Hydrogeology

• Hydrogeology


  The area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust
• Hydrology


  The study of water in the broadest sense, encompassing the occurrence, distribution and circulation of water, its physical and chemical properties and its relation to living things
• Hydrological Cycle / Water Cycle

  1. Continuous movement of water on, above and below the surface of the Earth

  2. Storage and movement of water between the Biosphere, Lithosphere, Atmosphere and Hydrosphere
• Hydrological Cycle


  • Due to solar radiation, water evaporates, generally from the sea, lakes, etc.
  • Water also evaporates from plant leaves through the mechanism of transpiration
  • As the steam rises in the atmosphere, it is being cooled, condensed, and returned to the land and the sea as precipitation
  • Precipitation falls on the earth as surface water and shapes the surface, creating thus streams of water that result in lakes and rivers
  • A part of the water precipitating penetrates the ground and moves downward through the incisions, forming aquifers
  • Finally, a part of the surface and underground water leads to sea
  • During this trip, water is converted in all phases: gas, liquid, and solid
• Stages of the Hydrological Cycle

  • Evaporation
  • Transpiration
  • Interception
  • Condensation
  • Precipitation
  • Run-off
• Evaporation


  The sun heats up liquid water and changes it to a gas
• Saturation humidity


  The amount of moisture the air can hold at a given temperature
• Relative Humidity


  The ratio of the measured humidity to the saturation humidity
• Transpiration


  The process by which plants lose water from their leaves
• Evapotranspiration


  The combined loss of water to the atmosphere via the processes of evaporation from free water or soil moisture and transpiration
• Evapotranspiration


  Includes evaporation from open water bodies, evaporation from bare soil, and transpiration from vegetation
• Precipitation


  When the water in the clouds gets too heavy, the water falls back to the earth
• Types of Precipitation

  • Orographic
  • Convection
  • Stratiform
• Stratiform precipitation

  Occurs when large air masses rise diagonally as larger-scale atmospheric dynamics force them to move over each other
• Condensation


  Water vapour in the air gets cold and changes back into liquid, forming clouds
• Runoff


  Water that collects in rivers, streams, and oceans
• Groundwater


  Water that exists in the pore spaces and fractures in rocks and sediments beneath the Earth's surface
• Sources of Groundwater

  • Meteoric Water (main source, received as rain and snow)
  • Connate Water (exists in pores and cavities of sedimentary rocks)
  • Magmatic Water (converts into water after condensation of vapour as a result of volcanic action)
• Groundwater Movement

  • Path of groundwater through an aquifer affects the hydraulic conductivity
  • Clay content and adsorptive properties
  • Packing density
  • Surface tension
  • Preferred orientation of grains
  • Shape (angularity or roundness) of grains
  • Grain size
• Factors controlling groundwater occurrence and distribution

  • Topography of the area
  • Stratigraphy
  • Morphology
  • Soil conditions
  • Lithology of the area
• Zone of Aeration


  The zone consisting of interstices occupied partially by water and partially by air
• Subdivisions of the Zone of Aeration


  • Soil water zone
  • Intermediate zone or vadose zone
  • Capillary zone
• Soil water zone


  Water exists at less than saturation except when excessive water reaches the ground surface as from rainfall or irrigation
• Hygroscopic water


  Absorbed from the air which forms thin layer of moisture on soil particles surface
• Capillary water


  Exists as continuous films around the soil particles and is yielded by surface tension and is moved by capillary action
• Gravitational water


  Excess soil water which drains through the soil under the influence of gravity
• Intermediate vadose zone


  Extends from the lower edge of the soil water zone to the upper limit of the capillary zone
• Capillary zone


  Extends from the water table up to the limit of capillary rise of water or capillary fringe
• Capillary fringe


  • Lower part contains water in all pores, moisture content equal to porosity, water pressure less than atmospheric pressure, thickness depends on water table fluctuation
• Water table


  The upper most surface of the zone of saturation
• Zone of saturation


  All interstices are filled with water under hydrostatic pressure
• Vertical Distribution gives the distribution of water in varies stages
• To access the movement of water either horizontally or vertically based on geological condition
• Most of the well which gives high yield it means to gives the surface to subsurface runoff easily through vertical distribution of ground water
• Vertical distribution of ground water helps the quantity of water availability in the system
• Porosity


  The ratio between the total voids or pores of a particular rock to the total volume of the same rock
• Types of Porosity

  • Primary Porosity (developed during final stages of sedimentation)
  • Secondary Porosity (developed after deposition through processes like solution, fracturing)
• Permeability


  The capacity of a porous medium to transmit water or fluid under unequal pressure
• Factors affecting Permeability

  • Groundwater temperature and pressure
  • Size of the pore openings
  • Number of the pore openings
  • Connectivity of the pores
  • Grain Size, sorting, solution openings
• Specific Yield


  Percentage of total volume of the saturated aquifer which can be drained from unit volume of saturated aquifer material under gravity