Targeting lateral connectivity and morphodynamics in a large river‐floodplain system: The upper Rhine River

Although there is increasing consensus that river restoration should focus on restoring processes rather than form, proven techniques to design and monitor projects for sediment transport processes are lacking. This study monitors bedload transport and channel morphology in a rural, an urban unrestored, and an urban restored reach. Objectives are to compare bedload transport regimes, assess the stability and self‐maintenance of constructed riffle‐pool sequences, and evaluate the impact of the project on coarse sediment continuity in the creek. Sediment tracking is done using radio frequency identification tracers and morphologic change is assessed from repeated cross‐section surveys. Mean annual velocity is used to quantify the average downstream velocity of tracers, defined as the mean overall tracer travel length divided by the total study duration. The channel reconstruction slows down the downstream velocity of particles in the D75 and D90 size classes, but does not significantly change the velocity of particles in the D50 size class or smaller. Surveys show that riffle features remain stable and that pool depths are maintained or deepened, while tracer paths match with what has been observed in natural riffle‐pools. However, the slowdown of coarse sediment and increase in channel slope may lead to future failures related to over‐steepening of the banks and a disruption in the continuity of sediment transport in the creek. This study demonstrates how bedload tracking and morphological surveys can be used to assess river restoration projects, and highlights the importance of incorporating coarse sediment connectivity into restoration design and monitoring.

Section: Introductionmentioning

confidence: 99%

Process‐based assessment of success and failure in a constructed riffle‐pool river restoration project

Papangelakis

MacVicar

2020

“…Low shear stress values are associated with reduced mobility of sediment, higher likelihood of vegetation colonisation and, in general, a tendency to achieve greater stability of the entire system, unless a high discharge provokes the necessary disturbance to rejuvenate the system (Corenblit et al, 2009; Díaz‐Redondo, Egger, et al, 2018; Díaz‐Redondo, Marchamalo, et al, 2018; Garófano‐Gómez et al, 2017; Gurnell et al, 2016). Since no significant peak or low flows were recorded in the time period studied (see Data S1), further research over an extended time period could permit an analysis of the impact of floods and droughts, increasingly associated with climate change scenarios in the Mediterranean region (Díaz‐Redondo, Marchamalo, et al, 2018; Skoulikidis et al, 2017), on the evolving fluvial landscape in the Manzanares River.…”

Section: Discussionmentioning

confidence: 99%

“…The fragmentation of rivers and their isolation from natural floodplains is a consequence of on‐going human impact on, and control of, natural features and landscapes (Díaz‐Redondo, Egger, et al, 2018; Grill et al, 2019; Jones et al, 2019). Today, fluvial dynamics, hydrological connectivity and riverine habitat are greatly diminished as a consequence of agriculture and urban expansion, deforestation, impoundment and flood control (Tockner, Pusch, Borchardt, & Lorang, 2010; Skoulikidis et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Naturalising a heavily modified urban river: Initial habitat evolution in the Manzanares River (Madrid, Spain)

Diáz-Redondo

Marchamalo

Morcillo

et al. 2022

Self Cite

Between the 1910s and 1960s, the segment of the Manzanares River in the city of Madrid was channelized to allow for intensive urban development and a series of barrages were built to maintain constant water levels and create the aesthetic of a large deep river. As part of a renaturalisation strategy for the river by the Madrid City Council, the complete opening of the barrages' hydraulic gates in spring 2016 allowed for natural physical processes to occur that, in turn, facilitated colonisation of newly‐formed habitats by vegetation and fauna. The present study evaluates the initial effects of the barrage gate openings on instream habitats through the analysis of (i) geomorphological, physico‐chemical and vegetation metrics, and (ii) hydraulic variables associated with potential preferential conditions for native fish fauna, whose populations were greatly diminished. This approach incorporates an integrative view of the multivariate nature of the fluvial ecosystem. Results show a substantial reactivation of habitat heterogeneity over a short timeframe. In addition, newly‐emerging habitat conditions, related to sediment activation, improved water quality and diversified hydraulic conditions, are promoting potential preferential habitats for native fish fauna. This study can help aquatic researchers and administrators in understanding how an urban river can evolve with a cost‐effective intervention focused on the recovery of self‐forming dynamics. This application of process‐based river restoration strategies to a heavily modified river can also lead to the improvement of its ecological potential, as required by the European Union's Water Framework Directive.

“…Visual observation of Landsat satellite images of November 1993 and April 1995 suggest that the lateral connectivity of the Ganga River within its channel belt is highly variable from one season to another (Figure 11). The extent of lateral connectivity of a river channel influences the geomorphic processes and the local diversity within a riverine habitat (Díaz‐Redondo et al, 2018; Goździejewska et al, 2016). For example, downstream of the Farakka barrage, the lateral connectivity of the river channel in November 1993 was relatively higher than in April 1995.…”

Section: Discussionmentioning

confidence: 99%

Assessing the impact of large barrages on habitat of the Ganga River dolphin

Sonkar

Gaurav

2020

Riverine habitats are degrading at an alarming rate due to anthropogenic interventions. Construction of large dams and barrages on the Ganga River has severely fragmented the riverine habitat of dolphins. This study examines the impact of structural barriers on the habitat of the Ganga River dolphin (Platanista gangetica) in a reach between Bijnor and Narora barrage in the middle Ganga and at the Farakka barrage in the lower Ganga Plain. We use time‐series remote sensing images and flow discharge data to assess the morphological and ecological impact in the proximity of these barrages. Our result suggests that after the construction of Bijnor barrage in 1985, the total bar area of the Ganga River has reduced from 150 to 45 km2, but the channel width has remained unchanged during the period between 1980 and 2010. A time‐series analysis of the discharge shows a slightly declining trend after the year 1982. However, this observed trend is not adequate to explain the habitat degradation of the Ganga River dolphins. Further width of the Ganga River in the downstream of the Farakka barrage has reduced from 4 to 1 km, and the total bar area has increased from about 5 to 35 km2 during the period between 1965 and 1980. Also during this period, the pre‐monsoon discharge of the Ganga River has reduced by one‐third in the downstream of Farakka barrage. This study concludes that the loss of dolphins in the downstream reaches of the Farakka barrage could be associated with the change in hydraulic geometry, flow characteristics, and loss of longitudinal and lateral connectivity. Conversely, the impoundments of water upstream of the Narora barrage have maintained the suitable habitat conditions for the dolphins to thrive. This has resulted in a reported growth in the dolphin population during the years 1993–2010.