Development 2D model
B.3 Development 2D model
An inundation model, or a so-called 2D model, was developed for the evaluation of the flooding characteristics. An inundation model comprises of a digital elevation model which is a 2D map describing the ground levels, and boundary conditions which describe the flow of water through the river over of time. The 2D elevation model for Stadswerven consists of a macro scale model with a grid resolution of 50x50m. The macro model covers the Island of Dordrecht. Within the macro-scale model, a more detailed elevation model is incorporated covering the area of Stadswerven. This detailed model has a grid resolution of 10x10m and is used to determine the effect of urban planning on the propagation of the flood wave. The different planning designs were schematized on this detailed model scale.
B.3.1 The macro-scale model
The macro-scale model was derived by filtering high object such as trees, lantern poles and houses from the ‘Algemeen Hoogtebestand Nederland’ (AHN) and converting it to
a 50x50 grid. Line elements which can cause an obstruction for flood water, such as dikes and roads were placed within the model. The bed level of the rivers were derived from WAQUA.
The following friction values were applied: •
Land: nikuradse 10 m •
Water: nikuradse 0.2 m
B.3.2 Hydraulic boundary conditions
For the 2D simulations, only a flood dominated by extreme river discharges was calculated (scenario B). A flooding dominated by an extreme sea surge (scenario A) was not considered because this would not provide additional information. For both type of floods, the maximum reached river levels are equal but the duration of a flood caused by extreme river discharges is larger than the duration of a flood caused by extreme see levels. The period of flooding of Stadswerven will therefore also be larger for a flood caused by a extreme river discharge.
An additional scenario C was simulated in which a situation with water levels of NAP +3.4m were evaluated. This water level corresponds to the foreseen design water level in 2100. By simulating this situation, the Stadswerven area is evaluated for the future design water level taking rising water levels due to climate change into account.
Scenario B The boundary conditions for scenario B were derived from the simulations made with the 1D model. From this model the river discharge for the upstream boundary was derived as well as the downstream water levels.
Scenario C
A water level of NAP +3.40m at Dordrecht was reached by raising the downstream water level boundaries with 30 cm.
B.3.3 Detailed models for Stadswerven
Two types of detailed models were developed for the Stadswerven area; the urban designs and the orientation of buildings
Urban designs The urban designs are modelled with a grid resolution of 10x10m. Buildings are implemented as solid 2D objects. The applied friction values are:
Land (Roads and buildings): nikuradse 0.4 m Water: nikuradse 0.2 m
Floating houses and bridges were not implemented in the model because these do not cause a serious obstruction. Objects which are not linked to the ground, can not be incorporated in a elevation model.
Orientation of buildings The detailed model for the evaluation of the orientation of buildings is modelled on a scale of 1x1m. Buildings are implemented as 2D solid objects. The applied friction values are:
Land (Roads and buildings): nikuradse 0.4 m Water: nikuradse 0.2 m
C Sedimentation during flooding for Stadswerven