Development and morphology of point bars in tidal rivers, observations from Sapelo and the Altamaha River, GA
Abstract
Many tidal creeks and rivers exhibit bars associated with meander bends. However, hydrodynamic and morphodynamic studies of these point-bars are scarce, compared with the extensive studies of fluvial-point bars. The few studies that have been undertaken suggest significant differences between tidal bars and their fluvial counterparts, including low rates of channel migration, a unique planform morphology resulting from the bi-directional tidal flows and tidal asymmetry, and variation in stage-discharge behavior. We examine point-bars in two closely situated estuaries on the Georgia coast: the Altamaha and Sapelo. Both sites are meso-tidal; however, the Altamaha has significant fluvial input, whereas the Sapelo creeks have minimal fluvial input. Both sites exhibit mixed sand-mud point bars of various sizes. However, sites dominated by fluvial processes are coarser-grained and contain a higher percentage of sand. Velocity measurements from vessel-mounted and moored acoustic Doppler current profilers record the separation of flood and ebb flows to either side of the tidal bars, which results in a residual circulation over their surface. Large bedforms with opposing migration directions are observed on either side of the bar, suggesting that each side of the channel experiences a separate sediment transport regime. Shallow seismic data at two resolutions (Boomer and Chirp) indicate that the internal architecture of the tidal bars consists of lateral accretion surfaces with multi-directional strike orientations and dips, suggesting a more complex pattern of growth and development. We compare and contrast the hydrodynamics and the resulting morphologies of the bars and identify differences between fluvially-influenced and purely tidal environments. This data set also allows us to examine the hypothesis that these forms are scale invariant by examining a wide range of bars in both large and small channels.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMEP42B..04H
- Keywords:
-
- 1825 HYDROLOGY / Geomorphology: fluvial;
- 4200 OCEANOGRAPHY: GENERAL;
- 4235 OCEANOGRAPHY: GENERAL / Estuarine processes