01-Intro + Hydro Cycle

7/30/2019 01-Intro + Hydro Cycle

1/34

INTRODUCTION

HYDROLOGY and HYDROGEOLOGY

Scope of Hydrogeology Historical Developments in Hydrogeology

Hydrologic Cycle

groundwater component in hydrologic cycle,

Hydrologic Equation

HYDROLOGYand HYDROGEOLOGY

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

movement, and chemistry ofALL waters of the earth.

HYDROGEOLOGY:includes the study of the interrelationship ofgeologic materials and processes with water, origin

Movement

development and management


2/34

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 poroussolid, and the transport of energy and chemicalconstituents by the flow".


3/34

Hydrogeology

Descriptive science

Analytical and

Quantitativescience

Why

hydrogeology?

Exploration

Development Inventory

Management


4/34

Scope Of HydrogeologyA. 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 earthsciences:

subsidence, sinkholes, earthquakes, mineral deposits etc.

D. Mathematical Hydrogeology:

an approximation of our understanding of the physical system


5/34

THE BUSINESS OFHYDROGEOLOGY

Groundwater Supply and Control

1.Design test wells

2.Construct productive wells

3.Develop regional sources of groundwater4.Review cost estimates

5.Determine water quality

6.Involve in aquifer protection and water

conservation7.Designing dewatering wells for construction

and mining projects


6/34


Solution of GroundwaterContamination Problems1.Remediate contaminated aquifers

2.Design Groundwater monitoring and quality

plans3.Analyze collected groundwater samples

4.Propose waste disposal sites for: Petrochemical plants

Mining industries Municipal wastes

Gasoline storage tanks


7/34


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


8/34

HISTORICAL DEVELOPMENT OFHYDROGEOLOGY

Old nations

Chines

Egyptians

Romans

Persians

Arabs

Central

trough

Portgarl and

wheel

Shaft to prime

mover


9/34

Mother well

Qanat End of qanat

Water table

Impermeablerock

Mountain

Water

producingsection Alluvium


10/34

Islamic Civilization

Canals and water ways

Storage ponds

Mathematics and geometry

Physical sciences


11/34

Nineteenth Century

1856 Darcys law

1885 Water flow under artesianconditions

1899 Flow of groundwater & fieldobservations


12/34

Twentieth Century

1923 Groundwater in USA

1928 Mechanics of porous media

1935 Solution of transient behaviorof water

1940 Development of governing flow

equations 1942 Well hydraulics fundamentals

1956 Chemical character of natural

water


13/34

1960 Regional geochemical

processes 1970 Geothermal energy

resources

1975 Environmental issues

1980 Contaminant transport

1985 Stochastic techniques 1990s modeling and management

issues


14/34

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 hold76.4% (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).


15/34

When atmospheric conditions are suitable, water vaporcondenses 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 anumber 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 theground by a process called infiltration (ultimatesource of recharge to groundwater).


16/34

Below land surface soil pores contain both air andwater: region is called vadose zone or zone ofaeration

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 theatmosphere

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

Water vapor in vadose zone can also migrate to landsurface, 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.


17/34

Top of saturated zone is called the water table.

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

Groundwater moves through rock and soil layers until itdischarges 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 evaporateto atmosphere


18/34

Groundwater componentin the hydrologic cycle

Vadose zone = unsaturated zone

Phreatic zone = saturated zone

Intermediate zone separates phreaticzone from soil water

Water table marks bottom ofcapillary

water and beginning of saturated zone


19/34

Distribution of Water

in the Subsurface


20/34


21/34

Units are relative to annual P on land surface

100 = 119,000 km3/yr)


22/34


23/34

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

expressed as Inp ut - Outp ut = Change in Storage (1)

Eq. (1) is a conservation statement: ALL water isaccounted 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 thechannel network Qo, and recharge to the groundwaterRN.


24/34

The groundwater reservoir may receivewater Qiand release waterQoto the

channel network of streams andatmosphere.

Streams receiving water fromgroundwater aquifers by base flow aretermed effluent or gaining streams.

Streams losing water to groundwaterare called influent or losing streams


25/34

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

P - E - T -Ro = DS (2)DSis the lumped change in all subsurface

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

Equation (2) may be expanded orabbreviated depending on what part of thecycle we are interested in. for example, forgroundwater component, equation (2) maybe written as

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


26/34

Over long periods of time, provided basin isin its natural state and no groundwater

pumping taking place, RNand Qiarebalanced by Tand Qo, so change in storageis 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 = DS (5)Qp= added withdrawal.


27/34

As pumping is a new output from thesystem,

water level will decline

Stream will be converted to a totally effluent,

transpiration will decline and approach zero.

Potential recharge (which was formerly rejected dueto a wt at or near gl) will increase.

Therefore, at some time after pumping starts,equation (5) becomes:

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


28/34

A new steady state can be achieved if

pumping does not exceed RNand Qi.

If pumping exceeds these values, water iscontinually removed from storage and wlwill continue to fall over time. Here, thesteady state has been replaced by atransient or unsteady state.

In addition to groundwater being depletedfrom storage, surface flow has been lostfrom the stream.

E l


29/34

Examplegroundwater 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 gw25

6. Spring flow 25


30/34

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

PETp ETgwQswo QgwoQso= S


31/34

Example, contd

Is the system in steady state?

Substitute appropriate values in above

equation:

2475 1175 -25 -525 -25 = S 0=


32/34

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 about1352 million km3 of water on Earth, most of it is either in oceans, andtherefore not suitable for human or animal consumption, or elselocked in glaciers and ice caps. Ground water comprises 98% of theworld's unfrozen supply of freshwater.

2. Most of the work of hydrogeologists is concerned with developing thisimportant resource and protecting the chemical and biological qualityof water. Significant contamination of ground water comes frominappropriate disposal of waste into the ground, widespread use offertilizers, herbicides, and pesticides, and accidental spills frompipelines or storage tanks.

3. Knowledge of hydrogeology is also essential for the construction ofdams and underground facilities. The geologic work of ground wateris important in shaping the landscape, especially in karst regions, informing some types of uranium and lead-zinc deposits, and in

contributing to the migration of oil.


33/34

4. The hydrologic cycle is the circulation of water from theoceans, to the atmosphere, to the land, and back to the

ocean. Water circulates among the major reservoirs (thatis, oceans, atmosphere, ice, and ground water) throughkey hydrogeological processes such as atmospherictransport, precipitation, evapotranspiration, river flow,and ground-water flow.

5. Our main interest in this course is with the subsurfacecomponent of the hydrologic cycle that begins as somesmall quantity of the precipitation falling on landinfiltrates to the subsurface. Some of this water istranspired; the remainder follows a groundwater flow

path through the subsurface and back to the surface. Theresidence time of this water varies from days tothousands of years.


34/34

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

7. The water balance equation (input -output = change instorage) describes the response of the major reservoirsor domains in the hydrologic cycle. Because water isneither created nor lost from the hydrologic cycle, this isa conservation equation. More detailed forms of theseequations are written for groundwater systems to accountfor the inputs due to recharge and infiltration fromsurface waters and losses due to transpiration andpumping.

01-Intro + Hydro Cycle

Documents

Transcript of 01-Intro + Hydro Cycle