Presentation on theme: "Prof. S. N. Panda Head, School of Water Resources"— Presentation transcript:
1 Prof. S. N. Panda Head, School of Water Resources Groundwater Modelling of Ganga Basin – Opportunities and ChallengesProf. S. N. Panda Head, School of Water Resources
2 Physiography and groundwater flow of Ganga basin (Source: Ministry of Environment and Forests, Government of India)
3 Annual groundwater draft in comparison with net annual availability in Ganga basin (Source: Ministry of Environment and Forests, Government of India)
4 Annual replenishable groundwater in comparison with annual draft in Ganga basin (Source: Ministry of Environment and Forests, Government of India)
5 Schematic illustration for evaluating stream-aquifer interaction Inflow or leakage to/from groundwaterChange in storageReach inflowReach OutflowStream ReachEvaporationGroundwater inflowGroundwater outflowStream inflowStream outflowRecharge to groundwaterEvapotranspirationRainfall
6 Problems with groundwater in the Ganga Basin Imbalance in groundwater draftWaterlogging and salinity in canal commandsGroundwater pollution
7 Types of Terrestrial Water Surface WaterSoil MoistureGround water
8 Movement of water through the hydrologic cycle (Source: usgs.gov)
9 Effluent and influent streams Gaining streamLosing stream with shallow watertableBase flowLosing stream with deep watertable
10 Water Balance Concept The basic concept of groundwater balance is: Input to the system ‑ outflow from the system = change in storage of the system (over a period of time)
11 Flow components for assessing groundwater balance BoundaryPrETPerCapQdrQperQlsiQdoQupQlsoClayWatertableSgrwOverland FlowIrSeepagePumping well
12 Groundwater Balance Equation Considering the various inflow and outflow components in a given study area, the groundwater balance equation can be written as:Rr + Rc + Ri + Rt + Si + Ig = Et + Tp + Se + Og + Swhere,Rr = recharge from rainfallRc = recharge from canal seepageRi = recharge from field irrigationRt = recharge from tanksSi = influent seepage from riversIg = inflow from other basinsEt = evapotranspiration from groundwaterTp = draft from groundwaterSe = effluent seepage to riversOg = outflow to other basins; andS = change in groundwater storage
13 Groundwater Survey and Investigation Water table contour mapWater table contour map showing a local mound and depression in water table and direction of groundwater flow
14 Flow netFlow net technique for estimation of subsurface horizontal flow
17 Components of a Mathematical Model Governing Equation (Darcy’s law + water balance equation) with head (h) as the dependent variableBoundary ConditionsInitial conditions (for transient problems)
18 General governing equation for steady-state, heterogeneous, anisotropic conditions, without a source/sink termwith a source/sink term
19 D is dispersion coefficient v is velocity Allows for multiplechemical speciesDispersionChemicalReactionsAdvectionSource/sink termChange in concentrationwith timeis porosityD is dispersion coefficientv is velocity
20 Model GridsFinite Difference GridFinite Element Grid
21 Modelling Process Conceptual Model Update Model Calibrate Model Compare Model and FieldMathematical ModelComputationConclude study(Decisions & Recommendations)Satisfactory ResultsPoor FitUnsatisfactory Results
22 Opportunities and Challenges in the Ganga Basin Wide variation in climate from semi-arid to sub-humid/sub-tropical regionsLarge-scale spatial variation inSoil texture and land-useType of aquifers and its propertiesSpatio-temporal variation in- meteorological parameters associated with uncertainties- groundwater recharge and discharge componentsGroundwater level monitoring is not being done regularly and intensivelySetting up/optimising monitoring networks and setting up groundwater protection zonesGroundwater resources too need to be planned and managed for maximum basin-level efficiency.
25 Diversified geological climatological and topographic set-up, giving rise to divergent ground water situationsExcessive use of our rivers, are causing downstream problems, of water quality and ecological stress.Climate change impacts directly on the availability of water resources both in space and time.The precarious balance between growing demands and supplies brings forth the importance of maintaining quality of both surface and ground water.
26 Application of existing groundwater models include water balance (in terms of water quantity) gaining knowledge about the quantitative aspects of the unsaturated zonesimulating of water flow and chemical migration in the saturated zone including river-groundwater relationsassessing the impact of changes of the groundwater regime on the environment
27 State-wise distribution of the drainage area of Ganga river (Source: Status paper on river Ganga, NRCD, MoEF, 2009)
28 Soil types in Ganga basin (Source: Central Pollution Control Board, National River Conservation Directorate (MoEF) (2009))
29 Data requirement for groundwater balance study over a given time period: PrecipitationRiverCanalTankWater tableGroundwater draftAquifer parametersLand use and cropping patterns
30 Management of a groundwater system, means making such decisions as: The total volume that may be withdrawn annually from the aquifer.The location of pumping and artificial recharge wells, and their rates.Decisions related to groundwater quality.Groundwater contamination by:Hazardous industrial wastesLeachate from landfillsAgricultural activities such as the use of fertilizers and pesticides
31 Groundwater Modelling The only effective way to test effects of groundwater management strategiesConceptual model Steady state model Transient modelProcessesGroundwater flow (calculate both heads and flow)Solute transport – requires information on flow (calculate concentrations)
32 Model Design Conceptual Model Selection of Computer Code Model GeometryGridBoundary arrayModel ParametersBoundary ConditionsInitial ConditionsStresses
33 Modelling Process Conceptual Model Update Model Calibrate Model Compare Model and FieldMathematical ModelComputationConclude study(Decisions & Recommendations)Satisfactory ResultsPoor FitUnsatisfactory Results
34 General governing equation for transient, heterogeneous, and anisotropic conditions Kx, Ky, Kz are componentsof the hydraulic conductivitySpecific StorageSs = V / (x y z h)
35 Types of Solutions of Mathematical Models Analytical Solutions: h= f(x, y, z, t)Numerical SolutionsFinite difference methodsFinite element methods
36 Model Design Conceptual Model Selection of Computer Code Model GeometryGridBoundary arrayModel ParametersBoundary ConditionsInitial ConditionsStresses
38 Suitability of groundwater in increasing dry season productivity in the coastal region of the Ganga basinHow the recharge mechanisms can be used to reduce salinity.Climate change impact on groundwater.
41 Mismatch between water supply and demand Management of Excess RainwaterMismatch between water supply and demandPossible solutionsRainwater conservation and recyclingMultiple use of harvested waterManaged aquifer rechargeManagement of stagnant water in lowland areas
42 Rainwater Conservation a. Storage of rainwater on surface reservoirb. Recharge to ground waterPitsTrenchesDug wellsHand pumpsRecharge wellsRecharge shaftsLateral shafts with bore wellsSpreading techniques
43 Methods of Rainwater Storage InfiltrationInjectionIncreased font size
45 Benefits Ideal solution to water problems in water stress areas Capture and storage of water in monsoon when rainwater is abundantMore water will be available for summer useRise in groundwater level - Improves declining aquifersMay increase base flow to streamsMitigates the effects of droughtReduces the runoff which chokes the storm water drainsFlooding of roads and low land areas are reducedQuality of water improvesSoil erosion will be reducedSaving of energy per well for lifting of ground water – 1 m rise in water level saves about 0.40 KWH of electricity
46 What is Managed Aquifer Recharge (MAR)? Managed Aquifer Recharge is:The infiltration or injection of water into an aquiferWater can be withdrawn at a later date but also left in the aquifer (e.g. to benefit the environment)Why Consider MAR?Allows storage of water in wet seasonsImprovement in groundwater qualityAllows increased use of groundwater from other parts of the aquifer systemsTo stop seawater intrusion in coastal areasTo maintain or increase available water supplies for use in agriculture, drinking water supply, and industry
53 Ganga River Basin, India The river systems in India are grouped into four broad categories:The Himalayan riversThe Peninsular riversThe Coastal riversThe Inland riversThe Ganga River (length: 2525 km long; catchment area: km2) is fed by runoff fromVast land area bounded Himalaya in the north.Peninsular highlands and the Vindhya Range in the south.The states of Haryana, Rajasthan, Uttar Pradesh and West Bengal, comprising 50% of the basin area.The basin spreads over four countries: India, Nepal, Bangladesh and China.
54 Soil and rainfall (isohyetal) map of Ganga Basin (Source: Ministry of Environment and Forests, Government of India)
55 Vegetation Types of Ganga Basin (Source: Ministry of Environment and Forests, Government of India)
56 GroundwaterAn important component of water resource systems and source of clean water.More abundant than Surface WaterExtracted from aquifers through pumping wells and supplied for domestic use, industry and agriculture.With increased withdrawal of groundwater, the quality of groundwater has been continuously deteriorating.Linked to Surface Water systems and sustains flows in streams
57 Groundwater in Hydrologic Cycle (Source: physicalgeography.net)
58 Dynamic Groundwater Resources of India Total replenishable groundwater in the country = 433 BCM5,723 units (blocks, talukas, mandals, districts) assessed –15% over-exploited4% critical10% semi-criticalDelhi, Haryana, Punjab, Rajasthan are overusing their groundwater resources.Andhra Pradesh has the highest number of over-exploited units.The agricultural (tube-well dependent) state of Punjab has developed (usage compared to availability) its groundwater upto 145%.Delhi is mining 170% of its groundwater.Countrywide percentage of groundwater development is 58%.
59 Annual replenishable groundwater in comparison with annual draft in Ganga basin
60 Ground Water and Surface Water Interaction Ground water and surface water contained in the hydrological system are closely interrelatedThe studies examines the processes of ground water flow generation and estimation of ground water discharge including ground water discharge to rivers (base flow)In a ground water basin, it is common to identify several aquifers separated either by less permeable or impermeable layers
61 the upper aquifer is recharged through the bed and banks of the river the upper aquifer is recharged through the bed and banks of the river. The lower aquifer is recharged through the intervening aquitardfinite difference equations describes the response of the aquifer system to applied stressesquasi three-dimensional model simulates a ground water system having any number of aquifers
62 The studies on the ground water/surface water interrelationship made it possible to solve a number of important scientific and practical problems :to estimate base flow and, therefore, sustained low river discharges of different probabilitiesto estimate the ground water contribution to total water resources and the water balance of regionsto evaluate quantitatively the natural ground water resources for determining the prospects of their use within large areas and as a component of the safe ground water yield
63 The methods for estimating the ground water discharge of the upper hydrodynamic zone are fairly well developed as compared to deep artesian aquifers and their contribution to surface runoff
64 Seawater IntrusionA natural process that occurs in virtually all coastal aquifers.Defined as movement of seawater inland into fresh groundwater aquifers, as a result ofhigher seawater density than freshwatergroundwater withdrawal in coastal areas
65 Sea Water IntrusionIn the coastal margins of ground water basin, the lowering of water level or potentiometric head results in the intrusion of sea waterInland gradient for saline intrusion result from pumping at rate higher than the recharge to the ground water basinwedge-shaped intrusion occurs as sea water is approximately times heavier than fresh water
66 Field surveys (geophysical and geochemical studies) can only reveal the present state of seawater intrusion but can not make impact assessment and prediction into the futureMathematical models are needed for these purposesGhyben-Herzberg relation is a highly simplified modelDynamic movement of groundwater flow and solute transport needs to be consideredA density-dependent solute transport model including advection and dispersion is needed for the modelling
67 Flow EquationAdvection-Dispersion EquationDistribution of HeadVelocity FieldSolute Transport ModelConcentration distribution in time and space
68 Ground Water Pollution Restoration to the original, non-polluted state of polluted ground water is more difficult than surface waterGeologic and hydrogeologic setting along with magnitude of the pollution hazard for a specific incident must be evaluated.Movement of contaminants and its control largely depends on the hydrogeologic environmentProcesses of migration and alterations present in ground water are also present in the unsaturated zone
69 Remedial action can be classified into three broad categories Physical containment measures, including slurry trench cutoff walls, grout curtains, sheet piling, and hydrodynamic controlAquifer rehabilitation, including withdrawal, treatment, reinjection (or recharge), and in-situ treatment such as chemical neutralization and biological neutralizationWithdrawal, treatment and use
70 use of models provide more appropriate and rigorous method for integrating all the available data togetherIt evaluates the response of the aquifer system to a contamination eventThe models are derived from the expression of the flow and transport processes in terms of mathematical equationsEquations are solved by incorporating appropriate parameter values and boundary conditions
71 Seawater IntrusionBefore extensive pumpingAfter extensive pumping by many wellsPumping causes a cone of depression and draws the salt water upwards into the well.
72 Groundwater An important component of water resource systems. Extracted from aquifers through pumping wells and supplied for domestic use, industry and agriculture.With increased withdrawal of groundwater, the quality of groundwater has been continuously deteriorating.Water can be injected into aquifers for storage and/or quality control purposes.
73 MANAGEMENT means making decisions to achieve goals without violating specified constraints. Once contamination has been detected in the saturated or unsaturated zones, requires the prediction of the path and the fate of the contaminants, in response to the planned activities.Any monitoring or observation network must be based on the anticipated behavior of the system.The tool for understanding the system and its behavior and for predicting the response is the model.Usually, the model takes the form of a set of mathematical equations, involving one or more partial differential equations. We refer to such model as a mathematical model.The preferred method of solution is the analytical solution.
74 For most practical problems we transform the mathematical model into a numerical one, solving it by means of computer programs.
75 What is a “model”?Any “device” that represents approximation to field systemPhysical ModelsMathematical Models (Analytical and Numerical)Modeling begins with formulation of a concept of a hydrologic system and continues with application of, for example, Darcy's Law to the problem, and may culminate in a complex numerical simulation.
76 TYPES OF MODELS CONCEPTUAL MODEL MATHEMATICAL MODEL ANALOG MODEL PHYSICAL MODEL
77 Line diagram of the Ganga with major tributaries (Source: Status paper on river Ganga, NRCD, MoEF, 2009)
78 Importance of ground water flow models Construct representations and helps understanding the interrelationships between elements of hydrogeological systemsEfficiently develop a sound mathematical representationMake reasonable assumptions and simplificationsUnderstand the limitations of the mathematical representation and interpretation of the resultsI want to show you how to use the power of hydrogeological modelingYou should be able to do more than just go through the motions of hydrogeological modeling, you should to be able to use the modeling process to further your understanding of the hydrogeological system that you are investigating.This will hinge on the development of a sound conceptual model, a concept in your mind of how the plumbing works and how it relates to the problem to be addressedWe will use mathematical models (analytical and numerical) as tools to address these problemsThe next step is to learn how to convert your conceptual model into a mathematical model. This could be as simple as applying 1-D Darcy’s Law and as complex as setting up and calibrating a 3-D, transient numerical model.In any case the procedure is the same: 1) Define the problem in lay-terms (demonstrate the significance to your audience), 2) define the specific objectives in technical (hydrogeological) terms, 3) Develop a conceptual model [site description and general hydrogeology], 4) convert the conceptual model into mathematical models that will address the objectives [methodology] 5) determine specifically where you will get the information from to set up your model [more methodology], 6) set up your model, calibrate and use it to address the objective [results]This will also help write the documentation which you should be writing all along
79 Groundwater models can be used : To predict or forecast expected artificial or natural changes in the system.To describe the system in order to analyse various assumptionsTo generate a hypothetical system that will be used to study principles of groundwater flow associated with various general or specific problems.
80 Processes to model Transport Groundwater flowTransportParticle tracking: requires velocities and a particle tracking code calculate path lines(b) Full solute transport: requires velocites and a solute transport model calculate concentrations
81 Processes we need to model Groundwater flowcalculate both heads and flows (q)Solute transport – requires information on flow (velocities)calculate concentrationsv = q/n = K I / nRequires a flow model and a solute transport model.
82 Modelling Process Establish the Purpose of the Model Develop Conceptual Model of the SystemSelect Governing Equations and Computer CodeModel DesignCalibrationCalibration Sensitivity AnalysisModel VerificationPredictionPredictive Sensitivity AnalysisPresentation of Modeling Design and ResultsPost AuditModel Redesign
83 Mathematical model:Simulates ground-water flow and/or solute fate and transport indirectly by means of a set of governing equations thought to represent the physical processes that occur in the system.(Anderson and Woessner, 1992)
84 Storage coefficient (S) is either storativity or specific yield. General 3D equation2D confined:2D unconfined:Storage coefficient (S) is either storativity or specific yield.S = Ss b & T = K b
85 Groundwater flow is described by Darcy’s law. This type of flow is known as advection.Linear flow pathsassumed in Darcy’s lawTrue flow pathsThe deviation of flow paths fromthe linear Darcy paths is knownas dispersion.Figures from Hornberger et al. (1998)
86 In addition to advection, we need to consider two other processes in transport problems. DispersionChemical reactionsAdvection-dispersion equationwith chemical reaction terms.
91 Selection of Computer Code Conceptual ModelA descriptive representation of a groundwater system that incorporates an interpretation of the geological & hydrological conditions.Selection of Computer CodeDepends largely on the type of problem(Flow, solute, heat, density dependent etc. along with 1D, 2D, 3D)Model geometryIt defines the size and the shape of the model. It consists of model boundaries, both external and internal, and model grid.GridIn Finite Difference model, the grid is formed by two sets of parallel lines that are orthogonal. In the centre of each cell is the node
92 BoundariesPhysical boundaries are well defined geologic and hydrologic features that permanently influence the pattern of groundwater flow (faults, geologic units, contact with surface water etc.)Hydraulic boundaries are derived from the groundwater flow net and therefore “artificial” boundaries set by the model designer. They can be no flow boundaries or boundaries with known hydraulic head.
93 Model Parameters Initial Conditions Time, Space (layer top and bottom), Hydrogeologic characteristics (hydraulic conductivity, transmissivity, storage parameters and effective porosity)Initial ConditionsValues of the hydraulic head for each active and constant-head cell in the model.
94 Calibration and Validation Calibration parameters are uncertain parameters whose values are adjusted during model calibration.Typical calibration parameters include hydraulic conductivity and recharge rate.Model validation is to determine how well the mathematical representation of the processes describes the actual system behavior.
95 Groundwater Flow Models MODFLOW (Three-Dimensional Finite-Difference Ground-Water Flow Model)When properly applied, MODFLOW is the recognized standard model.Ground-water flow within the aquifer is simulated in MODFLOW using a block-centered finite-difference approach.Layers can be simulated as confined, unconfined, or a combination of both.Flows from external stresses such as flow to wells, areal recharge, evapotranspiration, flow to drains, and flow through riverbeds can also be simulated.
96 Other Models MT3D (A Modular 3D Solute Transport Model) FEFLOW (Finite Element Subsurface Flow System)HST3D (3-D Heat and Solute Transport Model)SEAWAT (Three-Dimensional Variable-Density Ground-Water Flow)SUTRA (2-D Saturated/Unsaturated Transport Model)SWIM (Soil water infiltration and movement model)VISUAL HELP(Modeling Environment for Evaluating and Optimizing Landfill Designs)Visual MODFLOW (Integrated Modeling Environment for MODFLOW and MT3D)
97 Several methods to control saline intrusion Reduction of ground water extractionArtificial recharge by spreadingPhysical barrierMathematical modelling of unsteady flow of saline and fresh water in aquifer