CHANNEL AND BANK STABILITY OF BIG BLACK RIVER CANAL TRIBUTARY AT U.S. HIGHWAY 82 AT STEWART, MONTGOMERY COUNTY, MISSISSIPPI by K. Van Wilson and D. Phil Turnipseed Prepared in cooperation with the MISSISSIPPI STATE HIGHWAY DEPARTMENT Jackson, Mississippi 1989 Open-File Report 89-35 TABLE OF CONTENTS Definition of terms Abstract Introduction     Purpose and scope     General description of Big Black River Canal tributary     Channel modifications to Big Black River     Acknowledgments Channel bed     Botanical evidence of widening     Stability analysis     Widening analysis Conclusions References ILLUSTRATIONS 1. Map showing the location of Big Black River Canal tributary at U.S. Highway 82 at Stewart, MS 2. Channel-bed profiles for Big Black River Canal tributary in the vicinity of U.S. Highway 82 at Stewart, MS 3. Estimated patterns of degradation on Big Black River Canal tributary at U.S. Highway 82 at Stewart, MS 4. Cross section showing critical failure surfaces for channel banks on Big Black River Canal tributary 100 feet downstream of U.S. Highway 82 at Stewart, Mississippi 5. Existing channel cross section showing near-future widening for Big Black River Canal tributary, 75 feet upstream of U.S. Highway 82 at Stewart, MS 6. Existing channel cross section showing near-future widening for Big Black River Canal tributary, 100 feet downstream of U.S. Highway 82 at Stewart, MS 7. Existing channel cross section showing near-future widening for Big Black River Canal tributary, 500 feet downstream of U.S. Highway 82 at Stewart, MS TABLES 1. Channel-bed degradation on Big Black River Canal at the mouth of the tributary 2. Channel-bed degradation on Big Black River Canal tributary at U.S. Highway 82 at Stewart, MS 3. Shear-strength properties and bulk unit weights of soils as determined from borehole tests ABSTRACT The channel of Big Black River Canal tributary at the site of the proposed reconstruction of the U.S. Highway 82 crossing at Stewart, Mississippi, has degraded about 8 1/2 feet since the construction of the Big Black River Canal in about 1928. Channel degradation at the mouth of the tributary has totaled about 10 feet during the period. Several bank failures in the vicinity of the highway crossing have occurred within the past 5 years and the channel continues to degrade and widen in response to the degradation of Big Black River Canal that was partially excavated in about 1928 and further modified in 1939. Rates of channel degradation and widening--as determined from channel descriptions, discussions with local residents, and botanical evidence along the banks--were used in conjunction with soil properties to estimate probable future channel degradation and widening through the year 2010. By assuming that channel-bed elevations can be expressed as a power function with time, additional channel degradation through the year 2010 is expected to be about 1/2 foot at the highway crossing and at the mouth of the tributary. The channel top-bank width is expected to increase about 20 feet just downstream of the highway crossing in the next 5 to 10 years, based on the assumption that the present rate of widening continues. These projections are based on the assumption that no additional channel modifications and no unusually large and destructive flooding will occur by the year 2010. 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.