Revisiting Waal River Training by Historical Reconstruction

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.

Efficacy of Longitudinal Training Walls to Mitigate Riverbed Erosion

“…All data have been compiled into a video that can be downloaded as Supporting Information; Movie . The 2018 flood was the largest discharge in our study period and nearly doubled the bankfull discharge of 2,650 m 3 /s (Le et al., 2020). Meanwhile, the average inter‐flood discharge in both periods was lower than mean‐annual discharge of 1,490 m 3 /s (Le et al., 2020).…”

“… Cyclic patterns of aggradation and scouring during flooding periods and riverbed diffusion during inter‐floods following construction of the Longitudinal training walls (LTWs): (a) The hydrograph at Tiel gage (RK 915). The mean‐annual discharge Q avg (Le et al., 2020) is drawn with a dashed gray line. Approximate Bankfull discharge is drawn as a gray rectangle ranging from 2,650 m 3 /s (Le et al., 2020) to 3,500 m 3 /s (Figure 7).…”

“…Grill et al (2019) report that only a third of the largest rivers on earth are still free-flowing along their entire reach today. Many others are heavily modified with, for example, groynes, for example, Rhine River (Le et al, 2020), or bank revetments for example, Mississippi River (Biedenharn et al, 2000). Engineering practices may develop unforeseen side effects, which may become evident immediately or over the course of decades and centuries.One common effect of engineered rivers is long-term channel bed erosion (Simon, 1989).…”

Studies on River Training

“…River engineer Henk Eerden pioneered this idea by realizing a 10 km long pilot implementation of longitudinal training walls on the Waal River. Numerical model results [20] suggest that the bed would have eroded less and that the navigability would have been better if the Waal River would have been trained straightaway with longitudinal training walls instead of groynes in the 19th century.…”

River flood reconstruction in the Lower Rhine valley and delta

“…Three-dimensional reconstructions incorporating bathymetry are rare, due to available data limitations, but necessary for hydraulic calculations (Hesselink et al, 2006). Existing studies often cover only a small stretch of river, introducing potential problems for modelling purposes as results are affected by boundary conditions (Montes Arboleda et al, 2010;Le et al, 2020).…”