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5/14/2020 THUYLOI UNIVERSITY Division of Hydrology and Water Resources GROUNDWATER ENGINEERING (CIVE 4208) Introduction Ngo Le An annl@wru.vn 1 Course Introduction Lecturers: ◦ Ngo Le An, annl@wru.vn ◦ Nguyen Thi Thu Ha, nguyenthithuha@wru.vn ◦ Nguyễn Thị Thu Nga, nga_tvct@tlu.edu.vn Faculty of Hydrology & Water Resources  Textbook: ◦ Charles R Fitts (2002): ◦ Groundwater Science ◦ Academic, Elsevier ◦ ISBN 0‐12‐257855‐4 ◦ 450 pages  2 5/14/2020 Course Introduction  Optional References: ◦ Todd, D K., and Mays, L (2005) ◦ Groundwater Hydrology, 3rd Edition ◦ Wiley Interscience: Hoboken, NJ ◦ ISBN 0‐471‐05937‐4 ◦ M Karamouz , A Ahmadi, M Akhbari (2011): Groundwater Hydrology: Engineering, Planning, and Management, 1st Edition ◦ CRC Press ◦ ISBN: 978-1-4398-9121-6,1439891214 3 Course Introduction   Grading: 10% - Attending 20% - Homework 20% - Mid-term exam 20% - Mid-term exam 30% - Final exam Plus/minus grading will be used Homework: Submit on paper 4 5/14/2020 Course Introduction Week 1-2 3-5 7-12 13 14-15 Content Introduction Hydrologic Cycle & Water Balance, Role of groundwater in water resources system and their management Physical Properties of Porous Media, Aquifers and Aquifers Type Principle of Groundwater flow Hydraulic Conductivity, Darcy’s Law, , Dupuit assumptions, Ground water flow direction, General Equation of groundwater flow, Flow in confined and unconfined aquifers Mid-term Well Hydraulics Steady and unsteady flow to a well in a confined and unconfined aquifer - Partially penetrating wells - Wells in a leaky confined aquifer - Multiple well systems Mid-term Groundwater Modeling Techniques Types of Groundwater Models, Governing equations, Finite Difference Equations, Model calibration and verification, Parameter estimation Readings Chapter Chapter 3, 4, Chapter 6, Chapter 5 Course Description  Introduction to groundwater principles for students with interests in water resources, geotechnical and environmental engineering, geosciences 6 5/14/2020 Course Goals  Develop an understanding for solving basic hydrogeological problems;  Introduce the fundamentals of subsurface fluid flow;  Provide an overview of current issues in the field of groundwater engineering;  Provide a basis for groundwater coursework further applied 7 Engineering Applications Assessment of Groundwater Resources (Supply and Management) Migration of Contaminants in the Subsurface Geotechnical Problems Geological Processes 8 5/14/2020 Groundwater Resources Water supply: • Water supply wells for drinking water, irrigation, and industrial purposes are drilled after assembling data on the hydrogeology of the region (previous drilling data, well data, and geologic maps) • Test wells are drilled and hydraulic testing is done to estimate the long-term discharge capacity • The water chemistry is checked to make sure that the water is suited for its intended purpose Water resource management • Difficult decisions must be made about who is allowed to pump water, how much can be pumped, where wells can be located, and where potential contaminant sources like gasoline tanks may be located • Surface water projects including dams, diversions for irrigation, and sewer systems have an impact on groundwater levels and quality, and must also be carefully considered 9 Contaminants in the Subsurface 10 10 5/14/2020 Geotechnical Problems • Land subsidence • Slope Stability • Dewatering • Dams 11 11 Geotechnical Problems • Land subsidence 12 12 5/14/2020 Geotechnical Problems • Slope Stability 13 13 Geotechnical Problems • Dewatering 14 14 5/14/2020 Geotechnical Problems • Dams 15 15 Hydro‐geological processes Large-scale geologic processes involving groundwater are studied for purely academic interest and to better understand processes: • Origins of Fossil Fuels • Mechanics of Faults and Thrusts • Geo‐morphological development of landforms (glacial, fluvial process) 16 16 5/14/2020 Hydro‐geological processes • Fossil Fuels 17 17 Hydro‐geological processes • Mechanics of Faults and Thrusts 18 18 5/14/2020 Hydro‐geological processes • Development of landforms 19 19 Some Terminology Hydrology () ◦  - “water”;  - “study of” ◦ Study of Water: properties, distribution, and effects on the Earth’s surface, soil, and atmosphere  Water Management ◦ Sustainable use of water resources ◦ Manipulating the hydrologic cycle   Hydraulic structures, water supply, water treatment, wastewater treatment & disposal, irrigation, hydropower generation, flood control, etc 20 20 10 5/14/2020 ALTERNATING DIRECTION IMPLICIT PROCEDURE Example - Solution At 2nd time step t=2*t =1day : In this time step, computations are made by column • For column 2, i = 𝑙+1 • 𝐷𝑗 = −ℎ𝑖−1,𝑗 ∆𝑦2 ∆𝑥 𝑙+1 − ℎ𝑖,𝑗 0.5 • For j = 2, 𝐷2 = −ℎ1,2 • 𝐷2 = −20 3002 4002 ∆𝑦2 ∆𝑥 𝑆 ∆𝑦 ∆𝑦 − ∆𝑥 𝑇 ∆𝑡 0.5 − ℎ2,2 − 19.15 ∆𝑦 𝑆 ∆𝑦 − 𝑇 ∆𝑡 0.003 3002 240 0.5 𝑄𝑖𝑗 ∆𝑦2 𝑇 𝑙+1 − ℎ𝑖+1,𝑗 + ∆𝑥∆𝑦 ∆𝑥 2 ∆𝑦2 ∆𝑥 0.5 − ℎ3,2 ∆𝑦 +0 ∆𝑥2 3002 3002 − 4002 − 14.89 4002 = −41.17 85 ALTERNATING DIRECTION IMPLICIT PROCEDURE Example - Solution At 2nd time step t=2*t =1day : In this time step, computations are made by column • For column 2, i = 𝑙+1 • 𝐷𝑗 = −ℎ𝑖−1,𝑗 • For j = 3, 𝑞1 = ∆𝑦2 ∆𝑦 𝑙+1 𝑆 ∆𝑦 − ℎ𝑖,𝑗 − ∆𝑥 ∆𝑥 0.09 0.0648 = 300ì400 0.5 ã = −ℎ1,3 • 𝐷3 = −20 = −11.48 ∆𝑦2 ∆𝑥 3002 4002 0.5 − ℎ2,3 𝑆 ∆𝑦 ∆𝑦 − 𝑇 ∆𝑡 ∆𝑥 − 12.55 0.003 3002 240 0.5 ∆𝑦 𝑄𝑖𝑗 ∆𝑦2 𝑇 ∆𝑦2 0.0468 300 240 𝑙+1 − ℎ𝑖+1,𝑗 + ∆𝑥∆𝑦 ∆𝑥 0.5 − ℎ3,3 + ∆𝑥 3002 3002 − 4002 − 18.51 4002 + 0.0468 300 240 = 86 43 5/14/2020 ALTERNATING DIRECTION IMPLICIT PROCEDURE Example - Solution At 2nd time step t=2*t =1day : In this time step, computations are made by column 𝒍+𝟐 𝒍+𝟐 • For column 2, i = 2, 𝒉𝒍+𝟐 𝒊,𝒋−𝟏 + 𝑩𝒋 𝒉𝒊,𝒋 + 𝒉𝒊,𝒋+𝟏 = 𝑫𝒋 • 𝐹𝑜𝑟 𝑗 = 1, • 𝒉𝟏𝟐,𝟎 − 𝟒 𝟐𝟓𝒉𝟏𝟐,𝟏 + 𝒉𝟏𝟐,𝟐 = −𝟒𝟓 − 𝟒 𝟐𝟓𝒉𝟏𝟐,𝟏 + 𝒉𝟏𝟐,𝟐 = −𝟔𝟓 • For j = • 𝒉𝟏𝟐,𝟏 − 𝟒 𝟐𝟓𝒉𝟏𝟐,𝟐 + 𝒉𝟏𝟐,𝟑 = −𝟒𝟏 𝟏𝟕 • For j = 3, • 𝒉𝟏𝟐,𝟐 − 𝟒 𝟐𝟓𝒉𝟏𝟐,𝟑 + 𝒉𝟏𝟐,𝟒 = −𝟏𝟏 𝟒𝟖 • ℎ2,4 = ℎ2,3 • 𝒉𝟏𝟐,𝟐 − 𝟑 𝟐𝟓𝒉𝟏𝟐,𝟑 = −𝟏𝟏 𝟒𝟖 • Solving gives: 𝒉𝟏𝟐,𝟏 = 𝟏𝟗 𝟏𝟎𝒎, 𝒉𝟏𝟐,𝟐 = 𝟏𝟔 𝟏𝟖𝒎; 𝒉𝟏𝟐,𝟑 = 𝟖 𝟓𝟏𝒎 • Again, the heads at all nodes in columns are obtained by a similar procedure 87 ALTERNATING DIRECTION IMPLICIT PROCEDURE Example - Solution • Heads at the end of second time step (t = 1day) 88 44 5/14/2020 THREE-DIMENSIONAL GROUNDWATER FLOW MODEL • The partial differential equation for transient three-dimensional groundwater flow in a heterogeneous and anisotropic medium, for a confined or unconfined aquifer, is expressed as • • • 𝜕 𝜕𝑥 𝐾𝑥 𝜕ℎ 𝜕𝑥 + 𝜕 𝜕𝑦 𝐾𝑦 𝜕ℎ 𝜕𝑦 + 𝜕 𝜕𝑧 𝐾𝑧 𝜕ℎ 𝜕𝑧 = 𝑆𝑠 𝜕ℎ 𝜕𝑡 − 𝑅∗ The 3-D Equation, together with specification of flow and/or head conditions at the boundaries of an aquifer system and specification of initial head conditions, constitutes a mathematical representation of a groundwater flow system Use the finite difference method to find the solution of the 3-D Equation – Replaces the continuous system described by the 3-D Equation with a finite set of discrete points in space and lime, such that the partial derivatives are replaced by terms calculated from the head differences calculated at these points – A system of simultaneous linear algebraic difference equations results from this process, which is solved for the heads at specific points and times that constitute the approximation to the time-varying head distribution 89 THREE-DIMENSIONAL GROUNDWATER FLOW MODEL ✓ A three-dimensional hypothetical aquifer system is discretized into a mesh of blocks called cells, described by rows, columns, and layers ✓ The hypothetical system is discrefized into five rows, nine columns, and five layers 90 45 5/14/2020 Groundwater Modelling Softwares • The most widely used numerical groundwater flow model is MODFLOW which is a three dimensional model running on any platform (Windows, Sun, Unix, Linux,…) • Mostly written in standard FORTRAN (GMG is C++) • MODFLOW is originally developed by the U.S Geological Survey in 1983 (McDonald and Harbaugh) Written to serve USGS needs Education emphasized • Several versions available – MODFLOW 88, 96, 2000, 2005 (water.usgs.gov/nrp/gwsoftware/modflow.html) • The advantages of MODFLOW include numerous facilities for data preparation, easy exchange of data in standard form, extended worldwide experience, continuous development, availability of source code, and relatively low price 91 What is MODFLOW? • Can simulate GW flow in fully and quasi-3D systems, 2D in one horizontal layer or in cross section • Ground-water flow within the aquifer is simulated in MODFLOW using a block-centered finite-difference approach – The flow region is subdivided into blocks in which the medium properties are assumed to be uniform – In plan view, the blocks are made from a grid of muturally perpendicular lines that may be variably spaced – Model layers can have varying thickness – A flow equation is written for each block, or cell – Several methods are provided for solving the resulting matrix problem; the user can choose the best one for a particular problem – Flow rate and cumulative volume, which are balanced from each type of inflow and outflow, are computed for each time step • Aquifer Layers can be simulated as confined, unconfined, or a combination of both 92 46 5/14/2020 This model was developed for assessing the impacts of a groundwater extraction borefield (bores shown as red spots) Grid refinement is provided around the borefield and groundwater discharge sites in the northwest of the model domain Mustard coloured cells are inactive 93 What is MODFLOW? • Flows from external stresses such as flow to wells, areal recharge, evapotranspiration, flow to drains, and flow through riverbeds can also be simulated • Hydraulic conductivities or transmissivities for any layer may differ spatially and be anisotropic, ans the storage coefficient may be heterogenous • Specified head and flux boundaries can be simulated by this model • It is also capable of modeling head-dependent flux across the outer boundary of the model, which allows water to be supplied to a boundary block in the modeled area at a rate proportional to the current head difference between a source of water outside the modeled area and the boundary block 94 47 5/14/2020 What is MODFLOW? • Model is based on modular structure; consists of Main Program and series of highly independent subroutines called Modules – Activate the capabilities you need; no overhead from other capabilities (execution time, RAM) – The structure is clear and documented for adding additional capabilities such as new equations – Modularity in ‘Processes’ and ‘Packages’ 95 MODFLOW-2005 Processes • Latest release of USGS MODFLOW • Processes each solve a fundamental equation E.g: • Ground-water Flow (GWF) •K•h = S(h/t) … • Observation (OBS) y = y′ + e 96 48 5/14/2020 GWF Packages • Packages each represent a type of system feature • Package that defines model layers and properties: • Layer-Property Flow (LPF) Package • Packages used to add/remove water at a specified rate: • Well (WEL) • Recharge (RCH) • Packages that add/remove water based on head in the aquifer: • General-Head Boundary (GHB) • River (RIV) 97 How Processes and Packages Interact GWF Process OBS Process LPF Package Define K and S properties, possibly using parameters Calculate contributions to the matrix equations No observations are now defined for the LPF Package Possible observations are internal flows RIV Package Define river properties, River gain and loss possibly using observations can be parameters defined Calculate contributions to the matrix equations 98 49 5/14/2020 MODFLOW Softwares • Many other programs use results from or are based on MODFLOW: – Public domain/open source • MT3DMS (Simulation of transport of multiple reactive solutes in groundwater): Open source software that can be coupled with MODFLOW to compute coupled flow and transport • RT3D (Simulation of multi-species reactive transport in groundwater): Open source software that can be coupled with MODFLOW to compute coupled flow and transport • PHT3D (Simulation of multi-species reactive transport in groundwater): Open source software that can be coupled with MODFLOW to compute coupled flow and transport Includes MT3DMS and PHREEQC • SEAWAT (Simulation of saturated flow and transport of multiple solutes and heat): Open source software combining MODFLOW and MT3DMS for density-coupled flow and transport • ZONEBUDGET (Mass balance calculations for parts of a MODFLOW model domain): Open source software commonly distributed with MODFLOW GUIs • MODPATH (Particle tracking code used with MODFLOW): Open-source software commonly distributed with MODFLOW GUIs 99 MODFLOW Softwares • Many other programs use results from or are based on MODFLOW: – Commercial • • • • • MODFLOW-SURFACT Visual MODFLOW (GUI) Groundwater Vistas (GUI GMS (GUI PMWIN (GUI) 100 50 5/14/2020 http://www.groundwatermodels.com/ Groundwater Vistas (GV) is a sophisticated windows graphical user interface for 3-D groundwater flow and transport modeling It couples a model design system with comprehensive graphical analysis tools Groundwater Vistas GV is a model-independent graphical design system for MODFLOW MODPATH (both steady-state and transient versions), MT3DMS, MODFLOWT, MODFLOW-SURFACT, MODFLOW2000, GFLOW, RT3D, PATH3D, SEAWAT and PEST, the model-independent calibration software GV displays the model design in both plan and cross-sectional views using a split window (both views are visible at the same time) Model results are presented using contours, shaded contours, velocity vectors, and detailed analysis of mass balance 101 Groundwater Vistas 102 51 5/14/2020 https://www.waterloohydrogeologic.com/visualmodflow-flex/ Visual MODFLOW Visual MODFLOW is the most complete and easy-to-use modeling environment for practical applications in three-dimensional groundwater flow and contaminant transport simulations This fully-integrated package combines MODFLOW, MODFLOWSURFACT, MODPATH, ZoneBudget, MT3Dxx/RT3D, MGO, and WinPEST with the most intuitive and powerful graphical interface available The logical menu structure and easy-to-use graphical tools allow you to: •easily dimension the model domain and select units •conveniently assign model properties and boundary conditions •run the model simulations •calibrate the model using manual or automated techniques optimize the pumping well rates and locations •visualize the results using 2D or 3D graphics 103 Visual MODFLOW 104 52 5/14/2020 Processing Modflow for Windows (PMWIN) • http://www.pmwin.net/pmwin5.htm • Processing MODFLOW for Windows (PMWIN) is a complete simulation system for modeling groundwater flow and transport processes • It comes complete with a professional graphical preprocessor and postprocessor, the 3-D finite-difference ground-water models MODFLOW-88, MODFLOW-96, and MODFLOW 2000; the solute transport models MT3D, MT3DMS, RT3D and MOC3D; the particle tracking model PMPATH 99; and the inverse models UCODE and PEST-ASP for automatic calibration A 3D visualization and animation package, 3D Groundwater Explorer, is also included 105 Processing Modflow for Windows (PMWIN) 106 53 5/14/2020 Application of MODFLOW • Schematic flow system • Effects of pumping on shallow or deep water levels (drawdown) • Natural/ Artificial recharge to groundwater • Surfacewater and groundwater interactions • Sources of water to wells • … 107 GW Flow Model - Example • An unconfined aquifer is a coarse grained sand with a measured isotropic hydraulic conductivity of 160 m/day, the specific yield has been assessed as 0.06 • Recharge to the aquifer only occurs throughout the month wet season at a rate of 7.5 × 10-4 m/day, outside the wet season there is no recharge to the aquifer • The elevations of the aquifer top and bottom are 25 m and m, respectively The area of interest is 10000 m long and 6000 m wide and is bounded by “no flow” zones to the east and west There is also a volcanic mountain in the south east corner of the model area To the north an area of constant hydraulic head existd with a value of 15 m The southern boundary is a specified flux boundary with an inflow rate of 0.0672 m3/day per meter • A total of nine wells in the area are pumped at 45 l/s (3888 m3/d) each during the month dry season to supply water for irrigation and domestic purposes • Your task is to assess the water levels in the aquifer under the following conditions: (1) steady-state, with the mean recharge rate = 2.5×10-4 m/day, no pumping; (2) after months pumping during the dry season; and (3) the water levels by the end of the following wet season 108 54 5/14/2020 GW flow Model Steps Steps Create a new model, Define model size: Number of layers, rows, columns Refine model grid: Use a smaller grid in areas where the hydraulic gradient is expected to be large, i.e around the wells Assign model data: aquifer types, boundaries, aquifer geometry, aquifer parameters (hydraulic conductivity, storage coefficient), initial conditions, time paramters and recharge rates Perform simulations (steady-state flow simulation or Transient flow simulation) Extract and view results from the steadystate simulation (contour plots) Transient flow simulation Extract and view results from the steadystate simulation (contour plots) 109 PMWIN-Results Steady-state, with the mean recharge rate = 2.5×10-4 m/day, no pumping 110 110 55 5/14/2020 Transient Groundwater Models • We now need to change from a steady state simulation to a transient simulation • Transient models simulate changes over time – Necessary when boundary conditions vary with time (e.g., pumping rates, recharge, river stage, etc.) • Stress period: – Period of time during which boundary conditions are constant – Stress periods can have multiple time steps – Boundary conditions can change at the beginning of a stress period e.g., one day Time Steps Time Steps Time Steps Stress period Stress period Stress period • e.g., one month Time Pumping and boundary conditions can change 111 Transient Groundwater Models • In the transient simulation there are two stress periods, one of 240 days when pumping is occurring and no recharge and the other of 120 days when there is recharge only For period 1: Period Length = 240; Time Step = 12 For period 2: Period Length = 120; Time Step = 112 56 5/14/2020 PMWIN-Results After months pumping during the dry season; and 113 PMWIN-Results The water levels by the end of the following wet season 114 57