MONITORING THE SALTWATER INTRUSION BY TIME LAPSE ELECTRICAL RESISTIVITY TOMOGRAPHY: THE CHIOGGIA TEST SITE (VENICE LAGOON, ITALY)
| Autor: | DE FRANCO R, BIELLA G, TEATINI P, TOSI L, CHIOZZOTTO B, CLAUDE C, MAYER A, BASSAN V, GASPARETTO-STORI G |
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| Jazyk: | angličtina |
| Rok vydání: | 2007 |
| Předmět: | |
| Zdroj: | SESTO Forum Italiano di Scienze della Terra, pp. 62, RIMINI, 12-14 settembre 2007 info:cnr-pdr/source/autori:DE FRANCO R; BIELLA G; TEATINI P; TOSI L; CHIOZZOTTO B; CLAUDE C; MAYER A; BASSAN V; GASPARETTO-STORI G/congresso_nome:SESTO Forum Italiano di Scienze della Terra/congresso_luogo:RIMINI/congresso_data:12-14 settembre 2007/anno:2007/pagina_da:62/pagina_a:/intervallo_pagine:62 |
| Popis: | An electrical resistivity tomography (ERT) time lapse experiment aimed at monitoring the dynamics of the saltwater intrusion in the coastland bounding the southern Venice Lagoon, near the city of Chioggia (Italy), is presented. The experiment, operated for about one year from November 2005 to September 2006, was carried out by means of an apparatus developed ad hoc. Some preliminary test and calibration acquisitions allowed the final setup of the experimental parameters. The system acquired 10 apparent resistivity tomograms per day, five of which with high resolution by a 97.5 m long ERT line with a 2.5 m electrode spacing and five by a 300 m long and 5 m electrode spacing ERT line, suitable to monitor the intrusion process down to 50-60 m depth. A 50 m deep exploratory borehole drilled near the test site identified a shallow phreatic aquifer and two confined aquifers within the depth of interest and allow to constrain the electro-stratigraphy obtained by the resistivity tomography. The collected data point out a different time behavior of the salinization process in the upper aquifer with respect to the deeper ones. The shallow aquifer, located between 3 and 15 m depth below mean sea level, is the most contaminated by the salt intrusion with a minimum resistivity formation value of 0.8 ohm*m. For the upper 2-3 m depth the experimental data reveal a seasonal resistivity fluctuation with a minimum salt intrusion in March-April and a maximum in the dry summer season. An opposite behavior was experimented by the lower part. The deeper aquifers are characterized by a resistivity ranging from 3.0 ohm*m to 10 ohm*m and show a resistivity rise at the beginning of the summer time probably due to an increasing contribution of fresh water from sub-regional aquifers. The data collected by the experiment have been correlated with a number of environmental variables, i.e. tidal regime, rainfall, groundwater table, and water levels in the watercourses close the monitoring site. In particular, a correlation is found between the resistivity in the upper 5 m of the phreatic aquifer and the rainfalls, and between the water level in the adjacent main channel and the resistivity down to about 10 m depth. This relation is indicative of the draining/feeding influence exerted by the channel probably only to the first aquifer. Moreover a quite clear negative correlation with the tidal regime is observed at seasonal time scale, while at daily time scale the tidal oscillation doesn't affect the resistivity behaviour in the phreatic aquifer. |
| Databáze: | OpenAIRE |
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