Controls on the sedimentation and morphology of an oxbow lake along the Trinity River, Texas, USA
Abstract
Oxbow lakes and their subsequent filling by sediment play an important role in the dynamics of channel self-confinement and in the evolution of meander belts. In spite of this, research lacks in characterizing the rates and spatial changes in sediment deposition and bed aggradation along the limbs of oxbow lakes. The aim of this study is to understand the effect that floods have on oxbow sedimentation. Here we document the filling history of an oxbow lake along the Trinity River that has been cut off for 23 years. We observe significant flooding events on the river through analysis of aerial photographs and river hydrographs for the years after the oxbow cutoff, which occurred in 1995. Between 2011 and 2015, there were 76 days of major flooding spread out over 5 events, one of which lasted >55 days. Between 2015 and 2017, there were another 6 events totaling 146 days of flooding. Using time-lapse airborne lidar collected in 2011, 2015, and 2017, we observed varying amounts of aggradation within the downstream plug; thus allowing us to quantify the effects of different magnitudes of floods. The downstream plug shows 1.2x104 m3 of aggradation from 2011 to 2015, and 1.3x104 m3 of aggradation from 2015 to 2017. Meanwhile, only very small amounts of aggradation were observed at the upper limb, which had already been filled with sediment. Trenches dug into the downstream plug reveal 2-m high foresets that dip into the lake. This sediment accumulation is primarily composed of climbing-ripple stratification interpreted as suspension deposits that have been reworked by low rates of bedload transport. Grain size samples from the trenches document a well-sorted distribution of very fine-to fine sand with an average D50 of 120 μm. Chirp seismic lines were collected along the entire oxbow length to resolve sedimentation patterns within the lake. These transects reveal low-angle inclined strata prograding into the lake from both the upper and lower oxbow limbs. Our data set is intended to quantitatively describe the range of filling styles in oxbow lakes and the effect of floods on their filling histories.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP21D2290N
- Keywords:
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- 1815 Erosion;
- HYDROLOGYDE: 1820 Floodplain dynamics;
- HYDROLOGYDE: 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGY