Downstream Variation of Bankfull Geometry for the Continental and Overseas Hydro-Eco-Regions of France.
Abstract
Bankfull channel geometry is a fundamental and widely used concept in hydrology, fluvial geomorphology, and ecosystem studies. We develop and compare downstream hydraulic geometry relationships for bankfull channel width (w) and depth (d) as a function of drainage area A, respectively w=aAb (DHGwA) and d=cAf (DHGdA), for the 12 of the 21 French Hydro-Eco-Regions which are defined in terms of climate, topography and geology. The models have been built from a database (CARHYCE) that includes 1500 river reaches for which a unique standardized field protocol was used. River reach morphology was described based on a survey of 15 cross-sections spaced at intervals of one bankfull width. Sediment size and riverine vegetation were also measured and characterized. This database covers a wide range of French river diversity in terms of geomorphic types and anthropogenic impacts. Sampled stream reaches range from 1 to 70 000 km² in drainage area, 1 to 320 m in bankfull width and 0.3 to 8.5 m in bankfull depth. Approximately 500 poorly disturbed reaches were identified from several indices of disturbance at reach and basin scale (large dams, urbanization, channelization, etc.). For these reference sites, drainage areas display strong power-law relationships with both the width and the depth in most Hydro-Eco-Regions, with coefficients of determination (R²) ranging from 0.73 to 0.91 for DHGwA and from 0.57 to 0.77 for DHGdA (p-value < 0.001, t-test). The DHG exponent b and f ranges from 0.36 to 0.5 for DHGwA and from 0.21 to 0.3 for DHGdA. This implies that widths increase more strongly than depths with increasing drainage areas. The relative position of the models are compared to the national model and discussed with regard to the geologic, climatic and topographic characteristics. In Hydro-Eco-Regions which exhibit poor DHG relationships, the role of spatial variability in natural controls (climate, topography and geology) is discussed. Finally, reaches identified as potentially disturbed by human activities are compared to the reference models.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP51A0854T
- Keywords:
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- 1824 Geomorphology: general;
- HYDROLOGYDE: 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1856 River channels;
- HYDROLOGYDE: 1862 Sediment transport;
- HYDROLOGY