The impact of plants on fine sediment storage within the active channels of gravel‐bed rivers: A preliminary assessment

Abstract

The role of aquatic and riparian vegetation in driving morphodynamics of rivers is being increasingly recognized across all river types. Here, we focus on gravel‐bed rivers, where the ability of vegetation to influence morphodynamics depends upon the retention and stabilization of predominantly sand and finer sediments to build landforms within the active channel. One aspect of such interactions among vegetation, river flows and transported sediments that has received little research attention is their contribution to within‐channel storage of fine sediment as a potentially important component of the fine sediment budget of river reaches and catchments. In this article, we assemble some preliminary estimates of the fine sediments retained by vegetation across the active channels of four gravel‐bed rivers (12 river reaches) representing a wide range in river planform (near‐straight, meandering, braided), width (6–800 m), gradient (0.0008–0.004) and Q2 flood (2–1100 m3 s−1), and including reaches where submerged and emergent macrophytes and riparian trees and shrubs act as physical ecosystem engineers. Our results indicate that vegetation can retain sizeable quantities of fine sediment, ranging from 480 to >3000 kg m−2 in emergent vegetation‐engineered landforms, equivalent to 20–1000 kg m−2 when averaged across the entire active channel area. Vegetation retains virtually all the fine sediments stored on the bed surface of these active channels, increasing from 78% in the lowest energy to 100% in the highest energy river reaches investigated, with major differences in the locations of these vegetated fine sediment stores according to river planform style and unit stream power. These preliminary estimates suggest that fine sediment retention and storage by vegetation is potentially an important component of within‐channel sediment budgets as well as contributing to the hydrological, geomorphological and ecological functioning of rivers.

The sedimentology of gravel beds in groundwater‐dominated chalk streams: Implications for sediment modelling and management

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Understanding sediment in river systems—Building on a 50‐year contribution

“…In a sediment budget study of the Smith Creek watershed, Virginia, USA, a tributary to Chesapeake Bay which is under agricultural land use, Clifton et al (2022) highlight the importance of hydrological connectivity and develop a novel combination of a USLE‐type model incorporating high‐resolution topographic and land use data, a surface impedance weighting factor to index connectivity and floodplain and river channel metrics to assess the sources, storage and delivery of fine‐grained sediment. Gurnell and Bertoldi (2022) examine the role of vegetation in fine sediment storage within the active channels of gravel‐bed rivers, an aspect of sediment delivery that hitherto has been relatively little studied. Investigations of 12 reaches in four rivers of different character in England, France and Italy revealed a potentially important effect in that vegetation retained sizeable quantities of fine sediment, ranging from 480 to >3000 kg m −2 , in emergent vegetation‐engineered landforms.…”

Towards Biogeomorphic River Restoration: Vegetation as a Critical Driver of Physical Habitat

“…In low-energy rivers, aquatic macrophyte growth and senescence are intimately linked to sediment retention and loss (Jones et al, 2012;Wilkes et al, 2019). Gurnell and Bertoldi (2022) estimated fine sediment retention by vegetation across the active channels of three gravel-bed river types (near-straight, meandering and braided). Vegetation retained nearly all fine sediments found on the bed surface of these active channels, increasing from 78% in the lowest energy to 100% in the highest energy river reaches.…”