UNIT – I Hydrogeological Parameters.pptx

Hydrogeological parameters refer to the physical and hydraulic characteristics of subsurface materials (e.g., soil, rock, aquifers) that affect the movement, storage, and availability of groundwater. These parameters are essential for understanding and modeling groundwater flow and contaminant transport. Here are some of the key hydrogeological parameters:

1. Porosity (n)
Definition: The ratio of void space (pores) in a material to the total volume.
Significance: Determines how much water a material can store.
Types:
Total porosity: Includes all pore spaces.
Effective porosity: The portion of porosity that contributes to fluid flow.
2. Permeability (k)
Definition: The ability of a material to transmit fluids through its pore spaces.
Significance: Higher permeability means easier water movement. It is usually measured in Darcy or millidarcy.
3. Hydraulic Conductivity (K)
Definition: The rate at which water can move through a permeable medium.
Units: Often measured in meters per second (m/s) or meters per day (m/day).
Significance: Higher hydraulic conductivity implies higher ease of groundwater movement.
4. Transmissivity (T)
Definition: The rate at which groundwater can move through an aquifer section of unit width.
Formula:
𝑇
=
𝐾
⋅
𝑏
T=K⋅b, where
𝑏
b is the saturated thickness of the aquifer.
Significance: Important for assessing the ability of an aquifer to supply water.
5. Storage Coefficient (S)
Definition: The amount of water released or stored per unit area of the aquifer per unit change in head (typically used in confined aquifers).
Significance: Indicates how much water an aquifer can yield or store in response to pressure changes.
6. Specific Yield (Sy)
Definition: The volume of water that a saturated material will yield by gravity per unit volume of the material.
Significance: Relevant for unconfined aquifers and determines the amount of water available for use.
7. Specific Retention (Sr)
Definition: The volume of water retained by the material after it has been drained by gravity.
Significance: The water held by capillary forces that doesn’t drain under gravity.
8. Groundwater Velocity (v)
Definition: The speed at which groundwater moves through a porous medium.
Formula:
𝑣
=
𝐾
𝑛
𝑒
⋅
𝑖
v=
n
e
​

K
​
⋅i, where
𝑖
i is the hydraulic gradient and
𝑛
𝑒
n
e
​
is the effective porosity.
9. Hydraulic Gradient (i)
Definition: The slope of the water table or potentiometric surface, defined as the change in hydraulic head per unit distance.
Formula:
𝑖
=
Δ
ℎ
Δ
𝐿
i=
ΔL
Δh
​
, where
Δ
ℎ
Δh is the change in head and
Δ
𝐿
ΔL is the distance over which the change occurs.
10. Recharge and Discharge Rates
Definition: The rate at which water is added (recharge) or removed (discharge) from an aquifer.
Significance: Critical for water balance and sustainability of groundwater resources.
11. Diffusivity (D)
Definition: The ratio of transmissivity to storage coefficient.

1. KONGUNADU COLLEGE OF ENGINEERING AND TECHNOLOGY (Autonomous) Department of Agriculture Engineering Course: Groundwater and Well Engineering Topic :Hydro geologic parameters By Mr. M.Sundharan , Assistant Professor, Department of Agricultural Engineering, Kongunadu College of Engineering and Technology

2. Hydrogeology Hydrogeology: Hydro: Water, Geology: Study about earth crust. Hydrogeology is the area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the earth’s crust.

3. 1.1. Water Balance The law of water balance states that the inflows to any water system or area is equal to its outflows plus change in storage during a time interval.

4. Water Balance

5. 1.1. Distribution of Sub-surface water Subsurface water refers to water that is found beneath the Earth's surface, typically within the pores and spaces of soil, sediment, and rock.

6. AQUIFER An aquifer is a permeable stratum or a type of geological formation that is both porous and permeable. Hence, sufficient discharge can be obtained from them. Aquifers are capable of yielding appreciable quantities of groundwater under gravity. The term ‘appreciable quantity’ is relative, depending upon groundwater availability. Even fine-grained materials containing very small amounts of water may be classified as the primary aquifers in areas where groundwater is scarce. Ex- geological formations of fine sand and coarse silt can be considered as an aquifer.

7. Groundwater Develoment and Potential in India Ground Water Resources Assessment is carried out at periodical intervals jointly by State Ground Water Departments and Central Ground Water Board under the guidance of the respective State Level Committee on Ground Water Assessment at State Levels and under the overall supervision of the Central Level Expert Group .

8. Methodology Ground water resource as in 2022 have been estimated following the guidelines mentioned in the Ground Water Estimation Committee (GEC) 2015 methodology using appropriate assumptions depending on data availability. The assessment involves computation of dynamic ground water resources or Annual Extractable Ground Water Resource, Total Current Annual Ground Water Extraction (utilization) and the percentage of utilization with respect to annual extractable resources (stage of Ground Water Extraction). The assessment units (Talukas/blocks/mandals/firkas) are categorized based on Stage of Ground Water Extraction, which are then validated with long-term water level trends.

9. Source of replenishable ground water resources The main source of replenishable ground water resources is recharge from rainfall, which contributes to nearly 61 % of the total annual ground water recharge. India receives about 119 cm. of rain annually on average, with high spatial variation. A major part of the country receives rainfall mainly during SW Monsoon season, spread over the months of June to September, except in Tamil Nadu, where the major contribution is from NE monsoon during the period October– December. There are also States such as Jammu and Kashmir, Himachal Pradesh and Uttarakhand which receive significant rainfall in all seasons.

10. Over 75% of the annual rainfall is received in the four rainy months for June to September only thereby leading to large variations on temporal scale. The average annual rainfall is 119 cm, but it has great spatial variations. The areas on Western Ghats, Sub-Himalyan areas in North East and Meghalaya Hills receive heavy rainfall over 250 cm annually, whereas the areas of Northern parts of Kashmir and Western Rajasthan receive rainfall less than 40 cm. A major part of the country including Northern, Central and Eastern parts receives annual normal rainfall between 75 and 150 cm.

11. Type of rock formations and their storage and transmission characteristics have a significant influence on ground water recharge. Porous formations such as the alluvial formations in the Indo- Ganga-Brahmaputra basin generally have high specific yields and are good repositories of ground water. Ground water occurrence in the fissured formations occupying nearly two-thirds of the geographical area of the country, on the other hand, is mostly limited to the weathered, jointed and fractured portions of the rocks.

12. 2023 data The over-exploited assessment units are mostly concentrated in : the north western part of the country including parts of Punjab, Haryana, Delhi and Western Uttar Pradesh where even though the replenishable resources are abundant, there have been indiscriminate withdrawals of ground water leading to over-exploitation; the western part of the country, particularly in parts of Rajasthan and Gujarat, where due to arid climate, groundwater recharge itself is limited, leading to stress on the resource and the southern part of peninsular India including parts of Karnataka, Tamil Nadu Telangana and Andhra Pradesh, where due to inherent characteristics of crystalline aquifers, the ground water availability is low.

13. Groundwater Table Fluctuation Method The groundwater table fluctuation method is a technique used to measure changes in the groundwater level over time. Groundwater is the water that saturates the spaces between soil particles and rocks beneath the Earth's surface. The water table is the level at which the ground is saturated, and it fluctuates naturally due to factors such as precipitation, recharge, and withdrawal of water.

14. Here is a general overview of the groundwater table fluctuation method: Monitoring Wells: To measure groundwater fluctuations, monitoring wells are installed in strategic locations. These wells typically consist of a casing that extends below the water table and allows for the measurement of water levels. Water Level Measurements: The water level in the monitoring wells is measured at regular intervals. This can be done manually using a water level indicator or electronically with sensors. The measurements are recorded over time. Data Analysis: The collected data is then analyzed to understand changes in the groundwater table. Seasonal variations, responses to precipitation events, and anthropogenic influences (such as pumping for wells) can be identified through this method. Groundwater Modeling: In some cases, the data collected from the groundwater table fluctuation method is used to create models that simulate groundwater flow. These models can help predict future trends and understand the impact of various factors on groundwater levels.

15. REMOTE SENSING - SURFACE

16. Geophysical Techniques for Groundwater Exploration G eophysical investigations are used for exploration of groundwater and in delineating the underground structures which control the occurrence, distribution and movement of ground water.

17. ELECTRICAL RESISTIVITY METHOD Different materials have different electrical resistivities. By measuring the resistance of the subsurface to electrical current flow, one can infer the nature and composition of the materials present.

18. SEISMIC REFRACTION METHOD Seismic waves are generated at the surface and directed into the ground. These waves travel through the subsurface and are refracted (bent) at interfaces between layers with different seismic velocities. By measuring the travel times of the refracted waves at various offsets, it is possible to infer the depth and velocity of subsurface layers.

19. GRAVITY METHOD Gravity surveys measure the variations in gravitational acceleration caused by differences in subsurface density. Groundwater, being less dense than rock or soil, can cause a decrease in gravity in areas where it is present. The gravity anomalies can indicate the presence of subsurface features such as aquifers.

20. MAGNETIC METHOD The Earth's subsurface materials have varying magnetic properties. The magnetic method measures the variations in the Earth's magnetic field caused by differences in the magnetic susceptibility of rocks and minerals. Certain geological structures, like faults or magnetic minerals, can affect the magnetic field, and these variations can be detected and analyzed.

21. SUB-SURECE - GW EXPLORATION The Borehole geophysics is used in groundwater to obtain information pertaining to lithology, fractures, permeability, porosity and water quality so as to delineate subsurface disposition of aquifers.