Drones for Groundwater Research

 

waterdrone

Drones are growing in popularity in the water sector, because they can monitor water systems at places that are difficult to access on foot or by car. They can carry all kinds of monitoring equipment and give a new dimension to aerial photography. Deltares is developing a drone as well, to monitor salt concentrations in groundwater.

The intrusion of brackish water can be problematic for agriculture in low-lying delta areas, especially during droughts. The intrusion can either occur via surface waters, or via the groundwater. The growth of crops decreases at elevated salt concentrations. Therefore it is vital to know how fresh water and brackish water are distributed in agricultural areas.

Current methods to monitor salt concentrations in groundwater involve a lot of field work, or expensive helicopter flights. Drones can be the solution for these limitations. They can carry monitoring equipment over a reasonable distance, at an affordable price.

The prototype octocopter

The equipment for monitoring salt concentrations in groundwater is large and heavy, which poses serious challenges to the carrying capacity and the flight characteristics of a drone. Therefore Deltares and Aerial Innovate are developing a drone that is tailor made. The instruments are part of the construction of the drone. Our prototype is an octocopter, with a carrying capacity of 4.5 kilogrammes. Using the GPS, the drone can fly a grid autonomously and return by itself.


Salt concentrations are measured by transmitting an electromagnetic field and receiving the reflected signal. The salt concentration in groundwater determines the conductivity: the more salt, the higher the conductivity. By processing the reflected signal, and taking the conductivity of the soil into account, the salt concentrations can be deducted. The electromagnetic field is generated by a Ground Electro Magnetic device (GEM), which consists of copper coils inside a plastic jacket. The GEM must be long enough (and therefore heavy) to produce a proper electromagnetic field.

Helicopter flights over the Province of Zeeland

The technique to measure salt concentrations from the air has been applied in theProvince of Zeeland. The picture below shows the Helicopter Electro Magnetic system that was used by the FRESHEM project. A helicopter carrying the HEM has flown over the area in parallel lines, with 100m to 300m distance in between. Measurements were made every 4m.

helicoptertorpedo

The FRESHEM project delivers a 3-dimensional map of salt concentrations in the groundwater of the Province of Zeeland. The islands in the south-western delta of The Netherlands are surrounded by (former) estuaries and the North Sea. They are prone to salt intrusion and fresh water is scarce. The map provides valuable insight in the distribution of fresh, brackish and salt water. This information will be used to develop water management strategies for the islands.

Development of a mega drone

The development of a drone that can carry heavy equipment is a challenge in itself. In our case, the GEM device supports the frame of the prototype octocopter. The position of the propellers was adjusted in accordance for optimal balance. At the moment, the drone has only been operated at designated airfields, because of the regulations for operating a drone.

The future goal is to develop an even bigger drone that can carry 8 kilogrammes of equipment. The projected drone could be 6 meters long and 2 meters wide and have 16 propellers.

Conclusion

The drone for monitoring salt concentrations in groundwater is a promising new technique. The aim is to survey a couple of square kilometres of farmland, at an affordable price. With the joint development of a mega drone, measuring instruments and software, we have entered the highly interesting field of robotics.

Joost Icke, software manager at Deltares and environmental engineer.