INTRODUCTION

� 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".

Hydrogeology

• Descriptive science

• Analytical 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 contaminants

2. 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 HYDROGEOLOGY

• Groundwater Supply and Control

1.Design test wells

2.Construct productive wells

3.Develop regional sources of groundwater

4.Review cost estimates

5.Determine water quality

6.Involve in aquifer protection and water conservation

7.Designing dewatering wells for construction and mining projects

THE BUSINESS OF HYDROGEOLOGY

• Solution of Groundwater Contamination Problems 1.Remediate contaminated aquifers

2.Design Groundwater monitoring and quality plans

3.Analyze collected groundwater samples

4.Propose waste disposal sites for: • Petrochemical plants

• Mining industries

• Municipal wastes

• Gasoline storage tanks

THE BUSINESS OF HYDROGEOLOGY

• Research and Academy

1.Develop new methods and techniques 2.Solve hydrologic and contamination problems

3.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 HYDROGEOLOGY

• Old nations

• Chines

• Egyptians

• Romans

• Persians

• Arabs

Central

trough

Portgarl and

wheel

Shaft to prime

mover

Mother well

Qanat End of qanat

Water table

Impermeable

rock

Mountain

Water

producing

section Alluvium

Islamic Civilization

• Canals and water ways

• Storage ponds

• Mathematics and geometry

• Physical sciences

Nineteenth Century

• 1856 Darcy’s law

• 1885 Water flow under artesian conditions

• 1899 Flow of groundwater & field

observations

Twentieth 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 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 component 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 surface

100 = 119,000 km3/yr)

Hydrologic 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) becomes

RN + 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 groundwater changes in response 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. • 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, contd

• Is the system in steady state?

Substitute appropriate values in above

equation:

2475 – 1175 -25 -525 -25 = ∆S 0 =

Chapter 1 Highlights

1. Water is an important topic for study because it is an essential requirement for life on Earth as we know it. Although there are about

1352 million km3 of water on Earth, most of it is either in oceans, and

therefore not suitable for human or animal consumption, or else locked in glaciers and ice caps. Ground water comprises 98% of the

world's unfrozen supply of freshwater.

2. Most of the work of hydrogeologists is concerned with developing this important resource and protecting the chemical and biological quality

of water. Significant contamination of ground water comes from

inappropriate disposal of waste into the ground, widespread use of fertilizers, herbicides, and pesticides, and accidental spills from

pipelines or storage tanks.

3. Knowledge of hydrogeology is also essential for the construction of dams and underground facilities. The geologic work of ground water

is important in shaping the landscape, especially in karst regions, in forming some types of uranium and lead-zinc deposits, and in

contributing to the migration of oil.

4. The hydrologic cycle is the circulation of water from the oceans, to the atmosphere, to the land, and back to the ocean. Water circulates among the major reservoirs (that is, oceans, atmosphere, ice, and ground water) through key hydrogeological processes such as atmospheric transport, precipitation, evapotranspiration, river flow, and ground-water flow.

5. Our main interest in this course is with the subsurface component of the hydrologic cycle that begins as some small quantity of the precipitation falling on land infiltrates to the subsurface. Some of this water is transpired; the remainder follows a groundwater flow path through the subsurface and back to the surface. The residence time of this water varies from days to thousands of years.

6. The vadose or unsaturated zone is found above the water table and is an environment where the pore space is filled with both soil gas and water. In the phreatic or saturated zone, below the water table, the pores are filled completely with water.

7. The water balance equation (input -output = change in storage) describes the response of the major reservoirs or domains in the hydrologic cycle. Because water is neither created nor lost from the hydrologic cycle, this is a conservation equation. More detailed forms of these equations are written for groundwater systems to account for the inputs due to recharge and infiltration from surface waters and losses due to transpiration and pumping.