Graduation of Daniël Donkers

Conceptual Design of the Spillway into the Energy Storage Lake of Delta21

• Professor of graduation: Dr.ing. M. Z. Voorendt

• Supervisors: Dr. D. Wüthrich (TU Delft); Dr.ir.B.Hofland (TU Delft); ir. B. Belfroid (Ballast Nedam)

 

In the upcoming decades, the Netherlands is going to face challenges regarding the protection
against flooding. The reason for this is the expected rapid change in climate around the world. These
changes are also affecting the Netherlands. The climate change leads to a rise in sea level and an
increase in peak river discharges. This will result in higher water levels in the Dutch rivers. To deal
with this increase, the current flood defence system has to be improved. Although expensive, the
most commonly used method to improve the flood defence system is to increase the retaining
heights of existing dikes. A new method to improve the flood defence system in the Southwest Delta
of the Netherlands is the Delta21 concept. Besides the improvement of the flood defence system it
will also improve the nature in the Haringvliet basin and the balance on the energy market.

The focus of the Delta21 concept is on the Southwest Delta, the region around Rotterdam and the
Haringvliet. One of the biggest problems around this area is situated near Dordrecht. Close to
Dordrecht, there are multiple places that are not protected by existing flood defence structures and
this area is therefore vulnerable to flooding events. The idea is to create a lake, the Energy Storage
Lake, next to Maasvlakte II in the North Sea. During high discharge conditions in the rivers of the
Southwest Delta, the Rhine and the Meuse, the lake can be used to store excess river water. From
the Energy Storage Lake, the water can be pumped into the sea. In combination with a closed storm
surge barrier next to the Energy Storage Lake, the water level in the rivers upstream of the lake can
be lowered. To achieve the lowering of the water levels in the upstream rivers, a spillway is required
to let the water flow into the Energy Storage Lake.

The aim of this thesis is to come up with a conceptual design for the spillway discharging the water
from the Tidal Lake towards the Energy Storage Lake. This design must fulfil the functional and
structural requirements, must be affordable, constructable and must fit within the ideology of
Delta21. To achieve this, the hydraulic engineering design method is used. The first step in this
method is to analyse the problem, in which climate change plays a vital role.

In the second step, the basis of design is elaborated. This includes the boundary conditions of the
design and the requirements that need to be fulfilled. The main requirements for the spillway are
that the maximum discharge capacity should be 20 000 m3 /s and the water level near Dordrecht may
not exceed NAP + 2.5 m.

In the third step, the location of the spillway is first decided upon. The location is chosen based on
the results of a sieve analysis. For this sieve analysis, multiple criteria are used to eliminate
unfavourable locations. After this, four different concepts are generated that differ in, among other
things, the type of flow and the way the structure is part of the surrounding flood defence structures.
The different concepts are concept Siphon, concept Underflow, concept Caisson and concept Ogee.

The next step is the verification of the concepts. In this verification the functional requirements and
the stability requirements respectively are checked. The functional requirements are used to obtain
the size and shape of the structures and to obtain the discharge capacity of 20 000 m3/s for each
concept. The stability requirements are used to obtain the dimensions of the concepts. After the
verification, the concepts are evaluated and a the best scoring concept is chosen. This is done based
on a multi-criteria analysis and a cost estimation. The best scoring concept is the concept Caisson.
At last, the scour protection for the concept Caisson is designed and the strength of the concrete
elements of the concept are checked. This resulted in a final design for the spillway of the Delta21
concept.