Groundwater: Forms of Saturated Formation

Here are the study notes:

Groundwater and Saturated Formations

• Subsurface water is categorized into four forms:
  • AQUIFER: a saturated formation that stores and yields water in sufficient quantity
  • AQUITARD: a partially permeable formation that allows seepage but yields little water
  • AQUICLUDE: an impermeable formation that prevents water flow
  • AQUIFUGE: a formation with low permeability that neither stores nor transmits water

Subsurface Zones

• SATURATED ZONE (Groundwater Zone): all pores in the soil are filled with water
• AERATION ZONE: soil pores are partially saturated with water
• Three subzones in the Aeration Zone:
  • SOIL WATER ZONE: close to the ground surface, water is lost to the atmosphere through evapotranspiration
  • CAPILLARY FRINGE: water is held by capillary action
  • INTERMEDIATE ZONE: between the Soil Water Zone and Capillary Fringe

Aquifer Properties

• IMPORTANT PROPERTIES:
  • Capacity to release water
  • Ability to transmit water flow easily
  • POROSITY
  • SPECIFIC YIELD
  • DARCY'S LAW
  • COEFFICIENT OF PERMEABILITY
  • STRATIFICATION

Hydrogeologist's Job

• Identify geologic formations suitable for groundwater development
• Determine the importance of geologic formations for possible use as an aquifer

Wells and Drawdown

• WELLS: forms the most important mode of groundwater extraction from an aquifer
• CONE OF DEPRESSION: conical shape of the water table due to radial flow into the well
• DRAWDOWN: drop in water table elevation due to pumping
• AREA OF INFLUENCE: area extent of the cone of depression
• RADIUS OF INFLUENCE: radial extent of the cone of depression
• DRAWDOWN CURVE: develops gradually at a constant rate of pumping
• UNSTEADY FLOW: phase of drawdown curve formation
• STEADY FLOW: drawdown surface attains a constant position with respect to time
• RECUPERATION RECOVERY: gradual accumulation of storage until the original level is reached

Runoff

• RUNOFF: draining of flowing off of precipitation from a catchment area through a surface channel
• OVERLAND FLOW: portion of runoff that refers to the excess precipitation moving over the land surface to reach smaller channels
• SURFACE RUNOFF: flow in the mode where small channels form larger streams
• INTERFLOW/THROUGH FLOW/STORM SEEPAGE/QUICK RETURN FLOW: component of runoff that infiltrates, moves laterally, and returns to the surface
• BASE FLOW: delayed flow that reaches a stream easily as groundwater flow
• NATURAL FLOW/VIRGIN FLOW: stream flow unaffected by human works of diversion and reservoir structures

Hydrograph

• HYDROGRAPH: plot of discharge in a stream plotted against time
• ANNUAL HYDROGRAPH: shows variation of daily or weekly or 10-daily mean flows over a year
• MONTHLY HYDROGRAPHS: daily mean flow over a month
• SEASONAL HYDROGRAPH: variation of discharge during monsoon season or dry season
• FLOOD HYDROGRAPHS: due to a storm over a catchment area

Runoff Characteristics of Streams

• THREE CLASSES OF STREAMS:
  • PERENNIAL STREAM: always carries some flow, even during dry seasons
  • INTERMITTENT STREAM: limited contribution from groundwater, dries up during dry seasons
  • EPHEMERAL STREAM: does not have any base flow contribution
• YIELD OF STREAM: total quantity of surface water that can be expected in a given period from a stream at the outlet of its catchment