019) Karpack, Marissa Nicole, author; Morrison, Ryan, advisor; Julien, Pierre, committee member; Wohl, Ellen, committee member
Floodplain integrity can be defined as the ability of a floodplain to support essential geomorphic, hydrologic, and ecological functions that maintain biodiversity and ecosystem services. Humans alter floodplain functionality by changing the physical landscape of the floodplain or by altering river flow regimes and subsequent floodplain inundation dynamics. This research evaluates floodplain integrity by assessing the prevalence of anthropogenic modifications to hydrology and landscape. Specifically, the objectives of this research are to: 1) develop a methodology to assess floodplain integrity using geospatial datasets available for large spatial scales; and 2) use the methodology to evaluate spatial patterns of floodplain integrity in the state of Colorado. To accomplish these objectives, I evaluated the critical floodplain functions of attenuating floods, storing groundwater, regulating sediment, providing habitat, and regulating organics and solutes. At present, this work is the first to quantify the integrity of specific floodplain functions instead of measuring floodplain health solely by ecological integrity. I applied the index of floodplain integrity methodology in the state of Colorado to analyze the integrity of each of the five floodplain functions and the aggregated overall integrity. In Colorado, overall floodplain integrity decreased as stream order increased above third order streams. Floodplain integrity was also lower in floodplains that intersected urban areas than those that did not, which indicates the index of floodplain integrity captured the adverse relationship between development and floodplain health established in literature. By quantifying anthropogenic reductions to floodplain functionality at broad spatial scales, the index of floodplain integrity can help target restoration efforts towards the most affected functions and areas.
Open Access
The development of a decision support system for concurrently evaluating changes in instream and floodplain habitats caused by flow modifications
(Colorado State University. Libraries, 2020) Passero, Elaina, author; Morrison, Ryan, advisor; Ross, Matthew, committee member; Julien, Pierre, committee member
Assessments of changes to riverine ecosystems due to flow modifications have historically focused on instream habitat. Thus, considerations of floodplain habitat have often been neglected in assessment tools, creating difficulties for understanding the comprehensive impacts of flow changes to both instream and floodplain environments. To support improved habitat management and protection of naturally variable flows, I developed a decision support system that evaluates both fish and vegetation habitat availability in alternative flow scenarios. This system uses the results of high resolution 2D hydrodynamic models to quantify and map suitable habitat for fish and floodplain vegetation at a range of discharges in a river reach. Depth, velocity, and substrate habitat preference information was used to determine available fish habitat at each modeled discharge. Vegetation habitat was quantified from logistic regression equations relating long-term habitat inundation patterns to probability of occurrence of vegetation. I demonstrate the use of this tool on the Verde River in Arizona, USA. Habitat was evaluated for the historic flow record and two alternative flow scenarios: reduced high flows and reduced baseflows. The two scenarios were compared by evaluating changes in monthly and overall habitat availability, the balance of native and non-native fish habitat, and potential for vegetation movement. Reducing high flows created more habitat for fish with non-natives having the largest increases and led to vegetation encroachment. Reducing baseflows did not affect vegetation habitat, but native and non-native fish habitat was greatly reduced.
Open Access
The geography of artificial levees in the United States
(Colorado State University. Libraries, 2022) Knox, Richard Leo, author; Wohl, Ellen, advisor; Morrison, Ryan, advisor; Laituri, Melinda, committee member; Rathburn, Sara, committee member
Connectivity between different parts of the landscape is an important theme for river ecosystem functions. Recent advances in conceptual models of river ecosystems, computing power, and data availability, resolution, and extent have allowed the exploration of this theme at continental and global scales. However, these studies have not included the impacts of artificial levees on floodplain function and extent due to the lack of complete artificial levee databases. Local and regional studies have explored the harmful effects and identification of artificial levees. Several characteristics of artificial levees have inhibited the extension of these studies to greater spatial scales (e.g., artificial levees are shaped like other natural and anthropogenic features; artificial levee height and width are small compared to the vertical and horizontal resolution and accuracy of earth observation data available at continental and global scales; artificial levees have a long history of construction). I first present a methodology and data set for the identification of artificial levees in a case study of seven basins (ranging in size from 1,700 to 8,000 square km each) in the continental United States (CONUS) and then apply the methodology to the entire CONUS. This methodology, which includes a model that only uses land cover, distance from stream flow, and basin variables, detected over 182,000 km of artificial levees. Next, I use this dataset in combination with a pre-existing artificial levee database to determine how artificial levees influence floodplain extent, land cover, and association with stream order size in the CONUS. Surprisingly, this revealed that the 100-year CONUS floodplain was of greater extent with artificial levees than if they were not constructed. And not surprisingly, the 8,100 square km of CONUS floodplain that are disconnected by artificial levees are predominantly cultivated or developed land cover. Finally, I conduct a critical review of floodplain functions and analyze case studies of floodplain restoration involving the alteration of artificial levees. I define five interconnected floodplain functions that are vital to river ecosystems and are adversely impacted by artificial levee construction. Studies that analyze floodplain restoration are heavily concentrated in North America and Europe and evaluate effects within 30 years of restoration. In the United States, this type of restoration impacts less than 1% of river kilometers with artificial levees and 1-2% of disconnected floodplains. This dissertation provides an important advance in understanding the impacts of artificial levees on floodplain extent and function at a large spatial scale. It also provides several avenues for continued research.
Open Access
Toward understanding changes in large-scale floodplain connectivity caused by levees
(Colorado State University. Libraries, 2018) Scheel, Kara, author; Morrison, Ryan, advisor; Niemann, Jeffrey, committee member; Rathburn, Sara, committee member
The widespread construction of levees has reduced river-floodplain connectivity and harmed associated fluvial processes in many river systems. Despite the recognition that levees can alter floodplain connectivity, few studies have examined the role of levees in reducing floodplain areas at large watershed scales. In this paper we explore the application of a hydrogeomorphic floodplain mapping approach in the Wabash basin, U.S. to assess floodplain loss in levee-protected areas. We evaluate 10-m and 30-m topographic resolutions and spatially examine the influence of levees on floodplain area in relation to river network attributes within discrete HUC-10 sub-basins. Generally, we found that the floodplains mapped in levee-protected areas were influenced by topographic resolution, stream order, and elevation details of levees found in topography datasets. We show that, when compared to Federal Emergency Management Agency maps, our approach under predicts floodplain area when using 10-m resolution topography data but only slightly over predicts when using 30-m resolution topography. After removing details of levees from topography datasets, we found that basin-aggregate results changed little compared to topography datasets that contain levees, though larger floodplain areas were produced in some regions where levees were removed. This work contributes to a growing research emphasis on linking water resource management to river-floodplain connectivity.

Browsing by Author "Morrison, Ryan, advisor"

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