Sediment transport at the network scale and its link to channel morphology in the braided Vjosa River system

Abstract

In this article we apply the CASCADE network‐scale sediment connectivity model to the Vjosa River in Albania. The Vjosa is one of the last unimpaired braided rivers in Europe and, at the same time, a data scarce environment, which limits our ability to model how this pristine river might respond to future human disturbance. To initialize the model, we use remotely sensed data and modeled hydrology from a regional model. We perform a reach‐by‐reach optimization of surface grain size distribution (GSD) and bedload transport capacity to ensure equilibrium conditions throughout the network. In order to account for the various sources of uncertainty in the calculation of transport capacity, we performed a global sensitivity analysis. The modeled GSD distributions generated by the sensitivity analysis generally match the six GSDs measured at different locations within the network. The modeled bedload sediment fluxes increase systematically downstream, and annual fluxes at the outlet of the Vjosa are well within an order of magnitude of fluxes derived from previous estimates of the annual suspended sediment load. We then use the modeled sediment fluxes as input to a set of theoretically derived functions that successfully discriminate between multi‐thread and single‐thread channel patterns. This finding provides additional validation of the model results by showing a clear connection between modeled sediment concentrations and observed river morphology. Finally, we observe that a reduction in sediment flux of about 50% (e.g., due to dams) would likely cause existing braided reaches to shift toward single thread morphology. The proposed method is widely applicable and opens a new avenue for application of network‐scale sediment models that aid in the exploration of river stability to changes in water and sediment fluxes.

A width‐based approach to estimating historical changes in coarse sediment fluxes at river reach and network scales

“…In detail, this tool translates to a valuable contribution to linking channel morphological evolution, coarse sediment transport modifications and their relationships with human disturbances to sediment availability and dynamics (e.g., Syvitski & Kettner, 2011), possibly improving also the development of predictive models of morphological trajectories at the river network scale (e.g., Alcayaga et al, 2018). Emerging models of network‐scale sediment connectivity (Czuba & Foufoula‐Georgiou, 2014; Gilbert & Wilcox, 2020; Schmitt et al, 2019) would tremendously benefit such analyses, thereby clearing the way for integrating and further validating simulations and appropriately predicting future changes in sediment transfers and associated morphological adjustments (Bizzi et al, 2021). Furthermore, as observed, for instance, in the reaches of the Po River located close to the Isola Serafini Dam, the method could provide additional information about the perturbations affecting the equilibrium of sediment transfer along the river course; an example is the closure of filtering transverse structures and/or localized/intense sediment removal.…”

Data, knowledge, and modeling challenges for science-informed management of river deltas

“…On larger scales, studies using water resources and distributed hydrologic models to optimize the passage of sediment through dams and towards deltas [139][140][141] rely on very simplified representations of sediment transport processes. Also approaches for optimizing the siting of dams often represent sediment transport to downstream deltas in a highly stylized manner 87,96,142,143 To address this gap, new models are emerging that represent the transport of multiple grain sizes and their interactions (e.g., the presence of sand might impact the transport rates of gravel in a river 144 ) for longer river reaches 145 or entire basins [146][147][148][149][150][151][152]87 . Those models are probably best described as "process related models" as they leverage approaches from graph theory 153 , combined with empirical sediment transport equations, and a simplified handling of hydrology (and more recently, morphodynamics) to estimate the impacts of all sediment fractions on a network scale.…”

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

“…lakes and ponds) to compute budget components and reveal human impacts (Foster et al, 2021). Laboratory analyses of sediment samples have provided an indirect means of estimating proportional source contributions by 'fingerprinting' sediment characteristics (Pulley et al, 2017;Walling et al, 1998Walling et al, , 2006, with further advances extending the spatial and temporal scales of quantification using information from aerial and satellite imagery, lidar data and modelling (Bizzi et al, 2021;Khan et al, 2021;Piégay et al, 2020).…”