JAM Achiever series - Hydrogeology Part – 2

 Hydrogeology Part – 2 

Vertical distribution of Ground water

Zone of aeration

 Consists of interstices occupied partially by water and partially by air. Sub divided into the soil water zone, the intermediate vadose zone, and the capillary zone

Zone of saturation

     All interstices are filled with water under hydrostatic pressure. The saturated zone extends from the upper surface of saturation down to underlying impermeable rock. phreatic surface - is defined as the surface of atmospheric pressure and appears as the level at which water stands in a well penetrating the aquifer.

    Saturation extends slightly above the water table due to capillary attraction; however, water is held there at less than atmospheric pressure. Water occurring in the zone of saturation is in commonly referred to simply as groundwater, but the term phreatic water is also employed.

Types of Aquifers

    Aquifers may be classed as unconfined or confined depending on the presence or absence of a water table. 

• An unconfined aquifer is one in which a water table varies in undulating form and in slope depending on areas of recharge and discharge, pumpage from wells, and permeability.
• Perched water table occurs wherever a groundwater body is separated from the main ground water by a relatively impermeable stratum of small areal extent and by the zone of aeration above the main body of groundwater.
• Confined aquifers, also known as artesian or pressure aquifers, occur where groundwater confined under pressure greater than atmospheric by overlying relatively impermeable stata

Reference: 

• Introduction to Groundwater Science and Engineering  – Neven Kresic
• Applied Hydrogeology 4th edition –  C W Fetter 
• Groundwater Hydrology – D. K. Todd & L. W. Mays

JAM Question from (2005  2024)

Q.20 The saturated thickness of an unconfined aquifer is defined by the distance between (2024)

(A)(a) the ground surface and the water table

(B) the water table and the underlying confining layer

(C) the water table and the mean sea level

(D) the ground surface and the underlying confining layer

Q.30 Which one of the following statements is FALSE? (2021)

(A) Perched water table exists within the zone of aeration.

(B) Juvenile water is derived from sediment diagenesis.

(C) Zone of aeration lies above the zone of saturation.

(D) Both aquiclude and aquifuge are impermeable

Q.32 Which of the following statements is/are correct with reference to subsurface water? (2019)

(A) The perched water table occurs below the water table

(B) Vadose water occurs in the zone of aeration

(C) For significant groundwater underflow, the medium must be highly permeable

(D) Intersection of the water table with the land surface can result in the formation of a spring

Q.29 In an alluvial terrain, the general ground water table is at depth of 12.5m below the ground surface. What is the name of aerated zone above the ground water table? In this terrain, during exploration for ground water supply for a village, a clay lens has a spatial extent of 1 km × 1 km and a vertical thickness of 0.5 m. What is the type of aquifer formed above the clay lens? Comment on the suitability of this aquifer as a source for long-term supply of water. What will happen to this aquifer if the clay lens is punctured through? (2013)

Q.40 (a) Draw a labelled sub-surface hydrological section showing perched water table, confined aquifer and a free flowing well. (2008)

33. (a) (i) What is an aquifer ? (2006)

           (ii) Define the term ‘water table’. 

           (iii) Draw a neat, labeled sketch to show perched water table 

      (b)  (i) Define a confined aquifer. 

           (ii) Define an aquifuge.

9. Artesian condition results when the  (2005)

a) water table is perched

b) aquifer is unconfined

c) piezometric surface is above ground level

d) water table is above ground level

KEY👍

        Q.20 B (2024)

Q.30 B (2021)

Q.32 B,C,D (2019)

Q.9 C  (2005)