Sediment deposition along the channel margins of a reach of the middle River Severn, UK

Abstract

This paper investigates vegetational, hydrological and geomorphological influences on sedimentation within the river margin of a 1.7 km, sinuous reach of the River Severn, UK. The empirical study was designed to investigate the impact of the following factors on riparian zone sediment deposition: (i) land use, (ii) channel planform location, (iii) the flood stage at which inundation occurs, (iv) submersion time, (v) flood event timing and ordering. Sedimentation was observed using sediment traps located on 48 sample plots within four sites (one on pasture, one within a poplar plantation and two within mixed riparian woodland) during four flood events. A total of 177 observations of sediment deposition were analysed for total dry weight of sediment, particle size and organic content. All sample plots were located within a 30 m wide ribbon of the riparian zone, immediately above the limit of perennial vegetation (i.e. the edge of the low flow channel). Patterns and rates of sedimentation differed between flood events. Whilst significant differences were found in sedimentation between the four sample sites, these were interpreted to be more a function of planform location than land use. The most marked variations were found in the quantity, particle size and organic content of deposited sediment according to riparian zone cross-sectional morphology and elevation. Highest sedimentation occurred within a 1 m elevation band that correlated with the channel-ward face of a morphological bench. Percentage sand content of deposited sediment exhibited a change from approximately 35% in a band extending from the low flow channel to a 1 m elevation above the morphological bench edge to approximately 10% above this level. Organic matter content was low (less than 5%) in sediment deposited up to a 1 m elevation above the edge of the morphological bench. Above this level, there was a gradual increase in organic matter content. These observations suggest a link between the form of the riparian zone and the sedimentation process. The relative influence of vegetational, hydrological and geomorphological influences on sedimentation characteristics are also discussed.

Logjam controls on channel:floodplain interactions in wooded catchments and their role in the formation of multi-channel patterns

“…Site 4 is a lower order (Strahler stream order 4) semi-natural reach with a central Active logjam. At each site, two transects of 0.25 m 2 Astroturf™ mats were set up across the floodplain to measure sedimentation rates (Nicholas and Walling, 1995;Steiger et al, 2001). Mats were spaced across the floodplain at specific points designed to quantify processes associated with specific features of the floodplain geomorphology (e.g.…”

Carbon storage and soil organic matter stabilisation in near-natural, restored and embanked Swiss floodplains

“…Moreover, vegetation directly influences soil carbon accumulation and consequently soil development by aboveground and belowground inputs (Giese et al, 2000) leading to high spatial heterogeneity in terms of vertical and horizontal SOM distribution (Blazejewski et al, 2009;Drouin et al, 2011). Soil properties, such as profile development, texture, moisture and water table also greatly affect carbon storage (Mitra et al, 2005;Steiger et al, 2001). Carbon content is hence significantly and positively correlated with the clay content in alluvial deposits (Bai et al, 2005;Cabezas and Comin, 2010).…”

A hullámtér-feltöltődés folyamatának vizsgálata a Tisza középső és alsó szakaszán

“…Ez a vastagabb, főleg homokos üledékréteg egy viszonylag szűk sávban halmozódik fel a folyó mentén (Steiger et al 2001b, Szlávik 2001, Kiss et al 2002, Brooks 2005, és szabályosan követi a folyó medrét (Oroszi 2008). Egyes kutatók ennek a sávnak a szélességét 10-20 m-ben (Zhao et al 1999, Kiss et al 2002, mások 50-80 m-ben (Szlávik 2001, Hudson és Heitmuller 2003, Oroszi 2008) határozzák meg.…”

“…A folyótól távolodva exponenciálisan csökken az akkumuláció mértéke (Borsy 1972, Ritchie et al 1975, Pizzuto 1987, Asselman és Middelkoop 1998, Steiger et al 2001b, Brooks 2005, az árvízvédelmi töltések lábánál már csak hártyavékony üledék rakódik le (Borsy 1972, Kiss és Fejes 2000, Fiala 2002, Wyzga 1999. Oroszi és munkatársai (2006) vizsgálatai azt mutatják, hogy ez a tendencia a Maros esetében a folyótól 300 m-ig volt megfigyelhető, ettől távolabb, viszont az üledék vastagságot befolyásoló egyéb tényezők (morfológia és növényzet sűrűség) módosították az üledék-felhalmozódás mértékét.…”