Europe: Reducing flooding by storing water on top of greenhouses

Westland, The Netherlands, the largest continuous glass greenhouse area in Europe, has been having problems with flooding for years. A consulting and engineering company called DHV was commissioned by the Westland municipality and the Delfland Water Board to conduct a study on storing water on top of greenhouses. DHV developed, in cooperation with TNO, a 'water storage warehouse'. Existing gutters on the greenhouses were strategically blocked to temporarily store water. The findings will be tested in a practical setting which will start after the summer.

In urban areas, 50 percent of the ground consists of hard surfaces. In Westland that amount is upwards of 85 percent. This causes the rain water to flow easily into surface water which increases the risk of flooding. Hans van Leeuwen, project manager at DHV: "The chance of flooding occurring is once every ten years in some places, which according to the norm, this should only be happening once every fifty years."

Saves at least 2 hectares of ground

DHV developed, in cooperation with TNO, a 'water storage warehouse'. Existing gutters on the greenhouses were strategically blocked to temporarily store water. The effects on the Oude Lierpolder in Westland were calculated. Van Leeuwen: "If the concept was applied to all of the greenhouses in this polder, which could be possible in 15 to 20 years, this would lead to a lower water level of 7 centimetres by extreme rain. That would be equivalent to 10,000 cubic meters of open water storage. If you were to build that water storage in this polder, it would cost 2.2 hectares of scarce and expensive land, which is equal to the size of three UEFA football fields. The water storing greenhouses would make more land available for greenhouses and at the same time save the money spent in reducing the chance of flooding."

Support from the Industry

During its research, the DHV also looked into the support for the water storing greenhouse roofs amongst the important players in the industry. Van Leeuwen: "The industry was very positive about the concept from the beginning, but would like to know what the consequences might be, for example; on the strain of the glass, implications for insurance and contamination of the glass roof." TNO looked into the weight capacity of the foundations, ridge, gutter and the amount of water depth the glass roof can handle. They concluded that the gutters can handle a depth of at least 20 centimetres.

Practical setting

The idea will be further developed and tested in a practical setting. They will also look into any consequences there might be for things such as light levels. The practical testing is planned to take place in the Demokwekerij located in Honselersdijk, at the start of September. They are expecting the testing to be completed a year later.

Bron: DHV.nl