Vegetation-induced sedimentary structures:Porosity of riparian shrubs as control parameter of sedimentary processes during floods  

作　　者：Oliver Schlomer Seraphine Luneau Stephane Rodrigues Jürgen Herget 

机构地区：[1]Department of Geography,University of Bonn,Bonn,53115,Germany [2]German Aerospace Center(DLR),Space Agency and Earth Observation,Bonn,53227,Germany [3]Ecole Polytechnique,University of Tours,Tours,37200,France

出　　处：《International Journal of Sediment Research》2024年第4期497-513,共17页国际泥沙研究（英文版）

摘　　要：Vegetation-induced sedimentary structures(VIss)are bed features resulting from flow-vegetation feedback and turbulence induced by vegetation at riparian sites.Generally,these sedimentary structures commence at the individual plant level,but sediment accumulation over time may lead to the formation of fluvial islands.Additionally,riparian vegetation exposed to current may provoke local scouring.However,little research has been done on how the permeability of plants affects flow fields and sedimentary processes.Therefore,the main aim of the current study is to experimentally investigate patterns of local scour and deposition around artificial obstacles with six different levels of porosity,using a systematically designed flume experiment.Two experimental setups were implemented,with sediment transport occurring either as bed load or in suspension.Porosity,as a measure of the volume of porous space to bulk volume,was determined using optical porosity which was estimated from digital photographs.Furthermore,VisS of individual P.nigra shrubs were investigated at different seasonal stages(leafless and full foliage)at the Loire River,France,for comparison.Results show that increasing porosity caused a reduction in sediment deposition from suspension and locally scoured bed load sediment.A threshold value for optical porosity was determined,at which point a prolonged area of flow calm develops behind the barrier,promoting the accumulation of suspended sediment and suppressing local scour caused by bed load transport.An empirical model is presented,which assesses sediment erosion and deposition volumes at porous obstructions,considering(a)the flow-exposed surface area,(b)the obstruction's optical porosity,and(c)the intensity of the incoming flow.On the field scale,local scour holes were identified at P.nigra shrubs where flood-caused debris obstructions were stuck at their front,lowering the obstruction's porosity and encouraging local scour processes.

关 键 词：Local scour Sediment ridge Sediment transport Riparian vegetation Ecomorphodynamics Flume experiments 

分 类 号：TV14[水利工程—水力学及河流动力学]