LATERAL MOVEMENT AND STABILITY OF CHANNEL BANKS NEAR TWO HIGHWAY CROSSINGS IN THE PASCAGOULA RIVER BASIN IN MISSISSIPPI by D. Phil Turnipseed Prepared in cooperation with the MISSISSIPPI DEPARTMENT OF TRANSPORTATION Jackson, Mississippi 1993 Water-Resources Investigations Report 93-4131 TABLE OF CONTENTS Abstract Introduction     Purpose and scope     Description of the study areas         Chickasawhay River at State Highway 63 at Leakesville         Leaf River at U.S. Highway 98 near McLain     Acknowledgments Determination of lateral bank movement     Aerial photography mapping     Mapping error     Sinuosity computation     Geographic information system Channel stability     Soil properties     Channel-bank geometry Analysis of channel characteristics     Bank movement     Bank stability     Channel geometry Summary References ILLUSTRATIONS 1. Map showing location of study sites in the Pascagoula River Basin in Mississippi 2. Example of tops of channel banks and apparent channel shift caused by errors introduced during mapping and digitizing for the Pearl River in the vicinity of U.S. Highway 84 near Monticello, Mississippi 3. Cross sections from soundings made during historical and recent discharge measurements at the existing State Highway 63 crossing of the Chickasawahay River at Leakesville, Mississippi 4. Cross sections from soundings made during historical and recent discharge measurements at the existing U.S. Highway 98 crossing of the Leaf River near McLain, Mississippi 5. Map showing tops of channel banks from 1942 to 1985 in the vicinity of the existing and proposed State Highway 63 crossing of the Chickasawhay River at Leakesville, Mississippi 6. Map showing tops of channel banks from 1942 to 1985 in the vicinity of the existing and proposed U.S. Highway 98 crossing of the Leaf River near McLain, MS 7. Graph showing change in sinuosity with time near the U.S. Highway 98 crossing of the Leaf River near McLain and the State Highway 63 crossing of the Chickasawhay River at Leakesville, MS 8. Cross section showing probable critical failure surfaces for channel banks at the existing State Highway 63 crossing of the Chickasawhay River at Leakesville, MS 9. Cross section showing probable critical failure surfaces for channel banks at the existing U.S. Highway 98 crossing of the Leaf River near McLain, MS ABSTRACT The meandering of alluvial streams has caused localized channel-bank instability that has endangered bridge structures in Mississippi. Knowledge of the movement of channel banks in the vicinity of bridge crossings is important in bridge design. The lateral movement of channel banks at the existing and proposed crossings of both State Highway 63 at the Chickasawhay River at Leakesville and U.S. Highway 98 at the Leaf River near McLain in the Pascagoula River Basin was studied by mapping meanders at various times and measuring channel geometry and soil strength at these sites. Historical aerial photography was used to determine cartesian coordinates of tops of channel banks, channel-bank widths and lengths, and land use in the stream drainage basins, as well as to map the lateral movements of channel banks at the two study sites. Photographic data were quantified and entered into a geographic information system. Historical channel meandering at the sites was studied to determine patterns of change. Also, change in sinuosity (river length/valley length) was computed through time. General and site-specific soils data and channel geometry were collected at both study sites. Site-specific soils data, such as shear-strength properties of bank materials, in combination with hydraulic data, were used to compute exisiting channel-bank stability and to determine critical failure surfaces near the existing and proposed crossings of the Chickasawhay and Leaf Rivers. Although no recent significant lateral movement of channel banks was detectd at the existing crossings, movement was detected upstream from both proposed alignments. Channel cross sections obtained at the existing State Highway 63 crossing of the Chickasawhay River between 1942 and 1990 indicated about 7 feet of scouring of the thalweg at the bridge. As much as 8 feet of scour of the channel bed was indicated by temporal changes in channel cross sections at the existing U.S. Highway 98 crossing of the Leaf River. Change in sinuosity was not significant for either study site. LizardTech's Djvu plug-in is needed to view these reports. CLICK HERE TO VIEW THE ENTIRE REPORT For questions or comments, contact K. Van Wilson.