Revisiting Waal River Training by Historical Reconstruction

T B Le,A Montes Arboleda,A Crosato

doi:10.1061/(asce)hy.1943-7900.0001688

T B Le, A Montes Arboleda + Show 1 more

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https://doi.org/10.1061/(asce)hy.1943-7900.0001688

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Abstract

The Dutch River Waal, a branch of the Rhine, has been trained for centuries to mitigate the effects of ice-jams and improve navigation. The works, started in 1850, involved river straightening and narrowing by a series of transverse groynes. Besides fulfilling their goal, the groynes also created the need to raise flood protection works and caused undesirable channel incision. This study assesses the effectiveness of training the river with a longitudinal wall instead of with groynes. The investigation analyzes the long-term response of the historical river with a two-dimensional depth-averaged (2DH) morphodynamic model. The results show that the wall would create two parallel channels, one becoming deeper and the other one shallower. The former would be as suitable for navigation as an equally-wide channel obtained with groynes. The latter would contribute in conveying water during high flow events and improve the river ecology. Training the river with a wall would also lessen channel incision. The best performance is obtained if the wall is built on the channel centerline, starting just upstream of a point bar top.

Highlights

InformationThe frequency of dike breaches and flooding increased along the Waal River, a branch of the Rhine, in the early modern period
The results of the preruns show that a time step of 30 s ensures numerical stability and that after 50 years, the system reaches a state of morphodynamic equilibrium in which the longitudinal slope remains constant and cross-sectional changes of bed elevation are negligible (T 1⁄4 50 years)
The morphological evolution and the hydraulic conditions have been investigated by means of a 2DH numerical model developed using the Delft3D code

Summary

Introduction

The frequency of dike breaches and flooding increased along the Waal River, a branch of the Rhine, in the early modern period. At least 29 out of 51 river dike breaches between 1757 and 1926 were provoked by ice jams (Wijbenga et al 1993, 1994). As these ice jams formed preferentially at wider shallow sections with bars and islands, it was decided to give the river a narrow uniform width using a series of transverse groynes. Since 1850, the width of the Waal River was reduced to 360 m, 310 m, and to 260 m.

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