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«_ A Dissertation Submitted to the Faculty of the DEPARTMENT OF HYDROLOGY AND WATER RESOURCES In Partial Fulfillment of the Requirements For the ...»

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RIVER HYDRO- AND MORPHODYNAMICS: RESTORATION, MODELING, AND

UNCERTAINTY

by

Ari Joseph Posner

_____________________

A Dissertation Submitted to the Faculty of the

DEPARTMENT OF HYDROLOGY AND WATER RESOURCES

In Partial Fulfillment of the Requirements

For the Degree of

DOCTOR OF PHILOSOPHY

WITH A MAJOR IN HYDROLOGY

In the Graduate College

THE UNIVERSITY OF ARIZONA

THE UNIVERSITY OF ARIZONA

GRADUATE COLLEGE

As members of the Dissertation Committee, we certify that we have read the dissertation prepared by Ari J. Posner entitled River Hydro- and Morphodynamics: Restoration, Modeling, and Uncertainty and recommend that it be accepted as fulfilling the dissertation requirement for the Degree of Doctor of Philosophy Date: 11/30/2011 _______________________________________________________________________

Jennifer G. Duan Date: 11/30/2011 _______________________________________________________________________

Victor R. Baker Date: 11/30/2011 _______________________________________________________________________

Kevin E. Lansey Date: 11/30/2011 _______________________________________________________________________

Hoshin V. Gupta Final approval and acceptance of this dissertation is contingent upon the candidate‘s submission of the final copies of the dissertation to the Graduate College.

I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement.

________________________________________________ Date: 11/30/2011 Dissertation Director: Jennifer G. Duan

STATEMENT BY AUTHOR

This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

–  –  –

First and foremost I would like to that Dr. Jennifer Duan for her timeless mentoring, profound scientific insights, and unending support, encouragement, and motivation. Only through her hours of discussion with me could any of this work been accomplished and I am forever indebted. I would also like to thank other professors who mentored me through this endeavor and went above and beyond the call of duty in their teaching efforts, including: Vince Tidwell, Hoshin Gupta, Victor Baker, Kevin Lancey, Tom Meixner, and Ty Ferre.

The financial support of Sandia National Laboratories, the Salt River Project, and the UA Peace Corps Fellows was critical in allowing me the opportunity to pursue this work and provide a spring board to my career as a geoscientist.

Finally, I would like to thank my family, by blood and by choice, for their support and encouragement through this stupendous test of my resolve, commitment, and wear-withall. I could not have done this without you.

Thank you all so much.

–  –  –

LIST OF TABLES…………………………………………………………………….....6 ABSTRACT……………………………………………………………………………...7

1. INTRODUCTION…………………………………….………………………………..9

1.1 Explanation of the Problem and Its Context……………………………….….9

1.2 Literature Review…………………………………………………………….11 1.2.1. Channel Forming Processes……………………………………….13 1.2.2. Geomorphic Equilibrium………………………………………….17

1.3. Explanation of Dissertation Format…………………………………………21

2. PRESENT STUDY……………………………………………………………………22

2.1. River Avulsion and Main Channel Conveyance Loss……………………....22

2.2. Stochasticity in Meander Modeling…………………………………………23 REFERENCES………………………………………………………………………….25

APPENDIX A: 3D MORPHODYNAMIC INVESTIGATION OF SEDIMENT PLUG

FORMATION AND DEVELOPMENT IN THE RIO GRANDE………..……….……30

APPENDIX B: SIMULATING RIVER MEANDERING PROCESSES USING

STOCHASTIC BANK EROSION COEFFICIENT…………………………………….80

–  –  –

Table 1. Variables commonly used in fluvial geomorphology studies………………….





9 Table 2. Controls on river channel form in upland and lowland river channels………...12

–  –  –

The study of fluvial geomorphology is one of the critical sciences in the 21st Century. The previous century witnessed a virtual disregard of the hydro and morphodynamic processes occurring in rivers when it came to design of transportation, flood control, and water resources infrastructure. This disregard, along with urbanization, industrialization, and other land uses has imperiled many waterways. New technologies including geospatially referenced data collection, laser-based measurement tools, and increasing computational powers by personal computers are significantly improving our ability to represent these complex and diverse systems. We can accomplish this through both the building of more sophisticated models and our ability to calibrate those models with more detailed data sets. The effort put forth in this dissertation is to first introduce the accomplishments and challenges in fluvial geomorphology and then to illustrate two specific efforts to add to the growing body of knowledge in this exciting field.

First, we explore a dramatic phenomenon occurring in the Middle Rio Grande River. The San Marcial Reach of the Rio Grande River has experienced four events that completely filled the main channel with sediment over the past 20 years. This sediment plug has cost the nation millions of dollars in both costs to dredge and rebuild main channels and levees, along with detailed studies by engineering consultants. Previous efforts focused on empirical relations developed with historical data and very simple one dimensional representation of river hydrodynamics. This effort uses the state-of-the-art threedimensional hydro and morphodynamic model Delft3D. We were able to use this model to test those hypotheses put forth in previous empirical studies. We were also able to use this model to test theories associated with channel avulsion. Testing found that channel avulsions thresholds do exist and can be predicted based on channel bathymetric changes.

The second effort included is a simple yet sophisticated model of river meander evolution. Prediction of river meandering planform evolution has proven to be one of the most difficult problems in all of geosciences. The limitations of using detailed three dimensional hydro and morphodynamic models is that the computational intensity precludes the modeling of large spatial or temporal scale phenomenon. Therefore, analytical solutions to the standard Navier-Stokes equations with simplifications made for hydrostatic pressure among others, along with sediment transport functions still have a place in our toolbox to understand and predict this phenomenon. One of the most widely used models of meander propagation is the Linear Bend Model that employs a bank erosion coefficient. Due to the various simplifications required to find analytical solutions to these sets of equations, efforts to build the stochasticity seen in nature into the models have proven useful and successful. This effort builds upon this commonly used meander propogation model by introducing stochasticity to the known variability in outer bank erodibility, resulting in a more realistic representation of model results.

–  –  –

Fluvial geomorphology is the study of sediment sources, fluxes and storage within the river catchment and channel over short, medium, and longer timescales and of the resultant channel and floodplain morphology (Newson and Sear, 1993). Over the past two decades, river management policy and practice have identified the application of fluvial geomorphology as critical to addressing the financial and environmental costs of ignoring natural system processes and structure in river management (Evans et. al., 2002). Applied fluvial geomorphology is concentrated on answering three questions (Sear and Newson, 2010)

1. How is the problem linked to the catchment sediment system?

2. What are the local geomorphological factors that contribute to the problem?

3. What is the impact of any proposed/existing solutions on channel geomorphology, including physical habitat and sediment transport processes?

Attempts to understand the Earth‘s physical processes rely on studying three components, causes, effects, and laws. Causes and effects can also be thought of as independent and dependent variables, respectively. Natural laws are the relationships among those variables. Table 1 lists some of those components used in fluvial geomorphology.

–  –  –

These components are fit in to one of three logical explanation structures. Earth scientists use these structures to explain physical phenomena and attempt to understand how they relate to one another, so as to predict future outcomes.

1. Deduction is when initial conditions (causes) are used in combination with laws of nature to predict effects. Although deduction is a solid form of logic, the choice of relevant laws included in the model, the inclusion of generalizations rather than laws, numerical issues, and the initial and boundary conditions for the model which must be based on measurements that may be incomplete or contain errors are all significant limitations (Oreskes et al., 1994).

2. Induction is the use of statistical generalizations based on both causes and effects.

An often used example is the hydraulic geometry relations used to relate discharge and cross-sectional properties of natural river channels (Ferguson, 1987). These relations are limited in that relations are only valid in those systems where data is collected and it is impossible to collect enough data to make universally valid generalizations.

3. Abduction can be thought of as the opposite of deduction. In abduction the final conditions (effects) are combined with laws to arrive at a hypothesis that explains the observations (Kleinhans, 2010). In many cases, abduction is used to explain present day landforms with a combination of hypotheses. The major limitation being that the correct hypothesis may not have been considered.

Despite our best efforts to understand fluvial systems a number of factors make conclusive explanations elusive. Some of the difficulties include (1) that fact that measurement techniques often disturb the observed process, (2) the timescale of our observations is much shorter than the phenomenon being studied, (3) many processes and phenomenon cannot yet be observed directly or indirectly, and (4) the fact that many fluvial processes have an intrinsic random or chaotic component (Klienhans, 2010).

Nevertheless, much advancement exists in understanding these complex and dynamic systems.

–  –  –

The body of knowledge related to fluvial geomorphology goes back centuries, efforts to describe and understand these phenomenon date back to Leonardo de Vinci (Gyr 2010).

Most morphodynamic research was carried out in humid regions, and it has been argued that those results should not be extrapolated to the arid and semi-arid zones (Finlayson and McMahon, 1988).

Catchment-scale processes in the semi-arid regions of the southwestern US and northern Mexico are very distinctive. Precipitation regimes are clearly segmented into winter and summer events. Summer events being characterized by localized and highly intense storms, where winter rains are of longer duration and less intensity. Several researchers have found that light winter rains produce significantly less runoff than summer thunderstorms (Brown, 1983; Wells, 1976). However, Thomsen and Schumann (1968) found that in Sycamore Creek 90 percent of runoff was generated during the winter months. They attributed this to higher soil moisture content and reduced vegetation activity. Sources of streamflow in the arid southwest are highly variable from year to year and in different locations. The importance of winter snowpack, winter precipitation, and summer thunderstorms will vary in different catchments and locations within the catchment.

Semi-arid regions are also characterized by ephemeral channels with large transmission losses. Along Walnut Gulch (Tombstone, AZ), two flumes 10.9km apart recorded a loss of 57% during a single storm event (Renard and Keppel, 1966). The diversity of precipitation regimes, the differences in upland and lowland forcing controls (Table 2), and the diversity of vegetation communities in the arid southwest make setting the context of a stream reach critical to understanding the channel forming processes.

–  –  –

Long Profile Steep, stepped; frequent instability zones Gentle, often controlled by structures and flood impacts often local of seasonal vegetation growth Planform Full range present; most dynamic unless Confined, engineered, sinuous.

confined by cohesive soils, rock, or engineered structure

–  –  –



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