What drives riparian vegetation encroachment in braided river channels at patch to reach scales? Insights from annual airborne surveys (Drôme River, SE France, 2005-2011)

Ecohydrology ◽  
2017 ◽  
Vol 10 (8) ◽  
pp. e1886 ◽  
Author(s):  
Bianca Räpple ◽  
Hervé Piégay ◽  
John C. Stella ◽  
Dimitri Mercier
Keyword(s):  
Riparian Vegetation ◽  
Braided River ◽  
River Channels ◽  
Vegetation Encroachment ◽  
Se France

scholarly journals Influence of flood regime on riparian vegetation dynamics in rivers with alternate bars

2018 ◽  
Vol 40 ◽  
pp. 02025 ◽  
Author(s):  
Camille Jourdain ◽  
Nicolas Claude ◽  
Germain Antoine ◽  
Pablo Tassi ◽  
Florian Cordier
Keyword(s):  
Vegetation Cover ◽  
Riparian Vegetation ◽  
Steady Increase ◽  
River Channels ◽  
Vegetation Development ◽  
Flood Peak ◽  
Channel Dynamics ◽  
Alternate Bars ◽  
Morphodynamic Modeling ◽  
Vegetation Encroachment

Throughout the 20th century, many rivers worldwide have undergone important riparian vegetation encroachment, which can be problematic in terms of flood risks and biodiversity. Nowadays, controlled floods is often considered as a management option in anthropized rivers, with the aim of limiting vegetation encroachment within river channels, as well as maintaining a diverse habitat by reactivating natural channel dynamics. In this context, this study aims at investigating the influence of different flood regimes on river bar vegetation development and dynamics, focussing on alternate bar systems which are typically found in embanked streams. This question has been addressed through two-dimensional bio-morphodynamic modeling of a simplified gravel bed river reach. Four hydrological scenarios with different flood peak discharges have been run for 50 years. For all scenarios, a steady increase in vegetation cover strongly impacts the evolution of bar morphology, until a relatively stable equilibrium is reached after one to three decades. Numerical results suggest that vegetation development on bars is associated to an increase in bar wavelength and a decrease in bar width. Higher peak flood discharges lead to narrower and longer bars, and a longer adjustment duration. When vegetation cover is fully developed, interannual flood variability seems crucial to maintain bedform and vegetation turnover.

scholarly journals DEVELOPMENT OF A FLOOD RISK ASSESSMENT MODEL FOR A BRAIDED RIVER SYSTEM

2017 ◽  
pp. 25
Author(s):  
Mustafa Kemal Cambazoglu ◽  
Cheryl Ann Blain
Keyword(s):  
Risk Management ◽  
Flood Risk ◽  
Channel Model ◽  
River System ◽  
Flood Risk Management ◽  
High Flow ◽  
Water Levels ◽  
Pearl River ◽  
Braided River ◽  
River Channels

The aim of this study is to construct a modeling system that will assist flood risk management strategies in a coastal plain braided river system. The model configuration consists of a hydrodynamic model (ADCIRC) of the river basin that receives tidal forcing at the open boundary and river discharge forcing at upstream flux boundary. An unstructured mesh model resolving the Pearl River channels at higher resolution from the coastline to approximately 75km inland to upstream reaches of the river has been constructed. The modeling system produces water levels and currents throughout the Lower Pearl River Basin. Initial sensitivity analysis efforts on the channel model include consideration of low-flow, average-flow, and high-flow scenarios. Model results were found to be slightly sensitive to slope of river channels and bottom friction to control stability in predictions. The model results were shown to be highly sensitive to the bathymetry of the model that controls the discharge capacity of the narrow river channels and the channel model resulted in elevated currents and water levels under high flow conditions. A channel discharge capacity analysis was conducted and the results showed the need to construct a floodplain mesh around the channel model with more realistic bathymetry and topography so that the flooding scenarios could be modeled with wetting and drying capability of ADCIRC. An initial attempt to develop such a floodplain mesh has been made with preliminary results and more comprehensive validation of the developed floodplain modeling system will extend to reproducing events associated with the historical Hurricane Isaac that impacted the region in 2012. This modeling system will provide an important tool to decision makers that could be used in future flood risk management and mitigation efforts.

scholarly journals Riverine Sediment Changes and Channel Pattern of a Gravel-Bed Mountain Torrent

2020 ◽  
Vol 12 (18) ◽  
pp. 3065 ◽  
Author(s):  
Gernot Seier ◽  
Stefan Schöttl ◽  
Andreas Kellerer-Pirklbauer ◽  
Raphael Glück ◽  
Gerhard K. Lieb ◽  
...  
Keyword(s):  
High Resolution ◽  
Sediment Yield ◽  
Subsurface Water ◽  
Braided River ◽  
River Channels ◽  
Entire Study ◽  
Near Surface ◽  
Highly Active ◽  
Sediment Redistribution ◽  
Alluvial Channel

The alluvial channel of the Langgriesgraben (Austria) is a highly active geomorphic riverine subcatchment of the Johnsbach River with intermittent discharge and braided river structures. The high sediment yield entails both issues and opportunities. For decades, the riverbed was exploited as a gravel pit. Today, as part of the Gesäuse National Park and after renaturation, the sediment yield endangers a locally important bridge located at the outlet of the subcatchment. High-resolution geospatial investigations are vital for the quantification of sediment redistribution, which is relevant in terms of river management. Based on unmanned aerial system (UAS) surveys in 2015 (July, September, and October) and 2019 (August and October), high-resolution digital elevation models (DEMs) were generated, which enable us to quantify intra- and multiannual sediment changes. As surface runoff at the subcatchment occurs on only a few days per year with flash floods and debris flows that are not predictable and thus hardly observable, the subsurface water conditions were assessed based on electrical resistivity tomography (ERT) measurements, which were conducted in 2019 (November) and 2020 (May, June). Results of the UAS-based surveys showed that, considering the data quality, intra-annual sediment changes affected only small subareas, whereas multiannual changes occurred in the entire study area and amount to net sediment deposition of ≈0.3–0.4 m3m−2, depending on the channel section. In addition, the elevation differences for both intra-annual surveys revealed linear patterns that can be interpreted as braided river channels. As in both survey periods the same areas were affected by changes, it can be concluded that the channel mainly affected by reshaping persisted within the 4-year observation period. The subsurface investigations showed that although both near-surface and groundwater conditions changed, near-surface sediments are mostly dry with a thickness of several meters during the observations.

scholarly journals Braided-river and hyperconcentrated-flow deposits from the Carboniferous of the Lublin Basin (SE Poland) – a sedimentological study of core data

Geologos ◽  
2012 ◽  
Vol 18 (3) ◽  
pp. 135-161 ◽  
Author(s):  
Maria I. Waksmundzka
Keyword(s):  
Source Area ◽  
High Energy ◽  
Coarse Grained ◽  
Type I ◽  
Braided River ◽  
River Channels ◽  
Fine Grained ◽  
Braided Rivers ◽  
Base Level ◽  
Se Poland

Abstract Fining-upwards cyclothems found in five boreholes in the Carboniferous (Lower Bashkirian) of the Lublin Basin were analysed sedimentologically. It was established that the cyclothems represent fluvial deposits, and the lithofacies were grouped into lithofacies associations. Most lithofacies associations represent three types of sand-bed braided rivers: (1) high-energy, (2) deep and (3) distal sheetflood-affected. Other associations represent hyperconcentrated flows. Both coarse-grained (type I) and fine-grained (types IIa and IIb) occur among the fining-upward cyclothems. The formation of most thick cyclothems was related mainly to allocyclic factors, i.e. a decrease in the river’s gradient. The thickest fining-upward cyclothems are characteristic of hyperconcentrated flows and braided-river channels. The aggradation ratios were commonly high. During the early Namurian C and early Westphalian A (Early Bashkirian), the eastern part of the Lublin Basin was located close to the source area. The sedimentary succession developed due to a transition from high-energy braidedrivers and hyperconcentrated flows to lower-energy braided rivers, controlled by a rise of the regional base level.

scholarly journals IMPACT ASSESSMENT OF A LAGRE FLOOD ON RIPARIAN VEGETATION IN KINUGAWA RIVER CHANNELS BY USING UAV MEASUREMENT

2017 ◽  
Vol 73 (4) ◽  
pp. I_1069-I_1074
Author(s):  
Hayata IIMURA ◽  
Hitoshi MIYAMOTO ◽  
Toshiya INOUE ◽  
Yuka CHIGASAKI ◽  
Kenichiro HAMAGUCHI
Keyword(s):  
Impact Assessment ◽  
Riparian Vegetation ◽  
River Channels

Experimental Study on River Channel's Formation and Change Process of on the Surface of Delta Deposition

2013 ◽  
Vol 405-408 ◽  
pp. 2264-2272
Author(s):  
Fei Liu ◽  
Xiao Feng Zhang
Keyword(s):  
Experimental Study ◽  
Change Process ◽  
Sediment Supply ◽  
Channel Cross Section ◽  
Formation Processes ◽  
Braided River ◽  
River Channels ◽  
Forming Process ◽  
Meandering Channels ◽  
Braided Streams

Experimental study on river channels formation and change process with two different constant flows 2.45L/s and 4.9L/s that which come from mountains and into delta depositions surface, based on sediment supply 15.72kg/h at the water inlet. After 964h experiment, research on the study shows as follows: with 2.45L/s flow, on the surface of delta depositions forming process the channel appears as straight, braided, micro-bend and meandering form. The first formation processes of delta deposition are straight and braided river which appeared alternately every 50h on the surface. When time goes on the delta get longer and braided streams branch of the shunt decrease gradually, that made the channel appeared with slightly curved form. Combined with that flexural radius gets bigger because of the outer bank erosion of slightly curved channel backed off, finally the meandering channels presented. With 4.9L/s flow, the formation processes gave priority of braided river, which appeared every 15h cycle, following the aggravate of eroding in floodplain and scouring in main channel, the river pool board-shallow comes with the main-flow swing, the channel existed as slightly curved form, and appears two sides of deposition. Finally analysis and research the channel cross-section morphological and longitudinal slope. In conclusion, the delta depositions surface channel existed as micro-bend of no branch with single strands, under the constantly water and sediment conditions.

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