Recent Advances in Modeling Groundwater Dynamics

Summary:

• Focus on groundwater: 

  • Shallower ground: Unsaturated (some water and some gaps)

  • Deeper: Fully saturated with water

  • Boundary: water table

• Types: Water through …

  • Voids in rocks

  • Fractures in bedrocks

  • Channels/caves dissolved from carbonate rocks

• Ground and surface water are a single, connected resource

  • Naturally groundwater is near the surface

  • In stressed conditions groundwater is deep and hard to access for plant roots and wells

  • 99% of all liquid freshwater is groundwater

  • ½ humanity drinks groundwater

  • 70% of food irrigation has groundwater origins (much from irreversible depletion)

  • Nearly all aquifers are contaminated to some degree

• Groundwater vulnerability

  • Conflict, 

  • Ecosystems

  • Hazards

  • Energy & resources

  • Food security

  • Human Health

• Numerical modeling of groundwater flow/transport

  • Hydraulic head

  • Mass transport

  • 3D

• The changing nature of groundwater in the global water cycle, 2024: https://www.science.org/doi/10.1126/science.adf0630

  • Climate change has significantly impacted groundwater

  • Major gaps in research (modeling, data, etc.)

  • Key to model cycle of water through the economy and agriculture

• Modeling groundwater dynamics in Asia’s Water Tower

  • Tibetan Plateau: 2.5 million km2

    • Water for ~2billion people

    • >500GW Hydropower

  • Focus: Yarlung Zangbo River Basin

  • Mountain hydrology

  • Limited data

  • Challenging ground (e.g. permafrost)

  • Key questions: 

    • Where does Himalayan river water come from and 

    • What is the role of groundwater

  • Comprehensive hydrological models

    • Groundwater, surface water, glacial melt, evaporation

    • Rainfall: 40%, snowmelt: 24%, groundwater 36%

    • Excess water; suspected that it is discharging to deep fractured bedrock aquifers

      • Many deep faults in the basin

  • Simulated structure of water tower: good agreement with GRACE satellite data, all the way to discharge to Indian ocean

  • As glaciers melt the total availability of water will not change (still precipitation) but lack of storage means more variability year to year

  • Permafrost

    • Permafrost is degrading due to climate change

    • This modifies hydrology and landscape

    • Direct impacts: 

      • More water goes into ground (more space in melted ground)

      • Less overall surface water

      • More streamflow as water is discharged from permafrost

• Integrated modeling of flow, soil, nutrients

  • HEIFLOW: hydro-ecological integrated watershed-scale model based on USGS GSFLOW

    • Ecological modules

    • Soil erosion/nutrient

    • Surface vs groundwater

    • 2km x 2km

  • Marine model: FVCOM

    • Land-sea Boundary conditions for Hydrological model

    • 60-7000m grid

  • Subsurface parameterization from boreholes and geological maps

  • Application: Wastewater Treatment Plant (WWTP) discharge prediction

    • Predict flow of waste to water system

    • Used population migration map and data on locations of WWTP plants but not how much they discharge

    • Establish daily point source discharge database with some confidence based on hydrology and chemical sensor data

  • Coastal Algal Blooms from Remote sensing

    • Remote sensing identifies algal blooms (challenge: ⅔ of days are cloudy, so no data then)

    • Hydrological models infer their likely sources

    • Applied to the Pearl River

• Highlight: “MODFLOW and MORE” conference (Theme: AI, global change and the future)

• Groundwater modeling in the Global Energy and Water Exchanges (GEWEX) Project: https://www.gewex.org/

  • Groundwater is the missing link in Earth System Models

  • Challenges:

    • Data availability and quality

    • Model complexity and scale

    • Climate and human impacts

  • Need global scale groundwater models

  • Examples: 

    • Canada1Water model: https://www.canada1water.ca/

      • Physics-based model of the complete water cycle for Canada and connected watersheds

      • Bedrock, soil, etc.

    • ParFlow CONUS 2.0: https://hydroframe.org/parflow-conus2

    • China groundwater model

      • Identifies dropping groundwater levels and ove-rpumping in North/Northwest

      • Groundwater storage trends (1945-2020)

• Modeling trends:

  • Larger scale

  • Higher resolution

  • More comprehensive (physical-chemical-biological interactions)

  • Innovative approaches (AI, big data, big compute)