Why Groundwater Online Monitoring is Required and How it Works?
Groundwater is one of the Country’s most precious resources. We are presently faced with the grim reality of ever depleting fresh water resources due to a variety of reasons like over exploitation for human use, high degree of pollution, drying up or depletion of sources of recharge such as glaciers and run off of rainwater without percolating in ground. Depletion in fresh water reserves is going to make life extremely difficult for future generations. Efforts to save water and to reuse it are being made all across the World.
Water level measurements from observation wells are the principal source of information about the hydrologic stresses acting on aquifers and how these stresses affect groundwater recharge, storage and discharge. To assess groundwater conditions such that adverse situations can be efficiently handled, reliable and accurate groundwater data is required well in time.
Why online monitoring?
In order to plan the groundwater development and management programme, a database needs to be generated. Long term, systematic measurements of water levels provide essential database needed to evaluate changes in the resource over time, to develop groundwater models and forecast trends; also to design, implement and monitor the effectiveness of groundwater management and protection programs.
Earlier practice was to take groundwater level data four times a year that is pre-monsoon and post-monsoon, that is just twice or four times a year. Moreover, the monitoring task became gigantic and expensive when the number of sites to be monitored increased.
Since groundwater is a dynamic resource, best database can be generated only with continuous monitoring. The exploitation of the groundwater resource also give rise to the need for near real time or online monitoring at a large scale to take suitable corrective measures without losing time.
Automated groundwater monitoring systems are the best solution to collect large amounts of water level data with minimal time and effort. The systems not only allow data from remote locations to be monitored in near real time, but they also eliminate any chance of human error in recording data. Also the actual data cannot be intentionally or unintentionally modified by any person.
The data from these online systems can be accessed through web by anyone across the World, with required authorization credentials. A significant advantage of such systems is the ease and speed with which data can be updated and made available to the users. Alarm limits can also be set for which SMS or email alerts are sent to preset mobile phone numbers or email ids.
How the automated groundwater monitoring system works?
To monitor water level at a particular location, either an existing well/borehole is used or a borehole is drilled down to the aquifer that contributes most to the water table. A casing pipe is installed in the borehole to prevent the borehole wall from collapsing. At the level of the aquifer (lower end of casing pipe) a highly porous filter is provided. The filter generally consists of a section of slotted pipe covered with geotextile to prevent soil particles from clogging the borehole. The level of water in such a borehole or well corresponds to the water table at that location.
The automatic water level monitoring system is installed in the observation well by geotechnical companies to monitor the water level variation in it.
A typical system consists of following components:
· Absolute pressure/Level sensor (model EPP-30V, EPP-40V or EPP-60V) suspended down the observation well, up to the required installation depth. It measure the ware columns above it i..e height of the water columns above the pressure sensor.
· Automatic data logger (ESCL-10VT or ESDL-30) to record, store and transmit the data at required intervals, settable at even 5 seconds.
· Interconnecting cable from sensor to data logger, with Kevlar strain wire
· Temperature sensor inside pressure sensor to measure water temperature
· Barometric pressure sensor inside data logger to measure atmospheric pressure
· GSM/GPRS modem in the data logger for data retrieval/transmission with telemetry
The data logger measures the output from absolute pressure sensor, barometric pressure sensor and the temperature in ºC and calculates the pressure in terms of water column after correcting for the measured atmospheric pressure and water density. The data is stored, together with the current date, time and battery voltage, as a data record in internal non-volatile memory of the data logger.
The automatic data loggers have application software with features that allows the user to set the sensor calibration coefficients, recording intervals, data logger or borehole code (identification tag numbers), sensor serial number, real time clock time, transmission time interval, etc. They are programmed to wake up every day at a set time and send the data collected over the past one day to the remote PC/Server/Cloud.
