Groundwater: Forms of Saturated Formation

Study Notes

Here are the study notes:

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

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

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: 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: 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

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