Water storage in polders can be used in a new solution to water management problems that are arising as a result of changing climactic conditions (intensified periods of drought and water surplus). However, this requires space. In the context of multifunctional land use, a feasibility study has been prepared in which the development of new areas for greenhouses was combined with water storage in the polder landscape: floating greenhouses in the case study area in the Haarlemmermeerpolder in the western part of the Netherlands. First a study of the water availability was conducted, after which water quality and ecological processes in the pond were assessed.
From a hydrological point of view, it is possible to realise the floating greenhouse concept in the case study area. However, many assumptions and boundary conditions had to be defined first in order to arrive at this conclusion. If the location changes, these assumptions and conditions must change as well, and a new feasibility study will have to be initiated. No absolute conclusions may be drawn with respect to water quality and ecology. The results from the water quality analyses are fairly positive for the open water section of the pond, but the covered section of the water storage pond is causing problems, especially with regard to the oxygen concentrations. As the greenhouses cover some 70% of the surface area involved in the case study, this should definitely be taken into account, as it also has negative effects on the ecological functioning of the pond. Nature may be sturdy and flexible, but the large water level fluctuations observed in the case study do not occur in normal situations at present, which makes comparison impossible. Also, the uncertainties regarding the water quality situation mean that at best, only a rough estimation of what will happen may be provided.
During the project, suggestions have been made to implement technical solutions for the oxygen problems. A re-aeration system consisting of tubes installed underneath the floating greenhouses has been used elsewhere and was found to be effective in decreasing the oxygen deficit. These types of technical solutions can be very effective when the goal is to implement the floating greenhouses concept in a successful and sustainable way. In general, the effects which occur will need to be monitored in a real project to fill the gaps in knowledge which are present. At the time this was written (December 2002), plans were in the works to initiate a pilot study in which a floating greenhouse will be built as a test case. Financed by (a.o.) Ministry of: Transport, Public Works and Water Management / Education, Culture and Science |
