• Location: 16 locations in the area of Delfland
  • Retention: rainwater from 100 ha glass is connected to the Rainlevelr catchment systeem
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together we’ll keep the polder dry


Climate change is making rainfall heavier and less predictable, increasing the risk and intensity of future flooding events. To reduce flooding in the future, greenhouses in Delfland, the Netherlands, are working on optimizing the use of the available space for rainwater storage and the enhancement of the ‘sponge’ effect in the area.

Water basins in the greenhouse sector

The greenhouse sector covers approximately 10% of Delflands area. The greenhouse roof areas are designed to discharge all of their storm water to a reservoir, the water basin or a silo, to be used for the growing of plants within the greenhouses themselves. When the basins are full, the surplus storm water is discharged into the canals. The water authority is then responsible for the further discharge of the water. When heavy rainfall events occur, flooding can take place.

A shared vision

Delfland, the municipality of Westland, Glastuinbouw Nederland (the organization of growers) and the growers themselves have a shared vision of storing storm water more efficiently in the water basins. They believe that a more effective use of the water basin could prevent the area from flooding at a reasonable cost, maintaining profitability for the growers and with a minimal use of space. Rainlevelr is the result of this vision.

The concept

In normal circumstances the water level in the basin can only be lowered by using the water for watering the plants. In the Rainlevelr project we create capacity in the water basins before heavy rainfall occurs. When heavy rainfall is predicted, we ask the cooperative growers in the Rainlevelr project to create capacity in their water basins. This is done by installing control valve discharges from the water basin to the canal.

These valves and water level measurements in the water basins are visible in real-time via LetsGrow (the climate computer of the grower). This online system let growers remotely control their valve and in the future, it will be possible to fully automate it. These control devices can be included when a new water basin is built or an old one is renovated.

Rainlevelr basin control system

Through the dashboard of LetsGrow, levels and usage rates of the basin are visible and with the rainfall prediction it is possible to calculate whether the basin will completely fill or not.

Motivation to join the project

The motivation for the grower is to keep themselves, their neighbours and the community safer from flooding. Rainlevelr allows the growers to do something proactively themselves, utilising their own infrastructure.  As such this co-operation is on a voluntary basis. Water Board Delfland has a warning system for heavy rainfall and sends out a request to create capacity in the water basins, when necessary. The grower themselves then decide whether to follow up on this request or not. They remain responsible for their own decision. Through this division of responsibilities, the execution of the project remains simple. Moreover, it justifies the fact that growers are prepared to actively participate to help keep all our feet dry.

Initially, Delfland will cover the installation cost. The growers will then use and maintain the basin themselves. Through this cooperation the risk of flooding and water damage is reduced.
The animation below will give a more thorough explanation.

Recruiting new participants

Informed in time

The current concept of Rainlevelr is only available for renovations and new build water basins. Therefore, it is important that the growers engage with Rainlevelr at an early stage. Rainlevelr is creating more awareness by means of public meetings in order to recruit more participants.

Rainlevelr conference in December 2018

Project ambassadors:

  • The current participants
  • Neighbours (e.g. other growers)
  • Colleagues from Delfland and Westland visiting growers
  • Glastuinbouw Nederland (the organization of growers)
  • Suppliers and builders of water basins

The current participants are the best ambassadors. The reason being that they are the neighbours, family and friends of other growers. Next is the group of suppliers and contractors, because they talk to the growers at the right moment: When there are plans to renovate or build a basin. The contacts with this group are expanding, and some even mention Rainlevelr on their websites (in Dutch)

Informative conversation
When a grower has plans fort he replacement of the foil or more extensive renovation/ building projects, contact is sought with the grower for a non-binding conversation.

General conditions to participate

However, not every water basin is suitable:

  1. Condensation water is not allowed into the water basin. Condensation water is polluted with pesticides and therefore is not allowed to discharge into the Delflands water system.
  2. The online information must be available in LetsGrow. It is vital for Delfland to see the water level in the basin to ensure the correct management advice ahead of rainfall events.

The result

At this moment there are 16 participating growers and together there are 100 ha of greenhousing connected to Rainlevelr. There are even several new connections being installed this year. It is estimated that by the end of 2019, a total of 200 ha will be connected. This estimate can be seen in the graph below, as well as the current locations on a map underneath.

Predicted Rainlevelr glass connectivity in hectares as of July 2019

Locations of the current participans