DIKE ENGINEERING - Introduction to Soft Soil Geotechnique: Content, Context and Application - page 312

1. Lowering of floodplains. Lowering (excavating) an area of the floodplain
increases the space for the river at high water levels.
2. Dike relocation. Relocating a dike land inwards increases the width of the
floodplains and provides more space for the river.
3. De-poldering. The dike on the river side of a polder is relocated land inwards
and water can flood the area at high water levels.
4. Deepening summer bed. The river bed is deepened by excavating the surface
layer of the river bed. The deepened river bed provides more space for the
river.
5. Lowering groynes. Groynes stabilise the location of the river and ensure that
the river remains at the correct depth. However, at high water levels groynes
can form an obstruction to the flow of water in the river. Lowering groynes
increases the flow rate of the water in the river.
6. Removing obstacles. Removing or modifying obstacles in the river bed where
possible, or modifying them, increases the flow rate of the water in the river.
7. Water storage. The Volkerak-Zoommeer lake provides for temporary water
storage when exceptional conditions result in the combination of a closed
storm surge barrier and high river discharges to the sea.
8. High-water channel. A high-water channel is a embanked area that branches off
from the main river to discharge some of the water via a separate route.
9. Strengthening dikes. Dikes are strengthened in areas in which creating more
space for the river is not an option.
10. With regard to measures 5 and 9 special attention is to be paid to the local
geohydrology. Since the geological stratification in the area exists of a low-
pervious top layer (Holocene) and a sandy pervious second layer (Pleistocene),
the corresponding lowering of the hydraulic resistance of the top layer by
implementing the measure may provoke higher groundwater pressures in the
hinterland during high rivers. The measure may invoke the need to
strengthening the dike for higher pore pressures, particularly at the lee side.
Figure 17.8 Sand motor (erosion island) at the coast (Stive); start and finale