GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 3.2 143 Geophysical and hydrogeological characterization of Sirino Lake (Basilicata, Italy) V. Giampaolo 1 , L. Capozzoli 1 , E. Rizzo 1 , S. Grimaldi 2 1 CNR-IMAA. Laboratorio Hydrogeosite, Marsico Nuovo (PZ), Italy 2 Università degli Studi della Basilicata, Potenza, Italy Introduction. The presence of natural or artificial lakes and reservoir that can empty due to natural phenomena such as landslides, flood and piping is a serious hydrogeological problem because it can generate catastrophic events affecting urban and agricultural areas settled below the source area. This is the case of ��� ������ ���� ��������� �� ��� ���� �������� �� ���� ������� �� � ������ the Sirino Lake affected, in the last century, by many pipings as a result of sudden openings of sinkholes which resulted in the almost total lake depletion (Fig. 1). Moreover, t�� ��������� ����������� �������� ���� ��� ���������������� ��� ������� ����� he hydraulic instability combined with the geomorphological and seismic risks recognize the entire area as exposed to potential flood and landslide risk due to new episodes of siphoning. In order to mitigate this hydrogeological risk it is necessary to solve some fundamental questions regarding for example the thickness of the impermeable layer und the lake, the flow pathways and the presence of possible ����� ������ ������� ���������� ���������� ��������� water escape routes. Therefore, scientific community has devoted considerable attention to some geophysical methods, such as electrical resistivity tomography (ERT), Ground Penetrating Radar (GPR), and self-potential (SP) because these methods are relatively time and cost effective when working on large area and are reasonably user-friendly for geomorphologists (Naudet et al. , 2008). The electrical resistivity method is an important tool in the hydrogeological applications (Kosinski and Kelly, 1981; Daily et al. , 1992; Slater et al. , 1997; Binley et al. , 2002; Dam and Christensen, 2003; Darnet et al. , 2003; Rizzo et al. , 2004; Binley and Kemna, 2005; Straface et al. , 2007). One of the electrical resistivity surveys skill is the evaluation of subsurface condition in water-covered area (stream, river, wetland, lake, and see) for hydrogeological and environmental purposes. Surveys in water-covered areas includes conventional surveys using multi-electrodes resistivity system where part of the survey line crosses a river or a lake, and surveys conducted entirely within a water-covered environment (Loke and Lane, 2004). However, while on dry land the geoelectrical method is well known, the method in water-covered areas is not widespread. Still ���� ������ ��� ���������� ����������������������� �� ��������� ����� ��� ������ �������� less common are electrical resistivitymeasurements in wetlands, ponds and lakes. Examples of applications have been reported by Mansoor and Slater (2007) who performed aquatic electrical resistivity imaging to predict spatial and temporal patterns of pore-fluid conductivity in wetland soils using fixed floating electrodes, Baumgartner (1996) who used electrodes located underwater and orientated vertically, and ����Yang et al. (2006) who integrated GPR and resistivity image profiling methods at the water surface. ��������� ���������� ��������� ���� ��� ��������� Inversion algorithms generally used for inverting apparent electrical resistivity measurements in water covered areas are commonly iterative, nonlinear least squares methods, with regularization based on discretized first or second spatial derivative filters, to produce a flat or smooth tomogram, respectively. One strategy to improve the resolution of electrical resistivity tomograms in water covered areas is to incorporate constraints on the water-column resistivity and thickness (Loke and Lane, 2004). Ground penetrating radar (GPR) is a high resolution geophysical electromagnetic technique (10 MHz ÷ 2 GHz) designed primarily to investigate the shallow subsurface of the earth, building structures, roads, and bridges. However, GPR was used successfully to locate and characterize risk of subsidence of a sinkhole collapse in carbonate crock outcrops (Gómez- Ortiz and �������������� ������ �� ������ ����� �������� ������ ������ Martín-Crespo, 2012), to assess karst collapse hazard (Nuzzo et al. , 2004), to identify geological hazard for exploitation (Zayc et al. , 2014) in flyschoid rocks, to detect water surface of geological structures beneath rivers, ponds, and swamps (Yang et al. , 2006) and to predict and follow development sinkholes near lakes (Frumkin et al. , 2011).