Groundwater Modeling of Unconfined Aquifer System of Crystalline Area

8/2/2019 Groundwater Modeling of Unconfined Aquifer System of Crystalline Area

1/12

Groundwater modeling of unconfined aquifer system of crystallinearea - a case study in Lapsiya watershed, Hazaribagh, India

Ashok KumarEarth Resource Division

Remote Sensing Application CentreIGSC- Planetarium, Patna - 800 001, India

Tele# +91-612-689001, Mobile# [email protected]/ [email protected]

Web: http://www/geocities.com/ashok_bcst

In the India considerably large geographical area comes under crystalline area. Groundwateroccurrence and its management are the major task before the scientists and planner. These areaexperiences acute crisis of groundwater for drinking water and irrigation. In these areas dueunconfined nature of aquifer system, the storage and retrieval of groundwater is major task beforethe scientists. The weathered materials are the principal aquifer system and ground water occursunder water table condition. Beneath the weathered horizon, fractures system within the basementsurface is also supposed to be potential aquifer zone. But determination of fracture geometry isdifficult task and these fractures zone have not been fully exploited. It has been established thataquifer geometry of the unconfined aquifer system is important parameters in understanding thegroundwater storage, retrieval and recharge process in aquifer. The Digital Surface TerrainModeling (DSTM) and Digital Basement Terrain Modeling (DBTM) exercise provides the upper andlower limit of the unconfined weathered aquifer system (Kumar et. al., 1997). This approach hasbeen well tested in identifying the groundwater retrieval and storage sites in Chotanagpur region ofIndia. But for complete understanding the complex mechanism of groundwater, this approach is notsufficient. The long term planning and management of groundwater needs understandinggroundwater interaction with surface water, recharge, seepaze process, intake and rate ofwithdrawal in space and time and its long term effect on the aquifer system to achieve thesustainability. The entire exercise becomes complex process and it is outside preview of staticmodeling exercise such as DBTM approach. Several attempts have been made through computermodeling in alluvial plain of India but less stress has been made for the modeling of the aquifer inhard rock area.

In present study, modeling exercise has been attempted in Lapasiya watershed, Hazaribagh, India.It has helped in understanding the behavior of unconfined aquifer system with various varying inputparameters. The outcome of the model helped in identifying suitable area for groundwateraugmentation on the long term. The present model also helped in optimization of rate of new wells.The model has simulated up to a level to the near real field condition. The present modelingexercise and its results has given enough scope for taking up such types exercise in other parts ofhard rock of India. There is still possibility for further refinement of various parameters. The presentmodeling exercise is a parts of UNDP training programme and it may not been treated as final.

Groundwater ModelingModeling is an attempt to replicate the behaviors of natural groundwater or hydrologic system bydefining the essential features of the system in some controlled physical or mathematical manner.Modeling plays an extremely important role in the management of hydrologic and groundwater

system.

Objective of Modeling in Case Study

1. The first objective of model was to simulate the condition similar to aquifer behaviors withtime. The water table or equi-potential surface remains near to the surface after themonsoon; water table starts falling down from Nov. onwards and reaches maximum depthin the month of May/ June. After onset of monsoon, water table comes up.
mailto:[email protected]:[email protected]:[email protected]://www/geocities.com/ashok_bcstmailto:[email protected]://www/geocities.com/ashok_bcstmailto:[email protected]


2/12

2. To budget the groundwater resources

3. Find out the suitable area for bore well development and optimization ofpumping rate and duration. In study area, 20 deep bore well have beenidentified through geo-hydrological and geophysical survey. But itsustainability could not be determined on long term basis.

4. To determine the sensitivity of the model the various input parameters i.e.recharge/ evapo-transpiration, hydraulic conductivity. So more stressesshould be given in collection of field data.

Data required for the modeling and its source

Data Required by Model Source of Data

SystemGeometry

Boundaries,elevations,thickness, surfacedrainage, borelocation

GeologicalMap

Boundaries

HydraulicProperties

Hydraulicconductivity,Transimissivity,

Anisotropy, Leakge

GeophysicalSurveys

Sections, thickness,bed rock, DigitalBasement TerrainModel (DBTM)

StorageProperties

Specific yield,storage coefficient

Drilling Logs Aquifers, Aquitards,Thickness, Bedrock

Sources andSinks

Recharge,Pumpage,Leakage,Underflow,Baseflow,

Evapotransipiration

Pump Tests Transimissivity,Storage coeffecient,Leakage

PiezometricHeads

Water levels,Current andhistorical

BoreRecords

Census, Location,Pumpage,Schedule,Hydrographs

TransportProperties

Porosity, Strengths,Constituents,Radioactivity

SurfaceHydrology

Stream stage,Losses, Floodmaps, Drainage,Baseflow, Channels

Concentration Current andHistorical

Meteorology Rainfall,Evapotranspiration

Chemistry Water analyses,Clay samples,Concentrationmaps

Water Use Irrigation, Industrial,Urban, Efficiency,Waste, Backupsource

Land Use Soil map,Infiltration, Croptype

PiezometricSurfaces

Pre-pumping,Current, Short termdrawdown, eachaquifer, Hydraulic


3/12

gradient

Ground-Water Flow EquationThe partial-differential equation of ground-water flow used in MODFLOW is (McDonaldand Harbaugh,1988)

where

Kxx , K yy , and K zz are values of hydraulic conductivity along the x, y, and z coordinateaxes, which are assumed to be parallel to the major axes of hydraulic conductivity (L/T);

h is the potentiometric head (L);

W is a volumetric flux per unit volume representing sources and/or sinks of water, with W0.0 for flow in (T-1);

SS is the specific storage of the porous material (L-1); and t is time (T).

Study AreaThe Lapasiya watershed (AIS & LUS , 1988) is a part of Upper Hazaribagh plateau and forms the500-600 (above m.s.l.) meters erosion surface. On the whole the plain is undulating with someminor ridges interrupting the level nature topography. The area may be termed as buried pediplain.The cover material is formed by coarse alluvium in the immediate valley of streams while rest of thepediplain has a gravely ferruginous soil. The porosity of soil does not permit wetting of the topsoiland the water rapidly percolates to the lower horizons. The present study area is a part of upperHazribagh plateau. The watershed has total areal extent of 85 sq. km. Area on average receives1322.41 mm of rainfall.

Surface Water Resource

Total 55 water bodies mostly ponds/ tanks have been identified in the watershed with the help ofremotely sensed data. In which Charwa dam are the major water body and its areal extent areapproximately 100 ha. The entire water bodies nearly harvest 8-10 % of the total annual rainfall(Kumar, 1997).

Land UtilizationKharif (paddy crops) including current fallow, water body, settlements etc covers 67.43 percent ofwatershed whereas rabi crop covers 07.43 per cent of the watershed area. The areal extent of rabicrops is indicator of utilization status of surface and ground water (Kumar, 1997).

Aquifer SystemThick weathered material serves as potential aquifers. In the valley portion water table generallycuts the topographic surface and groundwater get lost as seepage (spring). Water table in the

valley portion ranges between 2.00m to 3.0m b.g.l. and generally deep on the upland in the rangeof 4 to 10m b.g.l. (Kumar, 1997). It has been observed that in case of maximum thickness ofsaturated weathered horizon of phreatic aquifer about 12m, yield of the dug wells range from 1.0m3to 2.5m3 / day for a draw down of 0.5m to 3.00 m and well recuperates within 2 to 24 hr. Specificcapacity of the aquifer varies from 1.39 to 5.61 lpm/m. draw down for the hilly areas having thinmantle of weathered material and 3.12 to 8.54 lpm/m draw down to low lying areas underlain bythick weathered material and soil covers. It has been observed that 70 per cent of total groundwaterreserves get lost as base flow in river (Bhattacharya , 1990 ).


4/12

Groundwater modeling of unconfined aquifer system ofcrystalline area - a case study in Lapsiya watershed,

Hazaribagh, India

Basement Topography / Depth of WeatheringBased on depth of basement obtained from anylysis of VES data, sub-surface topographic model/basement topographic model for Lapasiya (fig. 6) has been generated. Average depth ofweathering is approximately 15-20 m.

Conceptual Model

1. As discussed in the previous sections, topography is undulating and pediplain has

developed over granite gneisss with high drainage network. The channel of 4th orderdrainage remains wet throughout the year due to seepage of groundwater. Therefore, wetchannel may be assumed as constant head boundary for present modeling exercise.Otherwise, it will be difficult to do the modeling of the area. We may also assume, wetchannel as drain boundary condition. For this purpose, data on base flow in the channel isessential besides the drain conductivity. In the present exercise constant head boundarycondition has been taken into consideration.

2. Although, aquifer system in hard rock consists of weathered and fractured system. Themodeling of fractures is beyond the scope of present study because it is complex anddetailed field data on fracture geometry and geo-hydrological characteristics is required. Inhard rock area, the weathered material serves as principal aquifer. This aquifer isunconfined in nature and groundwater occurs under water table condition. Therefore, toplayer excluding fractures has been taken for modeling. This is single layer case (Fig. 1.1).

3. Other basic assumption has been made in delimiting the area i.e. watershed. In practicalpurposes, the major water divides i.e. Lapasiya watershed outer boundary has been takenas no-flow boundary in modeling (Fig. 1.2).


5/12

Software Used - Visual MODFLOW 2.8Visual MODFLOW is a computer program based on USGS MODLOW code with pre and postprocessor. It simulates three-dimensional ground-water flow through a porous medium by using afinite-difference method. Groundwater flow within the aquifer is simulated using a block-centeredfinite-difference approach. Flow associated with external stresses, such as wells, areal recharge,evapo-transpiration, drains, and streams, can also is simulated. The finite-difference equations canbe solved using different solvers.

Input to the Model

Upper Boundary

The Upperboundary of theaquifer has beentaken from theDigital SurfaceTerrain Model(Kumar, 1997).The upper surfaceof aquifer has

taken from thetopographicelevation valueavailable in theSurvey of Indiatopographicalsheets. The uppersurface of the

Constant HeadBoundary

As discussed earlierthe wet drainagechannel of 4th orderhave been taken asconstant headboundary. The largetanks have also beentaken as constant

head boundary. Inthe present studysame extent ofchannel has beentaken for constanthead boundary forthe entire period ofsimulation. Length

Evapo-transpiration

Its estimation needsinformation on soilphysicalcharacteristics, landcover types,atmosphericcondition etc. In thepresent case study,

evapo-transpirationvalue has beenapproximated fromthe data available forsame agro-climaticzone. There is scopefor furtherrefinement.


6/12

aquifer can befurther improved ifthe contour valuesavailable in1:25000 scale ofSurvey of India will

be taken intoconsideration. Themodel successvery muchdepends on thesimulation of theupper topographicsurface (Fig. 1a).

aspects of constanthead boundary canbe improved with thehelp of remotelysensed data ofdifferent time period

(Fig. 1.3).

Observation Wells

Sites used for initialhead have beentaken as observationwells. This is

required for testingthe simulated results(calculated) withobserved head(Kumar, 1997), Fig.1.7.

HydraulicConductivity

The hydraulicconductivity ofweathered materialis very difficult toestimate. Normalpumping test hasserious limitations inhard rock area andobtained results are

highly variable.Based on availabledata on the differentparts of Chhotanag-pur plateau, it hasapproximatedbetween as 0.5 to1.0 m/day (Athawale,1984 & Karnath,1994), Fig. 1.5.

Lower Boundary

The lowerboundary of theaquifer has been

inputted from theearlier DigitalBasementTopographic data(Kumar, 1997).This is also veryimportantparameter, whichis required toinputted in detaileddue to erraticbehavior ofbasement

topography (Fig.1b).

Pumping Wells

In the present studyarea, there is three

deep bore wells.Ground water isbeing mostlyaugmented by dugwell. In Initial phase,total drinking waterrequirement ofvillage has beentaken as onepumping well into thesystem. Similarlygroundwater draft forthe irrigation

purposes has beentaken as separatewell. Besides that thedeep bore well sitesidentified in theearlier NRDMSproject have alsobeen taken intoconsideration(Kumar, 1997), Fig.1.9.

Recharge

The total estimatedrecharge into thesystem have beenassumed for eachmonth dependingupon the amount ofrainfall during themonth. It has beendistributed inbetween 2 per centto 40 per cent. Therecharge frommonsoon rainfallhave assigned as

270, 136 and 40 mmfor the upland,midland and lowlandrespectively.Recharge from tankhas been assumedas 0.5 m /day(Athawale,1984 &Karnath, 1994 ), Fig.

Initial Head

The data collectedin the earlierNRDMS project(Kumar, 1997)hasbeen taken intoconsideration andit has beeninputted into themodeling

environment. Thewater table data ofJan 1994 has beentaken as initialhead in this modelin the model (Fig.1.6).


7/12

1.4

Model Simulation

Steady State SimulationFirst the model has been simulated in steady state for period of one day (Fig. 1.10 & 1.14). All data,such as constant head, recharge, evapo-transpiration have been inputted month wise so thattransient state run may carried out month wise. The grid cells representing hill in the watershedbecame dry in the steady state run. Some other area also became dry and it has been re-adjustedby re-defining the basement geometry at the particular point. It has been corrected some time byadjusting the hydraulic conductivity. Steady state run of model has been carried out by using thevarious solvers (Preconditioned Conjugate Gradient Package (PCG2), Slice Successive Over-relaxation Package (SOR), Strong Implicit Procedure Package (SIP), WHS Solver for VisualMODFLOW) available within the visual MODFLOW. Many time default solver WHS has notconverged whereas PCG2 has given good results.

Transient State SimulationAfter the successful run in the steady state, model was run for one-year period at the stress period(Fig. 1.15) of one month. Initially model was simulated without pumping well and simulated results

were compared. The model acted like the field situation i.e. rise of water table in the monsoonperiod, decrease in water table after the monsoon. This indicates conceptual model and initialparameters were ok. Input parameters can be further refined i.e. spatial variation of recharge atdifferent macro/micro-landform and soil types (topographic and soil maps used), spatial variation inevapo-transpiration in different land use units (land use map used), Variation in hydraulicconductivity on different landform and weathered material (aquifer hydro-geophysical propertyused). After refinement of the model input, model was finally calibrated for the actual field condition.

Thereafter model was simulated with the pumping wells (only drinking water wells and irrigation dugwells). Many of the pumping well dried up in one year (Fig. 1.13 & 1.16). This was due tocumulative pumping rate for the entire village was taken at one point. This can be further improvedif it will be distributed in different location within the village area instead of putting cumulative valueat one point. Similar results were obtained for the irrigation well. These error indicates that model is

behaving correctly with the parameters. Due to very less hydraulic conductivity, radius of influenceof wells in the weathered aquifer system is very limited even not more than 100m. Due to non-availability of spatial distribution of irrigation and drinking water wells, further improvement was notcarried out. Few wells have not gone dry which are pumping less amount of groundwater forirrigation and drinking water purposes.


8/12

Thereafter, earlier identified deep bore well sites have been added into the system with constantpumping rate starting from 200 m3/day. These wells have been active for the period of one year.Most of them have gone dry at end of the one year. This indicates that we can not take the water atthis rate. Model was thereafter model has been simulated with the reduced pumping rate. In thisway different conditions have been generated and deep bore well pumping rates have beenoptimized. After running model with irrigation well, drinking well, deep bore well, more wells with

less pumping rate was inputted into the system, this has helped in the determining the suitable areawhere we can observe the less draw down.

Model has been also simulated for the 10 years to generate the scenario for long tern planning ofground water of the aquifer system.

Groundwater modeling of unconfined aquifer system of crystallinearea - a case study in Lapsiya watershed, Hazaribagh, India

Model CalibrationThe observation well used in the model has been used forcalibration of the model. The model calculated heads andobserved heads have been analyzed. Majority of the heads

falls in the 90 per cent confidence level (Fig. 1.18). The 95per cent confidence level is supposed to be optimal.Therefore there is scope to refine the various parameterstaking in-homogeneity in the aquifer system. Same exercisehas been carried out in transient simulation. The calculatedand observed heads have been plotted for the all the stressperiod. It has been found that heads are behaving withseasonal change in the water table.


9/12

ResultsInspection of model output has indicated that a place where basement depth is more, failure well isless. This means that well success is hard rock area depends on the thickness of the aquifer

material. The largest water body in the watershed "charwa dam" effects on the surrounding groundwater movement has been noticed. It has been observed that the up stream drainage area of thedam drains the groundwater to the dam. But much lateral control on groundwater movement hasbeen noticed. The flow lines are coming to the dam area and it is moving towards down streamside.

The volumetric calculation of total available utilizable groundwater within aquifer has been madeusing output generated in the steady state. Total volume is 230.050x106 m3. This clearly indicatesthat availability of resource is not a problem. The model simulation has indicated that this type ofaquifer can be pumped with slow rate (most appropriately at the rate of 100 m3/day) due to high


10/12

draw down. Similarly, well can not be pumped for long duration at one stretch.

In the entire watershed putting huge number of dug wells can augment groundwater and shallowtube wells energized with 2 H.P. pumps. In middle portion and mid-north-east corner of thewatershed, we can pump the water even at high rate i.e. up to 200 m3/day. Because simulationresults are stable. This area gets ground water recharge from the upper reaches of watershed andrecharge guided by the main river channel.

Another observation has been made regarding seepage loss of groundwater in drainage (presentlyit is a constant head boundary). It is decreasing with time due to continuous pumping. The seepageloss of groundwater can be optimized through the modeling simulation.

Regional flow pattern of GroundwaterThe flow direction and velocity vector obtained for different period indicates (Fig. 1.11) that majorityof the flow direction is in NE direction. This is shortest route of the groundwater movement from theupper reaches to lower reaches. It has been also observed that micro water divides are alsocontrolling the flow patterns. Few heads of the observation sites located near the constant headboundary i.e. drainage channel has not shown any change with time. This is because no seasonalvariation has been taken into account in assigning constant head boundary for the whole simulationperiod.

Flow Budget from the model outputResults of flow budget (Fig. 1.17) indicate that an amount of 9712.80 m3 per day has been pumpedon the 1st Jan. from the 18702-m3 available effective storage of the aquifer. After end of 31st Jan.,all the pumping wells are not able to pump more than 4361.5 m3 per day. This indicates that someof wells have gone dry. Total storage available in the system also comes down to 7843.50 m3. Theresult indicates decrease in pumping volume till the month of June-July. The in out to the system isalso decreases till the month of June-July. After start of monsoon i.e. June- July, situation reversedafter increase in recharge to the system. Inspection of draw down of the individual pumping wellsindicated that radius of influence wells are very limited and rarely interfering the other wells. Furtherwells are going dry only where depth of basement is shallow and pumping rate is high. It has been


11/12

found that 50 m3/day upping rate is optimum. Even in some places, groundwater may be pumpedwith the rate of 100 m3/day - 200 m3/day

ConclusionsThe modeling exercise of unconfined aquifer system of hard rock area in Indian condition ispossible and model can be simulated to near real field condition. Based on present modelingexercise following points emerged out

1. Model accuracy very much dependent aquifer geometry.

2. Groundwater reserve estimation of the entire aquifer system can be determined from themodeling.

3. Model can be further improved if more and more spatial data on input parameter i.e.hydraulic conductivity, recharge, base-flow in the river, are to collected and inputted intothe model for better control.

4. Modeling is a complex exercise; lot of discussion with experts and consultation is required.

Groundwater modeling of unconfined aquifer system can provide solution for estimating theavailable groundwater resource, optimizing the pumping rate and identifying suitable locations/ areawhere there will less adverse effects on the aquifer system in long duration pumping. The pumpingrate of pumps can be optimised in the upper reaches to check groundwater seepage in thedrainage channel. The modeling exercise has given better understanding of the aquifer behaviorwith change in different input parameter.

Acknowledgement

Groundwater modeling of Lapasiya watershed, Siwane sub-basin, Hazaribagh, India was part ofUNDP-DST training programme on GIS based Groundwater Modeling at Centre for GroundwaterStudies, CSIRO, Wembley, Western Australia. Author is thankful to Dr. Chris Barber, Director,CGS, Western Australia, Dr. Kumar A. Narayan, Principal Research Officer; Dr. Ramsis Salama,Research Group Leader; Mr. Tonny Barr and Dr. Raiyast Ali, Scientists, Land and Water, CSIRO,Wembley, Western Australia, and Dr. Prabhakar Clement, Centre for Water Research, University ofWestern Australia, Perth, Australia for providing the training in the Visual MODFLOW and GMSpackage of groundwater modeling.

References

AIS & LUS ( 1988 ). Watershed Atlas of India, All India Soil and Land Use Survey, NewDelhi.

Athawale R. N. ( 1984 ). Nuclear tracer techniques for measurement of natural recharge inhard rock terrains. Proc. Int. Workshop on Rural Hydrogeology and Hydraulic in FissuredBasement Zones held at University of Roorkee, pp 71-80.

Bhattacharya B. B. ( 1990 ). Hydrogeology and Groundwater Resources of HazaribaghDistrict, Bihar. Unpublished Report, CGWB, Eastern Region, Calcutta.

Karnath K. R. ( 1994 ). Groundwater assessement, development and management, TataMcGraw Hill Publishing Company Limited, New Delhi.

Kumar Ashok ( 1997 ). Natural Resource Management for Sustainable Utilisation andManagement of Water Resources in Siwane sub-basin, Hazaribagh, Bihar, DST ProjectReport ( ES/011/212/95 ), BCST, Patna.


12/12

Kumar Ashok, Sinha Ranjan and Prasad B. B. ( 1997 ). Digital Basement Terrain Modeling( DBTM ) A tool for sustainable utilisation and management of groundwater in hard rockarea. National conference on emerging trends in development of sustainable groundwatersources held at Hyderabad from Aug. 17-28. JNTU.

McDonald, M.G., and Harbaugh, A.W., 1988, A modular three-dimensional finite-difference

ground-water flow model: U.S. Geological Survey Techniques of Water-ResourcesInvestigations, book 6, chap. A1, 586 p.

Page 3 of 3

Documents

Groundwater Modeling of Unconfined Aquifer System of Crystalline Area