INTRODUCTIONINTRODUCTION HYDROLOGY and HYDROGEOLOGY Scope of Hydrogeology Historical Developments in Hydrogeology Hydrologic Cycle groundwater component in hydrologic cycle, Hydrologic Equation

HYDROLOGY and HYDROGEOLOGY HYDROLOGY: the study of water. Hydrology addresses the occurrence, distribution,

movement, and chemistry of ALL waters of the earth.

HYDROGEOLOGY: includes the study of the interrelationship of geologic materials and processes with water, origin Movement development and management

• Geologic materials• Rocks• Minerals

• Processes• Mechanical processes• Chemical processes• Thermal processes • More comprehensive definition:

it is "the study of the laws governing the movement of subterranean water, the mechanical, chemical, and thermal interaction of this water with the porous solid, and the transport of energy and chemical constituents by the flow".

HydrogeologyHydrogeology• Descriptive science

• Analytic and Quantitative science

• Why hydrogeology?

• Exploration• Development• Inventory• Management

Scope Of Hydrogeology A. Physical Hydrogeology

1. Exploration: 2. Development:3. Inventory:4. Management:

B. Chemical hydrogeology 1. chemistry and transport of contaminants2. chemical characteristics of groundwater 3. chemical evolution along flow paths

C. Groundwater in eng. applications and other earth sciences:subsidence, sinkholes, earthquakes, mineral deposits etc.

D. Mathematical Hydrogeology: an approximation of our understanding of the physical system

THE BUSINESS OF HYDROGEOLOGYTHE BUSINESS OF HYDROGEOLOGY• Groundwater Supply and Control

1.Design test wells2.Construct productive wells3.Develop regional sources of groundwater4.Review cost estimates5.Determine water quality6.Involve in aquifer protection and water

conservation7.Designing dewatering wells for construction

and mining projects

• Solution of Groundwater Contamination Problems1.Remediate contaminated aquifers2.Design Groundwater monitoring and quality

plans3.Analyze collected groundwater samples4.Propose waste disposal sites for:

• Petrochemical plants• Mining industries• Municipal wastes• Gasoline storage tanks

• Research and Academy1.Develop new methods and techniques2.Solve hydrologic and contamination

problems3.Help developing new equipment

• Geophysical devices• Sampling apparatus

4.Develop computer programs to solve hydrogeologic problems

• Pumping test software• Numerical simulators• Hydrogeologic mapping programs

HISTORICAL DEVELOPMENT OF HISTORICAL DEVELOPMENT OF HYDROGEOLOGYHYDROGEOLOGY

• Old nations• Chines• Egyptians• Romans• Persians• Arabs

Centraltrough

Portgarl and wheel

Shaft to prime mover

Mother well

QanatEnd of qanat

Water table

Impermeable rock

Mountain

Water producing section

Alluvium

Islamic CivilizationIslamic Civilization• Canals and water ways

• Storage ponds

• Mathematics and geometry

• Physical sciences

Nineteenth CenturyNineteenth Century• 1856 Darcy’s law

• 1885 Water flow under artesian conditions

• 1899 Flow of groundwater & field observations

Twentieth CenturyTwentieth Century• 1923 Groundwater in USA• 1928 Mechanics of porous media• 1935 Solution of transient behavior of

water• 1940 Development of governing flow

equations• 1942 Well hydraulics fundamentals• 1956 Chemical character of natural

water

• 1960 Regional geochemical processes

• 1970 Geothermal energy resources• 1975 Environmental issues• 1980 Contaminant transport• 1985 Stochastic techniques• 1990’s modeling and management

issues

Hydrologic CycleHydrologic Cycle• Saline water in oceans accounts for 97.2% of total water on

earth. Land areas hold 2.8% of which ice caps and glaciers hold

76.4% (2.14% of total water)Groundwater to a depth 4000 m: 0.61%Soil moisture .005%Fresh-water lakes .009%Rivers 0.0001%.>98% of available fresh water is groundwater.

Hydrologic CYCLE has no beginning and no end Water evaporates from surface of the ocean, land, plants.. Amount of evaporated water varies, greatest near the equator. Evaporated water is pure (salts are left behind).

When atmospheric conditions are suitable, water vapor condenses and forms droplets. These droplets may fall to the sea, or unto land (precipitation)

or may evaporate while still aloft

Precipitation falling on land surface enters into a number of different pathways of the hydrologic cycle: some temporarily stored on land surface as ice and

snow or water puddles (depression storage) some will drain across land to a stream channel

(overland flow). If surface soil is porous, some water will seep into the

ground by a process called infiltration (ultimate source of recharge to groundwater).

Below land surface soil pores contain both air and water: region is called vadose zone or zone of aeration

Water stored in vadose zone is called soil moisture

Soil moisture is drawn into rootlets of growing plants

Water is transpired from plants as vapor to the atmosphere

Under certain conditions, water can flow laterally in the vadose zone (interflow)

Water vapor in vadose zone can also migrate to land surface, then evaporates

Excess soil moisture is pulled downward by gravity (gravity drainage)

At some depth, pores of rock are saturated with water marking the top of the saturated zone.

Top of saturated zone is called the water table.

Water stored in the saturated zone is known as ground water (groundwater)

Groundwater moves through rock and soil layers until it discharges as springs, or seeps into ponds, lakes, stream, rivers, ocean

Groundwater contribution to a stream is called baseflow Total flow in a stream is runoff

Water stored on the surface of the earth in ponds, lakes, rivers is called surface water

• Precipitation intercepted by plant leaves can evaporate to atmosphere

Groundwater componentGroundwater component in the hydrologic cycle in the hydrologic cycle

• Vadose zone = unsaturated zone• Phreatic zone = saturated zone• Intermediate zone separates phreatic

zone from soil water

• Water table marks bottom of capillary water and beginning of saturated zone

Distribution of Water in the Subsurface

Units are relative to annual P on land surface100 = 119,000 km3/yr)

Hydrologic EquationHydrologic Equation• Hydrologic cycle is a network of inflows and outflows,

expressed as• Input - Output = Change in Storage (1)

• Eq. (1) is a conservation statement: ALL water is accounted for, i.e., we can neither gain nor lose water.

• On a global scale– atmosphere gains moisture from oceans and land areas E – releases it back in the form of precipitation P. – P is disposed of by evaporation to the atmosphere E,– overland flow to the channel network of streams Qo, – Infiltration through the soil F. – Water in the soil is subject to transpiration T, outflow to the

channel network Qo, and recharge to the groundwater RN.

• The groundwater reservoir may receive water Qi and release water Qo to the channel network of streams and atmosphere.

• Streams receiving water from groundwater aquifers by base flow are termed effluent or gaining streams.

• Streams losing water to groundwater are called influent or losing streams

• A basin scale hydrologic subsystem is connected to the global scale through P, Ro , equation (1) may be reformulated as

P - E - T -Ro = S (2)S is the lumped change in all subsurface

water. All terms have the unit of discharge, or volume per unit time.

• Equation (2) may be expanded or abbreviated depending on what part of the cycle we are interested in. for example, for groundwater component, equation (2) may be written as

RN + Qi - T -Qo = S (3)

• Over long periods of time, provided basin is in its natural state and no groundwater pumping taking place, RN and Qi are balanced by T and Qo, so change in storage is zero. This gives:

RN + Qi = T + Q0 (4)

• => groundwater is hydrologically in a steady state.

• If pumping included, equation (4) becomesRN + Qi - T -Qo - Qp = S (5)

Qp= added withdrawal.

• As pumping is a new output from the system,

– water level will decline – Stream will be converted to a totally effluent, – transpiration will decline and approach zero. – Potential recharge (which was formerly rejected due

to a wt at or near gl) will increase. – Therefore, at some time after pumping starts,

equation (5) becomes:

RN + Qi - Qo - Qp = S (6)

• A new steady state can be achieved if pumping does not exceed RN and Qi.

• If pumping exceeds these values, water is continually removed from storage and wl will continue to fall over time. Here, the steady state has been replaced by a transient or unsteady state.

• In addition to groundwater being depleted from storage, surface flow has been lost from the stream.

Example Example groundwater changes in groundwater changes in

response to pumpingresponse to pumping

Inflows ft3/s Outflows ft3/s

1. Precipitation 2475 2. E of P 1175

3. gw discharge to sea 725

4. Streamflow to sea 525

5. ET of gw 25

6. Spring flow 25

Example, contd.Example, contd.• Write an equation to describe water balance.

SOLUTION:

Water balance equation:

Water input from precipitation – evapotranspiration of precipitation – evapotranspiration of groundwater – stream flow discharging to the sea – groundwater discharging to the sea – spring flow = change in storage

P –ETp – ETgw –Qswo – Qgwo –Qso = ∆S

Example, contdExample, contd

• Is the system in steady state?

Substitute appropriate values in above equation:

2475 – 1175 -25 -525 -25 = ∆S 0=