Hydrological properties of Rocks: Comprehensive Guide to Porosity, Specific Yield, and Storage Coefficient in Rocks

Table of Contents

Hydrological properties of Rocks:

Hydrological properties are the characteristics of rocks and soils that affect the movement, storage, and distribution of water within the Earth’s crust. These properties include porosity, permeability, specific yield, specific retention, and storativity, which determine the capacity of geological materials to store and transmit water.

POROSITY (n)

The bulk volume of rock includes the grains or crystals as well as the contained void space. The volumetric portion of bulk rock that is not occupied by grains, crystals or natural cementing material is termed porosity. Thus, porosity n, is the ratio of void volume to bulk volume (grains plus void space). Porosity is of two types: primary porosity and secondary porosity. 


POROSITY


Primary porosity

Primary porosity is the inherent characteristic that is developed during the formation of the rock, e.g. unconsolidated formations and sedimentary rocks have intergranular spaces. In basalts the primary porosity is due to gas cavities, the lava tubes and lava tunnels. The amount of pore space depends on the degree of compaction of the sediment (with compaction generally increasing with depth of burial), on the packing arrangement and shape of grains, on the amount of cementation, and on the degree of sorting. Typical cements are siliceous, calcareous or carbonate, or iron-bearing minerals. In consolidated rocks the openings are primarily present as fractures, at joints, along bedding planes and in the form of solution holes.  

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Secondary porosity

Secondary porosity is developed due to subsequent processes such as fracturing, jointing, and solution activities. In the igneous and metamorphic rocks as well as the hard sedimentary rocks porosity is secondary in nature.  

The effective porosity ne, is the volume of pores that is available for transport of water, divided by the bulk volume. The effective porosity is slightly less than the porosity as part of the water that is molecularly bound to the pores or is stored in dead end pores does not participate in the flow. Porosity is a non-dimensional number, which could range from 0-1, it is often reported as a percentage. In the fractured rocks the porosity depends upon the size of the individual fractures, joints and other openings. 

Sedimentary rocks and soils generally have the highest porosities, mostly from primary, while secondary contributes to fracturing and dissolution. Igneous & metamorphic rock generally have low primary porosity, with sometimes-significant secondary porosity (fractures, especially in volcanic rocks). Rounded grains have smaller pore spaces between them in relation to irregularly shaped grains. Compaction results in reduction in porosity due to weight of overburden. 

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SPECIFIC YIELD (Sy)   

In unconfined aquifers the water is released by gravity drainage in proportion to the amount of decline of the water table. The coefficient of storage of the water table aquifers is the specific yield of the desaturated material, given by:  

Sw = Sy + bSs  

where: Sw = storage coefficient (water table aquifers) [-]  

b = height of the water table above the impermeable layer [m]  

Sy = specific yield of the aquifer [-] Usually Sy >> bSs, thus Sw for all practical purposes is regarded as specific yield.  

The specific yield is defined as the ratio of the volume of water that a formation would yield by gravity to its volume. Thus, it effectively represents very closely the effective porosity. Table 2.2 gives some representative values of specific yield used in India. The coefficient of storage of the water table aquifer is expressed as a percentage of 0.01= 1%. When the values of the coefficient of storage and fluctuations of the water table or piezometric surface (∆h) are known, the quantity of water added or released from the aquifer (∆V) can be calculated as 

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∆V = Sw∆h 

Hydrological properties of Rocks: Comprehensive Guide to Porosity, Specific Yield, and Storage Coefficient in Rocks

Specific Retention:

Specific retention Sr is defined as the ratio of volume of water retained by a rock against gravity to the total volume of the rock. Thus specific retention refers to the volume of water that remains in the rock mass after gravity drainage. Thus, 

Porosity=Sy + Sr   

Storage coefficient

The storage coefficient, also called storativity (S) of a confined aquifer is defined as the volume of water released or gained by a unit surface area of the aquifer for a fall or rise of potentiometric surface by unity. Water will be released with fall of the potentiometric surface and gained with the rise of the potentiometric surface. The storativity for a confined aquifer is equivalent to the specific yield of an unconfined aquifer. 

Storativity values range from .005 to .00005 and is dimensionless. Water is released from confined aquifers primarily by compression of the aquifer and expansion of water when pumped. During pumping, the confined aquifer remains fully saturated, only the pressure is reduced in the aquifer reflected by the decline of the potentiometric surface. 

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CSIR NET Exam: EARTH, ATMOSPHERIC, OCEAN AND PLANETARY SCIENCES

Exam Pattern: EARTH, ATMOSPHERIC, OCEAN AND PLANETARY SCIENCES 

 PART APART BPART CTOTAL
Total questions205080150
Max No. of Questions to attempt15352575
Marks for each correct answer224200
Marks for each incorrect answer (Negative marking for part A & B is @ 25%, and part C is @ 33%)0.50.51.32–

The candidate is required to answer a maximum of 15, 35, and 25 questions from Part-A, Part-B, and Part-C, respectively. If more than the required number of questions are answered, only the first 15, 35, and 25 questions in Part A, Part B, and Part C, respectively, will be taken up for evaluation.

Below each question in Part A, Part B, and Part C, four alternatives or responses are given. Only one of these alternatives is the “correct” option to the question. The candidate has to find, for each question, the correct or the best answer.

Syllabus

EARTH, ATMOSPHERIC, OCEAN AND PLANETARY SCIENCES

PAPER I (PART B)

  1. The Earth and the Solar System

    • Milky Way and the solar system.
    • Modern theories on the origin of the Earth and planetary bodies.
    • Earth’s orbital parameters, Kepler’s laws of planetary motion.
    • Geological Time Scale; space and time scales of processes in the solid Earth, atmosphere, and oceans.
    • Radioactive isotopes and their applications.
    • Meteorites: chemical composition and primary differentiation of the Earth.
    • Basic principles of stratigraphy.
    • Theories about the origin of life and fossil records.
    • Earth’s gravity, magnetic fields, and thermal structure: Geoid and spheroid concepts; Isostasy.

  2. Earth Materials, Surface Features, and Processes

    • Gross composition and physical properties of important minerals and rocks.
    • Properties and processes responsible for mineral concentrations.
    • Distribution of rocks and minerals in Earth’s units and India.
    • Physiography of the Earth; weathering, erosion, and soil formation.
    • Energy balance of Earth’s surface processes.
    • Physiographic features and river basins in India.

  3. Interior of the Earth, Deformation, and Tectonics

    • Basic concepts of seismology and Earth’s internal structure.
    • Physico-chemical and seismic properties of Earth’s interior.
    • Stress and strain concepts; rock deformation.
    • Folds, joints, and faults; causes and measurement of earthquakes.
    • Interplate and intraplate seismicity; paleomagnetism.
    • Sea-floor spreading and plate tectonics.

  4. Oceans and Atmosphere

    • Hypsography of continents and ocean floors: continental shelves, slopes, abyssal plains.
    • Physical and chemical properties of seawater; residence times of elements.
    • Ocean currents, waves, tides, thermohaline circulation, and conveyor belts.
    • Major water masses, biological productivity, and fluid motion.
    • Atmospheric structure and heat budget; greenhouse gases and global warming.
    • General circulation, monsoon systems, ENSO, cyclones, and local systems in India.
    • Marine and atmospheric pollution, ozone depletion.

  5. Environmental Earth Sciences

    • Properties of water and the hydrological cycle.
    • Energy resources: uses, degradation, alternatives, and management.
    • Ecology, biodiversity, and natural resource conservation.
    • Natural hazards and remote sensing applications.

PAPER I (PART C)

I. Geology

  1. Mineralogy and Petrology

    • Point group, space group, and lattice concepts.
    • Crystal field theory, mineralogical spectroscopy, and bonding in mineral structures.
    • Genesis, properties, and crystallization of magmas.
    • Metamorphic structures, textures, and thermobarometry.
    • Petrogenesis of Indian rock suites: Deccan Traps, charnockites, ophiolites, and more.

  2. Structural Geology and Geotectonics

    • Stress and strain analysis; Mohr circles.
    • Geometry and mechanics of folds, faults, and ductile shear zones.
    • Plate boundaries, mantle plumes, and Himalayan orogeny.

  3. Paleontology and Applications

    • Life origin theories, evolution models, and mass extinctions.
    • Applications of fossils in age determination, paleoecology, and paleogeography.
    • Micropaleontology in hydrocarbon exploration.

  4. Sedimentology and Stratigraphy

    • Classification of sediments and sedimentary rocks.
    • Sedimentary environments and basin evolution.
    • Stratigraphic principles, correlation methods, and sequence stratigraphy.
    • Phanerozoic stratigraphy of India.

  5. Marine Geology and Paleoceanography

    • Ocean floor morphology, ocean circulation, and thermohaline processes.
    • Factors influencing oceanic sediments and paleoceanographic reconstruction.

  6. Geochemistry

    • Atomic properties, periodic table, thermodynamics of reactions, and isotopes in geochronology.
    • Applications of stable isotopes in Earth processes.

  7. Economic Geology

    • Ore formation processes, mineral deposit studies, and petroleum geology.
    • Coal and unconventional energy resources.

  8. Precambrian Geology and Crustal Evolution

    • Evolution of Earth systems and Precambrian characteristics of India.
    • Precambrian–Cambrian boundary.

  9. Quaternary Geology

    • Quaternary stratigraphy, climate variability, and human evolution.
    • Dating methods and tectonic geomorphology.

  10. Applied Geology

  • Remote sensing and GIS.
  • Engineering properties of rocks; construction investigations.
  • Methods of mineral exploration and groundwater studies.

II. Physical Geography

  1. Geomorphology: Landform processes, DEM analysis, extraterrestrial geomorphology.
  2. Climatology: Radiation balance, wind systems, ENSO, and climate classification.
  3. Biogeography: Plant and animal associations, Indian biogeography, and conservation.
  4. Environmental Geography: Man-land relationships, hazards, and ecological balance.
  5. Geography of India: Physical geography, climatology, agriculture, and population characteristics.

III. Geophysics

  1. Signal Processing: Fourier transforms, filters, and signal analysis.
  2. Field Theory: Newtonian potential, Green’s theorem, and seismic wave propagation.
  3. Numerical Analysis and Inversion: Least squares, optimization, and pattern recognition.
  4. Gravity and Magnetic Methods: Data interpretation and anomaly analysis.
  5. Seismic Methods: Ray theory, reflection/refraction techniques, seismic stratigraphy.
  6. Well Logging: Techniques for lithology, porosity, and fluid saturation interpretation.

(IV) METEOROLOGY

1) Climatology

  • Same as under Geography.

2) Physical Meteorology

  • Thermal Structure of the Atmosphere and Its Composition.
  • Radiation:
    • Basic laws – Rayleigh and Mie scattering, multiple scattering.
    • Radiation from the sun, solar constant, effect of clouds, surface and planetary albedo.
    • Emission and absorption of terrestrial radiation, radiation windows, radiative transfer, Greenhouse effect, net radiation budget.
  • Thermodynamics of Dry and Moist Air:
    • Specific gas constant, adiabatic and isentropic processes, entropy and enthalpy.
    • Moisture variables, virtual temperature, Clausius–Clapeyron equation.
    • Adiabatic processes of moist air, thermodynamic diagrams.
  • Hydrostatic Equilibrium:
    • Hydrostatic equation, variation of pressure with height, geopotential, standard atmosphere, altimetry.
  • Vertical Stability of the Atmosphere:
    • Dry and moist air parcel and slice methods, tropical convection.
  • Atmospheric Optics:
    • Visibility and optical phenomena – rainbows, haloes, corona, mirage, etc.

3) Atmospheric Electricity

  • Fair weather electric field in the atmosphere and potential gradients.
  • Ionization in the atmosphere, electrical fields in thunderstorms.
  • Theories of thunderstorm electrification, structure of lightning flash, mechanisms of earth-atmospheric charge balance, and the role of thunderstorms.

4) Cloud Physics

  • Cloud classification, condensation nuclei, growth of cloud drops and ice-crystals.
  • Precipitation mechanisms: Bergeron–Findeisen process, coalescence process.
  • Precipitation of warm and mixed clouds, artificial precipitation, hail suppression, fog and cloud dissipation.
  • Radar observation of clouds and precipitation:
    • Radar equation, rain drop spectra, radar echoes of hailstorms, tornadoes, hurricanes, and rainfall measurements.

5) Dynamic Meteorology

  • Basic Equations and Fundamental Forces:
    • Pressure, gravity, centripetal and Coriolis forces.
    • Continuity and momentum equations (Cartesian and spherical coordinates).
    • Scale analysis, inertial flow, geostrophic and gradient winds, thermal wind.
    • Divergence and vertical motion, Rossby, Richardson, Reynolds, and Froude numbers.
  • Atmospheric Turbulence:
    • Mixing length theory, planetary boundary layer equations, Ekman layer, eddy transport of heat, moisture, and momentum.
  • Linear Perturbation Theory:
    • Internal and external gravity waves, inertia waves, gravity waves, Rossby waves, wave motion in the tropics, barotropic and baroclinic instabilities.
  • Atmospheric Energetics:
    • Kinetic, potential, and internal energies; conversion into kinetic energy; available potential energy.

6) Numerical Weather Prediction (NWP)

  • Computational instability, filtering of sound and gravity waves.
  • Filtered forecast equations, barotropic and baroclinic models.
  • Objective analysis, data assimilation techniques, satellite applications in NWP.

7) General Circulation and Climate Modelling

  • Observed zonally symmetric circulations, meridional circulation models.
  • General circulation modelling principles: grid-point and spectral GCMs.
  • Climate variability phenomena: ENSO, QBO, MJO, etc.
  • Ocean-atmosphere coupled models.

8) Synoptic Meteorology

  • Weather observations and transmission, synoptic charts.
  • Synoptic weather forecasting, prediction of weather elements, and hazardous weather phenomena.
  • Tropical Meteorology:
    • ITCZ, monsoons, tropical cyclones, jet streams.
  • Extra-Tropical Features:
    • Jet streams, extratropical cyclones, anticyclones.
  • Air masses and fronts: sources, classification, frontogenesis, and associated weather.

9) Aviation Meteorology

  • Meteorological role in aviation, weather hazards during takeoff, cruising, and landing.
  • In-flight hazards: icing, turbulence, visibility issues, gusts, wind shear, thunderstorms.

10) Satellite Meteorology

  • Polar orbiting and geostationary satellites.
  • Applications in identifying synoptic systems, cyclones, temperature estimation, rainfall prediction, and temperature/humidity soundings.

(V) OCEAN SCIENCES

1) Physical Oceanography

  • T-S diagrams, mixing processes, characteristics of water masses.
  • Wind-generated waves, shallow and deep-water wave dynamics.
  • Coastal processes: wave reflection, refraction, diffraction, littoral currents, rip currents, tsunami, and more.
  • Ocean Circulation:
    • Global conveyor belt circulation, Ekman’s theory, upwelling processes.

2) Chemical Oceanography

  • Composition of seawater, chemical exchanges, and classification of elements.
  • Element chemistry under special conditions (estuaries, vents, etc.).
  • Carbonate chemistry, biological pumps, and sedimentary deposit factors.

3) Geological Oceanography

  • Topics as listed under “Marine Geology & Paleoceanography.”

4) Biological Oceanography

  • Classification of marine environments and organisms.
  • Primary and secondary production, factors affecting biodiversity.
  • Human impacts on marine communities and climate change effects.

 

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