Seasonal storage by realizing extra storage height
Designing the surface area for storage to handle greater fluctuations in water levels is a way of realising seasonal storage capacity. The advantage to this form of seasonal storage as compared with the previous method is that it requires no additional surface area. In many locations, however, the height required cannot simply be created by limited drainage (the difference between the groundwater level and the level of the streets and buildings). Greater fluctuations in water levels will place demands on how the banks are designed and planted, since those banks will be exposed to more extreme conditions: during the winter season, large parts of the banks will be under water almost permanently, while those same parts of the banks will be almost entirely dry in the summer. Not many plants are capable of surviving those changes.
Oude Lek in EVA-Lanxmeer is an example of this form of seasonal storage. The banks slope gently, are covered in reeds and partly covered by a play beach. The maximum fluctuation in water levels is 0.3 m in this project [Pötz et al., 2009]. The current water level is shown on an information sign.