Flow patterns and morphology of a prograding river delta
Tóm tắt
The transition of flow between laterally confined channels and the unchannelized delta front controls the morphodynamic evolution of river deltas but has rarely been measured at the field scale. We quantify flow patterns and bathymetry that define the evolution of the subaqueous delta front on the Wax Lake Delta, a rapidly prograding delta in coastal Louisiana. A significant portion of flow (∼59%) departs the channel network over lateral channel margins as opposed to the downstream channel tips. Bathymetric surveys and remotely sensed estimates of flow direction allow spatial changes in flow velocity to be quantified and patterns of erosion and deposition to be estimated. Shallowing along channel margins produces spatial acceleration and erosion. Lateral spreading, deceleration, and deposition occur within three to eight channel widths outside of the channel margins. In interdistributary bays, the shape of each flow path is constrained by “nourishment boundaries” that separate the outflows from neighboring channels. Deposit elevation decreases with a basinward slope of 2.4 × 10−4 with distance from a channel margin along any flow path, regardless of the channel or location that flow departed the network. Bathymetric depressions called “interdistributary troughs” form along nourishment boundaries where flow paths are the longest and deposit elevation is correspondingly low. We conclude that the deposit morphology exerts a strong control on bathymetric evolution and that interaction between neighboring channels and even neighboring deltas can influence delta front morphology.
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Tài liệu tham khảo
Alpers W., 2004, Synthetic Aperture Radar Marine User'S Manual, 263
Bates C. C., 1953, Rational theory of delta formation, AAPG Bull., 37, 2119
Hack J. T., 1957, Studies of Longitudinal Stream Profiles in Virginia and Maryland , Geol. Surv. Prof. Pap.
Kundu P. K., 2011, Fluid Mechanics
Morisawa M., 1985, Models in Geomorphology, 239
NOAA(2012) Tides and Currents Lawma Amerada Pass LA. [Available athttp://tidesandcurrents.noaa.gov/data_menu.shtml?stn=8764227%20Lawma%20Amerada%20Pass%20LA&Historic+Tide+Data.]
Roberts H., 2003, An embryonic major delta lobe: A new generation of delta studies in the Atchafalaya‐Wax Lake delta system, Gulf Coast Assoc. Geol. Soc. Trans., 53, 690
Smart J. S., 1971, Quantitative Properties of Delta Channel Networks
U.S. Geological Survey (USGS)(2012) National Water Information System data available on the World Wide Web (Water Data for the Nation). [Available athttp://waterdata.usgs.gov/nwis/] Accessed 2 Nov. 2012.
Wellner R., 2005, Jet‐plume depositional bodies—The primary building blocks of Wax Lake Delta, Gulf Coast Assoc. Geol. Soc. Trans., 55, 867