Ground water is a hidden and precious resource. Its availability in quantitative and qualitative means is difficult to ascertain. The behaviors of water present underground and its properties such as transmissivity and storitivity can be obtained only through measurement of water levels present in the ground water extraction structures. As water level is the manifestation of the stress undergone by the aquifers, its measurement and monitoring is essential for knowing about this resource.
Why ground water monitoring is required?
The nature and present situation of the any water bearing underground formations can be obtained only through water level measurements. Ground water is an extensive resource, concealed underground and in most of the area it is inaccessible for any physical measurement. So it is very essential to measure its levels which are indicative of hydrostatic balanced plane of underground gradient for water flow and over ground pressure on it. The changes in quantity and quality of the ground water occur through slow process. In order to understand this slow changes long term measurement and monitoring is very essential. Other than water level measurements, quick monitoring of this resource is not possible by any other means. As water levels are indicatives of hydrologic stresses undergone by the aquifer which is having impacts on ground water recharge, storage and discharge, its monitoring in short as well in long terms are very essential. Groundwater regime monitoring will also help in design, implementation and monitoring the effectiveness of the ground water management, protection and conservation programs.
What is ground water regime monitoring?
In its simplest definition ground water regime monitoring is water level measurements from a network of observation wells. It is a collection of data, generally at set locations and depths and a at regular time intervals in order to provide information which may be used to determine the state of groundwater both in quantitative and qualitative sense, provide the basis for detecting trends in space and time, and enable the establishment of cause-effect relationships. Objective of any ground water regime monitoring is to record information on ground water level and quality through representative sampling in space and time.
When can it be measured?
Hydrologically India is a monsoon centric country with heavy precipitation during few months and long span of lean period. This pattern is having an impact in ground water monitoring phases as well. In general ground water will be monitored four time of the year.
January – 1st to 10th of the month- represents the recession stage of ground water level
April\May – 20th to 30th of the month – represents water level of Pre-monsoon period. April is for southern portion of the country where monsoon arrives in first week of June and May for northern stages where monsoon arrives around middle of July
August – 20th to 30th of the month – represents peak monsoon water level
November – 1st to 10th of the month- represents water level of Post-monsoon period
How can we do ground water regime monitoring?
Ground water regime monitoring is part of the ground water management process. It is a cyclic process which starts with ground water management and end up with the same. The first activity in any ground water management program is to define the objectives of the program. Then the regime monitoring strategy will be defined. This will be followed by network design and data collection. Data collection will be for quantitative measurements as well as qualitative data collection. Then followed by data processing, analyses and report generations. This information will be later utilized in the ground water management programs. The steps involved in ground water regime monitoring are
Establishment of monitoring stations: A groundwater monitoring network is a system of dedicated ground water monitoring wells in a geo hydrological unit at which ground water levels and water quality are measured at pre-determined frequency.
It should be representative for hydro geological set up
There should be optimum number of stations based on management criteria
There should not be any immediate abstraction or drawdown effect
Station should be accessible
Station should be permanent and is representative of local area
There should be replacement possibilities
Due consideration of hydrological process in the unit
Monitoring stations can be:
A key hole to aquifer
An abstraction well (tube well, bore well, or dug well)
Base line data collection: During the stage of construction of the monitoring wells information such as various logs, like litho logs and first struck water levels etc were recorded as base information to compare the rest of the year’s data.
Done at the time of development of a well
A static water level will be recorded as m bgl
Estimate altitude of the location with respect to mean sea level in a msl
A well log will also be prepared
Water samples will be collected for individual aquifers
The analysis results will be recorded and retained for further comparison
Data collection: Ground water levels can be measured both manually and automatically. Frequency of measurement will be varied based on the purpose. For a pumping test water levels will be measured in minutes or less than a minute duration, but for long term analysis measurement will be done four times in a year. Various instruments used to measure water levels commonly are:
For Non-flowing wells
-Steel tape and chalk
For flowing wells
Data storage: The collected data will be first stored in a firm field book and later entered into firm registers as well as in digital format which later will be transferred to a central data repository after necessary quality controls
Role of GIS in data analysis: Once the data is in digital form various analysis can be done on the data for deriving useful information for the effective ground water management. The data can be plotted in GIS platforms both in 3D and 2D forms. Contour maps which are the basis for further flow net and related analysis and modeling can be performed on the data. The collected data with the help of GIS software can be plotted in space and time. When the data is of multiple year’s duration, time series analysis and trend analysis can also be performed on the data along with numeric and statistical analysis.
Interpretation: The analysis results can be brought out in the form of reports where long term and shot term trends can be established. The results will be implemented in further ground water management processes.
How regime monitoring will influence ground water management?
Ground water regime monitoring results can influence ground water management in following ways:
Monitor impacts of abstraction on ground water system on a regional and local scale
Ground water balancing and budgeting
Calibration of numeric aquifer models
Determining pump usage and horse power
Determining the usage of water (potable, irrigable, industrial etc)
Early warning of potential threats in quantity and quality of ground water
Monitoring and managing of salt water intrusions
Monitoring of health hazards
To establish legal liabilities for pollution incidents and quantity issues
Monitoring droughts and floods
Monitoring water logging
What are the challenges in ground water regime monitoring?
Data loss during and after measurement
Inefficient use of man power and machinery
Expensive instruments and logistics
No visible return of investment
Difficulty in vertical variation in quantity and quality
Accuracy of the data
Monitoring of deeper and confined aquifers is difficult