Impact of recent changes in river management on maintenance dredging in the Waal river

Impact of recent changes in river management on maintenance dredging in the Waal river

Kisoensingh, J.

Uijttewaal, W.S.J. (mentor)
Van Vuren, S. (mentor)
Paarlberg, A.J. (mentor)
Mosselman, E. (mentor)
Havinga, H. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

Hydraulic structures & Flood risks

2015-03-05

Over the last centuries, Dutch rivers such as the Rhine have been heavily trained for the purpose of the safe discharge of water, sediment and ice, and navigability. After the notorious flood events of 1993 and 1995 along the Rhine, new large-scale river works were initiated, such as the Room for the River (RfR) programme, to increase flood conveyance capacity. For a better navigation, in 2006 the minimum guaranteed depth on the Waal has been raised from 2.50 m to 2.80 m (relative to the Agreed Low Water level). It is inevitable that the measures of the large-scale works (depending on the type and magnitude of the measure) and changes in the minimum guaranteed depth will influence the morphology of the river and the dredging effort. Three schematisations are distinguished in this research, namely maintenance dredging in the situation with a minimum guaranteed depth of 2.5 m (‘Ref – 2.5 m’), the situation with a minimum guaranteed depth of 2.8 m (‘Ref – 2.8 m’), and the situation after the implementation of the Room for the River programme (‘RfR’, with a minimum guaranteed depth of 2.8 m). The aim of this research is to determine the impacts of the increase in the minimum guaranteed depth and the Room for the River programme on the maintenance dredging in the river Waal using the deterministic approach (traditional) and a stochastic approach, and to determine the potential of a stochastic approach with respect to the deterministic approach in river management practice. Currently, morphological calculations are being executed using a deterministic approach. The deterministic approach appears to be an effective tool to provide a quick expression of the physical morphodynamic processes. However, to fully acknowledge these morphodynamic processes and to derive a precise illustration using a deterministic model is very complex. By ignoring the complexity of the morphodynamic processes, the involved uncertainties are not made explicit. Identifying the uncertainty in morphodynamic predictions is necessary in order to come to grips with system behaviour of the Waal. Therefore, it is important to not only look at the deterministic calculation, but also to perform stochastic calculations. In this study, numerical calculations with a 2D depth averaged Delft3D model are performed using a deterministic and stochastic approach to determine the bed level changes, navigability, and dredging effort. For the deterministic approach a representative discharge hydrograph is used and for the stochastic approach 75 different discharge time series. From the present research it follows that the maintenance dredging volume in the ‘Ref – 2.8 m’ situation is twice as much as in the ‘Ref – 2.5 m’ situation. It increases drastically with 196%. The increase in the maintenance dredging volume in the ‘RfR’ situation compared to the ‘Ref – 2.8 m’ situation is approximately 10 times lower than the increase in the maintenance dredging volume in the ‘Ref – 2.8 m’ situation (which is related to the dredging effort in the ‘Ref – 2.5 m’ situation). This concludes that the increase of the minimum guaranteed depth has a bigger impact on the maintenance dredging than the impact of the Room for the River measures. According to the simulations it also follows that the dredging volume in all sharp bends (Millingen (rkm 869-870), Erlecom (rkm 875-876) and Nijmegen (rkm 883-885)) in total is more than the half of the total dredging volume on the Waal. Nijmegen (rkm 883-886) only covers more than one-third of the total maintenance dredging volume on the Waal. As regards to the deterministic and the stochastic approach, the differences between the mean value of the stochastic approach and the deterministic approach are rather high in the entire Waal (which lies between 30 and 40%). In the Nijmegen area this difference is negligible. Generally speaking, the mean value of the stochastic approach is not underestimated by the deterministic calculations. The large difference does not imply that the stochastic approach is more promising than the deterministic approach or vice versa. The uncertainty range (90%-confidence band) in the stochastic approach helps the river manager to decide where and how to interfere in the river system and it helps in drawing up performance based contracts with dredging companies. The stochastic approach gives more insight in the range or likelihood of predictions if it comes to dredging. If the river manager wants to employ a dredging company (contractor) for maintenance dredging, he can sign the contract for a lower amount of money, since the mean value of the stochastic approach is lower than the results of the deterministic approach.

room for the River
the Waal
the Rhine river
dredging
recent changes
deterministic approach
probabilistic approach
Monte Carlo Simulation
Delft3D model
Nijmegen

http://resolver.tudelft.nl/uuid:0c65e3d7-3104-4bfd-a7da-293edbe96301

Student theses

master thesis

(c) 2015 Kisoensingh, J.