Doing fieldwork with KWR

Researchers at KWR devote themselves daily to water practice, in an effort that frequently involves working in the field. Young Water Professional Janine de Wit introduces us to the world of subirrigation as a means of responding to water availability challenges. This work takes place underground, but a lot can be said about it above-ground.

Janine has the word: ‘Within the Lumbricus, KLIMAP programmes, and in my doctoral research, we work on the question of whether and how controllable drainage with subirrigation (reverse drainage) can contribute to a more robust water system. This technique means: retaining and supplementing water when possible, and discharging it only when necessary. Even in places like the Netherlands that have precipitation surpluses, it is becoming an increasingly complex matter to have sufficient water available of the right quality, and at the right time and place. This is the consequence for instance of climate change, more frequent extreme weather (wet and dry), urbanisation, and increased water use for multiple purposes. But in the Netherlands the water system is also a component of the water availability question, because it is designed primarily for the discharge of water.’

‘In different projects we are investigating the operation of subirrigation on a field-scale, but also how it might be incorporated into the regional system. We are doing this for example by collecting measurement data in field trials on the sandy grounds, as in Stegeren, America, Lieshout and Haaksbergen. We can test our computational models with these data, as a means of getting a picture of the opportunities and obstacles to subirrigation in other areas and periods.’

Controllable drainage with subirrigation

Janine explains how subirrigation works. ‘We know drainage as a pipe system under the ground that discharges groundwater to the surface water. When the end of this pipe system is connected to what we call a ‘collection well’, the system becomes controllable. By actively setting the water level in the well, and thus the ‘drainage basis’, one can control how much water is discharged (drainage), retained or infiltrated (subirrigation). In subirrigation, water is pumped into the collection well. As soon as the water level in the well is higher than the groundwater level in the land parcel, the water infiltrates out of the pipes into the soil, the groundwater level rises, and the water availability for the crop improves. In the field trials we make use of different water sources for subirrigation: surface water, treated residual water (industrial and household) and shallow-abstraction groundwater. We quantify the effect of the measures on the water availability for crops and in the change in the pressure on the groundwater.’

Work as a Young Water Professional

What is Janine enthusiastic about in her work as a Young Water Professional at KWR? She explains: ‘Having grown up in the polder and, following my studies at Wageningen University, I felt in the first instance more attracted to the practical side of water management rather than the science. But when I was working on my Master’s in Israel and my internship at KWR, I realised that I found the science extremely interesting. In 2019 I started working at KWR as a researcher in Ecohydrology. And in November 2020 I began my doctoral research under the supervision of Ruud Bartholomeus, who is a KWR researcher and is associated with Wageningen University. It was an incredible opportunity to develop myself further and to connect science to practice. Gaining an understanding of the water system through a combination of fieldwork, data analysis and modelling work is what energises me the most. I hope in this way to provide some pieces to the puzzle of how to improve our management of the freshwater resources available in the Netherlands. I am greatly looking forward to the years ahead!’

Controllable drainage with subirrigation can be implemented whenever there is a source of water available that can be introduced into the pipe system. The water source could for instance be surface water, treated residual water or groundwater. In Haaksbergen a field trial

has been set up in partnership with KnowH2O and the Vechtstromen Water Authority. In this field trial part of the WWTP effluent is pumped into the drainage system.  This means that the residual water is being reused rather than being discharged into a surface water body (the Bolscherbeek stream). The land parcel is monitored to measure the impact on both the quality and quantity of groundwater. This monitoring is incorporated within research programmes, such as WiCE, Lumbricus, KLIMAP en NWO-RUST.

Various monitoring wells are installed in the trial land parcel to assess the water quality. They also determine the groundwater levels, the drainage level (in the well), soil moisture and pump volumes. The sensors are mostly located underground and are measured [coordinates, NAP (Normal Amsterdam Level) levels] with special land surveying equipment (RTK-GPS), which is actually also used to later locate the sensors (photo).

The water level in the monitoring wells is measured both manually (left) and automatically. Measurements are taken every quarter-hour by pressure transducers, which – like soil moisture sensors – are connected to an online data portal via telemetry. The manual measurements permit the control and, if necessary, correction of the automatic ones. The measurements provide insight into the impact of subirrigation on the groundwater level.

When the groundwater level is lower than the drainage level in the well, water flows in the pipe system. A control mechanism in the well can be calibrated in such a way that water is retained in dry periods. In wetter periods water discharge might be necessary. In the photo Dion van Deijl (KnowH2O) reads out the sensor in the drainage well.

The treated residual water that is used in Haaksbergen for subirrigation still contains pollutants. It is important to understand how these pollutants spread to the crop’s root zone and to the deeper groundwater. To this end, a monitoring network has been installed to take water samples at specific points and depths (down to ± 10 meters).

On the fieldwork day, Dominique Narain-Ford (PhD-student NWO-RUST) filters the water samples, which are immediately sent to the lab for various analyses. These include determining the chloride/bromide ratio (as tracer) and investigating whether pharmaceutical residues are present.