1a.Objectives (from AD-416)
To collect field data of fluvial sediment deposition in the Tobitubby and Hurricane valleys in North Mississippi and to relate historic changes since the 1930s in fluvial sediment deposition to changes in land use.
1b.Approach (from AD-416)
A re-survey will be made of valley cross sections in selected catchments of the Tobitubby (22 km2) and Hurricane (12 km2) watersheds in northern Mississippi which were first surveyed by the U.S. Soil Conservation Service between 1935 and 1941. Several (7) of the 1930's survey beginning and end markers were found in a February 2008 reconnaissance. These sites till be re-surveyed with an RTK-GPS and automatic leveling equipment. Data on historic land use change for both watersheds will be collected from topographic maps, air photographs, and census data. Changes between on-the-ground surveys will be related to land use changes.
During the 1930's and 1960's, detailed topographic cross-valley profiles were measured at 60 locations in the Hurricane and Tobitubby river catchments, Lafayette County, Mississippi. Resurvey of the original profiles enabled scientists to calculate changes in sediment storage in these valley systems in relation to changes in land cover over the same time period. Within the context of this study, 25 of the original profiles were resurveyed in October-November 2008 with automatic leveling and GPS-devices. All profiles are located in the main valley of Hurricane and Tobitubby Creek or in the main tributary of Tobitubby, i.e. Goose Creek. Both catchments are situated in close proximity to Oxford, MS. The results show a steady decline in alluvial sedimentation through time for Hurricane Creek, which can be explained by the large reforestation in this catchment. For Tobitubby Creek, however, sedimentation increased again after 1968, even to much higher levels than what was observed during the main agricultural period (1830-1937). These higher rates are not spatially homogenous, though. High rates can be found near Lake Sardis (backwater effect) and at places where beaver activity is high. At other locations, sedimentation decreased. Through time, we also observed an increase in river channel depth and width. The rate of channel change was higher in the period 1937-1968, i.e. following the reforestation period, compared to the period 1968-2008. Monitoring activities included face to face meetings, phone calls, and e-mail messages.