Channel Migration and Geology on the Chickasawhay River, Southeast Mississippi

CHANNEL MIGRATION AND GEOLOGY ON THE CHICKASAWHAY RIVER, SOUTHEAST MISSISSIPPI

MARILYN C. OGBUGWO

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2005

To my Ocala family and my family back home, for love that’s free. To my friends who have helped to make the U.S. a little more like home. And to Chineke, for who you are.

ACKNOWLEDGMENTS

I thank my entire field team: Jim Rasmussen, for his invaluable help with the fieldwork and sample collection; Glenn Hermassen, for complaining, and for not complaining about my canoeing skills; and Miles, Cara, and Llew, for camping out and for the ride home.

I thank David Coley, for his help with creating and running the GIS, and for all his editing and quality assurance work on the GIS aspects of this project.

I thank my committee: Dr. Brenner for his suggestions, patience and great help, and for reviewing and editing the entire manuscript; Dr. Jaeger, for his helpful suggestions and invaluable help with the sedimentology aspects of this work. And I thank Dr. Mossa.

I thank her for her guidance and for all that I have learned. I thank her for always being the steer woman on our canoe trips, and for taking care of all the logistics.

Funding for this project was provided by the U.S Army Corps of Engineers, Mobile

District. Local sponsors include the Pat Harrison Waterway District, and the Mississippi

Nature Conservancy through the United States Geological Survey.

iii

TABLE OF CONTENTS

page

ACKNOWLEDGMENTS ...... iii

LIST OF TABLES...... vi

LIST OF FIGURES ...... viii

ABSTRACT...... xi

CHAPTER

1 INTRODUCTION ...... 1

Literature Review ...... 4 Bank Vegetation and Cohesiveness...... 4 Geologic Framework...... 6 Drainage Basin Size and Stream Power ...... 9 Flood Frequency and Channel Slope...... 11 Large Woody Debris ...... 12 Geographic Information Systems ...... 13

2 STUDY AREA...... 16

General Overview...... 16 Climate and Flood History ...... 21 Land Use/Land Cover and Geology...... 22

3 RESEARCH METHODS...... 28

GIS Methods...... 28 National Map Accuracy Standards (NMAS)...... 35 Field Methods ...... 35 Laboratory Methods...... 40

4 CHANNEL CHANGE...... 42

Lateral Migration By Geologic Reach...... 43 Width Change Analysis ...... 48 Analysis By Morphologic Reach...... 51

iv Sinuosity Analysis ...... 56 Results...... 57

5 DISCUSSION...... 66

Overview...... 66 Morphologic Patterns and Geology...... 66 Other Factors ...... 69 Channel Change and Bank Lithology...... 75 Conclusions...... 83

APPENDIX

A MAPS ...... 86

B TABLES ...... 107

LIST OF REFERENCES...... 115

BIOGRAPHICAL SKETCH ...... 120

LIST OF TABLES

Table page

2-1. 1:24,000 USGS quadrangle elevations...... 21

2-2. Geologic units and their description...... 24

3-1. Digitized channel parameters...... 34

3-2. Depth intervals and withdrawal times for pipette analysis...... 41

4-1. Map and digitizing scales for the three time periods...... 43

4-2. Calculated lateral migration values per reach...... 45

4-3. Lateral migration as a percentage of channel width...... 47

4-4. Correlation coefficients...... 47

4-5. Average channel widths...... 50

4-6. Reach parameters for the seven morphologic reaches...... 53

4-7. Mean lateral migration for the seven morphologic reaches...... 53

4-8. Calculated sinuosity per geologic reach...... 56

4-9. Calculated sinuosity values for the seven morphologic reaches...... 56

4-10. Mean lateral migration values...... 60

4-11. Particle size analysis results for percent mud and sand, WL samples...... 62

4-12. Particle size analysis results for percent mud and sand, MB samples...... 63

4-13. Estimated average channel cross sectional widths...... 64

4-14. Calculated channel change values...... 64

5-1. Lateral migration and width change values...... 76

B-1. Field observations...... 108

vi B-2. Grain size analysis results for waer line and mid-bank samples...... 109

B-3. Annual stream flow data ...... 113

B-4. GPS field locations...... 114

vii

LIST OF FIGURES

Figure page

1-1. Chickasawhay bridge at DeSoto...... 2

2-1. Study area showing drainage network and digitized reach of the Chickasawhay ...17

2-2. Map showing geologic formations in study area...... 18

2-3. Mississippi physiographic regions MARIS (1994)...... 19

2-4. Surface geological formations in the study area...... 23

3-1. Digitizing vertices on aerial photograph of the Chickasawhay, Clarke county ...... 31

3-2. Digitized channel boundaries for the 1990s coverage...... 31

3-3. Transects at 100m intervals, and clipped to channel extents...... 32

3-4. Valley lengths were digitized using USGS 1:24,000 topographic maps...... 33

3-5. Field sampling...... 36

3-6. Sampling locations in Clarke County...... 37

3-7. Sampling locations in Wayne County...... 38

3-8. Sample locations and associated surface geological units ...... 39

4-1. Digitized valley lengths and mean lateral migration rates for 41-year period...... 44

4-2. Mean lateral migration values in meters...... 45

4-3. Geologic reach parameters for the Chickasawhay...... 46

4-4. Mean lateral migration against sediment sizes...... 48

4-5. Relationship between channel width and mean lateral migration...... 49

4-6. Transects used to measure channel width...... 50

4-7. Relationship between channel widths and lateral migration...... 51

viii 4-8. Digitized channel centerlines showing virtually no channel movement...... 51

4-9. Straight, sinuous and jagged reaches at Enterprise ...... 52

4-10. Sand and mud % values for waterline (WL) and midbank (MB) samples...... 54

4-11. Morphologic reach parameters for the Chickasawhay...... 55

4-12. Meander cut off near Kittrell...... 57

4-13. Channel migration at Stonewall...... 58

4-14. Erosional planes of weakness...... 59

5-1. Consolidated bank material on the Chickasawhay River...... 67

5-2. Unconsolidated bank material on the Chickasawhay 2.5km south of Stonewall.....68

5-3. Faulting at Quitman...... 69

5-4. Suspended sediment load on the Chickasawhay...... 70

5-5. Old and new meander cut-offs of the Chickasawhay at Stonewall...... 70

5-6. Upstream and downstream discharge data for the two time intervals...... 72

5-7. Upstream peak stage data for the two time intervals...... 72

5-8. Downstream peak stage data for the two time intervals...... 73

5-9. Inadequate grass cover...... 74

5-10. Basal scour and overloading ...... 75

5-11. Geologic map of Clarke County...... 77

5-12. Wayne County Geologic map ...... 77

5-13. Geologic reach mud percent ratios for the Chickasawhay...... 79

5-14. Basal scour and bank loading...... 80

5-15. Relationship between channel width and lateral migration...... 82

A-1. Legend for land cover maps ...... 86

A-3. Land cover map for Clarke County...... 88

A-4. Land cover map for Greene County...... 89

ix A-5. Stable reach, Clarke County...... 90

A-6. Channel movements in Clarke County...... 91

A-7. Stable and unstable reaches, Clarke County...... 92

A-8. Channel movements in Wayne County...... 93

A-9. Stable reach, Wayne County...... 94

A-10. Channel movements in Greene County...... 95

A-12. Legend for Figures A-13 and A-14...... 97

A-13. Close up of Clarke County geologic map ...... 98

A-14. Close up of Clarke County geologic map ...... 99

A-15. Legend for Figures A-16 and A-17...... 100

A-16. Close up of Wayne County geologic map...... 101

A-17. Close up of Wayne County geologic map...... 102

A-18. Coverage tolerances used in digitizing...... 103

A-19. Polygon attribute table for the digitized 1990s coverage...... 103

A-20. Creating transects in ArcView...... 104

A-21. Measuring straight-line distance in Arcmap ...... 104

A-22. Converting measured values to raster for calculation ...... 105

A-23. Calculating straight-line distance between 50s and 80s centerlines ...... 105

A-24. Sampling locations ...... 106

Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science

CHANNEL MIGRATION AND GEOLOGY ON THE CHICKASAWHAY RIVER, SOUTHEAST MISSISSIPPI

Marilyn C. Ogbugwo

May 2005

Chair: Joann Mossa Cochair: Mark Brenner Major Department: Geological Sciences

Migrating channels and their effects on the environment and on structures like

bridges and homesteads are major concerns for private property owners, state and local

governments, and land management agencies in Mississippi. So also is the question of

what drives such channel instability. For this study, channel outlines of the Chickasawhay

River in SE Mississippi were digitized from aerial photographs that spanned a 41-year

period. Nine study reaches were examined, based on their surface geological units, and

changes in the positions of channel centerlines with time were measured for each reach.

The measured changes were used as indicators of channel instability. Different rates of lateral migration were attributed to differences in lithology in these reaches. Results from this study showed the lowest rates of lateral migration occurring in areas where the river flowed over limestone bedrock, and the highest rates occurring in the sand and sandstone

xi reaches. These results suggest that predictions of future lateral migration may be possible by combining these data with shear stress and erodibility data.

xii CHAPTER 1 INTRODUCTION

Channel migration and bank instability pose potential hazards to structures like

bridges and houses along many rivers. For instance, channel bank instability caused by

alluvial stream meandering has endangered bridge structures on the Chickasawhay River

in southeast Mississippi. In 1989, the State Highway 35 crossing of the Pearl River near

Carthage, Mississippi, almost collapsed as a result of local scour around a pile bent. The

problem began when the channel changed course near the crossing (Turnipseed, 1993).

Knowledge of channel movement patterns is therefore important and useful for safety and

management purposes in drainage basins. This is particularly true for the Chickasawhay

River, which has had very little prior geomorphic study.

In 1990 the United States Geological Survey and the Mississippi Department of

Transportation began an investigation of channel meandering at selected bridge sites on

the Leaf and Chickasawhay rivers that were due to recent lateral movements and bank erosion. A portion of the downstream section of the Chickasawhay River (Highway 63 at

Leakesville) was studied. Cross sections obtained at the highway crossing of the

Chickasawhay River between 1942 and 1990 indicated about 7ft of scouring of the thalweg at the bridge (Turnipseed, 1993).

Site visits to selected bridge locations along the Chickasawhay River in June 2004 revealed several instances of potential bridge instability due to channel migration. Figure

1-1 (a and b) shows bridge endangerment at the Chickasawhay bridge, County Road 114, in DeSoto.

1 2

(A) (B) Figure 1-1. Chickasawhay bridge at DeSoto. (A) and (B) show right and left banks respectively.

In 1991 and 1992, the USGS studied channel change and sediment transport in two desert streams in central Arizona. One tentative conclusion from that study was that the velocity and shear stress distribution of moderate flows had been affected by human activities, leading to highly unstable channels, so that moderate flows on the rivers could cause channel changes of engineering significance (Parker, 1995).

Channel migration analysis is fast becoming a modern and useful tool for assessing past channel movements as well as current bank instability. It is being used not just by geologists, geographers and engineers, but also by governments that define state regulations on human activities like mining, agriculture and urbanization.

This study examines the link between observed channel bank instability and valley geology along the Chickasawhay River basin. An attempt was also made to assess the role of land use in controlling channel change rates. The specific objectives of this study were to

• Digitize stream data to define recent channel migration. • Map and define the direction of channel meandering.

• Assess/define the effect of valley geology on rates of channel change. • Evaluate planform changes in channel dimensions. • Assess the effects of land use practices on bank erosion and channel migration. No attempt was made in this study to predict future channel meandering.

The study area starts at the confluence of the Chunky River and Okatibbee Creek,

and ends where the Chickasawhay River joins the Leaf River to form the Pascagoula

River. The area covers the entire reach of the Chickasawhay River, which runs through three counties (Clarke, Wayne and Greene), in southeastern Mississippi. Its principal tributary is the Buckatunna Creek, which joins the Chickasawhay approximately two miles south of Buckatunna in Wayne County.

Interpretations of lateral migration were made by digitizing two sets of rectified

aerial photographs and one set of USGS topographic maps that spanned four decades

(1950s to 1990s), and results showed lateral migration of the Chickasawhay River

occurring in several places (Appendix A). The position of channel centerlines over time

was used to estimate meander migration rates. The meander migration rate was then used

as a measure of lateral instability.

The behavior of a meandering stream is often related to several factors, thus

making its analysis complex. The threat posed by these migrating channels to human

lives and the environment is becoming more urgent due mostly to increased rates of

urbanization and an increased demand on water and land resources. The results of this

study will be useful to both local and state governments, as well as engineers and other

scientists, in better understanding the processes involved in lateral migration and bank

instability.

Literature Review

The consensus among geomorphologists and other environmental scientists is that

instability, in this case bank erosion and channel instability, is a consequence of several

factors. Field observations and other planform change studies (Nanson and Croke, 1992;

Lewin, 1987) have shown this to be the case. The factors that control channel mobility

can be short-term or long-term, natural or anthropogenic. They include variables like

bank geometry, vegetation cover, slope, flow characteristics and or regulation, and bank

material resistance among others. Knighton (1988a) discussed different causes of channel

change, distinguishing between allogenic change, resulting from floods and other climatic

variations, and autogenic change, affected by channel migration, both artificial and

natural. Such long-term natural adjustments, along with short-term anthropogenic effects,

often result in channel instability and can promote rapid complex responses (Park, 1995).

This review focuses mainly on the factors that are pertinent to the current study.

Bank Vegetation and Cohesiveness

The homogeneity of bank material plays an important role in bank erosion rates.

Hooke (1995), in her study on processes of planform change in the UK, observed that bank erosion rates were highest where the force on a bank most greatly exceeded the resistance of the bank. Simon and Thomas (2002) studied the processes and forms of the

Yalobusha River system in north-central Mississippi, an unstable alluvial system with resistant, cohesive streambeds. The study found that migration of knickpoints and erosion zones were highly dependent on the bed substrate, and severely limited by the erosion resistance of the Porters Creek Clay Formation in the area (Simon and Thomas, 2002).

The study further noted that upward-directed seepage forces can result from pressure imbalance at the bed surface, caused by the inability of the streambed to dissipate a

buildup of excess pore water pressure (Simon and Thomas, 2002). This is similar to

Parker’s (1995) observation that increased soil moisture weakened the forces of cohesion,

and, for bank erosion to occur, flows had to be of sufficient magnitude to cause the

needed shear stress, and last long enough to infiltrate banks and break down cohesive

forces. Parker (1995) also found channel instability in the Lower Hassayampa River in

Central Arizona to be due to the easily erodible sand on the channel banks and bottom, as

well as a lack of stabilizing bank vegetation.

Vegetation on channel banks is generally thought to help resist bank erosion, but

studies have shown that trees alone do not provide adequate protection from erosion.

Nanson and Hickin (1986) reported erosion on channel banks under trees and attributed

this to a lack of adequate grass cover. Micheli et al. (2003) analyzed meander migration patterns over a 50-year period for the central reach of the Sacramento River. They combined measured historical changes in channel centerline positions with mapped changes in floodplain vegetation and found that bank migration and erodibility rates increased by approximately 50% as riparian floodplains were progressively converted to agriculture. The study noted that the potentially destabilizing effects of bank loading and scour from large woody debris made the contributions of forest vegetation to bank stability more complex than that of dense herbaceous vegetation (Micheli et al., 2003).

The significance of grass/underbrush in reducing bank erosion was also noted by

Hooke (1995). She described banks on which fallen blocks had become vegetated and stabilized, as well as observations from monitoring of the River Dane in NW England, where already eroding banks under grass experienced increased erosion rates when the grass was ploughed.

Nanson and Croke (1992) related vegetation cover to floodplain geomorphology.

Their classification identifies different floodplain geomorphological features under a variety of energy and sediment conditions. The three classes of floodplain described are the high energy, non-cohesive class A, medium energy non-cohesive class B, and low energy, cohesive class C. These different energy conditions are indicative of the degree to which areas of the river channel and floodplain are likely to be impacted by different processes which might influence the vegetation character (Gurnell, 1995).

Amoros et al. (1987) in their study of fluvial hydrosystems on the River Rhone in

France, defined the gorge, braided, meandering and anastomosed floodplain sectors. They associated these four functional sectors with variations in bed stability and planform dynamism, among other factors. These functional sectors correspond to the A1, B1&B2,

B3 and C type floodplains of Nanson and Croke (Gurnell, 1995).

Elliot and Gyetvai (1999) in their study of channel pattern adjustments in Elkhead

Creek, Colorado, noted that bank erosion resistance was essentially a function of sediment size, cohesiveness, stratigraphic relation and vegetation. Thorne (1990) observed that riparian vegetation is an important factor in channel bank stability. It induces the deposition of sediments and aids bank sediment mass cohesiveness.

The Elkhead Creek study concluded in reaches unaffected by the Elkhead reservoir the increase in mean meander migration rate was influenced by other variables like annual runoff influencing the watershed (Elliot and Gyetvai, 1999).

Geologic Framework

Tooth et al. (2002) studied the effect of geology on the formation of alluvial meanders and floodplain wetlands on the Klip River in Eastern South Africa. They found that in reaches where sandstone cropped out on both sides of the valley, the channel

meandered through extensive floodplains with significant wetland areas, in contrast to reaches where dolerite cropped out on both sides of the valley. In the latter reaches, the

Klip flowed an essentially straight course and floodplains were either absent, or restricted

in width. One finding was that in certain settings, lithology could exert a strong and sometimes dominant control on alluvial river behavior, especially if the riverbed were positioned on or close to bedrock (Tooth et al., 2002).

By combining geological and topographic maps, and field evidence, they found that the marked variations in the width of the Klip valley and the associated changes in channel and floodplain geomorphology were strongly linked with variations in local lithology (Tooth et al., 2002). They found that wide valleys occur in sandstone reaches and narrow valleys in dolerite outcrop reaches. Down valley changes in lithology were strongly associated with marked downstream changes in river character (Tooth et al.,

2002). They described the geomorphology and sedimentology of floodplains in the sandstone valleys with their moderate bankfull unit stream powers (power per unit bed area, at the stage when the channel overflows its banks), as most closely corresponding to

Nanson and Croke’s (1992) “lateral migration, non-scrolled” class of floodplains. These floodplain types are progressively reworked over time through the process of meander migration, as cut-bank erosion releases sediment from storage, but concomitant point bar growth and over-bank deposition builds deposits anew (Tooth et al. 2002). Floodplain geomorphology and sedimentology in the dolerite reaches with their higher bankfull unit stream powers, were described as corresponding most closely to the “confined vertical accretion sandy” class of floodplains. These floodplain types are prone to catastrophic

8 stripping during large floods, due to concentration of flood flows through narrow valleys, and are progressively rebuilt in the intervals between large floods (Tooth et al., 2002).

Besides the influence of high magnitude floods, Gupta (1995) found that the volume and texture of available sediment acted as an important controlling variable in channel form and processes in the seasonal tropics. His study on the Aurunga River in eastern India found that a large supply of non-cohesive sand that could be moved as single grains, even during low flows, in association with seasonal pattern of flow, controlled channel physiography (Gupta, 1995).

On the Narmada River in central India, meandering movement was limited both by restrictions imposed by stable rocky sections at intervals, and high cliffs that hindered lateral movement (Gupta, 1995). Gupta also studied a set of rivers that drain the southern slopes of Jamaica’s Blue Mountains. One conclusion from this study was that local lithology governed the type of sediment reaching the streams, and the subsequent channel forms and sediment transfer. In mountain streams that were boulder-strewn, fine material was easily transported out of the system, in contrast to streams draining a quartz-diorite body, where a large amount of sand was carried, and point bars were built (Gupta, 1995).

Unlike the Aurunga River, the other study rivers showed that quantities of coarse sediment were moved only during high magnitude floods. On the Aurunga River, flood impressions were sparse, and the sand bed river adjusted form both during large floods, and seasonal floods. The study concluded that the Aurunga is an example of how local geology, through sediment texture, influences channel morphology (Gupta, 1995).

Ferguson and Brierley (1999) studied valley confinement as a controlling factor in floodplain morphology. They observed that although channel morphology was near

uniform along the lower 35 km of the Lower Tuross River in New South Wales, there was a marked downstream variability in valley width. They found that flat floodplain

surfaces underlain by cohesive clayey sands and gravels served to constrict the valley

floor trough, and wherever present, the cohesive clayey sand and gravel units constricted

the effective valley width. The higher stream power values of the confined valleys, coupled with low stream power values for vertically accreted silty floodplains are consistent with the findings of Lewin (1987) and Nanson and Croke (1992).

Gilvear et al. (2000) studied planform change and meander development on the

Luangwa River in Zambia. The study examined, among other things, the role of spatial

variations in bank resistance, as a control on meander development and planform change.

Field surveys, aerial photographs and GIS techniques were employed. One conclusion

from the study was that bank erosion rates in the study area were controlled primarily by

meander bend morphology. In-filled channels and localized calcium carbonate-rich deposits restricted erosion, as compared to other recent alluvial facies. The main mechanism of bank erosion was scour of basal sand lenses, followed by block failure

(Gilvear et al. 2000). This is one of very few studies on tropical rivers, and it is interesting to note that the main mechanism of bank erosion is similar to Hooke’s (1995) findings on laterally migrating rivers in the temperate UK.

Drainage Basin Size and Stream Power

The rate of bank erosion is also affected by the drainage basin size, and erosion rates generally appear to increase with increasing basin size. Hooke (1980) observed that for large drainage basins, the highest rates of lateral mobility occurred in the middle reaches because stream power is often high in these reaches. Nanson and Young (1981)

also found this to be true, and attributed the observed erodability to a combination of high

stream power and highly erodable materials found in these middle reaches.

Lewin (1983) found position change rates along river channels to be greatest where

stream power was highest. Stream power is the amount of energy available for moving

any kind of load within the channel, and is dependent on the water surface slope, stream discharge, and the specific weight of water. A few years later in his study of historical

river changes, he plotted bankfull specific stream power against channel shift rates, and

found that in both small and large scale streams, streams with low stream power shifted

as much as intermediate sized streams with higher stream power. The study concluded

that a multi-variate approach to predicting channel change rates was required (Lewin

1987). Lewin, Hughes and Blackwell attempted to predict historical channel change rates

at 38 mobile channel sites in Wales, by combining map data, like catchment area, with

field data like channel slope, and laboratory data like sediment size. Multiple regression

results showed that the most satisfactory regression results were those that explained

change rates expressed as a percentage of channel width in terms of sediment index,

slope and bankfull discharge per unit width (Lewin 1987).

Sediment supply, flow obstructions, and channel bank instability can result in pools or zones of increasing depth. Pools are zones of local bed scour that are due to convergent flow and macro-turbulence that mobilizes bed surface material and transports sediments away from the location faster than sediment is supplied (Buffington et al.

2002). Studying the controls on pool formation and sizes in coarse-grained forest rivers in northern California, southern Alaska, and southern Oregon, Buffington et al. (2002)

found that the majority of pools were formed by flow obstructions. Pool geometry

depended largely on obstruction characteristics like size, type, and frequency.

Hooke (1995) studied planform changes on meandering UK channels and

concluded that on the most laterally mobile rivers, fluvial entrainment and mass failure

were the dominant erosional processes. Erosion was further influenced, but not totally

controlled by flow characteristics, bank geometry, materials, and soil moisture. The study

found that erosion rates were lower in reaches with lower stream power or more resistant

materials. In these reaches other factors such as vegetation, became increasingly

important.

Flood Frequency and Channel Slope

Another controlling variable observed in this study was that of high-magnitude

flood events. Lewin (1987) had also noted the importance of flood magnitude to channel change. Channel change rates vary temporally because flood magnitude and frequency vary over time. Change factors and rates also vary on a site by site basis. Individual bends can respond differently to floods, leading to chute cut off in extreme cases, on sinuous bends (Lewin, 1987). A study of the River Vyrnwy and its junction with the Severn River showed that in the upper part of the reach where gradient was steep and gravel bed materials moved frequently, channel change was active, unlike in the lower part of the reach, where low gradients and fine silty banks resulted in rather stable channels (Lewin,

1987).

Grissinger and Murphey (1982) investigated the possible relation between channel instability features in the Bluff area of northern Mississippi, and long-term channel behavior. They found knickpoint (vertical step changes in bed surface elevation) bed lowering and gravity induced bank failure to be the main agents of present instability.

The study concluded that a complex interaction of flow properties with channel bed and

bank material strength properties was the main agent for channel failure.

Large Woody Debris

Keller and Swanson (1979) defined large woody debris (LWD) as logs, limbs or

root wads greater than 10cm in diameter. In 1995, Keller and MacDonald examined the

role of LWD in river channel change in seven reaches of Prairie Creek, California. They noted that the input of LWD from the forest could affect a stream channel through erosion. When streamside trees fell to the forest floor or into the stream channel, the up- thrown root wad exposed the channel banks to erosion by causing a bowl-shaped zone of erosion (Keller and MacDonald, 1995). The study found that in the headwaters of Prairie

Creek, nearly all pools were either directly formed by, or significantly influenced by

LWD. As drainage basin area and stream size increased, fewer pools were directly formed by LWD although it still played an important role in influencing pool morphology, especially pool depth (Keller and MacDonald, 1995). One conclusion from the study was that LWD produced plenty of temporary sediment storage areas in the stream channel, and these storage sites in turn served as important sediment buffer systems for the routing of sediments through the system (Keller and MacDonald, 1995).

Experimental removal of LWD from Larry Damm Creek in northwestern California from 1979 to 1982 was carried out to observe the effects of LWD on channel forms and processes. The study found that most of the relatively fine bed material present prior to

LWD removal was replaced by coarser, mostly gravel sediments. Also, formation of point bars, removal of a substantial part of another sandbar, erosion in the form of bank under cutting, and development of relatively deep pools, were observed as a result of changes in sediment storage (Keller and MacDonald, 1995). The study concluded that

LWD played an important role in the routing and storage of sediment in river channels, and the removal of LWD at Larry Damm Creek produced adjustments in the form of a series of riffles and pools similar to those found in natural meandering gravel bed channels.

Geographic Information Systems

GIS and aerial photography are being used increasingly by geomorphologists and practioners of historical science to document channel change over time. Elliot and

Gyetvai (1999) used meander migration rates to measure lateral instability in their study of channel pattern adjustments on Elkhead Creek in Colorado. Aerial photographs from

1937 to 1993 were combined with field surveys, sediment measurements, and gage records to determine the probable cause(s) of accelerated streambed and stream bank erosion in Elkhead Creek’s lower reaches. Changes in channel centerline positions were acquired from five sets of rectified aerial photographs and used to calculate meander migration rates (Elliot and Gyetvai, 1999). Discharge data were used to determine the effect of hydrology on meander migration rates. 1:24,000 USGS topographic maps were used to calculate valley and streambed gradients, and this enabled the authors to get a better idea of the planimetric character of the study reach. To determine channel pattern, sinuosity was calculated for the study reach. This was calculated from topographic maps as downstream, in-channel distance divided by down valley linear distance (Elliot and

Gyetvai, 1999).

In 1993, the USGS began a study of channel morphology along the Lower Virgin

River. By the end of the study in 1996, aerial photographs from 1938 to 1995, and recent satellite images had been digitally analyzed. The purpose of the study was to determine quantitative changes in channel morphology (Lieberman and Hilmes, 1996). Arc/Info and

Fortran programs were used to estimate channel extent and area, thalweg, sinuosity, area of sandbars, and maximum width of channel meander belt for each coverage. Transect lines perpendicular to channel boundaries were used to calculate channel width at the center of each segment. This study emphasized the use of overlays in planimetric analysis, a tool that I have also used, to show changes from one date to another. They concluded that the use of digital methods enabled the quick and easy processing of large data sets for analyzing and documenting channel changes through time, and in assessing channel stability as well as understanding geomorphic processes (Lieberman and Hilmes,

1996).

In 2003 Collins and Knox studied historical changes in the Upper Mississippi

River. GIS mapping was used to compare quantitatively, historical changes in mapped land and water, specifically the magnitude, direction and rates of floodplain change in relation to watershed land use changes, climatic fluctuations and navigation improvement projects. Digitizing and georeferencing was done using control points with known geographic coordinates so that locations on the digital map could be linked with their known ground locations, and then projected into the Universal Transverse Mercator system (Collins and Knox, 2003). The authors used GIS to automatically compute areal measurements for polygons representing delineated floodplain features like lakes, islands, and the main channel, and transects were used to estimate mean channel widths (Collins and Knox, 2003).

Laliberte et al. (2001) undertook a similar study, using remote sensing and GIS to analyze stream change. They found that on a small scale little channel movements were visible, but on a larger scale, localized changes became visible (Laliberte et al. 2001).

The authors concluded that remote sensing along with GIS/GPS and ground truthing provided a definite advantage over ground data collection alone (Laliberte et al. 2001).

They noted that the ability to overlay many factors and measure distances onscreen was helpful in analyzing change, that many of the statistics were quickly extracted from the

GIS database for analysis and that other parameters would have been difficult or nearly impossible to attain without these techniques (Laliberte et al. 2001).

CHAPTER 2 STUDY AREA

General Overview

The Chickasawhay watershed covers an area of approximately 2,970 square miles

(7692 km2) in southeastern Mississippi and covers five counties, Newton, Lauderdale,

Clarke, Wayne and Greene (USACE, Dec 1971). The river itself is formed by the confluence of the Okatibbee Creek and the Chunky River at Enterprise, and runs through

Clark, Wayne and Greene Counties (Figure 2-1).

As part of the Pascagoula drainage system, the river flows southwards for about

264km (USACE, 1971) before joining the Leaf River in northern George County to form

the Pascagoula River. The Pascagoula flows southward and drains into the Gulf of

Mexico. The drainage basin is the second largest in the state, draining about 23,051

square kilometers (USGS 1950).

Land cover along the entire stretch of the Chickasawhay is mostly forest. Small

percentages are used for pasture and urban development. Surface geological units vary

across the basin. Surficial geological units in the study area are Tertiary in age, and

consist of the Eocene Claiborne group, the Eocene Jackson group, the Oligocene

Vicksburg group, the Miocene Catahoula Formation, and the Miocene Pascagoula

Hattiesburg Formations. Figure 2-2 is a generalized geologic map of Mississippi. The

study area is highlighted with a rectangle. A more detailed map is presented later in this

section.

16 17

Figure 2-1. Study area showing drainage network and digitized reach of the Chickasawhay for this study.

The formations shown represent a variety of lithologies across the river’s stretch.

The Claiborne group is mostly glauconitic clay with several sand lenses. The Vicksburg group consists of fossiliferous limestone and clays, and the Catahoula formation is mostly sandy silt, silt and clay, interbedded with sandstone layers (Li and Meylan, 1994).

Figure 2-2. Map showing geologic formations in study area, courtesy Mississippi Geological Survey, (1976).

As part of the Gulf Coastal Plain, the state of Mississippi is divided into four main geographic regions. They are the Gulf Coast, the Southern Wooded Prairies, the Northern

Highlands, and the Delta. These broad regions are further divided into smaller physiographic regions based on topography, soil associations, and forest and land resource regions. Priddy (1960) described twelve, and the Chickasawhay runs through three of these twelve regions, namely the Jackson Prairie, the South Central/Vicksburg hills, and the Pine Belt region. The Pine Belt region is the most extensive in the study area (Figure 2-3). It has been further divided into the South Central hills and the Pine Belt

(MARIS, 1994).

Figure 2-3. Mississippi physiographic regions MARIS (1994).

Relief in this region is moderate and gently rolling, with densely forested prairies.

The soil consists of both sands and clays. Formations in this region are the Catahoula and the Pascagoula/Hattiesburg. The pines for which the region is named have been a major source of revenue for the region, as has petroleum. It is in this region that the Leaf and

Chickasawhay rivers meet to form the Pascagoula.

A small percentage of the study area lies within the Jackson Prairie sub-region, sometimes called the Central Prairie region. Land in this region is less forested, with wide rolling grasslands that make good pasture for cattle. Soil consists mostly of heavy, fossilferous clays that often erode into broad, relatively smooth stream valleys (Gilliland and Harrelson, 1980). Geologic Formations in the region are the Vicksburg and

Chickasawhay limestone, the Jackson group, the Forrest Hill/Red Buff clays, and the

Cockfield Formation (Ms. Geol. Survey, 1969).

The North Central Hills region of the study area exhibits the most relief. Thomas

(1942) described the region as well dissected sand hills uplands, broken by several pronounced cuestas and escarpments that follow the strike of the beds. Soil is a mixture of sand, clay, and marl, and vegetation is dense. Geologic formations in this region include the Winona/Zilpha, Tallahatta/Neshoba, Kosciusko, Cook Mountain and

Cockfield (Gilliland and Harrelson, 1980).

Slope direction in the study area is generally to the south, with elevations as high as

183m above mean sea level (amsl) in Clarke county, and as low as 11m amsl in Greene county (USGS 1983 and 1981). Table 2-1 shows elevation statistics for Clarke, Wayne and Greene counties from USGS 1:24,000 quadrangle maps.

Valley elevations along the Chickasawhay range southwards from 110m-18m amsl

(USGS 1983,1981).

Table 2-1. 1:24,000 USGS quadrangle elevations. County Name Highest Elevation msl Lowest Elevation msl (m) (m) Clarke 183 49 Wayne 146 31 Greene 116 11

Climate and Flood History

Small variations exist in climate conditions across the study area depending on

local topography or relief. Regional climate is strongly affected by the subtropical

latitude (31°N to 32.4°N), the Gulf of Mexico to the south and the landmass to the north.

Average annual temperatures statewide range from 20°C along the coast to 17°C in the

north. Relative humidity is high and mean annual precipitation is about 165cm in the

study area, with the greatest rainfall occurring between November and June (NOAA,

2001, USGS 1950).

Due to its geographic location and climate, the study area is very susceptible to

flooding. The USGS collects gage data on the Chickasawhay upstream at Enterprise, and

downstream at Leakesville. Flood data compiled by the USGS from August 1938 to

September 1948, showed maximum flood stage for the Chickasawhay at Waynesboro to

be 14 m on April 11,1938. A discharge of 1,504 m3/s was measured the day before by the

Army Corps of Engineers. Average discharge was 68 m3/s for the ten-year period.

Average discharge for the Chickasawhay at Leakesville was 114.1m3/s over the 10-year

period, and maximum flood stage was 10m on April 12, 1938 (USGS 1950). A discharge

of 1858m3/s was measured the day before. A US Weather Bureau record of flood marks

at Enterprise bridge indicate that approximately 97cm of rain fell at Meridian in April of

1900, resulting in the great flood of 1900 where stage reached 11m. Near Waynesboro,

stage on the Chickasawhay reached 15m. In May 1909, the Chickasawhay flooded again

due to over 31cm of rainfall at Meridian (USGS 1950).

Other floods were recorded in 1916, 1919, and more recently in April 2003. The

flood of 1938 was not restricted to the Chickasawhay, but covered much of the state.

Damages were estimated at about one and a half million dollars (USGS 1950). Damages from the April 2003 flood were estimated at about 21 million dollars, and the Red Cross reported that when the Chickasawahy at Enterprise crested, more than 50 people had to be rescued from their homes and local businesses and homes were destroyed (Gillespie,

2003).

Land Use/Land Cover and Geology

The Chickasawhay is not commercially navigable today, but it was used in the past to transport logs to mills downstream (May et al., 1974). Land along most of the river’s

valley is forested, with only a handful of homes built on stilts. Thus this study has

focused on the distribution and character of the surface geological units along the channel

banks. Figure 2-4 shows surface geologic formations encountered in the study area

(USGS 1969). This section offers a detailed description of surface geological units in the

study area because it is my hypothesis that bank geology plays the dominant role in

determining lateral migration rates.

Figure 2-4. Surface geological formations in the study area.

Table 2-2 contains descriptions for each formation. Published nomenclature from the Mississippi Department of Geology was used in this study.

Table 2-2. Geologic units and their description (Ms. Geological Survey, 1974, 1980). Group or Formation Name Subdivisions Lithology Study area

& Age (Formation) Occurrence

Miocene Pascagoula and Silty clay and sand. Downstream, Greene Hattiesburg formations county. Miocene Catahoula Fine to medium-grained Midstream, Wayne sands, silt. Some clay. and Greene counties Oligocene Chickasawhay Fossiliferous limestones and Marl. Oligocene Vicksburg Group Bucatunna, Byram, Mostly limestone, some Midstream, Clarke Glendon, Marianna, clays and Marl. and Wayne counties. Mint Spring. Oligocene Red Bluff and Forest Red Bluff is partially Midstream, Wayne Hill formations. indurated clay, Forest Hill and Clarke counties. is fine-grained, silty sand Eocene Jackson Group Yazoo formation Mostly clay, some Marl Upstream, Clarke and and sand Wayne Counties. Moody’s Branch Fossiliferous, clayey, Upstream, Clarke glauconitic Marl. county. Eocene Claiborne Group Cockfield formation Sand, fine to medium Upstream, Clarke grained, clayey, lignitic. County Cook Mountain Glauconitic sand, marl, Upstream, Clarke formation shale and limestone county Kosciusko formation. Fine to coarse grained Upstream, Clarke sand, lignitic,clayey. county. Zilpha and Winona Zilpha is clay with some Upstream, in Clarke Formations. silt, carbonaceous. Winona county is Marly, fossiliferous, glauconitic, clayey sand. The term Marl has been used to describe non-homogenous and often non-mappable units of mixed lithology.

The oldest surficial geological unit encountered is the Basic City Shale member of the Tallahata formation at Enterprise, part of the Claiborne group. It consists of glauconitic, carbonaceous claystone, clay, and sandstone (Gilliland and Harrelson, 1980).

The Tallahata extends from southern Alabama to north-central Mississippi, a prominent cuesta on the eastern flank of the Mississippi embayment. This sequence was deposited in a marine shelf and strandplain environment and forms the base of the Claiborne (Dockery and May, 1981). Siesser (1983) determined this sequence to be of early Eocene age.

Although soft in the subsurface, Basic City clays become lithified when exposed above

the water table, and Dockery (1986) notes that it is these lithified clays together with quartzite sand units, that form the erosion resistant cap on the Tallahata cuesta.

Other formations found in the study area that belong to the Claiborne group include the Cockfield, the Cook Mountain, Kosciusko, Zilpha and Winona. These formations range in age from middle to upper Eocene. Dockery (1986), described the formations in this sequence as being part of two marine transgressive events, each followed by an episode of delta progradation. From oldest to youngest the formations include the

Tallahata, described above, the Winona, which is recorded as marine shelf, Zilpha formation, recorded as a marine shelf and pro-deltaic unit, and the Kosciusko, recorded as being predominantly deltaic. The carbonate deposits of the Cook Mountain formation are recorded as being deposited in marine shelf and pro delta environments, and the

Cockfield formation was deposited under deltaic conditions.

The Yazoo and Moody’s Branch formations make up the Jackson group. The

Moody’s Branch formation in the study area is mostly fossiliferous, glauconitic marl, usually indurated at the surface. This formation is correlated with the Ocala limestone of

Florida, and was deposited under shallow marine conditions (May et al. 1974). The

Yazoo in Mississippi is mostly clay. In the study area, it is exposed as a combination of clay, sand and indurated marl.

The Red Bluff and Forest Hill formations form the base of the Oligocene series in the study area. On the Chickasawhay River, the Red Bluff clays are commonly ferruginous, and sometimes fossiliferous. May et al. (1974) described the Red Bluff deposits as shallow marine deposits. The Forest Hill formation in the area is exposed as laminated clays and silty micaceous sands. May et al. (1974), described these sediments

as fine to very fine grained silty, micaceous sands and silty carbonaceous clay,

interbedded with fossiliferous lenses.

The Vicksburg group in the area includes the Mint Spring, Marianna, Glendon,

Byram and Bucatunna formations. These formations represent a variety of lithologies and

depositional environments. The Mint spring is described as light greenish gray to dark

gray fossiliferous glauconitic marl, argillaceous to arenaceous, deposited under shallow

marine conditions. The Marianna formation is yellowish gray fossiliferous limestone,

deposited under deeper marine waters than the Mint spring (May et al. 1974). The

Glendon is also fossiliferous limestone, deposited in a shallow marine environment. The

Byram formation occurs as greenish gray to dark gray glauconitic and fossiliferous marl,

deposited in shallow marine conditions. May et al. (1974), considered the Bucatunna to

be the youngest formation in the Vicksburg group. Its sediments consist of mostly

laminated clays and silty clays, light to dark gray in color.

The Chickasawhay formation overlies the Bucatunna, and is recognizable in the

study area by its fossil imprints. It occurs as light gray to grayish yellow fossiliferous limestone, with clay interbeds. For the purpose of this study, the Upper Chickasawhay member described by Blanpied and others (1934), and commonly referred to as the

Payne’s Hammock formation, is grouped with the Chickasawhay formation, due to their similarity in lithology and depositional environments. May et al. (1974) described the

Payne’s Hammock as olive gray to grayish yellow, weathered, fossiliferous marl, with clay, silty limestone interbeds and sandstone ledges.

The Catahoula formation forms the base of the Miocene series in the study area. It is the most extensive in the study area, and occurs as fine to medium grained ferruginous

sands and sandstone, deposited under fluvial conditions. The Pascagoula/Hattiesburg

formation consists of locally fossiliferous clay, sandy clay and sand, as well as siltstone

and sand. These sediments are part of the sequence of transitional marine and fluvial

sediments that accumulated in central and eastern Mississippi, Alabama and the western

Florida panhandle during the Neogene. Sediment source was largely from the reworking

of older Coastal Plain deposits, and eroded materials from the southern Appalachian

Mountains and the Piedmont and Cumberland Plateau (Isphording, 1981). May et al.

(1974) thought that these sediments might have been deposited under marginal deltaic

conditions, indicated by the presence of carbonized wood. Recent alluvium overlies the

some of these geologic units in some parts of the study area.

Otvos (1990) has suggested that the Upper Miocene Pascagoula and Middle

Miocene Hattiesburg formations be referred to as Neogene undifferentiated nonmarine clastics, due to the absence of sufficient paleontological, lithologic or other stratigraphic support. For the purpose of this study, the name Pascagoula/Hattiesburg formation has been used for the bluish green clay, sandy clay and sand found in most of Greene County, sometimes overlain by the Citronelle.

Besides the problem of acceptable nomenclature, geologic mapping in Mississippi has been a major challenge and source of debate among local geologists. Most agree that the geologic map of the state published in 1969 contains errors (Otvos, 1990, Bowen

1990). More detailed maps were acquired and used alongside the 1969 geologic map in this study.

CHAPTER 3 RESEARCH METHODS

Applied geomorphology in this study involved utilizing field, laboratory and GIS tools in assessing channel evolution over time, and the underlying controls on channel evolution. The main objective of this study was to assess the relationship between observed lateral migration of the Chickasawhay River and bank geology and land use.

GIS Methods

Geographic information systems (GIS) methods were used in this study because it provided a cost effective and efficient way to extract, store and quickly process large amounts of data. Environmental monitoring was made quicker by the use of aerial photographs, which not only enabled the reconstruction of past channel positions, but also the measurement and storage of reach dimensions and channel change.

Sequential historical aerial photographs and maps were used along with the GIS to digitally analyze planform changes along the 264km stretch of the Chickasawhay River.

This approach has been used in other studies (Turnipseed and Smith, 1992; Gurnell,

1997; Mossa and MclLean, 1997). Aerial photographs for the 1990s were acquired in digital format from MARIS as MrSid (.sid) compressed Digital ortho quadrangle

(DOQQ) image files. Historical 15-minute USGS topographic digital raster graphics

(DRGs) for the 1980s were acquired from the University of Alabama map library

(http://www.ua.edu). DRGs were registered to the MSTM projection using public land survey system (PLSS) grid intersections as control points.

28 29

Historical aerial photographs for 1955-1960 were acquired from the US

Department of Agriculture’s Farm Services Agency (FSA). These photographs were

scanned at 508 dpi into digital images, and image - image registration into real world

MSTM coordinates was done using the Erdas Imagine 8.6 remote sensing software.

Scanned photographs were saved as geo-tiff images, and the AdobeR Photoshop

software was used to crop off image borders in order to acquire seamless images for geo-

referencing. For each photograph, between 20 and 30 ground control points were located

to match corresponding points on the digital 1990s base photo. A 1st order polynomial

geometric model was utilized, and adding or deleting ground control points as needed

helped to keep the root mean square error (RMSE) at or below 0.03 meters for each

photograph. The RMSE gives an idea of how accurately aligned the registered

photograph is with the base photo.

County boundary, watershed boundary, generalized surface geology, soil data and

land use data, as well as USGS quadrangle index data, were acquired from the

Mississippi Automated Resource Information System (MARIS). These data were

downloaded as either ArcInfo interchange files (.e00), or ArcView shapefiles (.shp). All

data acquired from MARIS were projected in the Mississippi Transverse Mercator

(MSTM) projection. Data from every other source were first re-projected to MSTM before use. The MSTM projection adopted for this project was jointly developed by the

MARIS technical center and the Mississippi Department of Transportation (MDOT), to eliminate the multiple zone problems (east-west zone divisions) that arise with both the

UTM and State Plane systems when viewing geographic data on a statewide scale. The

MSTM projection is based on the North American Datum of 1983 (NAD83).

Stream channels were digitized as ArcInfo coverages for the 1950s, 1980s and

1990s channel boundaries from the historic DRGs and DOQQs. Common coverage

tolerances were utilized for each set of coverage generated. Digitizing scale was chosen

so that channel boundaries and other pertinent floodplain features could be easily

identified while digitizing. A scale of 1:2000 was used for digitizing the 1990s set of

photographs, 1:3000 for the 1980s, and 1:2500 for the 1950s. These scales allowed good

image resolution while minimizing digitizing error. Figure 21 in Appendix A shows the

tolerance limits that were used in digitizing coverages. The nodesnap tolerance ensured

that any digitizing nodes that were within 5m of each other on the ground snapped to one

another.

Weed tolerance minimum was set at 0.5m, and maximum at ½ channel width to control vertice resolution during digitizing. The weed tolerance allows arcmap to weed

out unnecessary vertices during digitizing, such as vertices that are too close together.

Fuzzy tolerance controlled line resolution during building operations and the dangle

tolerance ensured that nodes did not dangle within 5m of any arc. The Edit tolerance set

limits for the entire coverage snap. To keep error at a minimum during data extraction,

digitizing of all three sets of aerial photos was done by the same person. Figures 3-1 and

3-2 show digitizing vertices and the digitized channel boundary for part of the 1990s

coverage. All the features digitized over the three different time frames were stored as three

separate ArcInfo coverages, and polygon attribute tables (PAT) were created for each

coverage. PAT for the 1990s coverage is included in Appendix A.

Figure 3-1. Digitizing vertices on aerial photograph of the Chickasawhay, Clarke county

Figure 3-2. Digitized channel boundaries for the 1990s coverage.

PATs were used to store information about the primary channel, like land use, year photograph used in digitizing was taken, geology, USGS quadrangle code etc. Land cover and surface geology data were acquired in digital format from the US Geological

Survey (1992), and MARIS (1969) respectively.

Changes in channel cross sectional widths were calculated for each time period, and any observed change was used as another indicator of channel instability. Width

change analysis was done using extracted data of channel boundaries for each time frame.

Channel centerlines were digitized for each extracted river coverage as shapefiles and transported into ArcView 3.3. Centerlines were analyzed on a quadrangle (USGS) by quadrangle basis, and on geologic reach basis. The script editor in Arcview was used to run the createtransectlines.ave script, so that transects perpendicular to the centerline were created (Appendix A). The X-tools convert graphic to shapes command was then used to convert the transects to shapefiles which were transported back into Arcmap, and clipped to the relevant channel boundaries, using the geo-processing wizard (Figure 3-3).

Figure 3-3. Transects at 100m intervals, and clipped to channel extents.

A cross section interval of 100m was used for all the centerlines. 100m was used for cross section length in most cases, in cases where 100m was not wide enough to intersect both the right and left channel banks, 150m was used as cross section length.

The calculate area, perimeter and length command in X-tools was used to update the lengths of the clipped transects and the tables were then exported as dbase to Excel for comparison.

In order to quickly pinpoint any huge changes in channel pattern over time, sinuosity values were computed for the entire channel for each time period. This variable was computed from aerial photos as the channel length (channel center line length), to valley length ratio for each set of coverage. To estimate sinuosity change from time period to time period, river valley length was digitized as down valley straight transects within the river flood plain (Figure 3-4).

Figure 3-4. Valley lengths were digitized using USGS 1:24,000 topographic maps.

Although floodplain features like sandbars and cut-offs were well displayed on the aerial photos, valley length was digitized from the USGS DRGs for the 1980s, primarily because the contour intervals on the DRGs were used as additional indicators of channel

valley walls. Table 3-1 shows digitized channel and valley length values for the three periods.

Table 3-1. Digitized channel parameters Channel_Length(m) QUAD_CODE Quad_Name V_length(m) 50s 80s 90s 3288B7 Stonewall 6468 7059 7054 7058 3288A7 Wautubbee 10741 28851 29665 30563 3188H6 DeSoto 18931 33077 33002 33002 3188G6 Shubuta 15277 26811 26724 26527 3188F6 Waynesboro 16259 25152 24349 24562 3188E5 Buckatunna 17167 30720 29514 29502 3188D5 Knobtown 14007 24478 22158 22062 3188C5 Clarke 13872 19658 19424 20094 3188B5 Leakesville 13812 22296 21872 22136 3188A5 Vernal 11648 19911 19149 17945 3188A6 LeakesvilleSW 13263 24126 24245 24760

Lateral migration from one time period to another was estimated using the spatial analyst’s straight line distance measuring tool in Arcmap. The straight line distance from the channel center line for a particular period (50s, 80s, 90s) was measured by creating

2m grids from the channel centerline. The channel centerline for the next time period was

then exported out and a value field was added to its PAT, and all the records in this field

given a value of 1. The center line was then converted to a grid using the convert features

to raster tool, and raster calculator was used to estimate the lateral migration values

between the two time periods by multiplying the two grids, say, the 50s distance grid and

80s center line grid (Appendix A). The output calculation grid is a grid that has the

distance grid values, and the same lateral extent as the centerline grid. Lateral

displacement values were then exported as dbf tables into Excel spreadsheets for

comparison. The same procedure was employed to measure migration values between the

80s and 90s channel, and the 50s and 90s channel.

National Map Accuracy Standards (NMAS)

The National Map Accuracy Standards (USGS 1947) require for horizontal

accuracy, that for maps on a publication scale larger than 1:20,000, not more than 10

percent of the points tested shall be in error by more than 1/30 inch, measured on the

publication scale. For maps on publication scales of 1:20,000 or smaller, not more than

10 percent of the points tested shall be in error by more than 1/50 inch.

The 1950s maps were on a 1:20,000 scale, corresponding to +/- 10m, and an allowable RMSE of 5m, at 95% confidence. The 1980s and 1990s map scales were

1:24,000 and 1:40,000 and these correspond to +/- 12m and 32m respectively. To meet the map accuracy standards, not more than 10% of data points tested for these periods can be in error by more than 6m and 10m respectively, at 95% confidence.

Field Methods

Field sampling was carried out from June 6 to June 21, 2004, to validate data acquired from the 1955 to 1996 collection of aerial photographs. Areas of interest were determined from estimated width change and lateral migration measurements, prior to field excursion. Latitude and longitude identification of each sampling point was determined in the field using the Garmin® GPS map 76CS hand held GPS locator, and recorded in the field notebook. Locational accuracy ranged from +/- 5m to +/- 2m, with an average accuracy of 3m.

Sediment samples were collected from both mid bank and water line levels with the use of either a hand trowel, a pick hammer or a shovel. Samples were bagged in Nasco

Whirlpak® plastic bags and labeled with identification numbers.

Topsoil was removed before sampling so that samples were collected at approximately 15cm to 30cm below ground surface (Figures 3-5a and 3-5b).

(A) (B) Figure 3-5. Field sampling. (A) shows bagged sediment samples and (B) shows sampling technique.

At each sampling location, samples were collected from both right and left banks, and observations about stream flow, as well as vegetation cover, slope, land use and lithology along both banks were recorded in the field notebook. A total of 102 sediment samples were collected. Figures 3-6 and 3-7 show sampling locations along the

Chickasawhay. A summary of field data collected at all sampling locations is included in

Appendix B, as Table B-1.

Figure 3-6. Sampling locations in Clarke County

Figure 3-7. Sampling locations in Wayne County.

Figure 3-8 shows an overlay of sampling locations on associated surface geology.

More detailed maps are shown in subsequent sections.

Figure 3-8. Sample locations and associated surface geological units

Efforts were made during field sampling to acquire samples from areas with little or no lateral migration, as well as from areas that showed lateral migration occurring from prior GIS analysis. Apart from the Cook Mountain formation and the

Pascagoula/Hattiesburg formations, samples were collected from every other lithology type in the study area.

Laboratory Methods

Grain size analysis was performed on sediment samples collected from both right and left banks at mid bank, and at water level locations. This analysis provided data on the mud to sand ratio of sediment samples, which enabled me to assess the role of bank lithology or cohesiveness, on channel change.

Samples were weighed in previously weighed aluminum dishes, placed in plastic cups and soaked in a standardized dispersal agent of 1% distilled water and sodium hexametaphosphate Na(PO3)6 solution (Rolfe et al. 1960). Samples were soaked in approximately 30mL of solution to each 15g of sample, or until sample was completely covered by solution. Samples were then vigorously shaken and allowed to sit for 2-4 days. The Fisher scientific® FS20H sonic bath vibrator was used to further disperse clumps. Wet sieving for sand fraction was done using a plastic funnel and a 63- micrometer #230 sieve. The sample was then placed in a 1000mL graduated plastic cylinder. A squirt bottle was used to wash mud fractions into the cylinder until water passing through the funnel was clean. Great care was taken during this procedure to ensure that 1000mL of distilled water was sufficient to wash each sample clean of all mud. In cases where all the mud was washed out with less than 1000mL, distilled water was added to a final volume of 1000mL. The mud mixture was allowed to sit for 1-2

hours to ensure stabilization at room temperature. Sand fractions were dried overnight at

70oC, allowed to cool, and weighed.

Pipette analysis was carried out to determine the distribution of silt and clay in the

mud fraction. The mixture was briskly stirred for two minutes to re-suspend sediment

material throughout the water column, and a 20mL aliquot was withdrawn at different

times and depth intervals using a pipette. The withdrawal times and depth intervals used

are shown in Table 3-2, and are based on G.G Stokes’ 1851 settling velocity law for a

sphere in a fluid.

Table 3-2. Depth intervals and withdrawal times for pipette analysis (from Folk, 1974). Depth (cm) Diameter (mm) Withdrawal time Temperature (C) phi

20cm 0.63 20 seconds 250C 4.0

10cm 0.004 2 hours 250C 8.0

Withdrawn samples were placed in pre-weighed aluminum dishes and oven dried

overnight at 60oC, allowed to cool, and weighed. Table B-2 in Appendix B contains grain

size distribution data tables for all samples analyzed. Values from the 20mL aliquot were multiplied by fifty in order to get the actual silt and clay values for the entire 1000mL cylinder.

CHAPTER 4 CHANNEL CHANGE

A two-step analysis was employed in assessing channel change on the

Chickasawhay for the period under consideration, whereby data were analyzed based on both the GIS, and results from sediment analysis. Variables such as the rate of lateral migration, changes in channel centerlines with time, changes in sinuosity, as well as changes in channel width, were used as indicators of channel instability. Percent mud and sand measurements for each reach were also used as indicators of reach susceptibility to change. The digitized channel centerlines were used to delineate channel positions for each time period.

Wet sieving and pipette analyses were performed on sediment samples from 28 sites, collected at both mid bank and water’s edge. GPS coordinates taken in the field were imported into the GIS as .dbf tables and converted into point features using the add

x y data tool in arcmap. Coordinate data for all sample locations is included in Appendix

B, as Table B4.

One possible error source in this study is the fact that a combination of aerial

photographs and maps from different sources were used, as described in section 3.1.

Small-scale, low-resolution black and white photographs from the 1950s were used along

with large-scale, higher resolution infrared photographs from the 1990s, and topographic

maps from the 1980s. Extreme care was taken to digitize at scales that allowed good

image resolution. Table 4-1 shows the different scales used for each set of photographs.

42 43

Although metadata show that the DRGs and DOQQs used in this study meet the

NMAS, a combination of mapping, digitizing and even waterline errors may affect the

measurement of true lateral migration in certain reaches more than in other reaches. This

is because this study measured and used the mean or average lateral migration to

determine degree of channel instability per reach. As such, in Table 4-2 where I show

estimated mean lateral migration results, I have also indicated by shading, the reaches

that I consider true and noteworthy migration to have occurred.

Table 4-1. Map and digitizing scales for the three time periods. Year Map scale Digitizing Scale

1955, 1958 1:20,000 1:2500

1981, 1982, 1983 1:24,000 1:3000

1992, 1996 1:40,000 1:2000

Because the smallest map scale used in my analysis was 1:20000, my accuracy assessments are based on this map scale as detailed in section 3.2. Average locational accuracy in the field was 3m, with the hand held GPS unit.

Lateral Migration By Geologic Reach

My objective was not only to measure lateral change, but also to determine if channel instability was related to geology, by assessing how dominant a control local lithology was to observed channel movements. The study area was divided into nine geologic reaches based on the Mississippi Office of Geology 1969 published state geologic map (Figure 3-8). Channel centerlines and valley lengths were digitized and mean lateral migration values were calculated for each geologic reach. In calculating lateral migration, the 1980s channel centerline was used as the source centerline, and movements of channel centerlines over time were quantified in ArcMap, by using the

spatial analyst tool to measure the straight-line distance from the 1980s channel

centerline position to its 1990s position, and from the 1950s channel position to its 1980s

centerline position. The raster calculator was then used to calculate lateral change by

multiplying the straight-line distance raster with its counterpart raster, as was described in

section 3.1. The histograms in Figure 4-1 are for the entire study period. They suggest

that individual reach scale is a factor that could directly influence lateral migration

values. The two younger formations, the Catahoula and Pascagoula/Hattiesburg, show

greater migration values because the channel is larger in those reaches.

1.20 50

1.00 40 Thousands 35 0.80 30

0.60 25 20

0.40 15

10 mean lateral migration(m) 0.20 5 Valley length (m) 0 0.00 n y a a n i ld a y g n i ld y y g ko son l ul ta on a nona fie ha n ie s cla h i us unta ck w ho kf ck f ck uff c ciusko ou c a aw sci o Ja ta /Wino s o J s tiesbur o Co B a M C a K k M kasa Ca Ko k Catahoula o ed c ilph o ick Z o h Zilpha/W Co R Chi C ll/ Red Buf /C / g Hill/ ur t b burg res s ks o ic F Forest Hi V Pascagoula/ Hat Vick Pascagoula/ Hattiesbur Figure 4-1. Digitized valley lengths and mean lateral migration rates for 41-year period.

Mean migration rates were calculated over a 41-year period, from 1955 to1996.

The 1950s to 1980s time span was calculated for a 28-year period, from 1955 to 1983 based on aerial photograph dates. The 1980s to 1990s period was for a 13-year span, from

1983 to 1996. Calculated mean lateral migration values are shown in Table 4-2, and

Figure 4-2 shows mean lateral migration values and lateral migration rates for the two

time intervals. The geologic reaches are arranged from the Zilpha Winona at Enterprise,

going downstream. Mean lateral migration rates were higher for the shorter (1983 to

1996) thirteen-year period than for the 28-year (1955 to 1983) year period (Figure 4-2).

Table 4-2. Calculated lateral migration values per reach. Geologic Reach V_length(m) mean lat.mgr (m) mean lat. mgr (m) Sum_mean mgr mean mgr 1955-1983 1983-1996 (41 yr period) rate (m/yr) Zilpha/Winona 3670 6 5 10 0.26 Kosciusko 6637 9 20 29 0.72 Cook Mountain 6652 15 12 27 0.65 Cockfield 18395 11 9 20 0.49 Jackson 11485 8 9 17 0.41 Forest Hill/ Red Bluff clay 8988 10 15 25 0.61 Vicksburg/Chickasawhay 14526 7 7 14 0.34 Catahoula 45163 23 21 44 1.07 Pascagoula/ Hattiesburg 38944 22 19 40 0.98 Note: Shaded cells indicate reaches where observed lateral migration is certain.

25 1955-1983 1983-1996 1.8 1.6 20 1955-1983 1983-1996 1.4 1.2 15 1.0 0.8 10 0.6 5 0.4 0.2 Mean Lateral Migration (m) 0 0.0 Lateral Migration Rates (m/yr) in a g eld lay fi bur inona k c uff c /W tahoul Mounta Co Jackson asawhay a Kosciusko k C lpha ok / Hatties i Red Bl a Z Co l/ il g/Chic t H bur cagoul es ks or c Pas F Vi

Figure 4-2. Mean lateral migration values in meters.

These values were then normalized by a width constant, derived as the mean of the average width values for individual reaches (Table 4-3). Figure 4-3 shows the longitudinal profile for the Chickasawhay River, with the 41-year mean lateral migration, normalized mean lateral migration, as well as sinuosity for the individual geologic reaches. The reduced migration values for the Catahoula and the Pascagoula/Hattiesburg, and the increased values for the Cook Mountain reach are immediately obvious.

Cummulative Valley Lengths Legend MPH: Pascagoula/Hattiesburg MC: Catahoula EZ OV: Vicksburg/Chickasawhay E W OF: Forest Hill/Red Bluff T EK EC EC EJ OF OV MC MPH M EJ: Jackson EC: Cockfield ECM: Cook Mountain EK: Kosciusko EZW: Zilpha/Winona ET: Tallahata

0 20 40 60 80 100 120 140 160 Valley Distance (km) Longitudinal Profile 80

50 Confluence Chunky and Okatibbee Creek 40

30 Confluence Leaf and Chickasawhay Elevation (m) 20

0 0 20406080100120140160 Cum. Valley Distance (km)

2.5 50 45 2.0 40 35 1.5 30 25

Sinuosity 1.0 20 15

0.5 Sinuosity 10 5 41-yr Mean Laletal Migration Mean Lateral Migration (m) 0.0 0 0 20 40 60 80 100 120 140 160 Valley Distance (km)

1.2

0.8

0.6

0.4

0.2

Normalized Mean Lateral Migr(m/m/) 0 0 20 40 60 80 100 120 140 160 Valley distance (km)

Figure 4-3. Geologic reach parameters for the Chickasawhay.

Table 4-3. Lateral migration as a percentage of channel width LatMig/Widthconst Normalized Mig. (m/m) Rate (m/m/yr) Geologic Reach Valley avgWidth avgWidth avgWidth 1955-1983 1983- 996 1955-1983 1983-1996 length(m) 1950s(m) 1980s(m) 1990s(m) Zilpha/Winona 3670 35 30 34 0.18 0.14 0.01 0.01 Kosciusko 6637 38 39 46 0.22 0.49 0.01 0.04 Cook Mountain 6552 22 26 35 0.54 0.43 0.02 0.03 Cockfield 18395 27 30 41 0.33 0.29 0.01 0.02 Jackson 11485 32 36 42 0.22 0.24 0.01 0.02 Forest Hill/ 8988 35 45 48 0.22 0.36 0.01 0.03 Red Bluff day Vicksburg/ 14526 37 39 41 0.18 0.17 0.01 0.01 Chickasawhay Catahoula 45163 61 80 83 0.31 0.28 0.01 0.02 Pascagoula/ 38944 88 81 94 0.25 0.21 0.01 0.02 Hattiesburg

Comparisons between calculated lateral migration, normalized mean lateral

migration and sediment size are shown in Figure 4-4. A total of 12 sediment samples

from the Zilpha Winona formation, 20 samples from the Kosciusko, 20 from the

Cockfield, 8 from the Jackson, 2 samples from the Forest Hill/Red Bluff Clay, 20

samples from the Vicksburg/Chickasawhay and 20 sediment samples from the Catahoula

formation were analyzed. The average sediment size value for each reach was used for all

analyses. Table B-2 in Appendix B shows the results for all analyzed sediment samples.

No samples were collected from the Cook Mountain and the Pascagoula and Hattiesburg

formations. Correlation coefficients for particle size and mean lateral migration are shown in Table 4-4.

Table 4-4. Correlation coefficients Fraction Correlation Coefficient Mean Lat. Mig Normalized Lat. Mig Average MB Sand % -0.19 0.20 Average MB Mud % -0.08 -0.30 Average WL Sand % -0.53 -4.8E-05 Average WL mud % 0.18 -0.14

70 Average WL Sand % Average WL Mud % 60

30 % Mud/Sand

0 100 Average MB Mud % 1.2 90 Average MB Sand % 80 1.0 Mean Lateral Migr 70 0.8 60 Normalized Lat. Mig 50 0.6 40 30 0.4 20 0.2

Mean Lateral Migration (m) 10 0 0.0

y y g a a la ield cl u ur inon usko ntain Normalized Lateral Migration (m/m) u esb W o ockf uff sawha ti / M C Jackson Bl a t ha Kosci d ck Cataho p ok i Ha il o Re a/ Z C / ill ul H go rest o F Vicksburg/Ch Pasca

Figure 4-4. Mean lateral migration against sediment sizes.

Particle size data for the Forest Hill/Red Bluff Clay reach may not be a true representative because only two sediment samples were collected from this reach, compared to a minimum of at least twelve samples from other reaches.

Width Change Analysis

The aim of this analysis was to compare channel outlines and widths for the

different time periods, and to identify the relationship between changes in channel size,

and planform change. Average cross sectional width per reach was determined using the

methods described in section 3.1. Stream widths were measured at 100m intervals (Figure

4-5), and maximum cross sectional length from bank to bank was set at 100m. Table 4-5 shows calculated average channel width values for the three time periods, and Figure 4-6

49 shows a simple linear regression plot of average channel widths and mean lateral migration rate.

Figure 4-5. Relationship between channel width and mean lateral migration.

Table 4-5. Average channel widths.

Geologic Reach Valley length(m) avgWidth_50s(m) avgWidth_80s(m) avgWidth_90s(m) avg_widths(m)

Zilpha/Winona 3670 35 30 34 33 Kosciusko 6637 38 39 46 41 Cook Mountain 3603 22 26 35 28 Cockfield 18395 27 30 41 33 Jackson 11485 32 36 42 37 Forest Hill/ Red Buff clay 8988 35 45 48 43 Vicksburg/Chickasawhay 14526 37 39 41 39 Catahoula 45163 61 80 83 75 Pascagoula/ Hattiesburg 38944 88 81 94 88

1.20 y = 0.0108x + 0.1136 2 1.00 R = 0.6615

0.80

0.60

0.40

0.20 Mean migration rate (m/yr) rate Mean migration

0.00 0 10 20 30 40 50 60 70 80 90 100 Average channel width idht idth ( ) Figure 4-6. Transects used to measure channel width.

A general trend of channel widening over time was observed for all nine geologic reaches, except for the most upstream and most downstream reaches. Figure 4-7 shows a general trend of increasing mean lateral migration with increasing widths, and decreasing normalized lateral migration with increasing channel widths.

100 avg_w idths(m) 1.2 90 normalized lateral migration 80 1.0 70 mean lateral migration (m) 0.8 60 50 0.6 40 30 0.4 20 0.2 10 0 0.0

d y Mean Lateral Migration(m) ko ain on ay a ula

Average Channel Widths (m) Widths Channel Average fiel inona us k ks ci unt /W oc ac sawh taho C J Kos Ca pha ok Mo cka o Red Buff cl hi Zil C / ill t H es or Pascagoula/ Hattiesburg F Vicksburg/C

Figure 4-7. Relationship between channel widths and lateral migration.

Analysis By Morphologic Reach

(A) (B) Figure 4-8. Digitized channel centerlines showing virtually no channel movement, and meander migration on the Chickasawhay, approximately 5km (A) and 10km (B) downstream of the confluence of the Chunky and Okatibbee at Enterprise.

Apart from the reservoir on the Okatibbee River to its north, the Chickasawhay

River is generally unregulated with no dams or mining along the stretch, so the channel is

52 relatively free to migrate. Overlay analysis of channel centerlines (Figures 4-8a and 4-8b above) show that while excessive lateral migration has occurred in certain reaches, there has been virtually no migration in some reaches.

Sediment size analysis was conducted on the basis of channel pattern, whereby the study area was divided into straight, sinuous and jagged reaches (Figure 4-9a-c).

Sediment samples were collected from one straight, two sinuous and three jagged reaches, a total of seven morphologic reaches.

(A) (B) (C) Figure 4-9. Straight, sinuous and jagged reaches at Enterprise (A), Stonewall (B) and Quitman (C). These three reaches make up the upper 30km of the Chickasawhay.

Table 4-6 shows digitized centerline and valley length values for the seven morphologic reaches examined, and Table 4-7 shows calculated mean lateral migration for the seven morphologic reaches. Sixteen sediment samples were analyzed for

straight1, jagged1, jagged3 and sinuous1 channel reaches respectively, and eight samples

each from sinuous2, jagged2 and straight 2 morphologic reaches.

Table 4-6. Reach parameters for the seven morphologic reaches.

ReachChannel(centerline) Length(m) V_length 50 80 90 Straight 1 7879 8178 7884 7459 Straight 2 7875 7879 7834 6743

Sinuous 1 11458 10889 11676 4110 Sinuous 2 16338 15404 15403 8450

Jagged 1 28128 27385 27758 11357 Jagged 2 33693 33717 36346 18619 Jagged 3 20703 20846 20875 13696

Table 4-7. Mean lateral migration for the seven morphologic reaches. Morphologic mean lat.mgr (m)max. lat.mgr(m)mean lat. mgr (m) max. lat.mgr(m) Sum_mean mgr mean mgr Reach V_length 1955-1983 50_80 1983-1996 80_90 (41 yr period) rate (m/yr) Straight 1 7459 6 28 5 47 11 0.27 Straight 2 6743 11 25 6 49 17 0.41

Sinuous 1 4110 14 106 23 110 37 0.90 Sinuous 2 8450 22 251 15 82 37 0.91

Jagged 1 11357 10 135 7 40 17 0.42 Jagged 2 18619 8 39 11 190 19 0.46 Jagged 3 13696 8 43 7 49 14 0.35

The histograms in Figure 4-10 show comparisons of sand and mud percent for the

seven morphologic reaches, for both waterline and mid bank sediments. Sediment

samples were not collected from the straight2 reach. Overlay analysis of land use and

land cover attributes, as well as field observations of straight1, sinuous1, and jagged1

reaches, show that most of the sinuous reaches occur over forested wetlands, and on some

mixed forest land. The two straight reaches studied occurred on land that was used mostly for cropland and pasture, and on some evergreen forests. The jagged reaches

occurred mostly on evergreen forestland, and on some mixed forestland. The USGS land

cover data used in this study are included in Appendix A.

90 Average WL Sand % 80 Average WL mud %

80 Average MB Sand % 70 Average MB Mud %

0 Straight 1 Straight 2 Sinuous 1 Sinuous 2 Jagged 1 Jagged 2 Jagged 3

Figure 4-10. Sand and mud % values for waterline (WL) and midbank (MB) samples.

Sinuosity and mean lateral migration for the seven morphologic reaches studied are shown against the longitudinal profile for the Chickasawhay in Figure 4-11. The valley distance shown is the cumulative valley distance, from the confluence of the Chunky

River and Okatibbee Creek at Enterprise, to approximately 250km south of the confluence of the Leaf and Chickasawhay Rivers, on the Pascagoula River. Sinuosity and mean lateral migration for the reach between the jagged2 and jagged3 reaches are also shown in Figure 4-11.

ST S J ST J J S 1 1 1 2 2 3 2 ST: Straight S: Sinuous J: Jagged

0 20 40 60 80 100 120 140 160 Valley Distance (km)

Longitudinal Profile 80

50 Confluence Chunky 40 and Okatibbee Creek

30 Elevation (m) Confluence Leaf and Chickasawhay 20

0 0 20 40 60 80 100 120 140 160 Valley Distance (km)

3.0

2.5

2.0

1.5

Sinuosity 1.0

0.5

0.0 0 20 40 60 80 100 120 140 160 Valley Distance (km)

45 40 35 30 25 20 15 10 41-yr Mean Lateral Migr(m) 5 0 0 20 40 60 80 100 120 140 160 Valley distance (km)

Figure 4-11. Morphologic reach parameters for the Chickasawhay

Sinuosity Analysis

Sinuosity change was estimated for each time period by dividing the channel length for that period and reach, by the down valley linear length. Tables 4-8 and 4-9 show digitized valley and centerline lengths as well as calculated sinuosity values for the geologic and morphologic reaches respectively. Comparisons of sinuosity for geologic and morphologic reaches are shown in Figures 4-3 and 4-11 of previous sections.

Table 4-8. Calculated sinuosity per geologic reach. Geologic Reach Valley length(m) Channel(centerline) Length(m) Sinuosity_geologic Reach 50 80 90 50s 80s 90s Zilpha/Winona 3670 4112 4083 4107 1.12 1.11 1.12 Kosciusko 6637 9104 9122 9313 1.37 1.37 1.40 Cook Mountain 6552 11892 11550 11951 1.81 1.76 1.82 Cockfield 18395 37563 36849 37136 2.04 2.00 2.02 Jackson 11485 16072 16011 16046 1.40 1.39 1.40 Forest Hill/ Red Bluff clay 8988 20448 19406 19198 2.28 2.16 2.14 Vicksburg/Chickasawhay 14526 19464 19720 19759 1.34 1.36 1.36 Catahoula 45163 78796 74971 75661 1.74 1.66 1.68 Pascagoula/ Hattiesburg 38944 67402 65528 65539 1.73 1.68 1.68

Overlay analysis like the one in Figure 4-12 showed several instances of neck and chute cut offs, even though sinuosity values remained relatively the same for the time period studied. Overlay analysis also showed amplitude increase in some meander bends, which could account for the relatively constant sinuosity values.

Table 4-9. Calculated sinuosity values for the seven morphologic reaches. ReachChannel(centerline) Length(m) V_length Sinuosity_pattern 50 80 90 50s 80s 90s Straight 1 7879 8178 7884 7459 1.06 1.10 1.06 Straight 2 7875 7879 7834 6743 1.17 1.17 1.16

Sinuous 1 11458 10889 11676 4110 2.79 2.65 2.84 Sinuous 2 16338 15404 15403 8450 1.93 1.82 1.82

Jagged 1 28128 27385 27758 11357 2.48 2.41 2.44 Jagged 2 33693 33717 36346 18619 1.81 1.81 1.95 Jagged 3 20703 20846 20875 13696 1.51 1.52 1.52

Figure 4-12. Meander cut off near Kittrell, less than 1km north of highway 42, and approximately 1km south of the Wayne/Greene county line.

Results

Overlay analysis of digitized channel outlines showed channel movements in several places on the Chickasawhay. Results showed that migration was mostly downstream, and towards the least resistant bank. Points a to h in Figure 4-13 show channel movements on the Chickasawhay at Stonewall.

Figure 4-13. Channel migration at Stonewall.

At point a, the 1990s channel centerline has not only widened, but has moved at least 140m southeast from its 1950s position. At point b, the straight-line distance between the 1950s and 1990s centerline is approximately 70m.

Analysis showed that although the degree of bank material cohesiveness was

important in determining channel stability, a more dominant control was the degree of

bank lithification. These two variables dominate to varying degrees on a reach-by- reach

basis. In some cohesive reaches, increased bank saturation served to inhibit channel

movements, and in some sandy reaches, forest cover was boosted by the presence of

grass under brush. In some lithified reaches, planes of weaknesses undermined bank

stability, by serving as starting points for erosional work (Figure 4-14).

Figure 4-14. Erosional planes of weakness

Land cover in the area is mostly forest, and there are different kinds of forest cover

(mixed forests, evergreen, deciduous). Small percentages are used for cropland and pasture, and these areas are where some of the straight reaches occur. Over 80% of observed channel movements occur on forested wetlands.

Mean lateral migration values were calculated for three time periods (1950s, 1980s,

1990s) and two time intervals (1955 to 1983 and 1983 to 1996). The highest mean lateral migration rate for the entire 41-year period was for the Catahoula geologic reach, at

1.07m/yr. The lowest mean lateral migration rate was 0.26m/yr, recorded for the Zilpha

Winona reach. Mean lateral migration was highest for the Catahoula for both the 1955 to

1983, and the 1983 to 1996 time intervals. The mean lateral migration remained relatively unchanged for the Jackson geologic reach during the two time intervals,

60 showing just a slight increase from 8.08m (1955 to 1983) to 8.78m (1983 to 1996). With the exception of the Kosciusko and the Forest Hill/Red Bluff reaches, mean lateral migration values were higher for the longer time interval for all other geologic reaches.

After these values were normalized as a function of their reach average width, all but the Pascagoula/Hattiesburg and the Catahoula were relatively unchanged. The Cook

Mountain geologic reach had the highest migration value for the 41-year period, at 0.97 m/m. The Zilpha Winona reach again had the lowest corrected lateral migration value, at

0.008 m/m. Corrected mean migration values were highest for the Cook Mountain for the

1955 to 1983 interval, and for the Kosciusko, for the 1983 to 1996 interval. Corrected lateral migration values remained relatively unchanged for the Jackson and

Vicksburg/Chickasawhay geologic reaches during the two time intervals, showing just a slight increase from 0.22 m/m to 0.24 m/m and a slight decrease from 0.18 m/m to 0.17 m/m respectively, for the 1955 to1983 and 1983 to1996 time intervals. With the exception of the Kosciusko and the Forest Hill/Red Bluff reaches, mean lateral migration values were higher for the longer time interval for all other geologic reaches. Table 4-10 shows both normalized and un-normalized lateral migration values for each geologic reach.

Table 4-10. Mean lateral migration values. Mean Lateral migration (m) Mean lat mig/Avg_widths Geologic Reach 1955-1983 1983-1996 1955-1983 1983-1996 Zilpha/W inona 6 5 0.18 0.14 Kosciusko 9 20 0.22 0.49 Cook Mountain 15 12 0.54 0.43 Cockfield 11 9 0.33 0.29 Jackson 8 9 0.22 0.24 Forest Hill/ Red Bluff clay 10 15 0.22 0.36 Vicksburg/Chickasawhay 7 7 0.18 0.17 Catahoula 23 21 0.31 0.28 Pascagoula/ Hattiesburg 22 19 0.25 0.21

Sinuosity analysis showed the Forest Hill/Red Bluff Clay geologic reach to be the

most sinuous for the three time periods with an average sinuosity of 2.19. The lowest

sinuosity values were recorded for the Zilpha Winona reach with an average sinuosity of

1.12 for the 41-year period. No significant changes in sinuosity were observed on a reach

by reach basis. The high sinuosity reaches stayed high and the low sinuosity reaches

stayed low during the study period. No significant changes were also observed for the

entire Chickasawhay River, sinuosity decreased from 1.73 in the 1950s, to 1.70 in the

1980s and 1990s.

Average waterline (WL) sand percent was highest for the Forest Hill/Red Bluff and

Zilpha Winona reaches, and lowest for the Catahoula. WL mud percent was highest for the Jackson reach, and lowest for the Forest Hill/Red Bluff and Zilpha Winona reaches.

Tables 4-11 and 4-12 show the results of particle size analysis for mid bank (MB) and

WL samples. No sediment samples were collected from the Cook Mountain and the

Pascagoula/Hattiesburg geologic reaches. The Catahoula had the lowest MB sand percent, and the Jackson geologic reach had the highest MB mud values.

Average cross sectional channel widths for the entire channel increased from approximately 56m to 63m from 1955 to 1996. Apart from the Zilpha Winona and the

Pascagoula and Hattiesburg reaches which showed decreased channel widths in the 80s, average channel widths for all geologic reaches showed an increasing trend for each time period. The greatest average channel width was recorded for the Pascagoula and

Hattiesburg reach, and the lowest for the Cook Mountain reach (Table 4-13). Channel widths generally increased as one progressed downstream. This is likely scale dependent,

62 due to increasing discharge and more extensive floodplains. Actual width change in meters for the two time periods are shown in Table 4-14.

Table 4-11. Particle size analysis results for percent mud and sand, WL samples. Sample # fraction sand, mud % Sample # fraction sand, mud % Sample # fraction sand, mud % xs1-LB-wl Sand 78 xs9-RB-wl Sand 85 xs18-RB-wl Sand 61 Mud 22 Mud 15 Mud 39

xs1-RB-wl Sand 58 xs10-LB-wl Sand 85 xs19-LB-wl Sand 43 Mud 42 Mud 15 Mud 57

xs2-LB-wl Sand 75 xs10-RB-wl Sand 85 xs19-RB-wl Sand 23 Mud 25 Mud 15 Mud 77

xs2-RB-wl Sand 79 xs11-LB-wl Sand 9 xs20-LB-wl Sand 36 Mud 21 Mud 91 Mud 64

xs3-LB-wl Sand 64 xs11-RB-wl Sand 80 xs20-RB-wl Sand 59 Mud 36 Mud 20 Mud 41

xs3-RB-wl Sand 84 xs12-LB-wl Sand 1 xs21-LB-wl Sand 52 Mud 16 Mud 99 Mud 48

xs4-LB-wl Sand 22 xs12-RB-wl Sand 84 xs21-RB-wl Sand 91 Mud 78 Mud 16 Mud 9

xs4-RB-wl Sand 10 xs13-LB-wl xs22-LB-wl Sand 50 Mud 90 Mud 50 xs13-RB-wl Sand 71 xs5-LB-wl Sand 92 Mud 29 xs22-RB-wl Sand 72 Mud 8 Mud 28 xs14-LB-wl Sand 40 xs5-RB-wl Sand 89 Mud 60 xs23-LB-wl Sand 88 Mud 11 Mud 12 xs14-RB-wl xs6-LB-wl Sand 96 xs23-RB-wl Sand 29 Mud 4 xs15-LB-wl Sand 73 Mud 71 Mud 27 xs6-RB-wl Sand 25 xs24-LB-wl Sand 82 Mud 75 xs15-RB-wl Mud 18

xs7-LB-wl Sand 88 xs16-LB-wl xs24-RB-wl Sand 46 Mud 12 Mud 54 xs16-RB-wl Sand 79 xs7-RB-wl Sand 79 Mud 21 xs13a-LB-wl Sand 92 Mud 21 Mud 8 xs17-LB-wl Sand 71 Mud 29 xs13a-RB-wl Sand 1 xs8-LB-wl Sand 74 Mud 99 Mud 26 xs17-RB-wl Sand 72 Mud 28 xs14a-LB-wl Sand 10 xs8-RB-wl Sand 96 Mud 90 Mud 4 xs18-LB-wl Sand 96 Mud 4 xs14a-RB-wl Sand 96 xs9-LB-wl Sand 78 Mud 4 Mud 22

Table 4-12. Particle size analysis results for percent mud and sand, MB samples. Sample # fraction sand, mud % Sample # fraction sand, mud % Sample # fraction sand, mud %

xs1-LB-mb Sand 93 xs9-RB-mb Sand 50 xs18-RB-mb Sand 49 Mud 7 Mud 50 Mud 51

xs1-RB-mb Sand 88 xs10-LB-mb Sand 48 xs19-LB-mb Sand 60 Mud 12 Mud 52 Mud 40

xs2-LB-mb Sand 59 xs10-RB-mb Sand 58 xs19-RB-mb Sand 23 Mud 41 Mud 42 Mud 77

xs2-RB-mb Sand 54 xs11-LB-mb Sand 33 xs20-LB-mb Sand 78 Mud 46 Mud 67 Mud 22

xs3-LB-mb Sand 40 xs11-RB-mb Sand 93 xs20-RB-mb Sand 87 Mud 60 Mud 7 Mud 13

xs3-RB-mb Sand 64 xs12-LB-mb Sand 8 xs21-LB-mb Sand 25 Mud 36 Mud 92 Mud 75

xs4-LB-mb Sand 56 xs12-RB-mb Sand 83 xs21-RB-mb Sand 85 Mud 44 Mud 17 Mud 15

xs4-RB-mb Sand 66 xs13-LB-mb Sand xs22-LB-mb Sand 70 Mud 34 Mud Mud 30 xs13-RB-mb Sand 45 xs5-LB-mb Sand 64 Mud 55 xs22-RB-mb Sand 89 Mud 36 Mud 11 xs14-LB-mb Sand 80 xs5-RB*mb Sand 74 Mud 20 xs23-LB-mb Sand 89 Mud 26 Mud 11 xs14-RB-mb Sand xs6-LB-mb Sand 89 Mud xs23-RB-mb Sand 27 Mud 11 xs15-LB-mb 93 Mud 73 Sand 7 xs6-RB-mb Sand 62 Mud xs24-LB-mb Sand 88 Mud 38 xs15-RB-mb Mud 12 Sand xs7-LB-mb Sand 88 xs16-LB-mb Mud xs24-RB-mb Sand 45 Mud 12 Mud 55 xs16-RB-mb Sand 42 xs7-RB-mb Sand 81 Mud 58 xs13a-LB-mb Sand 74 Mud 19 Mud 26 xs17-LB-mb Sand 16 xs8-LB-mb Sand 52 Mud 84 xs13a-RB-mb Sand 11 Mud 48 Mud 89 xs17-RB-mb Sand 60 xs8-RB-mb Sand 97 Mud 40 xs14a-LB-mb Sand 13 Mud 3 Mud 87 xs18-LB-mb Sand 30 xs9-LB-mb Sand 61 Mud 70 xs14a-RB-mb Sand 66 Mud 39 Mud 34

Average cross sectional channel widths for the entire channel increased from

approximately 56m to 63m from 1955 to 1996. Apart from the Zilpha Winona and the

Hattiesburg reach, and the lowest for the Cook Mountain reach (Table 4-13). Channel widths generally increased as one progressed downstream. This is likely scale dependent, due to increasing discharge and more extensive floodplains. Actual width change in meters for the two time periods are shown in Table 4-14.

Table 4-13. Estimated average channel cross sectional widths. Geologic Reach Valley length(m) avgWidth_1950s(m) avgWidth_1980s(m) avgWidth_1990s(m)

Zilpha/Winona 3670 35 30 34 Kosciusko 6637 38 39 46 Cook Mountain 3603 22 26 35 Cockfield 18395 27 30 41 Jackson 11485 32 36 42 Forest Hill/ Red Buff clay 8988 35 45 48 Vicksburg/Chickasawhay 14526 37 39 41 Catahoula 45163 61 80 83 Pascagoula/ Hattiesburg 38944 88 81 94

Table 4-14. Calculated channel change values. Width Change(m) Mean Lateral migration (m) Mean Lat. Mig/Avg_Widths Geologic Reach 1955-1983 1983-1996 1955-1983 1983-1996 1955-1983 1983-1996 Zilpha/Winona -5 4 6 5 0.18 0.14 Kosciusko 1 7 9 20 0.22 0.49 Cook Mountain 4 9 15 12 0.54 0.43 Cockfield 3 11 11 9 0.33 0.29 Jackson 4 6 8 9 0.22 0.24 Forest Hill/ Red Bluff clay 10 3 10 15 0.22 0.36 Vicksburg/Chickasawhay 2 2 7 7 0.18 0.17 Catahoula 19 3 23 21 0.31 0.28 Pascagoula/ Hattiesburg -7 13 22 19 0.25 0.21 Note: Negative values indicate decreasing channel widths.

Figure 4-15 shows a simple histogram plot of average reach sinuosity against

average channel cross sectional widths for the three time periods.

10 0 2.5 90 80 2.0 70 60 1. 5 50 40 1. 0

30 Sinuousity 20 0.5 10 0 0.0 Average Channel Widths (m) Widths Channel Average

Average channel widths (m) average sinuosit y

Figure 4-15. Sinuosity versus channel width.

Analysis showed lateral migration to be somewhat scale dependent. Pre-normalized lateral migration results showed a general trend of increasing mean lateral migration with increasing channel widths, while the normalized results showed a trend of decreasing lateral migration with increasing width (Figure 4-16).

100 Average Channel widths (m) 1.2 90 41-yr Mean lateral migration (m) 80 1.0 70 Normalized lateral migration (41-yr) 0.8 60 50 0.6 40 30 0.4 20 0.2 10 Migration Mean Lateral Average Channel Widths (m) Widths Average Channel 0 0.0

a o y g n ha ula ur iusk ntain kfield w o b ino c u c a s s /W o Jackson atah tties a K Mo Co C a H ed Buff clay / Zilph R Chicka Cook / ula rg o Hill/ u st ag e ksb ic For V Pasc Figure 4-16. Average cross sectional channel widths and mean lateral migration.

CHAPTER 5 DISCUSSION

Overview

As dynamic systems, rivers are subject to change. The main objective of this study was to measure channel instability on the Chickasawhay, and to assess the role of geology as a dominant control on planform change. Measures of lateral migration, changes in channel width and sinuosity were used as indicators of channel instability.

Analysis show that bank instability along the Chickasawhay is a result of several factors.

The variability in magnitude and rate of channel change, and the variability in channel pattern shows the river’s response to what appears to be a variability in controlling factors for individual reaches, even on reaches that are contiguous. Apart from bridge constructions, human interventions like channelization, agriculture and bank stabilization are not very extensive along the floodplain. Land Use/Land Cover (LU/LC) maps, field observations, and published literature (USACE, 1962, USGS 1992), led to the conclusion that while LU/LC plays some role, it is not the dominant factor in channel change. Other factors include the presence of large woody debris, type of forest cover, bank geometry, discharge/frequency of high flows, texture and type of transported sediment load, and bank geology. The most dominant factor influencing channel instability was geology, in the form of bank and channel bed lithology, and bank geometry.

Morphologic Patterns and Geology

The most dominant control on channel shape and size on the Chickasawhay River is geology. The variations in channel pattern are due to variations in bank lithology, slope

66 67

and the degree of both bank material cohesiveness, and induration. While factors like

discharge, land cover, and sediment load affect channel change to varying degrees on a

reach by reach basis, bank geology exerts strong structural controls on the entire channel.

As a result of this variation in valley types, the river’s floodplain is relatively narrow and

stable in some places, and extensive and mobile in other places.

(A) (B) Figure 5-1. Consolidated bank material on the Chickasawhay River. (A) and (B) show bank material in two Jagged reaches at Quitman.

Field visits were made to straight, sinuous and jagged reaches. The visits revealed that in the lithified reaches (Figures 5-1a and b above), sediments are not readily available for erosion, and since channel changes involve erosion, lateral migration rates are low in these reaches, and change often comes in the form of increased channel depths.

Highly lithified shales and claystones make up the valley floor and walls in these reaches, and the channel is not free to migrate. These bedrock-confined valleys are high and steep,

also making floodplain deposition difficult. These are the straight and jagged reaches, and they exhibit the lowest migration rates.

The sinuous and actively migrating reaches on the other hand exhibit low slopes, sandy banks with coarse, alluvial channel beds (Figures 5-2a and b).

(A) (B) Figure 5-2. Unconsolidated bank material on the Chickasawhay 2.5km south of Stonewall. (A) shows right bank, and (B) shows left bank of a sinuous reach.

Tooth et al. (2002) also studied the effect of geology on alluvial meanders and floodplain wetlands on the Klip River in Eastern South Africa, and found that in reaches where sandstone outcropped on both sides of the valley, the channel meandered through extensive floodplains with significant wetland areas, in contrast to other reaches with dolerite outcrops on both sides of the valley. In the bedrock reaches, as on the

Chickasahway, the Klip River flowed an essentially straight course with floodplains

either absent, or restricted in width. On the jagged reaches of the Chickasawhay, the river

exhibits sudden, sharp, and sometimes ninety-degree-angled changes in flow directions.

In these reaches the river flows an essentially straight course until it runs into bedrock

obstruction, causing these flow direction changes. The shallow faults that splay over most

of these jagged reaches may account for these sudden changes in flow direction and the

observed channel pattern (Figure 5-3).

Figure 5-3. Faulting at Quitman

Other Factors

The volume and texture of transported sediments is also an important variable that has affected channel change on the Chickasawhay. Field observations suggest that suspended sediments make up the majority of sediment load (Figure 5-4). However, during high magnitude flows such as the flood of April 2003, we found, like Gupta’s

(1995) study in Central India and Jamaica, that vast quantities of coarse sediments are

transported and deposited. Field data and conversations with local landowners show that

the 2003 flood produced at least one new cut-off on Wayne Hemingway’s property, about

2.5km south of Stonewall town (Figure 5-5). When such deposition occurs and cut-offs

form, velocity and even channel slope increases, due to channel shortening in such

reaches. Such an occurrence can lead to higher migration rates, as a result of increased velocity and erosive power.

Figure 5-4. Suspended sediment load on the Chickasawhay.

Figure 5-5. Old and new meander cut-offs of the Chickasawhay at Stonewall.

Schumm (1968) in studying the Murrumbidgee River in Australia, found that a high suspended sediment load favored meandering. Channel pattern on the Chickasawhay appears however, to be predominantly a function of valley geology, since both the sinuous and straight reaches appear to carry approximately the same amount of suspended sediment load. The influence of suspended sediment varies on a reach by reach basis, depending on whether the channel is free to migrate or not.

Sinuosity remained relatively constant for the entire channel during the study period, even though several cut-offs occurred, mostly through neck cut offs, and probably during periods of unusually high flows like the 2003 flood. Overlay analysis shows increased meander amplitude in several places on the Chickasawhay, a likely explanation for the stable sinuosity. For example, in Figure 4-13, at points A, B, and C, the channel has widened. On a reach by reach basis however, there was some variability in sinuosity, although sinuosity for each reach stayed relatively constant. This variability in sinuosity per reach, reflects changes in valley floor and bank lithology, as well as differences in degree of bank material induration

The USGS maintains continuous gages on the Chickasawhay, upstream at

Enterprise, and downstream at Leakesville. Annual discharge data for the 41-year period is included in Appendix B. The hydrographs in Figure 5-6, 5-7 and 5-8 show that apart from the 1961 peak, daily discharge has stayed relatively constant. And while upstream peak annual gage heights show a slight increase, downstream gage heights stayed relatively constant during the 41-year period.

Daily Discharge for 41-year Period

2500 Leakesville Enterprise 2000

1500

1000 Q (m3/s)

500

0 1953 1963 1973 1983 1993 Year

Figure 5-6. Upstream and downstream discharge data for the two time intervals.

Enterprise

Peak Annual Gage Heights (m) 64

7 0 3 6 49 52 55 58 61 64 67 70 93 94 94 94 9 9 9 9 9 9 9 9 994 997 000 1 1 1 1 1 1 1 1 1 1 1 1 1973 1976 1979 1982 1985 1988 1991 1 1 2 Year

Figure 5-7. Upstream peak stage data for the two time intervals.

Leakesville

Peak Annual Gage height (m) 5

0 9 2 5 8 1 4 7 0 3 6 9 2 5 8 1 4 7 0 3 6 9 90 93 94 94 94 95 95 95 96 96 96 96 97 97 97 98 98 98 99 99 99 99 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Year

Figure 5-8. Downstream peak stage data for the two time intervals

Although average discharge was higher at the downstream station for both time

intervals, peak annual gage heights were higher at the upstream station. Annual gage

peaks appear to have also increased upstream since the 1955 to 1983 interval. With the

exception of the Kosciusko and the Cook Mountain, channel widths increase

downstream, and the lower upstream discharge is likely due to not just valley confinement upstream, but also to the fact that the Buckatunna Creek joins the

Chickasawhay downstream of the Enterprise gage station. However, the highest width normalized lateral migrations occur in the upstream reaches of the Chickasawhay, and this is where peak annual gage heights for the period exhibit the highest variability. So the frequency of high flows plays some role in channel migration, but to what extent varies from reach to reach.

Another factor that affects lateral migration is the rich forest vegetation that covers much of the study area. Root networks in the forested reaches help to stabilize channel

banks, thereby limiting lateral movement. This suggests that without this forest cover, lateral migration rates would have been much higher. Forest consists mostly of pines, oaks and some gum trees.

Nanson and Hickin (1986) attributed the erosion of channel banks under trees to a

lack of adequate grass cover (Figure 5-9). I found that even in some bedrock reaches, bank loading and scour from large woody debris (LWD) affected bank stability (Figure

5-10). Micheli et al. (2003) observed destabilizing effects of scour and LWD even on forested banks. Planform changes depend on erosion and the transport of sediments, and in some reaches this depends on the presence or absence of LWD, since LWD restricts sediment transport and slows flow velocity. This variable appears most effective in the sinuous reaches, where the floodplain is constantly being reworked and sediment is deposited as channel bars as a result of the drop in velocity.

Figure 5-9. Inadequate grass cover

Figure 5-10. Basal scour and overloading

Channel Change and Bank Lithology

Apart from the generalized Mississippi Geological Survey (1969) geologic map used in the field, detailed geologic maps for Clarke and Wayne counties were also used in this study and are shown in Figures 5-11 and 5-12. Enlarged versions of both maps are included in Appendix A. Minor differences in lithology descriptions, as well as some variations in the geographic extents of geological units were noted between these maps and the 1969 map. Descriptive emphasis in this study is placed on the more detailed maps. The three main lithologies that are present in the study area are sands, clays and limestones. On the Chickasawhay’s banks, these three lithology types outcrop at different points as weathered, lithified, faulted, jointed, as interbeds or as mixed sediment types.

These other factors play into the channels behavior as it flows over the different rock types.

The nine formations represented were the Zilpha and Winona, the Kosciusko, the

Cook Mountain, the Cockfield, the Jackson formation, the Forest Hill/Red Bluff Clay, the

Vicksburg and Chikcasawhay, the Catahoula, and the Pascagoula and Hattiesburg formations. These formations are arranged in a downstream direction to follow river’s

flow. The formations also go from oldest (Eocene) to youngest (Miocene) in the

downstream direction.

The Zilpha is described as mostly carbonaceous shale and clay, and the Winona is

mostly greensands and glauconitic sands. This reach exhibited the lowest lateral migration (Table 5-1), and it formed part of the straight1 reach. Field visits showed that the Chickasawhay in this reach flows mostly over lithified shales and cohesive clays.

This is the main reason this reach had such low migration rates. Land cover maps and field observations show that of the seven geologic reaches visited, the Zilpha Winona and

Kosciusko were the only reaches that were not completely forested. Signs of cattle, and vegetation breaks from forest to pasture were observed at two sites visited in the area.

These pockets of cropland appear to be in alluvial material deposited on the flood plain atop lithified shales. The importance of lithological controls in this reach was underscored by the fact that in spite of the active farming, this reach had the lowest lateral migration value.

Table 5-1. Lateral migration and width change values.

Width Change(m) Mean Lateral migration (m) Mean Lat. Mig/Avg_Widths Dominant Geologic Reach 1955-1983 1983-1996 1955-1983 1983-1996 1955-1983 1983-1996 Lithology Zilpha/Winona -5 4 6 5 0.18 0.14 Clay, Marly Sand Kosciusko 1 7 9 20 0.22 0.49 Sand Cook Mountain 4 9 15 12 0.54 0.43 Sand, Shale, Limestone Cockfield 3 11 11 9 0.33 0.29 Sand Jackson 4 6 8 9 0.22 0.24 Clay, Marl Forest Hill/ Red Bluff clay 10 3 10 15 0.22 0.36 Clay, silty sand Vicksburg/Chickasawhay 2 2 7 7 0.18 0.17 Limestone, some clay Catahoula 19 3 23 21 0.31 0.28 Sand, some clay Pascagoula/ Hattiesburg -7 13 22 19 0.25 0.21 Silty clay, sand Negative values suggest channel narrowing.

Figure 5-11. Geologic map of Clarke County (Gilliland and Harrelson, 1980).

Figure 5-12. Wayne County Geologic map (May et al. 1974)

Bank failure due to loading of coarser, unconsolidated sands was observed in several places, but the erosion-resistant bed and bank material restricts lateral movement, and the channel is considerably deeper. The channel banks were usually as high as 8m.

Figure 5-13 shows percent mud ratios for left and right banks for the nine geologic reaches. At least twelve samples per reach were collected for each reach, except for the

Forest Hill/Red Bluff clay reach where only two samples were collected, both samples collected from the left bank, and the Cook Mountain and Pascagoula/Hattiesburg reaches from which no samples were collected.

Next to the Zilpha Winona reach, the Jackson and Vicksburg/Chickasawhay reaches exhibited the lowest lateral migration of the study period (Table 5-1). The consistently low migration rates observed for these reaches is believed to be because both banks have high, and almost equal percentages of mud. Field observations on the

Chickasawhay show that even in the slow migrating reaches, the highest rates of erosion occur at the cut bank, where stream velocity is highest, and lateral migration is often toward the less cohesive bank. The Jackson in the study area outcrops as indurated marl and clay, with some sand, and its slightly higher migration rate compared to the other two reaches could be due to its midstream position. The Vicksburg/Chickasawhay is mostly limestone and clays. These limestone and shale reaches exhibit lower migration rates and sinuosity than the alluvial reaches.

70 Mud% LB

60 Mud% RB

0 g a in ld ay la n a e on h ur o sko t fi s clay ou b n iu n w h c u ck uff a ies /Wi s o ack sa o C J B ha K d Cat p e Hatt il R / Z a Cook Mo ll/ /Chicka rg oul u st Hi ag e sb ck asc For Vi P

Figure 5-13. Geologic reach mud percent ratios for the Chickasawhay

The Kosciusko reach showed an almost dramatic increase in mean lateral migration for the 1983 to 1996 time interval (Table 5-1). The Kosciusko in the study area outcrops mostly as fine to coarse-grained clayey sand. The Chickasawhay flows an almost straight course for most of this reach and most of the observed channel movements occur in a small part of this reach where the river starts to meander. This portion is most likely the less clayey portion of the reach. The sudden increase in migration rate is probably related to the cut off that occurred during this time period. The Kosciusko and the Jackson reaches had identical mud ratios for their individual banks, although the Kosciusko reach had much more sand on its banks than the Jackson. It is clear that lateral migration is restricted in the Jackson reach because of the cohesive nature of its sediments, and that the coarse sands of the Kosciusko reach allows higher rates of migrations.

The Forest Hill and Red Bluff formations outcrop as ferruginous, sometimes laminated clays, with micaceous sands. Due to inaccessibility at the time of my field

80 visit, no right bank samples were collected for the Forest Hill and Red Bluff formations.

The increase in lateral migration rate between the two time intervals is also attributable to the cut-off that occurred during the latter time interval.

Gupta (1995) studied the Aurunga River in eastern India and found that channel physiography was controlled by a large supply of non-cohesive sand that could be moved as single grains, even during low flows. Erodable sandy reaches like the Kosciusko result in high rates of lateral migration. In the slower migrating reaches, local bank scour and eventual bank failure appear to be the main mechanism for erosion, and thus the slower migration and width change rates (Figure 5-14).

Figure 5-14. Basal scour and bank loading.

Gilvear et al. (2002) studied planform change on the Luangwa River in Zambia, and also found that spatial variations in bank resistance controlled planform change. In the calcium carbonate-rich reaches, erosion was restricted, compared to reaches with recent, alluvial facies. Like Hooke’s (1995) study on laterally migrating rivers in the UK,

they found the main mechanism of bank erosion to be basal scour, followed by block

failure.

Of the nine geologic reaches, the five quickest migrating reaches have all had

meander cut-offs sometime during the 41-year period. The general trend appears to be an increase in lateral migration rates during the time interval that the cut-off occurred, most likely as a result of the increased flow velocities that follow meander cut-offs.

The Catahoula and Pascagoula/Hattiesburg reaches had the highest pre-normalized lateral migration, and the Cook Mountain reach had the highest width normalized lateral migration. Even after lateral migration values were normalized, the Catahoula maintained its high lateral migration, despite being the second widest reach at approximately 75m. In the study area, the Catahoula is exposed as sands and sandstones, with some silt and clay.

The easily erodable sands account for its high pre and post normalization migration rates.

The Cook Mountain on the other hand is exposed as mostly blocky shales with some marl. Most of the observed migration in this reach occurs in the uppermost part of the reach, before the river gets into the blocky shale units. So the higher post normalization rate may be merely a function of this reach’s channel width. The reach had the lowest average channel width of 28m.

The Pascagoula and Hattiesburg formations outcrop as clays, sands and siltstones in the study area. The high pre-normalization migration values and low post- normalization values is most likely also a function of reach channel width. Compared to the Catahoula, the channel in this reach is wider but shorter, and the observed differences in migration rates could be due to local induration. Although no sediment samples were collected from this reach, it would be interesting to compare average mud to sand ratios.

The general trend of increasing lateral migration with increasing channel widths is

shown in Figure 5-15. The 1955 to 1983 time interval had an R2 of 0.68. Reach by reach

variability in factors like discharge and bank vegetation would account for the remaining

32% of variation.

1955-1983 1983-1996

15 y = 0.25x + 0.80 R2 = 0.68 10 y = 0.20x + 3.86 R2 = 0.46

Mean Lateral Migration (m) 5

0 0 102030405060708090100 Average Channel Widths (m)

Figure 5-15. Relationship between channel width and lateral migration.

The variability in channel widths and channel change rates are also controlled

mainly by variations in channel bank geology. Average channel widths increase with increasing reach sand percent, so that the sandstone reaches like the Catahoula and

Kosciusko have wider valleys, while reaches like the Cook Mountain and Zilpha Winona have narrow valleys. Because the wide range of width change and lateral migration values represent the four main bank material types in the study area, differences in the degree of channel instability in say, two reaches with similar bank material would depend on the factors like jointing and weathering, or frequency of lop cut-off in the sinuous reaches, and breakage along bedding planes.

The general direction of channel meandering is southeast, often toward the left

bank, and is controlled by bank resistance. In areas where one bank was much more

cohesive than the opposite bank, channel movements were always toward the least

resistant/concave bank, this is often where stream velocity is highest and more erosive

work can be done. The main mechanism of migration appears to be through this erosion

of the outer banks, and deposition on the inner banks. The channel narrows when more deposition than erosion occurs, which might have been the case in the Zilpha and

Winona, and Pascagoula and Hattiesburg reaches during the 1955 to 1983 interval.

Conclusions

The Chickasawhay, apart from recreation purposes, is almost completely free of

human intervention. Fieldwork and GIS technology have however revealed significant

changes in channel positions and dimensions. The highest bank instability rates were

observed for the sandstone/floodplain reaches. Limestone/incised reaches had the lowest

instability rates. The degree of channel instability is determined largely by the degree of

bank material lithification, but reach-by-reach variability exists as a result of reach

position with respect to other reaches. In the lithified reaches, the presence of planes of weakness from which erosion work can begin, also play an active role in determining the

degree of bank stability. In the non-lithified reaches, the presence of grass with forest

appears more effective in maintaining bank stability than forest alone, and structural

controls affect channel pattern, especially in the jagged reaches.

From the confluence of the Okatibbee and Chunky Creeks at Enterprise, the

Chickasawhay flows 264km before joining the Leaf River to form the Pascagoula in

George County. Whether on the basin scale, or on a reach-by-reach scale, the magnitude

of channel change recorded in this study was significant. Having observed the

devastations to both government and private property during field visits, these changes in channel positions and dimensions are big problems that property owners have to deal

with on a yearly basis.

Channel instability is always as a result of a river adjusting to changes in its

environment. It could be changes in discharge, or available sediment load. These

adjustments come in the form of erosion and deposition until a new equilibrium is

achieved. On the Chickasawhay, channel adjustments have primarily taken the form of

increasing rates of lateral migration, channel widening at times, and more infrequently,

channel narrowing.

GIS technology has enabled the collection, storage and manipulation of large

amounts of data in a cost effective and time efficient manner. By allowing the

combination and analysis of geologic, geographic and historical data, environmental

monitoring and research is made more effective. The use of remotely sensed data and a

GIS cannot take the place of field investigations and sampling however, and a

combination of the two approaches is most reliable and thorough.

The objective of this study was to assess the effect of bank geology on the selective

channel instability observed on the Chickasawhay. Bank instability on the Chickasawhay

is a danger not only to bridges, but to homesteads built close to the channel, most of

which are inherited property passed down through generations, and systematically being

lost.

Of all the major rivers and creeks that make up the Pascagoula watershed, the

Chickasawhay and its major tributary the Buckatunna, have had the least amount of

geomorphic work or environmental monitoring. This work is therefore important not just

because of the calculations of lateral migration and channel change rates, but also

85 because it adds to what little work that has been done. Results from this study will help both government and local property owners to better understand some of the processes involved in channel bank migration and bank instability. More work needs to be done however, with shear stress and bank erodibility tests to determine if there are any critical bank failure values for the various lithologies exposed on the Chickasawhay. Because I was unable to collect samples from all the reaches, further research should focus on creating a more complete particle size database for the Chickasawhay.

In spite of the reach by reach variability and processes observed, historical planform changes like the ones seen on the Chickasawhay involve the entire watershed as a system. Upstream processes will affect downstream processes at both the basin and reach scale.

APPENDIX A MAPS

Figure A-1. Legend for land cover maps

86 87

Figure A-2. Land cover map for Wayne County (USGS 1992).

Figure A-3. Land cover map for Clarke County (USGS 1992).

Figure A-4. Land cover map for Greene County (USGS 1992).

Figures A5 to A10 show stable and unstable reaches on the Chickasawhay

Figure A-5. Stable reach, Clarke County.

Figure A-6. Channel movements in Clarke County.

Figure A-7. Stable and unstable reaches, Clarke County.

Figure A-8. Channel movements in Wayne County.

Figure A-9. Stable reach, Wayne County.

Figure A-10. Channel movements in Greene County.

Figure A-11. Index Map for the Chickasawhay River, courtesy Mossa and Coley (2004).

Figure A-12. Legend for Figures A-13 and A-14

Figure A-13. Close up of Clarke County geologic map (Gilliland and Harrelson, 1980).

Figure A-14. Close up of Clarke County geologic map (Gilliland and Harrelson, 1980).

100

Figure A-15. Legend for Figures A-16 and A-17

101

Figure A-16. Close up of Wayne County geologic map (May et al. 1974).

102

Figure A-17. Close up of Wayne County geologic map (May et al. 1974).

103

Figure A-18. Coverage tolerances used in digitizing.

Figure A-19. Polygon attribute table for the digitized 1990s coverage.

104

Figure A-20. Creating transects in ArcView

Figure A-21. Measuring straight-line distance in Arcmap

105

Figure A-22. Converting measured values to raster for calculation

Figure A-23. Calculating straight-line distance between 50s and 80s centerlines

106

Figure A-24. Sampling locations

APPENDIX B TABLES

Table B-1. Field observations Sample # Location Slope Flow (ft/sec) Bank Features and Land use (estimated) Vegetation

XS1-LB 32 09.73’N 30° 2ft/sec Mixed vegetation Signs of cattle (hooves) 88 48.83’W 6m high XS1-RB 32 09.75’N 40° 2ft/sec Dense. Better root Forested 88 48.85’W 8m high network. XS2-LB 32 09.46’N 40° 2ft/sec A few areas of bank Break from forest to pasture 88 48.69’W failure XS2-RB 50° 2ft/sec Grassy bank Break from grassy to forest

XS3-LB 32 09.15’N 40° 2ft/sec Dense vegetation. Forested. 88 48.58’W Wider, channel XS3-RB 32 09.18’N 40° 2ft/sec Dense vegetation Forested. 88 48.60’W XS4-LB 32 08.90’N 80° 2ft/sec Dense vegetation. Forested 88 48.65’W

XS4-RB 32 08.93’N 30° 2ft/sec Dense vegetation Forested. 88 48.67’W Woody debris XS5-LB 32 06.39N 30° 2.5ft/sec Sand bar on left 88 48.03’W 2m high. bank. XS5-RB 32 06.41N 60° 2.5ft/sec Dense vegetation. Forested 88 48.06’W 3m high mid meander bend XS6-LB 32 06.31’N 2.5ft/sec Vegetated sand bar. Break to forest behind bar 88 48.01’W ~4m high XS6-RB 32 06.33’N 70° 2.5ft/sec Bedding planes on Forested bank. 88 48.04’W 5m high cut bank. XS7-LB 32 06.14’N 40° 2.5ft/sec Dense vegetation Forested 88 47.85’W 4m high. XS7-RB 32 06.16’N 60° 2.5ft/sec Dense vegetation Forested. 88 47.87’W 5m high XS8-LB 32 06.056’N 88 47.79’W XS8-RB 32 06.058’N 88 47.81’W XS9-LB 32 03.60’N 60° 3ft/sec Dense vegetation Forested 88 44.74’W 6m high XS9-RB 32 03.62’N 45° 3ft/sec Woody, not too Veg. break atop sand bar 88 44.76’W 5m high dense. XS10-LB 32 03.26’N 60° 3ft/sec Steep banks, bedrock Forested 88 44.49’W 5m high XS10-RB 32 03.28’N 60° 3ft/sec Steep banks. Erosion Forested 88 44.51’W 5m high resistant XS11-LB 32 03.13’N 45° 3ft/sec Middle of sharp bend Shrubby-forest 88 44.22’W 6m high XS11-RB 32 03.15’N 60° 3ft/sec lithified clay bank Forested atop bank. 88 44.25’W 9m high XS12-LB 32 02.729’N 70° 3ft/sec Veg. break from Break from shrubs to forest. 88 44.34’W 7m high. LEW to bank top XS12-RB 32 02.749’N 60° 3ft/sec Bank material less Shrubs to forest 88 44.37’W 7m high cohesive. XS13- 31 33.241’N 40° 1.5ft/sec Dense vegetation on Forested RB* 88 33.16’W 6m high both banks XS14-LB* 31 40.883’N 40° 1.5ft/sec Mixed vegetation Forest 88 41.01’W 7m high XS15-LB* 31 50.929’N 35° 3ft/sec Dense vegetation Forested 88 41.37’W 5m high XS16- 32 02.555’N 40° 2.5ft/sec Mixed vegetation Break from grassy to forest. RB* 88 44.65’W 5m high

108 109

Table B-2. Grain size analysis results for water line and mid-bank samples Sample # FRACTIONS % weight Sample # FRACTIONS % weight xs1-LB-wl Sand 78 Silt 17 xs7-RB-wl Sand 79 Clay 4 Silt 12 Clay 8 xs1-RB-wl Sand 58 Silt 25 xs8-LB-wl Sand 74 Clay 17 Silt 9 Clay 18 xs2-LB-wl Sand 75 Silt 12 xs8-RB-wl Sand 96 Clay 12 Silt 4 Clay 0 xs2-RB-wl Sand 79 Silt 4 xs9-LB-wl Sand 78 Clay 16 Silt 15 Clay 7 xs3-LB-wl Sand 64 Silt 24 xs9-RB-wl Sand 85 Clay 12 Silt 8 Clay 8 xs3-RB-wl Sand 84 Silt 0 xs10-LB-wl Sand 85 Clay 16 Silt 0 Clay 15 xs4-LB-wl Sand 22 Silt 8 xs10-RB-wl Sand 85 Clay 70 Silt 11 Clay 4 xs4-RB-wl Sand 10 Silt 42 xs11-LB-wl Sand 9 Clay 48 Silt 50 Clay 41 xs5-LB-wl Sand 92 Silt 0 xs11-RB-wl Sand 80 Clay 8 Silt 13 Clay 7 xs5-RB-wl Sand 89 Silt 8 xs12-LB-wl Sand 1 Clay 4 Silt 57 Clay 42 xs6-LB-wl Sand 96 Silt 0 xs12-RB-wl Sand 84 Clay 4 Silt 9 Clay 7 xs6-RB-wl Sand 25 Silt 50 xs13-LB-wl Clay 25 xs13-RB-wl Sand 71 xs7-LB-wl Sand 88 Silt 13 Silt 0 Clay 17 Clay 12

110

Sample # FRACTIONS % weight Sample # FRACTIONS % weight xs14-LB-wl Sand 40 xs21-LB-wl Sand 52 Silt 38 Silt 29 Clay 21 Clay 19 xs14-RB-wl xs21-RB-wl Sand 91 Silt 4 Clay 4 xs15-LB-wl Sand 73 Silt 14 xs22-LB-wl Sand 50 Clay 14 Silt 29 Clay 21 xs15-RB-wl xs22-RB-wl Sand 72 xs16-LB-wl Silt 28 Clay 0 xs16-RB-wl Sand 79 Silt 12 xs23-LB-wl Sand 88 Clay 8 Silt 8 Clay 4 xs17-LB-wl Sand 71 Silt 29 xs23-RB-wl Sand 29 Clay 0 Silt 41 Clay 30 xs17-RB-wl Sand 72 Silt 20 xs24-LB-wl Sand 82 Clay 8 Silt 7 Clay 11 xs18-LB-wl Sand 96 Silt 0 xs24-RB-wl Sand 46 Clay 4 Silt 18 Clay 36 xs18-RB-wl Sand 61 Silt 23 xs13a-LB-wl Sand 92 Clay 16 Silt 0 Clay 8 xs19-LB-wl Sand 43 Silt 33 xs13a-RB-wl Sand 1 Clay 24 Silt 47 Clay 52 xs19-RB-wl Sand 23 Silt 38 xs14a-LB-wl Sand 10 Clay 38 Silt 43 Clay 48 xs20-LB-wl Sand 36 Silt 41 xs14a-RB-wl Sand 96 Clay 23 Silt 0 Clay 4 xs20-RB-wl Sand 59 Silt 18 Clay 23

111

Sample # FRACTIONS % weight Sample # FRACTIONS % weight xs1-LB-mb Sand 93 xs7-RB-mb Sand 81 Silt 4 Silt 11 Clay 4 Clay 7 xs1-RB-mb Sand 88 xs8-LB-mb Sand 52 Silt 8 Silt 28 Clay 4 Clay 20 xs2-LB-mb Sand 59 xs8-RB-mb Sand 97 Silt 26 Silt 0 Clay 15 Clay 3 xs2-RB-mb Sand 54 xs9-LB-mb Sand 61 Silt 30 Silt 26 Clay 15 Clay 13 xs3-LB-mb Sand 40 xs9-RB-mb Sand 50 Silt 35 Silt 32 Clay 25 Clay 18 xs3-RB-mb Sand 64 xs10-LB-mb Sand 48 Silt 28 Silt 36 Clay 8 Clay 16 xs4-LB-mb Sand 56 xs10-RB-mb Sand 58 Silt 29 Silt 17 Clay 15 Clay 25 xs4-RB-mb Sand 66 xs11-LB-mb Sand 33 Silt 21 Silt 42 Clay 13 Clay 25 xs5-LB-mb Sand 64 xs11-RB-mb Sand 93 Silt 25 Silt 3 Clay 10 Clay 3 xs5-RB*mb Sand 74 xs12-LB-mb Sand 8 Silt 11 Silt 61 Clay 15 Clay 31 xs6-LB-mb Sand 89 xs12-RB-mb Sand 83 Silt 7 Silt 9 Clay 4 Clay 9 xs6-RB-mb Sand 62 xs13-LB-mb Sand Silt 27 Silt Clay 12 Clay xs7-LB-mb Sand 88 xs13-RB-mb Sand 45 Silt 0 Silt 25 Clay 12 Clay 29

112

Sample # FRACTIONS % weight Sample # FRACTION% weight xs14-LB-mb Sand 80 xs21-LB-mb Sand 25 Silt 12 Silt 43 Clay 8 Clay 32 xs14-RB-mb xs21-RB-mb Sand 85 Silt 8 xs15-LB-mb Sand 93 Clay 8 Silt 0 Clay 7 xs22-LB-mb Sand 70 Silt 17 xs15-RB-mb Clay 13 xs16-LB-mb Sand xs22-RB-mb Sand 89 Silt Silt 11 Clay Clay 0 xs16-RB-mb Sand 42 xs23-LB-mb Sand 89 Silt 39 Silt 11 Clay 19 Clay 0 xs17-LB-mb Sand 16 xs23-RB-mb Sand 27 Silt 51 Silt 42 Clay 34 Clay 31 xs17-RB-mb Sand 60 xs24-LB-mb Sand 88 Silt 27 Silt 12 Clay 13 Clay 0 xs18-LB-mb Sand 30 xs24-RB-mb Sand 45 Silt 44 Silt 11 Clay 26 Clay 44 xs18-RB-mb Sand 49 xs13a-LB-mb Sand 74 Silt 34 Silt 13 Clay 17 Clay 13 xs19-LB-mb Sand 60 xs13a-RB-mb Sand 11 Silt 22 Silt 47 Clay 18 Clay 42 xs19-RB-mb Sand 23 xs14a-LB-mb Sand 13 Silt 45 Silt 37 Clay 32 Clay 51 xs20-LB-mb Sand 78 xs14a-RB-mb Sand 66 Silt 7 Silt 23 Clay 14 Clay 11 xs20-RB-mb Sand 87 Silt 7 Clay 7

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Table B-3. Annual stream flow data (USGS 2004)

leakesville Enterprise USGS 02478500 USGS 02477000 Year Annual Stream flow Year Annual Stream flow (cubic feet/sec) (cubic feet/sec)

1955 1,715 1955 587 1956 2,455 1956 1,162 1957 2,679 1957 880 1958 4,197 1958 1,200 1959 3,337 1959 912 1960 3,406 1960 994 1961 7,606 1961 2,318 1962 3,585 1962 1,186 1963 1,320 1963 407 1964 4,230 1964 1,402 2,762 1965 1965 807 3,971 1966 1966 1,135 2,145 1967 1967 707 1968 2,245 1968 793 1969 3,015 1969 894 1970 2,292 1970 798 1971 4,974 1971 1,698 1972 3,676 1972 1,093 1973 5,633 1973 2,043 1974 6,022 1974 1,949 1975 6,037 1975 1,870 3,783 1976 1976 1,245 1977 4,892 1977 1,845 1978 2,888 1978 853 7,062 1979 1979 2,410 6,828 1980 1980 2,244 2,226 1981 1981 741 3,425 1982 1982 1,170 7,149 1983 1983 2,459 3,466 1984 1984 986 2,950 1985 1985 908 2,431 1986 1986 660 4,073 1987 1987 1,277 2,372 1988 1988 754 4,740 1989 1989 1,703 5,830 1990 1990 1,932 5,382 1991 1991 1,722 3,726 1992 1992 1,043 4,352 1993 1993 1,569 1994 4,132 1994 1,603 1995 3,437 1995 1,286 1996 3,200 1996 1,079 gage datum 51.13 ft above sea level gage datum 207.62 ft asl NGVD 29 NGVD 29

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Table B-4. GPS field locations.

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BIOGRAPHICAL SKETCH

Marilyn was born in Warri, Nigeria. She graduated from the University of Benin with a B.Sc in geology in 1994, and spent the next year in national service under the government run National Youth Service Corps program.

From 1996 to 1998, she wrote and published poetry and children’s books, before moving to the US. She hopes to work as an environmental geologist for a while, and to one day work as a consultant in her native country.

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