Hydrochemical inspection of landslide drainage structures reveals high risk for scaling processes

The limited accessibility during visual inspections remains a central problem for maintaining and repairing of landslide drainage structures. Unwanted mineralization processes cause clogging and damage to drainage pipes, leaving reconstruction as the only option for remediation. Studies of water wells and tunnel drainages have shown that hydrochemical inspections can efficiently detect chemically triggered clogging processes at an early stage. However, these processes have barely been recognized in landslide drainages. Three drainage structures from sites with varying traffic intensity were selected from the road network in south-eastern Austria. Drainage waters and mineral scalings were analyzed to assess the hydrochemical conditions causing unwanted clogging processes. All sites exhibited unexpectedly high electrical conductivity values reaching up to 2500 μS/cm compared to the natural environmental background of ∼400-600 μS/cm, due to the application of road salt during the winter season. The resulting high Na⁺ concentrations (up to 300 mg/L) triggered Ca²⁺ exchange reactions within the soil and leaching of concrete elements, which both favored the formation of Ca-carbonate (CaCO₃) deposits of up to ∼1500 kg and the neoformation of ∼12 kg of kaolinitic clay per year within the drainage systems. Based on these results, a concept for the integration of hydrochemical methods during drainage inspections was developed, allowing the identification of problematic sites and mitigation measures at an early stage.