In the context of the project iDrain (research line 1) of WaterNexus, we have developed a site to conduct experimental research. This site has been constructed in the summer of 2018 and experimentation is intended to begin in August. The location of the site is at the premises of the Golf Field “The International” in Haarlemmermeerpolder, close to Schiphol, with kind permission of Mr. M. Welling.
The experiments that are intended are aimed at investigating how well controlled drainage (the innovated drainage strategy that is much more flexible for managing water conditions in soil, and that is being introduced at a growing number of farms in The Netherlands) can be used for anticipatory soil water management, or anticipating drainage. It is well known, that the weather can be forecast well on the short term (of days), but for longer times of weeks or months, this is difficult and prone to uncertainty. If it is known that a dry or wet period is forthcoming, we can adjust our drainage level, respectively by making it more shallow or more deep. This would be aimed at to avoid drought stress, and inundation or anaerobicity in the root zone, as both situations are counterproductive for a good quality grass (or crop) cover. If the fresh (non-saline) groundwater is floating on deeper saline water, as is the case in the Dutch coastal provinces, the management of root zone water availability through adaptive drainage becomes more complicated, but even more relevant as high salt concentrations in root zones are detrimental for crop growth. This complexity is the topic of study in WaterNexus project 1.2.1, entitled “iDrain”.
The site has dimensions given by 32m x 9m and a total depth of 1.5m. With a water impermeable foil, the basin has been hydrologically insulated from its surroundings. The basin is subdivided into two sub-basins, each with a width of 4.5m. The base of the basin is filled with highly permeable drainage sand, the rest is filled with a sandy clay.
In the sandy base infiltration drains have been positioned, through which we can simulate seepage of (saline) groundwater. At depths of 40 and 80 cm we have placed collector drains along the length of the field in both basins, with nine drains attached perpendicularly. These drains can be shut off individually by inflatable tubing, thereby creating flexibility in drain system layout. The tubing ascertains drains do not act as preferential flow path. Drains are spaced such that drain distances of approximately 5, 10 and 15 meters can be used. The collector drains end inside a manhole, in which the outflow height can be set to create a controlled drainage system.
Figure 1: Sketch of the Southside of the site. The basin is represented in green color with a drainage sand layer at the bottom in yellow. The main drain is in blue. The main drain ends in a collector well for which the overflow level can be adjusted. Water that flows out of the collector well ends up in another barrel.
Figure 2: Impressions of the site.
Most of the soil – and drain related work has been finished by June 2018, although some minor problems still need to be resolved. Also, installation of most sensors for measuring groundwater depth and – conductivity, as well as soil moisture content and – conductivity was finished. Data is transmitted to the internet, such that (near) real time assessment of the current field conditions can be combined with the expected weather. Sensors are placed in cooperation with Eijkelkamp and the University of Twente, for which we test two independent methods of data collection and – transmission. This gives insight into which measurement method can best be deployed for anticipating groundwater management under normal field conditions. In particular, the interaction between controlling drainage and monitoring strategies using the collection/transmission systems will be given consideration.
Currently, we are installing the final part of this field site which entails regulation and measurement of fluxes. Seepage via the lowest infiltration drains and (sub)irrigation via top drains or sprinkler system is done using a set of pumps and valves coupled to a data logger, which can operate individually but can also be remotely controlled from any location with an internet connection. This logger also collects and transmits information regarding applied fluxes and basin averaged discharge fluxes. Finally, grass will be sown on both basins once the weather permits.
The combination of isolated basins, flexible drain system layout, detailed measurements and the possibility to mimick saline groundwater infiltration gives us the unique capability to play with saline seepage, density driven flow and adaptive drainage in which the water levels are adjusted dynamically, depending on (anticipating) drainage strategies that are investigated in the project.
Figure 3: Photograph of the site at the end of June 2018.
We appreciate the hospitality of Marcel Welling, CEO of The International Golf Club at Oude Haagseweg 200, 1171PE, Badhoevedorp, who allowed us to construct our experimental field site on the premises of The International Golf Club. This work was funded by NWO and the Ministry I&W.
Text: Daniël van de Craats & Sjoerd van der Zee, Wageningen University