DETERMINING LONG TERM BENCH STABILITY ALONG STREAMS OF THE SOUTHERN ...

102 Pages·2014·4.49 MB·English

by  Nicholas Ryan Haney

DETERMINING LONG TERM BENCH STABILITY
ALONG STREAMS OF THE SOUTHERN PIEDMONT USING
HYDRODYNAMIC AND HYDROLOGIC THRESHOLDS

by
NICHOLAS HANEY

LISA DAVIS, COMMITTEE CHAIR
SAGY COHEN
DAN ROYALL

A THESIS

Submitted in partial fulfillment of the requirements
for the degree of Master of Science
in the Department of Geography
in the Graduate School of
the University of Alabama

TUSCALOOSA, ALABAMA

2014
Copyright Nicholas Haney 2014
ALL RIGHTS RESERVED
ABSTRACT
Benches are bank-attached channel deposits occurring at an elevation between the
channel banks and the bed. Their occurrence in a variety of geologic and hydrologic settings has
led to confusion about the mechanisms driving their formation, which in turn contributes to
difficulty identifying the active floodplain, bankfull stage, and the determination of
environmental flows in some rivers. This research sought to identify the hydrodynamic and
hydrologic processes involved in bench formation and use this information to predict bench
stability. Sites at Talladega and Hillabee creek were selected and are located in the southern
Piedmont (USA). Using hydrodynamic modeling software (River 2D) in combination with
sediment particle size analysis and topographic surveys, the flow conditions necessary for the
entrainment and deposition of the d84, d50, and d15 particle sizes were simulated. Results
suggest that bench erosion requires flows at least 150% larger than benchfull stage at the
Talladega site, while the Hillabee site experienced erosion at much smaller discharges due to its
smaller mean sediment size. An analysis of USGS historical flow data showed the recurrence
interval for erosive flows at the Talladega site has increased from 1.8 to 2.3 years since 1985. An
analysis of precipitation data and historical landuse show this change in hydrologic regime likely
being driven by reforestation, and to a lesser extent a change in precipitation timing, intensity,
and yearly totals. This muted flow regime experienced by the study streams creates an optimum
environment for vertical accretion, leading to the maintenance of alluvial benches. This research
suggests that benches are stable (actively accreting) features functioning as incipient floodplains
in over-widened rivers of the southern Piedmont. It also supports the idea that the main valley
flat is not always the best field indicator of bankfull stage, and that bench surfaces are important
forms of channel complexity that should not be neglected by stream management and restoration
planning.
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LIST OF ABBREVIATIONS
1. ADV: Acoustic doppler velocimeter
2. AMC: Antecedent moisture condition
3. CSX: The CSX transportation corporation
4. EPA: Environmental Protection Agency
5. GSA: Geologic Survey of Alabama
6. GIS: Geographic information system
7. NRCS: National Resources Conservation Service
8. NWS: National Weather Service
9. p: Probability of case
10. Q: Discharge
11. QI: Quality Index
12. USGS: United States Geological Survey

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ACKNOWLEDGEMENTS

I would like to thank Michelle Saunders and Allison Tarbox for their help in data
collection. Special thanks goes to Ryan Vaughn for his help in data collection, idea generation,
and method testing. I also thank Douglas Sherman for the use of his total station, which enabled
this research. I especially thank Lisa Davis for her expertise, patience, and guidance throughout
the research process and her help in data collection and editing. I also thank Mickey Haney for
his help in navigating the back roads of East Central Alabama. I also thank Leigh Ann Franklin
for her aid in the acquisition of field equipment. Finally, I also thank Sagy Cohen and Dan
Royall for their service on my thesis committee and their continued assistance and support.

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TABLE OF CONTENTS
ABSTRACT ii
LIST OF ABBREVIATIONS iii
ACKNOWLEDGEMENTS iv
LIST OF TABLES viii
LIST OF FIGURES ix
LIST OF EQUATIONS xi
1 A REVIEW OF BENCH LITERATURE 1
1.1 INTRODUCTION 1
1.1.1 WHAT IS A BENCH? 1
1.1.2 THE HYDROGEOMORPHOLOGY OF BENCHES 4
1.2 IMPLICATIONS OF BENCH RESEARCH 9
1.3 SUMMARY 11
1.4 REFERENCES 12
2 HYDRAULIC CONTROLS OF BENCH FORMATION AND DESCTRUCTION 17
2.1 INTRODUCTION 17
2.1.1 OVERVIEW OF BENCH RESEARCH 17
2.1.2 HYPOTHESES 19
2.2 STUDY SITES 21
2.2.1 THE PIEDMONT PHYSIOGRAPHIC PROVINCE 21
2.2.2 TALLADEGA AND HILLABEE CREEK BENCH SITES 23
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2.3 METHODS 30
2.3.1 THE RIVER 2D HYDRODYNAMIC MODEL 30
2.3.2 DATA GATHERING AND MODEL BUILDING 32
2.3.3 PERFORMING MODEL SIMULATIONS 35
2.3.4 DETERMINING INTERVALS OF DEPOSITION AND EROSION 37
2.3.5 EVALUATING AREAS OF REVERSE FLOW 41
2.4 RESULTS 41
2.4.1 MODEL PERFORMANCE 41
2.4.2 VEGETATED VS UNVEGETATED SIMULATIONS 43
2.4.3 INTERVALS OF DEPOSITION AND EROSION 45
2.4.4 AREAS OF REVERSE FLOW 48
2.5 DISCUSSION 50
2.5.1 MODEL ACCURACY 50
2.5.2 THE INFLUENCE OF VEGETATION 52
2.5.3 THE LONG TERM STABILITY OF BENCHES 54
2.5.4 THE ROLE OF REVERSE FLOW IN BENCH DEVELOPMENT 59
2.6 CONCLUSION 60
2.7 REFERENCES 61
3 HYDROLOGIC AND RELATED LAND USE CONTROLS OF BENCH FORMATION
AND DESTRUCTION 66
3.1 INTRODUCTION 66
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3.1.1 OVERVIEW OF BENCH RESEARCH 66
3.1.2 HYPOTHESIS 67
3.2 STUDY SITES 68
3.3 METHODS 69
3.4 RESULTS 73
3.5 DISCUSSION 79
3.6 CONCLUSION 82
3.7 REFERENCES 82
4 SUMMARY AND CONCLUSIONS 85
4.1 SUMMARY 85
4.1.1 BENCHES AS AN INTEGRAL PART OF PIEDMONT WATERHSEDS
85
4.1.2 THEORETICAL MODEL OF BENCH DEVELOPMENT 86
4.2 FUTURE WORK 88
4.3 CONCLUSION 88
4.3 REFERENCES 89

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LIST OF TABLES
Table 2.1 Selected data for study sites 23
Table 2.2 Comparison of River 2D and Continuity equation outputs 42
Table 2.3 Particle size analysis 43
Table 2.4 Erosion thresholds for the Talladega and Hillabee sites 45
Table 2.5 Intervals of deposition and erosion 47
Table 2.6 Bench inundation events 47
Table 2.7 Model output from the simulation of the 1951 flood event 56
Table 3.1 Comparing pre and post 1985 erosive flows at Talladega 73
Table 3.2 Precipitation data for Talladega 75
Table 3.3 t-tests comparing pre and post 1985 yearly precipitation totals 75
Table 3.4 Results of the Graphical Peak Discharge method modeling 78

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LIST OF FIGURES
Figure 1.1 The Vietz bench classification scheme 2
Figure 1.2 A diagram of a linear bench 3
Figure 1.3 Feature benches formed behind a mill dam 8
Figure 2.1 Location of the Talladega and Hillabee sites 22
Figure 2.2 Impoundments in the Talladega and Hillabee watersheds 24
Figure 2.3 Aerial view of the Talladega study site 26
Figure 2.4 The surface of Talladega bench 1 26
Figure 2.5 A cross section showing Talladega bench 1 and 2 27
Figure 2.6 Aerial view of the Hillabee study site 29
Figure 2.7 A cross section showing Hillabee bench 2 29
Figure 2.8 Diagram showing the bench surveys 33
Figure 2.9 Survey DEM of Talladega Creek 38
Figure 2.10 Survey DEM of Hillabee Creek 39
Figure 2.11 Ideal representation of an erosion threshold 40
Figure 2.12 River 2D model output 42
Figure 2.13 Vegetated vs. unvegetated deposition 44
Figure 2.14 Vegetated vs unvegetated erosion 44
Figure 2.15 Erosion and deposition on Talladega bench 2 46
Figure 2.16 Erosion threshold for the d84 particle size on Talladega bench 1 46
Figure 2.17 Reverse flow over Talladega bench 1 49
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