GroenLeven needed an accurate, cost-effective way to identify the best location for the anchor rods in two lakes in the Dutch provinces of Drenthe and Gelderland to derisk construction, ensure the longevity of the installation, and protect the lake flora and fauna. But building floating solar farms in sand excavation lakes is challenging because of the complex irregular lakebeds and water depths.
We applied our innovative WAGEO geophysical technology, which combines electrical resistivity tomography (ERT) underwater, together with bathymetric measurements of the lakebed and as ERT on land for correlating CPT data, to meet GroenLeven’s requirements in full.
Our WAGEO ERT technique characterises subsurface materials in terms of their electrical properties. It measures electrical resistance in the sediment and variations in particle size, clay ratio and the conductivity of the pore fluid in soil. Based on the patterns recorded, it distinguishes between clay, silt, sand and gravel layers, mapping them out with a high degree of accuracy.
We used our special technique to perform underwater ERT investigations using an innovative streamer cable design with 24 electrodes. The streamer cable was attached to a boat and pulled across the lakebed while taking electrical conductivity measurements at various electrode settings.
WAGEO technology is used for underwater ERT research
To analyse the data from the underwater ERT investigations, we also acquired:
- Bathymetric datasets relating to the depth, vertical electrical conductivity and temperature of the body of water above the electrodes
- Geological datasets from cone penetration tests or manual drilling
- Knowledge of electrical sediments features to interpret the 2D conductivity soil model.
At both lake locations, we measured eight ERT conductivity profiles: six in the water for location of the anchor rods and two on land for correlating the CPT data and thus be able to classify the WAGEO ERT for lithology. We used this information to identify four sediment categories:
By combining and interpolating the ERT profiles, we created a comprehensive overview map for each lake area, detailing the various soil layers beneath the lakebed.
Our non-intrusive WAGEO survey technology measured and analysed the lakebed without damaging any of the flora and fauna.
The innovative 24-electrode streamer cable measured electrical conductivity across a range of electrode configurations and accurately defined the safest anchor locations in areas of complex former sand excavation lakes.
Our WAGEO solution provided GroenLeven with accurate soil datasets so they could optimise the precise location and burial depth for the rod anchors at both lakes.
Accurate Geo-data measurements of the soil layers will help GroenLeven achieve the safe, cost-effective construction and continuous operation of these two important floating solar farms.
"With WAGEO Fugro offers an innovative method to determine subsurface parameters in former sand extraction lakes, as opposed to expensive CPT from the water."
*Banner image courtesy of GroenLeven