Conductivity measurements for the evaluation of the entrance of the salt wedge
Conductivity measurements for the evaluation of the entrance of the salt wedge
The salt wedge phenomenon is generated in environments close to the coasts. It shows why seawater with a high salt content enters the continental aquifer over distances that can sometimes be significant. This extraordinary event is the source of important problems that can cause difficulties for water supply systems both, linked to agriculture and human consumption.
Tecnopenta has always supported large companies connected with management of water resources, through the installation and maintenance of automatic monitoring systems for parameters such as conductivity and rivers and canals water levels. Installing sensors of this type can be difficult. The first point to take into account is the installation site. Generally we tend to install the probes immersed in loops or small recesses in the banks. In this way, protection is offered in the event of floods or in the event of risks of collision with material transported by the current. However, care must be taken because the water must not be too subject to stagnation, as the chemical and physical parameters at the point of installation may not undergo the same changes as the rest of the volume of interest. The second thing to evaluate is how to protect in the best way the probes. In order to measure correctly, the sensors must be immersed and a body immersed in a fluid flow, that varies over time, can be subject to many problems, for example it could suffer impacts or move excessively and become damaged. A third problem is the need to access data quickly and easily. It makes necessary to evaluate the energy requirements of the equipment very carefully because the installation locations are often remote and not served by the national electricity grid.
Tecnopenta has always supported large companies connected with management of water resources, through the installation and maintenance of automatic monitoring systems for parameters such as conductivity and rivers and canals water levels. Installing sensors of this type can be difficult. The first point to take into account is the installation site. Generally we tend to install the probes immersed in loops or small recesses in the banks. In this way, protection is offered in the event of floods or in the event of risks of collision with material transported by the current. However, care must be taken because the water must not be too subject to stagnation, as the chemical and physical parameters at the point of installation may not undergo the same changes as the rest of the volume of interest. The second thing to evaluate is how to protect in the best way the probes. In order to measure correctly, the sensors must be immersed and a body immersed in a fluid flow, that varies over time, can be subject to many problems, for example it could suffer impacts or move excessively and become damaged. A third problem is the need to access data quickly and easily. It makes necessary to evaluate the energy requirements of the equipment very carefully because the installation locations are often remote and not served by the national electricity grid.
THE CASE STUDY: INSTALLATION OF CONDUCTIVITY PROBES ON RIVER BANKS IN THE ABSENCE OF STRUCTURES OR ARTEFACTS TO ATTACH TO.
PREPARATION OF MEASUREMENT POINTS
In August 2022, in a particularly dry period, Tecnopenta installed the first part of a much larger monitoring system involving the largest rivers in the Veneto area.
Especially, three automatic conductivity detection systems were installed on a single natural watercourse and at various distances from the mouth.The embankments at the installation points did not have structures that could be used to mount the meters, so stainless steel pipes approximately 4 m long were installed on the embankment which connect the floodplain to the river water. The pipes in question descend into the river with a variable inclination depending on the case but allow the probe to be safely installed up to a certain depth. The walls of the pipes have been appropriately drilled to allow the passage of water and ensure a relevant measurement.
Especially, three automatic conductivity detection systems were installed on a single natural watercourse and at various distances from the mouth.The embankments at the installation points did not have structures that could be used to mount the meters, so stainless steel pipes approximately 4 m long were installed on the embankment which connect the floodplain to the river water. The pipes in question descend into the river with a variable inclination depending on the case but allow the probe to be safely installed up to a certain depth. The walls of the pipes have been appropriately drilled to allow the passage of water and ensure a relevant measurement.
THE DATA LOGGER
Il compito di leggere, interpretare e memorizzare i dati misurati dai sensori di conducibilità è affidato ad una data logger FlexLog appositamente equipaggiato per svolgere al meglio il compito affidatogli.
In questa versione infatti il consumo di energia elettrica è minimo e l’alimentazione è assicurata da una batteria ricaricata da un pannello solare di piccole dimensioni (potenza 5 o 10 Watt a seconda delle caratteristiche di esposizione).
Le elettroniche sono protette da una scatola IP67 chiusa a chiave che poi è agganciata ad un palo cementato sull’argine
THE PROBES
The installed probes are made of steel and PVC and have the possibility of being calibrated with two ranges, 80 mS and 8 mS. In this specific case, the 8 mS range was chosen. The diameter of the probe is approximately 60 mm and it is designed to operate correctly underwater. The connection cable has a polyurethane sheath with high cut and chemical attack resistance, and inside it there is a Kevlar core which ensures its mechanical seal.
DATA STORAGE
The data is both, stored locally on a removable SD card and sent to a web platform where it is processed and graphed. It is possible to set alarm thresholds on all acquired values including the battery voltage. In this case, data is stored every 15 minutes and sent to the web platform every 30 minutes.
A special space dedicated to the data measured with the GPS positioning of the measurement stations has been created on the METRA web platform. Access takes place through an administrator profile which allows the creation of different access level to different sub-users accounts.
A special space dedicated to the data measured with the GPS positioning of the measurement stations has been created on the METRA web platform. Access takes place through an administrator profile which allows the creation of different access level to different sub-users accounts.
CALIBRATION AND MAINTENANCE SERVICE
The work is completed by a multi-year maintenance contract which includes visits by qualified and competent personnel.
During maintenance operations, the status of the electronics and probes is checked, the data from the local memories is downloaded, and the batteries and solar panels are checked.
Calibration is scheduled using certified sample solutions with known conductivity.
During maintenance operations, the status of the electronics and probes is checked, the data from the local memories is downloaded, and the batteries and solar panels are checked.
Calibration is scheduled using certified sample solutions with known conductivity.
