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Research with 'plethora of gauges' sheds light on draining rainwater from greenhouses

For the Water Board of Delfland in the Netherlands, a student researched how the drainage of rainwater occurs in a horticultural company at different quantities of water. Holstein Flowers from De Lier cooperated in the project. Mathieu van Holstein: "Water which cannot be collected because of bottlenecks in the system is really a loss. This project has yielded insights which are very useful in new constructions."

The Netherlands has a lot of (built-up) areas where processing large quantities of rainwater in a short time often causes problems, such as the Westland, which belongs to the jurisdictional area of the Delfland Water Board. When analyzing the bottlenecks in the quantitative water management and looking for solutions, the water board cannot get around greenhouse horticulture.

Senior policy maker Saskia Jouwersma: "Rainfall is increasing and because of the scale enlargement in horticulture, the connected built-up areas are getting larger and larger. Insight in the manner in which the water is transported over the greenhouse roof and through the drainage system - particularly during heavy rainfall - can help both growers and water managers remove the bottlenecks in water storage. Water nuisance is a recurring problem and we need each other to deal with this problem."

With the company layout spread out, Keizer (left), his graduation supervisor Oliver Hoes (right) and Van Holstein determine where the various gauges have to be placed (credit: Hoogreemraadschap Delfland).

Plethora of gauges
Two years ago, Jouwersma registered a research question with TU Delft, to which graduating student Kasper Keizer responded positively. Gerbera nursery Holstein Flowers from De Lier was prepared to facilitate his final project. Mathieu van Holstein: "When possible, we like to cooperate in this kind of initiative. Moreover, water nuisance is quite an issue here in the Oude Lierpolder, so if this research could contribute to improvement, we want to help." 

In March 2019, Keizer installed a plethora of gauges in strategic places. The four corners of the roof were equipped with rain gauges, cameras were installed, and a lot of drainage pipes were equipped with level gauges. With these gauges, it could be determined whether the capacity of the drainage system was sufficient to also process large quantities of rainfall without problems.

Van Holstein: "If there are bottlenecks in the system, the drainage pipes behind it cannot drain the water fast enough and fill up. If this lasts too long, the water will run over the gutter edges down the facade. Particularly in spring and summer, we would like to have this water in the basin."

Little precipitation, limited results
All image and measuring equipment yielded a lot of information, although heavy rainfall, very useful for the research, stayed away. Saskia Jouwersma: "Our interest is particularly focused on the failure systems in the drainage systems. To bring those in focus, we need heavy rainfall which did not occur during the duration of the project. There has been no overflow from the basin to the ditch, and the company's standing pipes were well suited to their tasks. We have been able, however, to determine that a lot of precipitation - around 10 percent - is lost due to evaporation from the roof." Maybe this could be a focal point in the development of new, advanced greenhouse roofing materials or coatings

Mathieu van Holstein: “The most important learning point for us is to dimension the storage and drainage capacity spaciously, taking inertia of the system into account. We have always paid attention to this when expanding the company. Now, I would pay even more attention to this, and that is the message I want to give to all growers: make sure the standing pipes and horizontal pipes do not fill up too rapidly and keep a large margin. Climate change is a given and precipitation will come more and more in the form of short heavy rain bursts. You have to be properly prepared."

Source: Glastuinbouw Waterproof

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