In the Southwest Netherlands Delta the availability of fresh water cannot be taken for granted. Fresh groundwater, or fresh water supplied from the Lake Volkerak-Zoom and/or the pipeline transporting river water, is only available in a limited number of areas. It is expected that climate change will further impact fresh water availability in the future. At the same time, the availability of water has become an important production requirement for the development and growth of the local fruit sector. The night-frost sensitivity of the fruit stands increasingly requires means of combating night frost. Moreover there is increasing market pressure, based on delivery guarantee and quality considerations, to irrigate in the summer season.
Freshwater supplies in trouble
For the reasons mentioned above the existing systems are being used more and more intensively. The horticulturalists and the province are therefore looking into ways of using, and possibly expanding, the fresh water volumes in creek ridges, but there is a danger of harming this sensitive source of fresh water (Figure 1). The limited capacity of the river water pipeline during drought periods has led to the study of buffering options to better absorb demand peaks on the system.
Solution path: storing freshwater underground (aquifer storage and recovery)
Since large quantities of fresh water are available from surface water sources (or the agricultural water system) in many areas over the winter period, the collection and storage of water at this time is a good solution to cover temporary water shortages in the summer. There are a number of advantages to storing water underground compared, for example, to doing so in above-ground foil basins:
- The capacity of the underground is generally larger.
- There is limited above-ground storage space.
- Fresh water underground is protected against dust, evaporation, temperature fluctuations and algal bloom.
On the other hand, aquifer storage and recovery in a saline underground is not simple. The injected fresh water can become irrecoverable because of groundwater flow, or due to buoyancy caused by its relatively low density compared to the surrounding or underlying saline or brackish groundwater. In addition, well clogging can occur. The problems of the water’s rising movement and well clogging were observed in the 1980s in a test at Kapelle-Biezelinghe by the Commissie Grondwaterbeheersing en Verzilting (Groundwater Management and Salinisation Commission).
Storing water using the Freshmaker
One of the relatively new innovative options for successfully storing fresh water is the Freshmaker. It’s inspired by the success of Horizontal Directional Drilled Wells (HDDWs) and the implementation of the “Freshkeeper” concept for the protection of drinking water abstraction. The Freshmaker offers a technology whereby, in the winter, the (thin) fresh water aquifer situated below agricultural areas is enlarged, so that more fresh water can be extracted. Using a (deep) horizontal well, saline or brackish water is abstracted at a depth of 10 to 15 meters, thus freeing up space for the (artificial) infiltration of the precipitation surplus which is thus not discharged through the waterways. In the summer this fresh water aquifer is used to meet the water needs of the agricultural sector (Figure 2).
The Freshmaker is being implemented for the first time in Ovezande, and fruit-grower Rijk-Boonman should have enough available fresh water even during long periods of drought. Researchers will be monitoring the water’s infiltration, storage and recovery closely to learn more about the Freshmaker’s potential.
Field trial in Ovezande (Zuid-Beveland)
In the summer of 2012, a potential site for the Freshmaker trial in Ovezande was studied in detail. The area has a fresh water aquifer about 9 m thick. By using the Freshmaker, this could be significantly expanded over a length of 70 m by infiltrating fresh water from a waterway during the rainy period. A local fruit-grower (Maatschap Rijk-Boonman) should therefore have enough available fresh water, even during long periods of drought. The drilling work was carried out in the winter of 2012/2013 for the wells and the monitoring network. The fresh water for the infiltration was also let in from the waterway in wet periods. Following its infiltration in the spring the water should be recovered in the summer. The infiltration, storage and recovery of the fresh water are subject to close monitoring to learn more about the Freshmaker’s potential.
Knowledge for Climate Tranche 3 (2012-2013)
The Freshmaker research is part of the GO-FRESH project, which is a component of the Knowledge for Climate research programme Tranche 3 (Hotspot Southwest Netherlands Delta). Deltares, Alterra, Acacia Water, Hogeschool Zeeland and KWR Watercycle Research Institute are working together researching hydrological solutions in the Southwest Netherlands Delta. The research has the following parts:
1. Fresh water storage in and around creek ridges (including the Freshmaker)
2. Improved drainage techniques in saline seepage areas.
The project is being cofinanced, among others, by: