GW Montoring

8/11/2019 GW Montoring

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GROUND WATER REGIMEMONITORING and OPTIMIZATIONOF GROUND WATER

MONITORING NETWORKBy

H.P.Jayaprakash&

Dr.Anathkumar Ars



Groundwater MonitoringProvide vital and much needed information about the hydrologicstresses the aquifer undergoes and how these stresses affect

groundwater recharge, storage and dischargeLong term systematic groundwater monitoring provides essential

data needed to evaluate changes in the resource over time, togenerate groundwater models and predict trends

The principal variables required to be monitored are water levelor head, chemical quality and temperature

The monitoring of the ground water regime also includes

monitoring of spring discharges and their quality & base flowmeasurements in streams and rivers

UN Task Force on Monitoring and Assessment, (1999) is thecollection of data, generally at set locations and depths and at

regular time intervals in order to provide information



Groundwater Monitoring

Ground water systems are dynamic in nature and adjust continuallyto short term and long-term ChangesGroundwater storage fluctuates in response to natural conditionsas well as artificial conditionsNaturalcondition involves recharge from rainfall, discharge byevapotranspiration and sub surface inflow/outflowArtificial condition concerns mainly ground water exploitation andadditional input to the system through surface irrigation networkEfficient and economic operation of groundwater storage, its

monitoring becomes necessary in order to avoid adverse impact onthe system on account of anthropogenic activities



Objectives• Background information against which future changes can be

assessed• An early tracing system for both quality and quantity variation• To evaluate the impact of surface water irrigation system on

groundwater regime• Evaluate the impact of surface water irrigation system on

groundwater regime• Study the influence of geology, geomorphology and land use

on ground water regime• To understand the role of groundwater in hydrological cycle

and influence of recharge/discharge on ground water storage• To study the hydrochemical behaviour of groundwater• To study the temperature variation of ground water in space

and time



Network design

• Dedicated ground water monitoring wells in ahydrogeologial unit

• Measured at pre‐determined frequency.



Why GW measurement• Proven to be indispensable to monitor the

anthropogenic induced and/or natural changes inwater levels

–

Detect early signs of over‐exploitation, water loggingand/or other consequences of human impacts ongroundwater levels

– Provide the necessary information allowing fortailor‐made use and need oriented ground waterresource management

– Provide information for the interpretation ofgroundwater quality data



Objectives of GW Quality Monitoring

• Collection of basic data for general surveillance purposes• Abstracted groundwater and the impact of pollution from both

diffuse, air‐borne and point sources • Forecast the impact of possible pollution from known sources• Identification of the groundwater quality trends• Pollution impacts and its consequences due to new abstraction

projects• Data support for groundwater quality and quantity modeling• Collection of groundwater quality data for mapping• Used in research and scientific work• Observation of the effects on groundwater from large‐scale

processes like global• climate changes or man‐induced changes in reaction‐rates of

natural processes like acidification caused from acid rain



Design of GW Monitoring

Should Cover• Entire hydrogeological system• Long‐term information on the different aquifers

being developed• Shallow aquifers tapped by open wells, deeper

multi‐layer aquifers tapped through open dugwells/dug cum bore well/ bore well/tube wells

• Groundwater development issues (Trend, CoastalSalinity, water logging & pollution)



Network Types

• Basic networks• Specific networks•

Temporary networks



Basic networks

• Information about the availability and quality ofthe groundwater

• Cover the entire country• Should have a permanent character over long

time• The information from this network

– basis of the evaluation of the water level and/or waterquality trends

– basis for both countrywide and local hydrogeologicaland other scientific investigations



Basic networks- Basic network criteria

• Representative stations with fixed distancebetween the stations

• Should be placed in the main aquifers• Other important aquifers of the area selected on

the basis of representativeness• Reference stations providing background

information should be established outside theareas affected by direct human activities such asgroundwater pumping and other anthropogenicchanges



Basic networks- Hydrologicalbenchmark or baseline station

• continuing series of consistent observations on hydrologicaland related climatological variables (Rainfall, Temp.,Humidity, Infiltration, Evaporation etc.)

• They should reflect local, regional and geographicdifferences

• Variables varies with the purpose of the network• Spatial and temporal densities of the observations are

concerned, these usually increase with the transition fromthe national or regional level to the project specific sites

and/or to the level of local warning requirement• Length of record depends on the duration or the purpose of

the network



Specific networks • Constructed for monitoring selected areas (surveillance) to monitor

the influences of projects and water management systems ongroundwater

• Local scale; for specific kinds of pollution, for example, point

sources.• Act as impact stations.• Separate network, or they can be an extension of the basic network• The specific network can have a permanent character, or will be in

operation• For information at that specific place.

– For example, around landfills, this could be during the period ofactivity and for a period after the landfill has been closed.



Temporary networks

• Established to collect data in connection withparticular groundwater projects

• Impact stations• Operational during the project period after

which it is closed or may be transferred toBasic stations



Dimensions of Monitoring Network

• The dimensions of network have two aspects – density of network – sampling frequency.

• observation well network will provide datarepresentative of various topographic, geologic,climatic, and land‐use environments

• Areal distribution and depth of completion ofpiezometers also should consider the physicalboundaries and geologic complexity of aquifersunder study



Basic principles -Location ofmonitoring wells

• Location of the observation monitoring wells should bebased on hydrogeological, social and economicconsiderations

• Optimal design Density of the network through statisticalalgorithms

• Largely guided by local area conditions• The data collected should be unbiased• Not subjected to interference from production wells, canals

or surface water bodies in the neighbourhood• Round the year accessibility• Protection to the monitoring station and the monitoring

equipment(s)



Network Density • Limited number of stations should be established in

each hydrogeological unit having homogeneous waterquality, along the main flow lines

• For extending this network additional stations arelocated along detailed cross sections of a hydrologicalsystem to provide for adequate representation in therecharge, discharge and intermediate areas.

• For further extension of network, a subdivision of themain hydrogeological units/homogeneous area type isused.



Frequency of recording/sampling • The frequency of measurement should be adequate to detect short

term and seasonal groundwater level fluctuation of interest and todiscriminate between the effects of short and long term hydrologicstresses

• Dependent like aquifer type and position, groundwater flow and

recharge rate, aquifer development and climatic conditions• Desirable to have daily water level, at least monthly water levels are

needed for any meaningful analysis.• In areas of high development, continuous daily readings are

required to separate out the effects of cyclic pumpage fromlong‐term trends

• In regional studies, where even monthly readings are not possible,frequency must be planned considering the timing of onset andcessation of monsoon



Frequency of recording/sampling

• The frequency of the monitoring should be such thatone or more of the following attributes could beestimated from the monitored water level data aftergenerating the water level hydrograph.Peak and trough of the hydrograph,Time of shallow water level i.e. time during which thewater level falls below a stipulated shallow critical levelTime of deep water level, i.e. time during which thewater levels rises above a stipulated deep critical levelRate of rise or decline and response time after anevent.



Frequency of recording/sampling

• The dates of onset and cessation of monsoon are not uniform throughout the country.• The peak water level may not be achieved in the same period throughout the country

– the peak water level measurement in the first half of September in the areas receivingmajor part of rains during south‐west monsoon.

– The areas under the influence of northeast monsoon another peak is reached in secondhalf of December.

• The decline of water table is steep in post monsoon months, an additional measurement inpost‐monsoon period is essential to have a more realistic hydrograph

– first half of November in the areas under the influence of southwest monsoon and inMarch in the areas under the influence of northeast monsoon.

• Since the rate of ground water flow is slow, its quality does not generally change rapidly withtime.

• Quality change in confined aquifers is a rather slow process as compared to unconfinedaquifers. Annual sampling schedule describes satisfactorily changes in ground water quality.

• The current annual sampling schedule during premonsoonperiod (April/May) generallyserves the purpose of regional background monitoring of long‐term quality changes.



Current scenario- Groundwatermonitoring

• Presently two types of monitoring are in practice in India• Periodic monitoring and continuous monitoring• Periodic: scheduled ground water level measurements daily, weekly, fortnight,

monthly, or season intervals. – Carried out through manual measurement techniques – The most popular the groundwater agencies is either monthly or seasonal.

• Continuous monitoring is near real time monitoring which are certain fraction ofwells within the monitoring network – Provide unambiguous and quantitative real‐time information on unique and potentially

damaging ground‐ water level events that are occurring and signal these events as early aspossible:

– Represent ground‐water conditions over a substantial area of the aquifer. – Monitor specific areas where the aquifer may be more susceptible to water level related

problems, and – Provide information that aids in the assessment of salt‐water intrusion in those areas – of the aquifer where such considerations are relevant – usually carried out using Digital Water Level Recorders (DWLR)



Optimization

• Network by interpolation required wherethere is no data

• Statistical techniques• However the hydrogeological conditions,

nature of study are the guiding factor to fix upnetwork density



Optimization



Modified Cv



Other techniques

• Krigging• Estimation of Regionalized Variable



Storage and Retrieval of Data •

The preexisting system of manual data replaced by dedicated anduser‐friendly software • The primary module of groundwater data processing system (including

water quality) developed in course of implementation of the HydrologyProject is called Ground Water Data Entry Software (GWDES)

– The software has a Microsoft Access data base structure at the back end andthe front end has been developed using visual basic for Application.

• This GWDES has been replaced by the dedicated software GEMS (GroundWater Evaluation And Management System).

– This software uses relational data base management system ORACLE – Both raw and processed data sets are being stored and archived. – Necessary features like data security protection from data corruption and

provision of controlled accessibility is a part of the system design. – An efficient and user‐friendly query system helps in data retrieval. – The dedicated groundwater data processing software includes GIS support to

visualize, – manipulate and analyze spatial data. – The details of operation of the software are available as on line help



Analysis and presentation of data • The water level reflects cumulative effect of natural recharge‐discharge condition

and draft.• The water table, which forms the upper surface of the saturated zone, is subjected

to seasonal fluctuation.• This fluctuation is dependent on rainfall infiltration, consumptive use, topography,

soil characteristics, temperature, humidity, lithology of the formation etc.•

Ground water levels, observed over a period provide changes due to recharge anddischarge.• The difference between these two factors results in the decline or rise in the

ground water storage.• When the recharge exceeds discharge, there will be rise in the ground water

storage• whereas decline in storage will be observed when recharge is less than discharge.• For every set of measurement (four times seasonal as discussed earlier), the data

is analyzed to prepare a report



Water level analysis • Depth to Water level: General range of water level during the specific

period of measurement – depth to water level ranges viz. 0 – 2 m, 2 – 5 m, 5 – 10 m, 10 – 20 m, >

20 m etc• Annual Fluctuation: Water level data of specific period as compared

with the corresponding period of the previous year• Seasonal Fluctuation: Comparison of water level with respect to that

during pre‐monsoon • Decadal Fluctuation: Comparison of water level data with the mean of

water level data of the previous decade• wells showing different range of water• The data is presented in the form of numerical tables• District wise minimum and maximum range of water level rise and fall

– Water level rise or fall e.g. rise range of 0 – 2 m, 2 – 4 m, > 4m etc. andfall range of 0 – 2 m, 2 – 4 m, > 4m etc



Maps prepared on the basis of analysisof monitoring data

• Depth to water level in the particular month ofmeasurement.

• Water level fluctuation in comparison to that in the samemonth in the previous year.

•

Water level fluctuation in comparison to pre‐monsoonwater level.• Water level fluctuation in the month of measurement with

reference to the decadal mean for the same month.• Maps prepared by software like Surfer, MapInfo

professional• Dedicated software (GEMS) is capable of generating data in

a number of formats, Maps, Queries, reports, graphicalrepresentation etc.



Water Quality Analysis • The water quality reflects the chemistry of the

aquifer and effect of anthropogenic activities onthe ground water regime

• chemical constituents (such as Fluoride, Iron,Nitrate, Hardness etc.) above the permissiblelimit are demarcated

• contour maps for different constituents areprepared and compared with the results of theprevious year

• Based on the analysis, poor ground water qualityareas are delineated



GROUND WATER HYDROGRAPH

• Plotting of water levels against time ofobservation & Providing the information onthe behavior of water level with time and is

termed as ground water hydrograph• a well hydrograph also shows rising limbs and

lowering limbs•

The water level rises when the ground waterstorage increases and declines when there is adecrease in storage.



Hydrograph



Hydrograph• The smoothness of the hydrograph depends on the

frequency of observations.• Higher the frequency more smooth is the hydrograph

and lower the frequency less smooth is the hydrograph• Central Ground Water Board, the present frequency of

measurement, for the All India Network of HydrographStations, is four times in a year.

• The purpose‐built piezometers water level data arerecorded through Digital Water Level Recorders(DWLR) at higher frequency even 4 times in a day



Hydrograph

GW Montoring

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