ESM226 Groundwater Management

Author

John Robin Inston

Published

September 25, 2026

0.1 Material

  • Administration Material
    • [[esm226-jasechko-fall2024-pdf]]
  • Learning Material
    • Lectures:
      • [[01-groundwaterhydrologypart1-pdf]]
      • [[02-groundwaterhydrologypart2-1-pdf]]
      • [[03-groundwaterhydrologypart3-pdf]]
      • [[04-rechargedischarge-pdf]]
      • [[05-groundwater-quality-pdf]]
      • [[06-well-hydraulics-management-frameworks-pdf]]
      • [[07-groundwater-levels-pdf]]
      • [[08-groundwater-storage-pdf]]
      • [[09-seawater-intrusion-pdf]]
      • [[10-land-subsidence-pdf]]
      • [[11-streamflow-depletion-pdf]]
    • Other Resources:
    • Lecture Notes:
      • [[esm226-lecture-notes]]
  • Articles
    • Reading List:
      • Alley, W. M., Healy, R. W., LaBaugh, J. W., & Reilly, T. E. (2002). Flow and storage in groundwater systems. Science, 296, 1985-1990.
      • Taylor, R. G. et al. (2013). Ground water and climate change. Nature Climate Change, 3, 322.
      • Famiglietti, J. S. (2014). The global groundwater crisis. Nature Climate Change, 4, 945- 948.
      • Scanlon, B. R., Faunt, C. C., Longuevergne, L., Reedy, R. C., Alley, W. M., McGuire, V. L., McMahon, P. B. (2012). Groundwater depletion and sustainability of irrigation in the US High Plains and Central Valley. Proceedings of the national academy of sciences, 109, 9320-9325.
      • Foster, S. (2020). Global Policy Overview of Groundwater in Urban Development—A Tale of 10 Cities! Water, 12, 456.
      • https://gw-project.org/books/
      • Pavelko, M.T., Wood, D.B., Laczniak, R.J. Las Vegas, Nevada: Gambling with water in the desert. In: Land subsidence in the United States (Galloway, D., Jones, D., Ingebritsen, S., eds.) US Geological Survey Circular 1182, pp. 49-64. Accessed May 29, 2024 via https://pubs.usgs.gov/circ/circ1182/pdf/circ1182_intro.pdf (1999).
      • Deacon, J.E., Williams, A. E., Williams, C.D., Williams, J.E. Fueling population growth in Las Vegas: how large-scale groundwater withdrawal could burn regional biodiversity. BioScience, 57, 688-698 (2007).
      • Guillory, J., Brantley, D., Davis, J. Las Vegas Valley groundwater pumpage inventory calendar year 2021. Nevada Division of Water Resources Report, 414 pp. Accessed May 30, 2024 via http://epubs.nsla.nv.gov/statepubs/epubs/31428003098197-2021.pdf (2021).
      • Morgan, D.S. Dettinger, M.D. Ground-Water conditions in Las Vegas Valley, Clark County, Nevada: Part 2, hydrogeology and simulation of ground-water flow. US Geological Survey Water Supply Paper 2320-B, B1-B124 (1995).
      • Pavelko, M.T. Ground-water and aquifer-system-compaction data from the Lorenzi Site, Las Vegas, Nevada, 1994-99. US Geological Survey Open-File Report 00-362, 26 pp. Accessed May 30, 2024 via https://pubs.usgs.gov/publication/ofr00362 (2000).
      • Burbey, T.J., Zhang, M. (2015). Inverse modeling using PS-InSAR for improved calibration of hydraulic parameters and prediction of future subsidence for Las Vegas Valley, USA. Proceedings of the International Association of Hydrological Sciences, 372, 411-416 (2015).
      • Zhang, M., Burbey, T.J., Inverse modeling using PS-InSAR for improved land subsidence simulation in Las Vegas Valley, Nevada. Hydrological Processes, 30, 4494-4516 (2016).|
    • [[ems226-article-library|ESM226 Article Library]]
  • Final Project
  • Article:
    • Sources of water that supply withdrawals from major aquifer systems in the US (Modl simulations for various periods).

People to read into: - Christina Tague - Jasechko - Worked on aquifer mapping, see if they worked on mapping aquifer’s in California, how accurate are our maps? - Kelly Caylor

0.2 Topics

0.2.0.1 Key Topics
  • Primary and Secondary Porosity
  • Permeability
  • Aquifers, Aquitards, Confined and Unconfined Conditions
  • Hydraulic Conductivity / Intrinsic Permeability
  • Darcy’s Law & Applications
  • Water Table & Mapping
  • Gradient & Head
  • Water Table
  • Hydraulic Head
  • Specific Yielf and Storativity
  • Wells and Piezometers
  • Transmissivity
  • Specific discharge and average linear velocity
  • Homogeneity and Isotropy
  • Recharge and Discharge Areas
  • Steady flow in aquifers

0.3 Summary

  • Groundwater
    • Groundwater
    • Groundwater Wells
    • Groundwater Usage
  • Hydrologic Cycle
    • Groundwater is a reservoir in the hydrologic cycle
    • Groundwater interacts with other parts of the hydrologic cycle (gaining streams receive influxes of groundwater, losing streams loser flow due to water percolation)
    • Groundwater generates baseflow in rivers (the portion of river streamflow derived from deep subsurface and delayed shallow flows).
  • Fossil Water
    • Deep groundwater can be very old (likely more than half of all groundwater is ‘fossil’ in its age meaning it first moved underground more than 12,000 years ago).
    • There is widespread and increased drilling of wells into aquifers in the USA (read publications by lecturer Scott Jasechko)
  • Groundwater Inputs and Losses (Recharge & Discharge)
    • Groundwater has inputs via recharge ~16% if global land precipitation.
    • Recharge is the downward flow of water reaching the groundwater table, adding to groundwater storage (a.k.a. water that moves from the unsaturated zone into the saturated zone).
    • Groundwater has losses via discharge - where groundwater flows and exits the aquifer - such as pumping from wells.
  • Porosity
    • Void space in material.
    • Porosity indicates how much groundwater can be stored in materials (denoted \(\phi\) or \(n\)).
    • Reported in percent voids in total volume of geologic material i.e. \(n = \frac{V_{v}}{V}\times 100\%\) where \(V_{v}\) is the volume of void space, \(V\) is the volume of material (Voids + Solids).
    • Primary Porosity - spaces between grains in a sediment or sedimentary rock. It tends to be higher in well-sorted materials (particles of uniform size) and lower in unfractured, crystalline, endogenous (forms beneath the Earth’s surface through internal geological processes) bedrock. This is because in poorly-sorted materials smaller particles call fill the spaces between larger particles.
    • Secondary Porosity - porosity that develops after the rock forms (e.g. formation of fractures, joints and faults).
    • Porosity tends to decline with depth but does not always do so. Global porosity is ~20% close to the land surface and tends to diminish with depth
    • these trends cannot be expected everywhere and local variations are considerable.
  • Permeability
    • In geology, permeability refers to the ability of a material (such as rock, soil, or sediment) to allow fluids, like water or oil, to pass through it. This property is determined by the size and connectivity of the pores, fractures, or spaces within the material.
    • Key Factors Affecting Permeability:
      1. Porosity: The proportion of a material’s volume that is made up of open spaces (pores). However, high porosity does not always mean high permeability. If the pores are not connected, fluids cannot easily flow through.
      2. Grain Size: Coarser-grained materials like gravel tend to have higher permeability because larger grains create bigger, more connected pores.
      3. Compaction: Highly compacted materials, such as clay or shale, have low permeability because their pores are small and poorly connected.
      4. Fracturing: In materials like rock, fractures or cracks can greatly increase permeability by providing pathways for fluid flow.
    • Permeability Measurement - Permeability is typically measured in units called darcies or millidarcies (mD). High permeability materials, such as gravel, allow fluids to move easily, while low permeability materials, like clay, greatly restrict fluid flow.
    • Permeability is crucial for understanding groundwater movement, oil and gas extraction, and the behavior of soils in environmental and engineering applications.
    • Permeability depends on: (1) abundance of conduits; (2) size of these conduits; (3) connectivity and tortuosity of conduits.
  • Hydraulic Conductivity
  • Water Table
    • The water table is the level below which the porous media is saturated with water (often expressed in units of depth below the land surface).
    • Tends to be deeper in steeper, arid areas and shallower in places where precipitation and evapotranspiration rates are similar.
  • Aquifer & Aquitards
    • Relative terms, conceivable that two rock layers in different locations that have the same characteristics are named one or the other based on the material that surrounds it and its relative permeability.
    • Aquifer
      • Water-saturated, porous and more-permeable layer of geological material capable of transmitting groundwater.
      • An aquifer is an underground layer of permeable rock, sediment, or soil that stores and allows the movement of groundwater. Aquifers can supply water to wells, springs, and other water sources. They act like natural reservoirs, holding water that has infiltrated the ground through precipitation or surface water bodies.
      • Aquifers are typically categorized into two main types:
        1. Confined Aquifer:
          • This is sandwiched between layers of impermeable rock or clay, which traps the water under pressure. When tapped by a well, the pressure often causes water to rise on its own, sometimes reaching the surface without the need for a pump (artesian well).
        2. Unconfined Aquifer:
          • Groundwater stored in an aquifer has direct contact with the atmosphere through pore spaces in overlying rock / sediment.
          • The water table marks upper surface of the groundwater.
          • This lies closer to the Earth’s surface and is not capped by an impermeable layer, allowing water to flow freely into it from above. Its water level fluctuates depending on rainfall and other surface conditions.
      • Aquifers play a crucial role in supplying fresh water for agricultural, industrial, and residential use.
      • Hydraulic Head
        • The potential of fluid at the measurement point.
      • Rock Types
        • Consolidated Materials (i.e. like bedrock) take many forms, generally grouped into three rock types (sedimentary, metamorphic and igneous).
        • Unconsolidated Materials overlie consolidated materials across most of earth’s surface e.g. sands, gravel.
    • Aquitard
      • Less-permeable layer of geological material preventing the transmission of groundwater
      • An aquitard is a geological formation or layer that restricts the flow of groundwater between adjacent aquifers. It is typically made of materials with low permeability, such as clay, silt, or dense rock, which allow only limited water movement through them.
    • Aquifer Systems
      • Sequences of aquifers and aquitards with spatially-variable connectivity.
  • US Aquifers
    • Three critical aquifer systems in the US are:
      1. California’s Central Valley Aquifer
      2. High Plains Aquifer
      3. The Mississippi Embayment
    • Two thirds of all historical groundwater depletion took place in just these three systems.
  • Heterogeneity & Anisotropy
    • Heterogeneity
      • (in hydrology) quality of comprising diverse elements (usually referring to the architecture of pore spaces and grain sizes).
      • No groundwater model has ever overestimated the heterogeneity of the real-world
    • Anisotropy
      • Variable physical properties with respect to orientation (antonym: isotopy)
      • The anisotropy ratio is calculated as the ratio of vertical hydraulic conductivity divided by the horizontal hydraulic conductivity.
  • Case Study - Dasht-e-Abbas (West Qazvin Plain Iran)
    • Example of too much of a good thing, 15 years of groundwater decline was reversed with the construction of a damn and irrigation ditches.
    • Replenishment has gone too far leading to saturated ground and poor growing conditions.
  • Phreatophytes & GDEs
    • Deep rooted trees and shrubs that obtain a dependable water supply from the phreatic surface i.e. from the saturated water table.

Lecture 4 - Storage - Specific Yield \(S_{y}\) - Specific Yield \(S_{y}\) is the volume of water that can be drained from porous media by gravity relative to the total porous media volume - Specific Retention \(S_{r}\) is the volume of water that is retained in porous media despite gravity relative to the total porous media volume (i.e. \(\text{Porosity}=S_{y}+S_{r}\)). - - Specific Storage \(S_{s}\) - Specific Storage \(S_{s}\) is the amount of water per unit volume of saturated formation that is stored or expelled from storage owing to the compressibility of the mineral skeleton and the power water per unit change in hydraulic head. - Specific storage is given by the equation \[ S_{s}=\rho_{w}g(\alpha+n\beta), \] where: (1) \(\rho_{w}\) is the density of water; (2) \(g\) is gravitational acceleration; (3) \(n\) is porosity; and \(\beta\) is the compressibility of water. - - Storativity \(S\) - Storativity \(S\) is the volume of water that a permeable unit will absorb or expel per unit area per unit change in hydraulic head. - Storativity in unconfined aquifers is the sum of specific yield and specific storage (\(\times\) aquifer thickness) - Storativity in confined aquifers derives only from specific storage (\(\times\) aquifer thickness) - Storativity for a confined aquifer with thickness \(b\) is given by \(S_{s}b\) - Key point:. The same amount of pumping from an unconfined versus confined will induce a far greater drawdown of hydraulic head in the confined aquifer relative to the unconfined. - Potential ramifications associated with pumping from confined aquifer systems: 1. Land subsidence 2. Compaction - Residence Times - The average time interval that a water molecule spends in a reservoir, often denoted \(\tau\). - At steady state (volume of water stored in the reservoir doesn’t change over time) this equations to the volume of water in a reservoir divided by the rate of inputs or losses \[ \tau=\frac{V}{F}, \] where: (1) \(V\) is the volume of water in the reservoir and (2) \(F\) is the flux in (or out) of the system. - Recharge, Flow and Discharge - Groundwater recharge occurs as precipitation traverses unsaturated zones (e.g. soil profiles) to cross the water table and enter the saturated zone (also termed phreatic zone). - Groundwater can then flow through aquifers, flowing down the hydraulic gradient. Some groundwater eventually flows out of aquifers to become streamflow (baseflow) or directly enter the oceans (submarine groundwater discharge) with these flows collectively known as groundwater recharge. - Darcy’s Law - Hydraulic Gradient \(\frac{dh}{dL}\): the change in hydraulic head between two points separated by a distance \(L\). - Darcy’s law is used to estimate groundwater fluxes which are calculated as \[ Q=-K_{H}A\left( \frac{dh}{dL} \right), \] or we can calculate specific discharge as \[ q=-K_{H}\left( \frac{dh}{dL} \right) \] - Example - Wells 1 and 2 are drilled 100m apart on a flat landscape. The water level of well 1 is 2.2m below the land surface, the water level at well 2 is 3.0m below the land surface. The hydraulic conductivity of the aquifer is 0.03m/d and the porosity is 0.21. Calculate the hydraulic gradient and estimate the average linear velocity of the groundwater (in mm/d). - Solution: From Darcy’s Law we have that \[ q=-K_{H}\left( \frac{dh}{dL} \right)\implies q=-0.03\left( \frac{0.8}{100}\right) \] and so our velocity is \[ v=\frac{q}{0.21}=-\frac{0.03}{0.21}\left( \frac{0.8}{100} \right). \] - (Ground)Watersheds - A watershed is an area of land that drains all the streams and rainfall to a common outlet such as the outflow of a reservoir, mouth of a bay, or any point along a stream channel. - While watersheds are commonly derived from topographic data (e.g. a digital elevation model) identifying groundwater flow directions is more challenging. - Understanding the direction and rate of groundwater flow is critical to many hydrogeologic problems. - Hydraulic Head - Hydraulic head (\(h\)) is separated into two components: - Pressure head \(\Psi\) - vertical distance from the well screen interval to the water level in the well. - Elevation head \(z\) - vertical distance from a datum (e.g. sea level) to the screened interval in the well. - Commonly measured as water level in a well. - Flownets - Flownets are frequently constructed across sections that comprise of at least two components: - Lines of equal hydraulic head - Groundwater flow lines - Equipotential lines - Lines of equal hydraulic head. - Assumptions with flownets: - Homogeneity in aquifer; - Aquifer is isotropic, - Heads do not vary over time, - Aquifer (and groundwater) is incompressible, - Flow is laminar. - Implicit assumptions with flownets are numerous and the validity of some is, at best, uncertain. - Reading Flownets: - - No flow lines: A-B, and (C-D) - Point “D” is a groundwater divide - Recharge areas (E-D) are uplands (where vertical hydraulic gradients are downwards) - Discharge areas (A-E) are valleys (where flowlines intersect the land surface) - Line separating recharge area from discharge area sometimes referred to as hinge line. - Other ways to visualize equipotential lines - - Vertical Hydraulic Gradient - Slope of the potentiometric surface in vertical dimension - Often determined by comparing hydraulic hears in two different wells with different depths. - Expressed as a change in hydraulic head (h) over a vertical distance (z) \(\frac{dh}{dz}\). - - Hydraulic heads are theorized to decline with depth in recharge areas, and increase with depth in discharge areas. - I.e. Vertical hydraulic - Where do streams gain (or lose) flow from (to) aquifers? - Identifying gaining and losing river reaches relevant for: - Mapping and protecting aquatic habitat - Understanding the evolution of stream networks - Predicting where polluted water may enter streams. - Quantifying CO2 degassing from streams - Managing groundwaters and rivers as interconnected resources, and quantifying headwater runoff generator. - River-Aquifer Exchanges - Some methods to measure groundwater discharge (and/or baseflow) include: - Seepage meters - Streamflow monitoring - Highly imperfect assumptions, most poorly supported of which may be: groundwater influxes remain steady or increase only modestly during stormflows - Hydrochemical tracers - See below for more informatin - - Piezometers - Measurements of hydraulic head can be used to identify hydraulic gradients relative to stream surfaces. - Discharge (Baseflow) - Map-view (“birds eye view”) contours of water table elevations can be used to identify gaining versus losing river reaches. - Stable isotopes of O and H in H20 - Important terminology: - Atomic number (Z) - number of protons in a nucleus - Neutron number (N) - number of neutrons in nucleus - Electron number (e\(^-\)) - number of electrons in atom - Nucleon: Proton or Neutron - Mass Number (A) = N + Z (number of nucleons) - Neutral Atom - An uncharged atom where \(Z=e^{-}\) - Isotopes - atoms with the same number of protons (Z) but with different numbers of neutrons (N) - Three types of isotopes: - Stable - Unstable (radio active) - spontaneous change in nucleons - Radiogenic - of radioactive origin, can be stable or unstable. - Isotopologues used to describe molecules with identical elements and atomic arrangement but different isotopes. - Act as a hydrological fingerprint, allows scientists to identify where water is sourced from. - Examples of isotopologues of oxygen: - SMOW - SMOW stands for Standard mean ocean water - It is what we compare other samples too - Stable Isotope Systematics - Molecules are energetically stabilized by inclusion of heavier isotope (lower vibrational frequencies for heavier molecules). - Some phases (e.g. liquid vs vapor) have different preferences for heavy isotopes (think of them as more greedy for stabilization than other phases). - Generally the heavy isotope tends to partition (fractionate) into species with stronger chemical bonds, which is often the denser phase. - Gaining and Loosing Streams - What do we know about gaining and losing streams? - We know that geology (hydraulic conductivity and its 3D spatial pattern) is critical. - We know that streams may even gain on one side only to leak (i.e. los) on the other, a condition known as throughflow. - We know that conditions (i.e. gaining vs losing) can fluctuate over time for a given location. - We know that biogeochemical reactions at the aquifer-stream interface (the hyporheic zone) is critical to aquatic habitat and nutrient cycling. - Patterns of Gaining and Losing Rivers - Gaining streams are more prevalent in humid climates and in steeper terrain (again this is a soft pattern and has many counter-examples). - Losing streams tend to be more prevalent in arid climates and where historic groundwater pumping is high. - Rivers can (and do) switch between gaining / losing conditions under low-vs-high flow. - Diffuse vs Focussed Groundwater Recharge - Diffuse Recharge - Recharge that is distributed over large areas in response to precipitation infiltrating the soil surface and percolating through the unsaturated zone to the water table (or alternatively stated, recharge distributed across expansive areas that occurs as precipitation infiltrates then traverses the unsaturated zone to reach the water table). - This generally dominates in humid climates. - Focused Recharge - Movement of water from surface-water bodies (such as streams, canals or lakes) to an underlying aquifer.
- This generally dominates in arid areas. - Mountain Front (Block) Recharge - Used in arid and semiarid climates to describe the contribution of mountainous regions to the recharge of aquifers in adjacent basins. - Assessing Recharge Rates - - Immense variations in recharge rates through space and time. - Units often expressed in L/T (e.g. mm/month, mm/year) - Quantifying recharge via: - Modelling - Simulations of real-world groundwater recharge. - Synthesis of global water, geologic and climate data and embedding these data into water budget framework. - Water table fluctuations - Assumption is that a rise in water table elevation (as interpreted from water level time series in shallow monitoring well) is the result of recharge to the shallow aquifer. - Recharge \(R\) is calculated as \[ R(t_{j})=Sy\times DH(t_{j}) \] where \(R(t_{i})\) (cm) is recharge occurring between times \(t_{0}\) and \(t_{i}\), \(S_{y}\) is specific yield (dimensionless), and \(DH(t_{i})\) is the peak water level rise attributed to the recharge period. - - Drawbacks: - must estimate specific yield (this can be non-trivial) - assumption that fluctuations in well water level time series are due to recharge, issues arise where (i) pumping from nearby wells, (ii) nearby stream stage fluctuations (bank storage), (iii) evapotranspiration, (iv) atmospheric pressure. - largely applicable only to shallow unconfined aquifers; impact of well depth on results remains unclear - The specific yield of a rock or soil with respect to water is the ratio of (1) the volume of water which, after being saturated, it will yield to gravity to (2) its own volume \[ \text{Specific Yield}=\text{Porosity}-\text{[Specific Retention]} \] - Chloride Mass Balance - Recharge \(q\) is given by \[ q=P\cdot \frac{Cl_{wap}}{Cl_{gw}}, \] where \(P\) is annual precipitation rate; \(CL_{wap}\) is chloride concentration of weighted annual precipitation; \(Cl_{gw}\) is chloride concentration of groundwater. - Often used for measuring low rates of recharge (as few other methods available). - Implicit assumption is that runoff is minimal, may be appropriate for estimates of diffuse recharge rates (i.e. perhaps less applicable to focussed recharge rate estimates). - Radioactive Isotopes - Tritium has half-life of 12.3 years (a radioisotope of hydrogen embedded in water). - Radioactivity in precipitation spiked in 1950s-60s due to thermonuclear testing. - Its presence at levels exceeding common laboratory detection limits (< 0.8 tritium units - where 1 T.U. equals 0.118 Bequerel per liter) indicate the presence of recently-recharges water in a groundwater sample. - Recharge from Depth-Radioactivity Profiles - Recharge Estimates Compiled - Managed Aquifer Recharge - Managed Aquifer Recharge (MAR) is the intentional storing and treatment of water in aquifers. - Globally approximately 10km\(^3\)/year of MAR occurs. Global groundwater extractions are approximately 1000km\(^3\)/year. - Different from unmanaged aquifer recharge induced by humans: -

Questions: 1. How well do we understand the dynamic between precipitation levels and groundwater recharge? 2. How well do we understand flows between aquifers?

Three sources of pumped groundwater - Existing aquifer resources - Drawing more water from other regions - Drawing water - Cone of depression?

  • [[esm226-lecture-1]]

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