Geomorphological response to system‐scale river rehabilitation <scp>II</scp>: Main‐stem channel adjustments following reconnection of an ephemeral tributary

Marteau, Baptiste; Gibbins, Chris; Vericat, Damià; Batalla, Ramón J.

doi:10.1002/rra.3682

Cited by 7 publications

(5 citation statements)

References 61 publications

(121 reference statements)

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“…Sediment augmentation through the reactivation of old side channels can increase sediment transport [40] but it may take decades until a new (quasi)equilibrium of the bedload budget is reached. Under natural boundary conditions, a positive cascading effect on channel dynamics, bedload structure and interstitial habitat may develop (Figure 2).…”

Section: Injection Methodsmentioning

confidence: 99%

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Sediment Augmentation for River Rehabilitation and Management—A Review

Mörtl

Cesare

2021

Land

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Sediment management is an important part of river rehabilitation and management. Global case studies provide a growing number of examples of successful sediment augmentation measures that can counter the adverse effects of disturbed sediment regimes. The initial river state and the objectives of the reported measures can vary largely, however. In this review, a summary of selected case studies is presented, and an objective-focused classification of sediment augmentation measures is introduced. Case-specific restrictions, design approaches and assessment methods based on the literature review and our own experience from working in the field are presented. This summary aims to provide an overview on up-to-date knowledge for applied river rehabilitation and management.

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Section: Injection Methodsmentioning

confidence: 99%

“…Sediment augmentation was performed by reconnecting a formerly diverted headwater sub-catchment back to its mainstem. The reconnected tributary has a significant level of control over coarse sediment supply and dynamics and has proven to be an important source of fine material [40].…”

Section: Europementioning

confidence: 99%

Sediment Augmentation for River Rehabilitation and Management—A Review

Mörtl

Cesare

2021

Land

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“…Increasingly gravel augmentation projects are designed to increase bedload below dams (Kondolf et al, 2014), letting the river redistribute the gravel into more ‘natural’ features with higher habitat value (Gaeuman, 2014). However, dams are not the only cause of downstream sediment starvation and rehabilitation initiatives are launched in rivers suffering from other forms of alteration (Brousse et al, 2021; Marteau, Gibbins, et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Can gravel augmentation restore thermal functions in gravel‐bed rivers? A need to assess success within a trajectory‐based before–after control–impact framework

Marteau

Michel

Piégay

2022

Hydrological Processes

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Gravel augmentation has become common practice to mitigate the effects of decline in upstream sediment supply in gravel‐bed rivers. However, the functional aspects of river systems are often left out of rehabilitation monitoring programmes. Despite temperature being a fundamental parameter determining the general health of rivers, a limited number of studies have tested whether gravel augmentation can aid restoring thermal functions. Using airborne thermal infrared (TIR) imagery, this paper explores potential positive outcomes through the monitoring of gravel augmentation actions on three rivers in France using hydro‐morphological indicators within a trajectory‐based before–after control–impact (BACI) framework. This design, combining long‐term geomorphic evolution with TIR‐based CI strategy, indicated that restoring forms was not sufficient to restore thermal functions in their spatial dimension. Despite forms showing various degrees of recovery, the thermal regime of rehabilitated reaches (i.e. temperature gradient, cold‐water patches density, etc.) failed to recover. Nonetheless, hydro‐morphological indices can be used to estimate long‐term evolution of groundwater‐surface water interactions. We emphasise the benefits of trajectory‐based BACI assessment to identify current conditions, understand the past evolution (trajectory) of the system to define the framework within which rehabilitation can be objectively assessed, especially when assessing hydrological (here thermal) processes. From a hydrological perspective, the gap between restored forms and restored thermal processes stems from the alteration of connectivity pathways, which potentially require more time (or efforts) to be recovered than forms do. With an increasing number of rehabilitation schemes and increasing pressure of global changes on rivers, we suggest that monitoring of water temperature becomes a routine part of rehabilitation projects.

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“…The overarching goal of the work described in the present and its companion paper (Marteau, Gibbins, Vericat, & Batalla, 2020) was to understand how reconnecting rivers to their sources areas, as an alternative to artificial gravel augmentation at a given point in time and space, influences fluvial processes and geomorphic conditions. The present paper reports on the geomorphic evolution of the tributary following its reconnection to the Ehen, as well as the volumes of coarse material eroded from its channel and delivered to the main‐stem.…”

Section: Introductionmentioning

confidence: 99%

“…Its specific objectives are: (a) to quantify the volumes and temporal dynamics of coarse sediment delivered from the reconnected sub‐catchment, and (b) to assess the development of a newly formed confluence bar and its role in mediating the interaction between this sub‐catchment and its main‐stem. Marteau et al (2020) present information on the geomorphic responses of the river Ehen to this renewed delivery of coarse material.…”

Section: Introductionmentioning

confidence: 99%

Geomorphological response to system‐scale river rehabilitation I: Sediment supply from a reconnected tributary

Marteau

Gibbins

Vericat

et al. 2020

River Research & Apps

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This paper is the first of a pair that report the findings of a river rehabilitation project centred on the reconnection of a formerly diverted headwater tributary (Ben Gill) to its main-stem river (the River Ehen). The present paper describes the geomorphic evolution of the tributary in the 2 years following its reconnection, with a particular focus on assessing the volumes of sediment now being supplied to the main-stem Ehen. Structure-from-Motion photogrammetry was used to produce Digital Elevation Models (DEMs) of the newly connected tributary, with successive DEMs compared to assess topographic changes in the channel and quantify volumes of material exported. 3D errors in the DEMs were small relative to the scour and fill observed in the channel (error 0.016-0.056 m compared to up to 1.7 m vertical change between consecutive surveys). Erosion was the dominant process in the tributary channel, though this varied spatially and temporally. Over the 2-year period, an estimated minimum of 384 m 3 of coarse sediment was exported from Ben Gill and delivered to the confluence zone, where a new bar feature developed as a result. This estimate is twice as high as earlier ones. Analysis of the growth of this bar suggested that much of the material supplied by Ben Gill remains here temporarily, with onward conveyance constrained by the competence of the regulated main-stem. The work shows that, thanks to the reconnection, this small (0.55 km 2) ephemeral tributary (flowing for only around 20% of the time) has become a key source of sediment for the main-stem Ehen. The second in the pair of papers focuses on the geomorphic responses of the main-stem to this renewed supply of sediment.

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Geomorphological response to system‐scale river rehabilitation II: Main‐stem channel adjustments following reconnection of an ephemeral tributary

Cited by 7 publications

References 61 publications

Sediment Augmentation for River Rehabilitation and Management—A Review

Sediment Augmentation for River Rehabilitation and Management—A Review

Can gravel augmentation restore thermal functions in gravel‐bed rivers? A need to assess success within a trajectory‐based before–after control–impact framework

Geomorphological response to system‐scale river rehabilitation I: Sediment supply from a reconnected tributary

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