Chapter 2 hydrologic cycle

Chapter 2

The Hydrologic Cycle and hydrologic processes

Prof. Dr. Ali El-NaqaHashemite University

June 2013

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

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 vadosezone (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 baseflowTotal 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 componentin 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 waterand 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 unittime.

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

1. Basic Hydrology Concept

Water is vital for all living organisms on Earth.

For centuries, people have been investigating wherewater comes from and where it goes, why some of it issalty and some is fresh, why sometimes there is notenough and sometimes too much. All questions andanswers related to water have been grouped togetherinto a discipline.

The name of the discipline is hydrology and is formedby two Greek words: "hydro" and "logos" meaning"water" and "science".

1.1. Introduction

What is Hydrology?

It is a science of water.

It is the science that deals with the occurrence, circulation and distribution of water of the earth and earth’s atmosphere.

A good understanding of the hydrologic processes is important for the assessment of the water resources, their management and conservation on global and regional scales.

In general sense engineering hydrology deals with

Estimation of water resources

The study of processes such as precipitation, evapotranspiration, runoffand their interaction

The study of problems such as floods and droughts and strategies to combat them

Sabie Flood 2minute.mpeg

1.2 Hydrologic Cycle

Water exists on the earth in all its three states, viz. liquid, solid, gaseous and in various degrees of motion.

Hydrologic cycle….

Water, irrespective of different states, involves dynamic aspect in nature.

The dynamic nature of water, the existence of water in various state with different hydrological process result in a very important natural

phenomenon called Hydrologic cycle.


Evaporation of water from water bodies, such as oceansand lakes, formation and movement of clouds, rain andsnowfall, stream flow and ground water movement aresome examples of the dynamic aspects of water.

Evaporation from water bodies

Water vapour moves upwards

Cloud formation

Condensation

Precipitate

Interception

Transpiration

Infiltration

Runoff–streamflow

Deep percolation

Ground water flow



The hydrologic cycle has importance influence in a varietyof fields agriculture, forestry, geography, economics,sociology, and political scene.

Engineering application of the knowledge are found inthe design and operation of the projects dealing withwater supply, hydropower, irrigation & drainage, floodcontrol, navigation, coastal work, various hydraulicstructure works, salinity control and recreational use ofwater.

1.3 Water Budget Equation

The area of land draining in to a stream or a water course at a given location is called catchment area / drainage area / drainage basin / watershed.

A catchment area is separated from its neighbouring areas by a ridge called divide / watershed.

Catchment area

1.3 Water Budget Equation

A watershed is a geographical unit in which thehydrological cycle and its components can beanalysed. The equation is applied in the form ofwater-balance equation to a geographicalregion, in order to establish the basichydrologic characteristics of the region. Usuallya watershed is defined as the area that appears,on the basis of topography, to contribute all thewater that passes through a given cross sectionof a stream.

Catchment area….

Watershed and watershed divide

Watershed/ catchment

Watershed/ catchment

If a permeable soil covers an impermeable substrate,the topographical division of watershed will not alwayscorrespond to the line that is effectively delimiting thegroundwater.

Catchment area….

Watershed characteristics

Water Budget Equation

For a given catchment, in an interval of time ∆t, the continuity equation for water in its various phases can be given as:

Mass inflow – Mass outflow = change in mass storage

If the density of the inflow, outflow and storage volumes are the same:

Vi - Inflow volume in to the catchment, Vo - Outflow volume from the catchment and ∆S - change in the water volume

i oV V S

Water Budget Equation…

Therefore, the water budget of a catchment for a time interval ∆t is written as:

P – R – G – E – T = ∆SP = Precipitation, R = Surface runoff, G = net ground water flow out of the

catchment, E = Evaporation, T = Transpiration, and ∆S = change in storage

The above equation is called the water budget equation for a catchment

NOTE: All the terms in the equation have the dimension of volume and these terms can be expressed as depth over the catchment area.

Components of hydrologic cycle

Precipitation

Infiltration

Evapo transpiration

Inter flow

Groundwater flow

Base flow

Stream flow

(Runoff)

1.3 World Water Budget

Total quantity of water in the world is estimated as 1386 M km3

1337.5 M km3 of water is contained in oceans as saline water

The rest 48.5 M km3 is land water

13.8 M km3 is again saline

34.7 M km3 is fresh water

10.6 M km3 is both liquid and fresh

24.1 M km3 is a frozen ice and glaciers in the polar regions and mountain tops

Estimated World Water Quantitites

96%

1%

1%

2% Ocean-saline

Land - saline

Fresh - Liquid

Fresh - Frozen

Global annual water balance

SN Item Ocean Land

1 Area (km2) 361.3 148.8

2 Precipitation (km3/year)

(mm/year)

458,000

1270

119,000

800

3 Evaporation (km3/year)

(mm/year)

505,000

1400

72,000

484

4 Runoff to ocean

Rivers (km3/year)

Groundwater (km3/year)

44,700

2,200

Total Runoff (km3/year)

(mm/year)

47,000

316

Water Balance of Continents

Area (M km^2)

30.3

8.7 9.8

20.717.8

45

0

10

20

30

40

50

Africa Asia Australia Europe N.America S.America

Precipitation (mm/yr)

686 736 734 670726

1648

0

500

1000

1500

2000


Water Balance ……. Precipitation (mm/yr)

686 736 734 670726

1648

0

500

1000

1500

2000


Evaporation (mm/yr)

547 510415 383

1065

433

0

200

400

600

800

1000

1200


Total Runoff (mm/yr)

139

226

319287293

583

0

100

200

300

400

500

600

700


Drop of water ….. Matter…..

Water Balance of Oceans

10712

75167

780

240

1010

1210

1040

120

1380

1140

0

200

400

600

800

1000

1200

1400

1600

Atlantic Arctic Indian Pacific

Area M km^2

Precp (mm/yr)

Evap. (mm/yr)

Water flow in Ocean

200 230

70 60

350

-300

130

-60

-400

-200

0

200

400

Atlantic Arctic Indian Pacific

Continental Inflow (mm/yr)

water exch. with ocean(mm/yr)

1.4 Application in Engineering

Hydrology finds its greatest application in the design and operation of water resources engineering projects The capacity of storage structures such as reservoir

The magnitude of flood flows to enable safe disposal of the excess flow

The minimum flow and quantity of flow available at various seasons

The interaction of the flood wave and hydraulic structures, such as levees, reservoirs, barrages and bridges

Chapter Headings The hydrologic cycle

Precipitation

Runoff

Surface and groundwater storage

Evaporation

Condensation

Climate and weather

Climate

Monitoring climate change

Weather

Weather modification

Floods

Drought

Groundwater Storage

Fetter, Applied Hydrology

Groundwater Storage Groundwater recharge

Water added to groundwater usually through percolation down through the soil to the water table

Groundwater discharge

Water lost from groundwater usually through springs, streams, and rivers

Groundwater Storage

Fetter, Applied Hydrology

Introduction Precipitation is any form of solid or liquid water that

falls from the atmosphere to the earth‟s surface. Rain, drizzle, hail and snow are examples of precipitation.

Evapotranspiration is the process which returns water to the atmosphere and thus completes the hydrologic cycle. Evapotranspiration consists of two parts, Evaporation and Transpiration.

Evaporation is the loss of water molecules from soil masses and water bodies. Transpiration is the loss of water from plants in the form of vapour.

Precipitation types The can be categorized as.

Frontal precipitation

This is the precipitation that is caused by the expansion of air on

ascent along or near a frontal surface.

• Convective precipitation

Precipitation caused by the upward movement of air which is

warmer than its surroundings. This precipitation is generally

showery nature with rapid changes of intensities.

• Orographic precipitation

Precipitation caused by the air masses which strike the mountain

barriers and rise up, causing condensation and precipitation. The

greatest amount of precipitation will fall on the windward side of the

barrier and little amount of precipitation will fall on leave ward side.

Measurement of rainfall One can measure the rain falling at a place by placing a measuring

cylinder graduated in a length scale, commonly in mm. In this way,

we are not measuring the volume of water that is stored in the

cylinder, but the „depth‟ of rainfall.

The cylinder can be of any diameter, and we would expect the same

„depth‟ even for large diameter cylinders provided the rain that is

falling is uniformly distributed in space.

In practice, rain is mostly measured with the standard non-

recording rain gauge the details of which are given in Bureau of

Indian Standards code IS 4989: 2002. The rainfall variation at a point

with time is measured with a recording rain-gauge, the details of

which may be found in IS 8389: 2003. Modern technology has

helped to develop Radars, which measures rainfall over an entireregion

Variation of rainfall Rainfall measurement is commonly used to estimate the amount of

water falling over the land surface, part of which infiltrates into the

soil and part of which flows down to a stream or river. For a scientific

study of the hydrologic cycle, a correlation is sought, between the

amount of water falling within a catchment, the portion of which that

adds to the ground water and the part that appears as streamflow.

Some of the water that has fallen would evaporate or be extracted from the ground by plants.

Variation of rainfall In Figure 1, a catchment of a river is shown with four rain gauges, for

which an assumed recorded value of rainfall depth have been shown

in the table. It is on the basis of these discrete measurements of

rainfall that an estimation of the average amount of rainfall that has

probably fallen over a catchment has to be made. Three methods are

commonly used, which are discussed in the following section.

Average rainfall depth Average rainfall depth The time of rainfall record can vary and may typically range from 1 minute to

1 day for non – recording gauges, Recording gauges, on the other hand,

continuously record the rainfall and may do so from 1 day 1 week,

depending on the make of instrument. For any time duration, the average

depth of rainfall falling over a catchment can be found by the following three

methods.

The Arithmetic Mean Method

The Thiessen Polygon Method

The Isohyetal Method

Arithmetic Mean Method

The simplest of all is the Arithmetic Mean Method, which taken an average of all the rainfall depths as shown in Figure 2.

Average rainfall depth Average rainfall as the arithmetic mean of all the records of the four rain

gauges, as show in below:

The Theissen polygon method

This method, first proposed by Thiessen

in 1911, considers the representative area

for each rain gauge. These could also be

thought of as the areas of influence of each

rain gauge, as shown in Figure 3.

Average rainfall depth

These areas are found out using a method consisting of the following

three steps:

1. Joining the rain gauge station locations by straight lines to form

triangles

2. Bisecting the edges of the triangles to form the so-called

“Thiessen polygons”

3. Calculate the area enclosed around each rain gauge station

bounded by the polygon edges (and the catchment boundary,

wherever appropriate) to find the area of influence corresponding to

the rain gauge.

For the given example, the “weighted” average rainfall over the catchment is determined as


Average rainfall depth The Isohyetal method

This is considered as one of the most accurate methods, but it is

dependent on the skill and experience of the analyst. The method

requires the plotting of isohyets as shown in the figure and

calculating the areas enclosed either between the isohyets or

between an isohyet and the catchment boundary.

The areas may be measured with a planimeter if the catchment mapis drawn to a scale.

Average rainfall depth For the problem shown in Figure 4, the following may be assumed to be the

areas enclosed between two consecutive isohyets and are calculated as

under:

Area I = 40 km2

Area II = 80 km2

Area III = 70 km2

Area IV = 50 km2

Total catchment area = 240 km2

The areas II and III fall between two isohyets each. Hence, these areas may

be thought of as corresponding to the following rainfall depths:

Area II : Corresponds to (10 + 15)/2 = 12.5 mm rainfall depth

Area III : Corresponds to (5 + 10)/2 = 7.5 mm rainfall depth

For Area I, we would expect rainfall to be more than 15mm but since there is

no record, a rainfall depth of 15mm is accepted. Similarly, for Area IV, a

rainfall depth of 5mm has to be taken. Hence, the average precipitation by the isohyetal method is calculated to be

Average rainfall depth Please note the following terms used in this section:

Isohyets: Lines drawn on a map passing through places having

equal amount of rainfall recorded during the same period at these

places (these lines are drawn after giving consideration to the

topography of the region).

Planimeter: This is a drafting instrument used to measure the areaof a graphically represented planar region.

Class A evaporation panwww.novalynx.com

Evaporation Evaporation – loss of liquid water from land and water

surfaces as it is converted to a gas (water vapor)

Transpiration – liquid water moving from soil through a plant and evaporating from the leaves

Evapotranspiration (ET) – combination of evaporation and transpiration

Chapter 2 hydrologic cycle

Technology

Transcript of Chapter 2 hydrologic cycle