ABSTRACT
In the context of an environmental impact assessment the response of the Nieuwe Waterweg (New Waterway) to deepening of the navigation channel was evaluated. The New Waterway is the primary channel that discharges the water from the River Rhine to sea. It’s median discharge is (Q50) is approximately 1350 m3/s, only during peak discharge the Haringvliet floodgates open and the discharge to the Haringvliet becomes larger. The New Waterway is the primary access to one of the busiest ports in the World. In order to make the inland parts of this port accessible to larger ships, dredging of the navigation channel is planned. The current guaranteed bed level, the guaranteed nautical depth (NGD), is 15 m −NAP, or approximately 15 m below the local ordinance level (NAP) that approximates the average sea level. The channel will be deepened to 16.3 m −NAP. This level increases stepwise towards the city of Rotterdam.
The research questions in this study are: What are the effects of the deepening on the hydro- morphological system, locally and upstream? How does the deepening affect the yearly amount of dredging maintenance in the navigation channel and the harbor basins? What effects does the increased maintenance dredging have on the turbidity of the water?
The approach followed in this study is a combination of literature study, 2D and 3D hydrodynamical modelling at a fine and a coarse resolution using Waqua in Simona, a 1D sediment transport study using the TSAND model by van Rijn (2015), a 3D morphological model in Delft3D and empirical relations to estimate the discharge cross section.
The hydrodynamics have been modelled and studied for the 5, 25, 50, 75 and 95 percentile discharges of the Rhine at Lobith (at the Dutch-German border) for a spring tidal cycle, a neap tidal cycle and an average tidal cycle. Salinity effects were included in all cases as these proved crucial for capturing the natural flow patterns.
The TSAND model has been extended for the purpose of the study. TSAND is a 1DV model that incorporates the effects of tidal velocities including asymmetries, the rivers flow velocity profile, density currents and their distribution over depth and the sediment composition (sand and mud). This 1DV model was fed with data from the detailed 3D hydrodynamic simulation. The net transport was calculated as the weighted average over the 15 transport conditions. From these results we were able to confirm that the use of bed shaping discharge gives reliable results with much less effort (See Fig. 1). The bed shaping discharge was used to calculate the development in the reference situation and the deepened situation. The overall picture of the area is that it is sediment importing from both the fluvial and marine side. The sedimentation of the coarser fraction primarily takes place in the navigation channel while the harbor basins act as efficient sediment traps for the fine suspended sediment (silt and mud). The sedimentation in the harbor basins is linked to the presence of the turbidity maximum where suspended sediment concentrations reach several hundred milligrams per liter. Further effects regarding the deepening will be presented, the analysis will be finished in the coming weeks. Average TSAND transport rate from 15 conditions (blue) and 3 conditions: spring neap and mean tide (red). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315623207/4fbc492d-6678-4a12-aaf6-5c2b8ea38e5f/content/fig82_1.tif"/>
