JAM Achiever series - Hydrogeology Part – 1
Hydrogeology Part – 1
Hydrogeology
Hydrogeology is the study of groundwater – it is sometimes referred to as geohydrology or groundwater hydrology. Hydrogeology deals with how water gets into the ground (recharge), how it flows in the subsurface (through aquifers) and how groundwater interacts with the surrounding soil and rock (the geology). (ref: International Association of Hydrogeologists)
Hydrology is a branch of Earth Science. The importance of hydrology in the assessment, development, utilization and management of the water resources, of any region is being increasingly realized at all levels
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| JeanBaptiste Lamarck |
The term hydrogeology (hydrogéologie in French) was first created by the French biologist and naturalist JeanBaptiste Lamarck in 1802 in a publication with the same name published in Paris by the Museum of Natural History (Lamarck, 1802).
The Water cycle
Juvenile water is “new” water that is in, or derived from, materials deep within the Earth and has not previously appeared at the Earth’s surface or circulated in the atmosphere. Hydrogeological classification of rocks
The porosity (n) is a measurement of the void or empty spaces of a rock, expressed in percentage.
Permeability is a measure of the ability of water to move through a rock.
A water bearing geologic formation or stratum capable of transmitting water through its pores at a rate sufficient for economic extraction by wells is called ‘aquifer’. Formations that serve as good aquifers are: unconsolidated gravels, sands, alluvium, lake sediments, glacial deposits, sand stones, limestones with cavities, granites and marble with fissures and cracks, weathered gneisses and schists, heavily shettered quartzites.
A geologic formation, which can absorb water but can not transmit significant amounts is called an ‘aquiclude’. Examples are clays, shales, etc.
A geologic formation with no interconnected pores and hence can neither absorb nor transmit water is called an ‘aquifuge’. Examples are basalts, granites, etc.
A geologic formation of rather impervious nature, which transmits water at a slow rate compared to an aquifer (insufficient for pumping from wells) is called an ‘aquitard’. Examples are clay lenses interbedded with sand.
Specific yield & Specific retention
While porosity (n) is a measure of the water bearing capacity of the formation, all this water can not be drained by gravity or by pumping from wells as a portion of water is held in the void spaces by molecular and surface tension forces.
The volume of water, expressed as a percentage of the total volume of the saturated aquifer, that will drain by gravity when the water table (Ground Water Table (GWT) drops due to pumping or drainage, is called the ‘specific yield (Sy)’ and that percentage volume of water, which will not drain by gravity is called ‘specific retention (Sr )’.
Thus, porosity = specific yield + specific retention n = Sy + Sr Specific yield depends upon grain size, shape and distribution of pores and compaction of the formation. The values of specific yields for alluvial aquifers are in the range of 10–20% and for uniform sands about 30%.
Reference: Introduction to Groundwater Science and Engineering – Neven Kresic
Applied Hydrogeology 4th edition – C W Fetter
JAM Question from (2005 2024)
Q.29 Which one of the following statements about the hydrological cycle is CORRECT? (2023)
(A) Groundwater represents the largest share of fresh water on Earth
(B) ‘Precipitation rate greater than infiltration rate’ is a necessary condition to generate surface runoff
(C) All precipitation falling on the land finally ends up as groundwater
(D) Groundwater flows in curved and concave-upward path
Q.6 Rivers that received water from groundwater seepage are termed as (2017)
(A) effluent river
(B) consequent river
(C) influent river
(D) braided river
Q.21 A geological formation neither containing nor transmitting water is termed as (2017)
(A)Aquiclude
(B)Aquitard
(C)Aquifer
(D)Aquifuge
Q.3 A unit which is semi-permeable and does not yield any significant quantity of groundwater is called: (2015)
(A) Aquiclude
(B) Aquifer
(C) Aquitard
(D) Artesian Aquifer
Q.16 Match the lithological units in Group I with hydrogeological nomenclature in Group II. (JAM-2013)
Group I Group II
P. Massive granite 1. Aquitard
Q. Shale 2. Aquifer
R. Clayey sandstone 3. Aquiclude
S. Gravelly sandstone 4. Aquifuge
(A) P-1, Q-2, R-3, S-4
(B) P-1, Q-4, R-3, S-2
(C) P-4, Q-3, R-1, S-2
(D) P-2, Q-1, R-4, S-3
Q.22 The ratio of volume of underground water released under gravity to the total volume of saturated aquifer is called (2011)
(A) transmissivity
(B) permeability
(C) storage coefficient
(D) specific yield
Q.26 Match the hydrological terms in Group I with those in Group II. (JAM-2010)
Group I Group II
P. Aquifer 1. Non porous, non permeable
Q. Aquiclude 2. Porous, non permeable
R. Aquitard 3. Poorly porous and poorly permeable
S. Aquifuge 4. Porous and permeable
(A) P-1, Q-2, R-3, S-4
(B) P-2, Q-3, R-4, S-1
(C) P-4, Q-2, R-3, S-1
(D) P-4, Q-3, R-1, S-2
Q. 22What is the porosity of sandstone with solid rock volume of 70% ? (2009)
(A) 0.7
(B) 0.4
(C) 0.3
(D) 0.07
Q.16 In hydrological context, a porous and impermeable earth mass is known is (2008)
(a) aquifer
(b) aquitard
(c) aquiclude
(d) aquifuge
Q.28 Which of the following rocks can form aquifers (JAM-2007)
a) sandstone ans highly joined granite
b) sandstone and massive granite
c) sandstone and shale
d) shale and massive granite
Q.24 A rock that is porous but not permeable is (2006)
(A) sandstone
(B) siltstone
(C) shale
(D) marble
29. B (2023)
6. A (2017)
21. D (2017)
3. C (2015)
16. C (2013)
22. D (2011)
26. C (2010)
16. C (2008)
28. A (2007)
24. C (2006)
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