Effect of non‐migrating bars on dune dynamics in a lowland river

Abstract

As dunes and larger‐scale bed forms such as bars coexist in rivers, the question arises whether dune dynamics are influenced by interaction with the underlying bed topography. The present study aims to establish the degree to which dune characteristics in two and three dimensions are influenced by an underlying topography dominated by non‐migrating bars. As a case study, a 20 km stretch in the Waal River in the Netherlands is selected, which represents a sand‐bed lowland river. At this location, longitudinal training dams (LTDs) have recently been constructed to ensure sufficient navigation depth during periods with low water levels, and to reduce flood risk. By using data covering 2‐year‐long periods before and after LTD construction, the robustness of the results is investigated. Before LTD construction, dune characteristics show large variability both spatially and temporally, with dunes being longer, lower, less steep and having a lower lee side angle when they are located on bar tops. The correlation between dune characteristics and the underlying bed topography is disrupted by unsteady conditions for which the dunes are in a state of transition. The bar pattern causes tilting of dune crest lines, which may result from a transverse gradient in bedload sediment transport. As a result of LTD construction, the hydraulic and morphological conditions have changed significantly. Despite this, the main conclusions still hold, which strengthens the validity of the results. ©2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Feedback Mechanism in Bifurcating River Systems: the Effect on Water-Level Sensitivity

“…However, the relationship of form roughness with discharge is even more complex. Amongst other factors, the shape of the bedform and its lee-side angle [38] as well as the water depth [26] play an important role. While in the upper reach of the Dutch Rhine discharge-dependency is clearly present [3,29], this was not as pronounced not found for downstream locations in the Waal branch [26,29].…”

“…However, correlation of the roughness between the branches may be expected. The primary source of possible correlation between the roughness of the branches is the history of the upstream discharge by which the bedforms have developed [25,38]. Other factors that can cause correlation between the roughness of the branches can be grain characteristics [25,26], similar cross-sectional shape [25] and the shape of the discharge wave [40].…”

(En)gage the flow! : striking the balance in deltas under pressure

“…This may be used to improve the roughness predictors, and to better be able to close the water balance. The bed dynamics like you can see in the movie implicitly hides detailed information about sediment transport ( Figure 5) [5]. With a river section where the bed sediment is reasonably uniform, it should be possible to verify how well existing sediment transport formula perform at the scale of an entire river section.…”

“…Maintenance scans of the bottom topography of the River Waal reveal how sand dunes migrate over the underlying sand bars[5].…”

Discharge and water level uncertainty in bifurcating rivers

“…However, correlation of the roughness between the branches may be expected. The primary source of possible correlation between the roughness of the branches is the history of the upstream discharge by which the bedforms have developed (Wilbers and Ten Brinke, 2003;De Ruijsscher et al, 2020). Other factors that can cause correlation between the roughness of the branches can be grain characteristics (Wilbers and Ten Brinke, 2003;Frings and Kleinhans, 2008), similar crosssectional shape (Wilbers and Ten Brinke, 2003) and the shape of the discharge wave (Warmink, 2014).…”