Origin and assessment of deep groundwater inflow in the Ca' Lita landslide using hydrochemistry and in situ monitoring

Abstract

Abstract. Changes in soil water content, groundwater flow and a rise in pore water pressure are well-known causal or triggering factors for hillslope instability. Rainfall and snowmelt are generally assumed as the main sources of groundwater recharge. This assumption neglects the role of deep water inflow in highly tectonized areas, a factor that can influence long-term pore-pressure regimes and play a role on local slope instability.This paper aims to assess the origin of groundwater in the Ca' Lita landslide (northern Italian Apennines) and to qualify and quantify the aliquot attributable to deep water inflow. The research is essentially based on in situ monitoring and hydrochemical analyses. It involved 5 yr of continuous monitoring of groundwater levels, electrical conductivity and temperature and with groundwater sampling followed by determination of major ions (Na + , K + , Mg 2+ , Ca 2+ , Cl − , HCO Results show that the groundwater balance in the Ca' Lita landslide must take into account an inflow of deep and highly mineralised Na-SO 4 water (more than 9500 µS cm −1 ) with non-negligible amounts of Cl − (up to 800 mg l −1 ). The chemical and isotopic fingerprint of this water points to oilfield water hosted at large depths in the Apennine chain and that uprises through a regional fault line crossing the landslide area. It recharges the aquifer hosted in the bedrock underlying the sliding surface (at a rate of about 49 000-85 700 m 3 yr −1 ) and it also partly recharges the landslide body. In both the aquifers, the hydrochemical imprint of deep water mixed with rainfall and snowmelt water was observed. This indicates a probable influence of deep water inflow on the mobility of the Ca' Lita landslide, a finding that could be applicable to other large landslides occurring in highly tectonized areas in the northern Apennines or in other mountain chains. The paper demonstrates that hydrochemistry should, therefore, be considered as a valuable investigation method to define hydrogeological limits and the groundwater sources in hillslope and to assess groundwater flow patterns in deepseated landslides.

Groundwater—Surface waters interactions at slope and catchment scales: implications for landsliding in clay‐rich slopes

“…In particular, by allowing the development of preferential flow‐paths driving groundwater from far away, they can lead to the creation of multi‐scale hydrological systems (Tóth, ) in which spatial connections among different reservoirs are possible (Roques et al, ). The role of these geological structures and of the possible preferential water flows has already been demonstrated for controlling slope instability (Guglielmi et al, ; Bonzanigo et al, ; Cervi et al, ; Vallet et al, ). However, at the best of our knowledge, no work concerned the analysis of the interaction between local (1–10 km) and meso‐scale (10–100 km) hydrological systems, limiting the representativeness of simplified hydrological models as they mislead the water origin and flow paths.…”

Contribution of time-related environmental tracing combined with tracer tests for characterization of a groundwater conceptual model: a case study at the Séchilienne landslide, western Alps (France)

“…The groundwater chemistry can also be influenced by the landslide hydromechanical processes, thus distinguishing water which flowed through the unstable zone from the water which did not flow through the unstable zone (Binet et al 2009). In addition, geochemical inverse modelling allows one to characterize solid phases involved in the water-rock interaction processes, to estimate the mass transfers and to validate the flowpath hypotheses with the results of tracer tests and δ 18 O values (Cervi et al 2012).…”

“…Methods are mainly based on chemical analyses of major elements (Cappa et al 2004;Binet et al 2007a), but additional parameters can be used to identify and quantify specific processes. These parameters include water stable isotopes (Guglielmi et al 2002;Lin and Tsai 2012), trace elements (Cervi et al 2012), natural fluorescence (Charlier et al 2010) and artificial tracers (Bonnard 1988;Binet et al 2007b). However, hydrochemistry surveys are time-consuming, expensive and require specific expertise.…”

Identifying the origin and geochemical evolution of groundwater using hydrochemistry and stable isotopes in the Subei Lake basin, Ordos energy base, Northwestern China

“…These techniques have been widely used to obtain groundwater information such as its source, recharge and the interaction between groundwater and surface water (De Vries and Simmers, 2002;Yuko et al, 2002;Yang et al, 2012a). The technique of stable isotopes as excellent tracers has been widely used by many scholars in the study of hydrological cycle (Chen et al, 2011;Cervi et al, 2012;Garvelmann et al, 2012;Yang et al, 2012a;Hamed and Dhahri, 2013;Kamdee et al, 2013). Greater knowledge on the origin and behavior of major ions in groundwater can enhance the understanding of the geochemical evolution of groundwater.…”