GROUP 1: Introduction to Hydrology I. Introduction II. Hy drologic Cycle

III. History of Hy drology IV. Hy drology in Engineering

HYDROLOGY I. INTRODUCTION TO HYROLOGY Definition: Hydrology is the science that encompasses the occurrence, distribution, movement and properties of the w aters of

the earth and their relationship w ith the env ironment within each phase of the hy drologic cycle. The term hy drology is from Greek: hydro, "water"; and logos, "study".

Water distribution: 70% of the Earth’s surface is covered with water but 97.5% of this water is salt water. Only 2.5% of the planet’s w ater is freshwater, and only 1% of that ex ists on Earth’s surface:

1%=lakes, rivers

20%=groundw ater

79%=ice caps and glaciers

Components Of The Earth System:

Lithosphere: the solid Earth; land Hy drosphere: the liquid Earth; water

Atmosphere: the gaseous Earth; air

Biosphere: living things (organisms)and the parts of the lithosphere, hydrosphere, and atmosphere in which

things liv e

Cry osphere: frozen or solid water such as ice caps, glaciers, snow and permafrost

In nature water is present in three aggregation states:

solid: snow and ice;

liquid: pure w ater and solutions;

gaseous: vapors under different grades of pressure and saturation

II. THE HYDROLOGIC CYCLE

Definition: The Water or Hy drologic Cycle: Describes the movement of w ater on, in, and above the earth; Water is always changing and mov ing from one place to another Cy cling of water in and out of atmosphere and between all the earth’s components.

All of the w ater on our planet is recy cled and a given molecule of w ater is used over and over throughout time.

Water is the primary medium by which energy and matter move are circulated through the Earth sy stem components. Hy drologic Cycle is powered by Solar Energy and Gravity.

This cy cle is made up of a few main parts:

Evaporation: is the process by which water is converted from its liquid form to its v apor form and

thus transferred from land and w ater masses to the atmosphere.

Transpiration: is essentially evaporation of w ater from plant leaves.

Condensation: the process in which the warm, moist air (containing water vapour) rises and cools

Precipitation: occurs when the w ater in the clouds gets too heavy, the w ater falls back to the earth --

either as rain or snow depending on altitude. These are all forms of water that reach the earth from the atmosphere.

The usual forms are

Rainfall: Is precipitation in the form of w ater drops of size larger than 0.5 mm to 6mm. The rainfall is classified in to:

Light rain – if intensity is trace to 2.5 mm/h Moderate – if intensity is 2.5 mm/hr to 7.5 mm/hr Heavy rain – above 7.5 mm/hr

Snow: formed from ice crystal masses, which usually combine to form flakes

Hail: (v iolent thunderstorm) precipitation in the form of small balls or lumps usually consisting of concentric layers of clear ice and compact snow. Hail v aries from 0.5 to 5 cm in diameter and can be damaging crops and small buildings.

Sleet: droplets that freeze once entering the freezing lay er of air.

Infiltration: is the process where rain water soaks into the ground, through the soil and underlying

rock lay ers

Run Off- the rainw ater flow either over the ground into rivers and back to the ocean, or underground

Groundwater flow- run off w ater that infiltrates dow nwards through the soil rocks where it is returned

to the oceans.

Cycling of water in and out of the atmosphere and between all the earth’s components: Water ev aporates from the surface of the earth, rises and cools, condenses into rain or snow and falls again to the surface. The w ater falling on land collects in rivers and lakes, soil, and porous layers of rock, and much of it flow s back into the ocean.

Plays an important role in:

determining climatic patterns

plant grow th

heat energy transfer

erosion rates

rates of rock w eathering

III. HISTORY OF HYDROLOGIC CYCLE

3200 BC – irrigation canals start to ex ist in Egypt under the reign of King Scorpion

1st Century BC - Marcus Vitruvius described a philosophical theory of the hy drologic cycle, in which precipitation

falling in the mountains infiltrated the Earth's surface and led to streams and springs in the lowlands. With adoption of a more scientific approach, Leonardo da Vinci and Bernard Palissy independently reached an accurate representation of the hy drologic cycle.

17th Century - hydrologic variables began to be quantified.

Pierre Perrault, Edme Mariotte and Edmund Halley - Pioneers of the modern science of hydrology include

o Perrault showed that rainfall w as sufficient to account for flow of the Seine, by measuring rainfall,

runoff, and drainage area. o Marriotte combined velocity and river cross-section measurements to obtain discharge, again in the

Seine. o Halley showed that the ev aporation from the Mediterranean Sea was sufficient to account for the

outflow of riv ers flowing into the sea.

18th century

o Daniel Bernoulli - the Bernoulli piezometer and Bernoulli's equation o Henri Pitot - the Pitot tube

19th century - saw development in groundwater hydrology, including Darcy's law, the Dupuit-Thiem well

formula, and Hagen-Poiseuille's capillary flow equation.

20th Century - Leroy Sherman's unit hy drograph, the infiltration theory of Robert E. Horton

1930 - The great ex pansion of activity in flood control, irrigation, soil conservation, and related fields gave the first

real impetus to organized research in hydrology, as need for more precise design data became evident. IV. HYDROLOGY IN ENGINEERING

Engineering hy drology includes those segments of the field related to planning, design, and operation of engineering projects for the control and use of w ater.

Deals with: estimation of w ater resources

the study of processes such as precipitation, runoff, Evapotranspiration and their interaction and

the study of problems such as flood and draught and strategies to combat them.

Applications:

The capacity of storage structures such as reservoirs

The magnitude of flood flow s to enable safe disposal of the ex cess flow.

The minimum flow and quantity of flow available at various seasons.

The interaction of the flood w av e and hydraulic structures, such as levees, reservoirs, barrages and bridges.

GROUP 2: Weather and Hydrology

I. Temperature

II. Jet Streams III. Temperature IV. Humidity V. Geographic Distribution of Temperature

VI. Winds

WEATHER AND HYDROLOGY

I. RADIATION Radiation: the transfer of energy though space by electromagnetic waves.

Figure: Sea Breeze during daytime

Figure: Land Breeze during Nighttime

Heat Can Be Transferred In 3 Ways:

Conduction, Radiation, Convection

What Happens To Incoming Solar Radiation?

Reflection: Light Bounces Back From An Object At The Same Angle And Intensity. Scattering: Produces A Large Number Of Weaker Rays Traveling In Different Directions.

Backscattering: Scattering, Both Backwards And Forwards Reflection And The Earth’s Albedo: Albedo Is The Percent(%) Of Radiation Reflected By An Object.

***The Albedo For Earth Is About 30%.For The Moon, The Albedo Is About 7%. Light Objects Hav e Higher Albedos And Darker Objects Have Lower Albedos. Larger Angle: More Intense Heat (Hotter) Acute Angle: Less Intense Heat (Cooler)

Measurement of Radiation:

Actinometer and Radiometer: are general names for instruments used to measure intensity of radiant energy. Pyrheliometer: For measuring intensity of direct solar radiation. Pyranometer: For measuring hemispherical shortwave radiation, i.e., the combined intensity of direct solar

radiation and diffuse sky radiation.

Pyrgeometer: For measuring long wave radiation. Pyrradiometer or Total Hemisphrical Radiometer: For measuring all- wave radiation flux . Net Pyrradiometer or Net Radiometer: For measuring net all-wave radiation flux.

The General Circulation: Thermal Circulation If the earth w ere a non-rotating sphere, a purely thermal circulation would result. The equator receives more solar radiation than the higher latitudes. Equatorial air, being w armer, is lighter and tends to rise. As it rises, it is replaced by cooler air from

higher latitudes. Examples of Thermal Circulations:

sea breeze

land breeze

monsoons

mountain and v alley breezes

Effects of Earth’s Rotation: The earth from w est to east, and a point at the equator mov es at about 1670 km/hr. while one at 60◦ lat mov es at one half this speed.

II. JET STREAMS Jet streams: are fast flow ing, narrow air currents found in the atmospheres of some planets, including Earth. The strongest w inds in the atmosphere. Jet streams may start, stop, split into tw o or more parts, combine into one stream, or flow in various

directions including the opposite direction of most of the jet.

Air Current: is a flowing movement of air w ithin a larger body of air. Air currents flow in the atmosphere, the layers of air surrounding the Earth. Their speeds usually range from 129 to 225 kilometers per hour (80 to 140 miles per hour), but they can reach more than 443 kilometers per hour (275 miles per hour).

Westerly Winds: The major jet streams on Earth flow ing west to east. Their paths typically have a meandering shape. Two Parts of Jet stream:

• Polar Jets: The strongest jet streams at around 7–12 km (23,000–39,000 ft) abov e sea level • Subtropical Jets: The higher and somewhat weaker at around 10–16 km (33,000–52,000 ft).

Effect of Land and Water Distribution:

• The horizontal flow of air in any layer of the atmosphere always has a component directed toward low pressure. • Heat gains and losses are distributed through relatively great depths in large bodies of water by mixing, while land

is affected only near the surface. Consequently, land surface temperatures are more variable than those of the surface of large bodies of w ater. This condition is further emphasized by the lower specific heat of the soil and its

higher albedo, especially in winter, when snow cover reflects most of the incident radiation back to space. In w inter there is a tendency for the accumulation of cold dense air over land masses and warm air over oceans. In summer, the situation is reversed.

Migratory Systems of Jet Streams: The Semi-permanent features of the general, or mean, circulation are statistical and at any time may be distorted or displaced by transitory , or migratory system. Both semi-permanent and transitory features are classified as cyclones or anticyclones.

• Cyclone-a more or less circular area of low atmospheric pressure in w/c the wind blow counter clockwise in the Northern Hemisphere.

• Tropical cyclone-form at low latitudes and may develop into hurricane or ty phoon w/ wind exceeding 33m/s over areas as large as 300km in diameter.

• Extra tropical Cyclone-usually form along the boundaries between warm and cold air masses. Type of Fronts:

• Frontal Surface: boundary between two adjacent air masses of different temperature and moisture content. Frontal “surfaces” are actually layers or zone of transition. The line of intersection of a frontal surface with the earth is called a surface front.

• Upper-Air Front: formed by the intersection of tw o frontal surface aloft and hence marks the boundary between three air masses.

• Warm Front: the air masses are moving so that w arm air displaces colder air. • Stationary Front: If the front is not mov ing • Occluded Front: is formed during the process of cyclogenesis when a cold front ov ertakes a warm front.

III. TEMPERATURE

Definition of Terms: • Temperature: is a numerical measure of hot and cold; Is a measure of a quality of a state of a material. • Air temperature: is a measure of how hot or cold the air is. It is the most commonly measured weather

parameter.

• Terrestrial (Ground) Temperature: is nominally measured at 9 am and is the low est temperature recorded since 6 pm the prev ious day.

• Lowest maximum temperature (°C): The lowest (by month and overall) maximum air temperature observed at the site.

• Mean minimum temperature (°C): The long-term average daily minimum air temperature observed during a calendar month and ov er the year.

• Lowest temperature (°C): The lowest recorded temperature observed at the site, calculated overall years of record.

• Highest minimum temperature (°C): The highest recorded minimum temperature observed at the site, calculated ov erall years of record.

• Average High or Low Temperature: is a statistical average.

• Typical Temperatures: are the most common temperatures a location experiences. • Mean maximum temperature (°C): The average daily maximum air temperature, for each month and as an

annual statistic, calculated overall years of record. • Highest temperature (°C): The highest maximum air temperature observed at the site.

• Mean daily terrestrial minimum temperature (°C): The long-term average daily terrestrial (ground) minimum temperature observ ed at the site for each month and the y ear.

• Lowest terrestrial temperature (°C): The lowest terrestrial minimum temperature observed at the site ov er the period

• Degree Day: is a measure of heating or cooling. • Lapse Rate: the rate at w hich atmospheric temperature decreases with increase in altitude.

Types of lapse rates: Environmental Lapse Rate: is the rate of decrease of temperature with altitude in the stationary

atmosphere at a giv en time and location

Dry Adiabatic Lapse Rate: is the rate of temperature decrease with altitude for a parcel of dry or

unsaturated air rising under adiabatic conditions. Saturated adiabatic Lapse Rate: This lapse rate varies strongly with temperature.

Super-adiabatic Lapse Rate: is usually caused by intense solar heating at the surface.

Measurement of Temperature:

• Thermometer: are mainly closed glass tubes that contain a liquid like alcohol or mercury.

• Stevenson Screen: or instrument shelter is an enclosure to shield meteorological instruments against precipitation and direct heat radiation from outside sources, while still allowing air to circulate freely around them.

• Terrestrial Minimum Temperature thermometer: This thermometer measures the minimum temperature close to ground lev el.

• Pyrometer: is a type of thermometer used to measure high temperatures. • Thermocouple: is a temperature-measuring device consisting of tw o dissimilar conductors that contact each

other at one or more spots. • Thermistor: is a type of resistor whose resistance varies significantly with temperature, more so than in standard

resistors. • Langmuir Probe: used to determine the electron temperature, electron density, and electric potential of a

plasma. • Gas Bulb Thermometer: measures temperature by the variation in volume or pressure of a gas • Infrared Thermometer: A type of thermometer that senses electromagnetic waves in the infrared wavelengths,

and compares the emissions from a body to an internal reference for relativ e temperature. IV. HUMIDITY

Humidity: refers to the amount of moisture (water vapor) in the surrounding air. Humidity indicates the likelihood of precipitation, dew , or fog.

Higher humidity reduces the effectiv eness of sweating in cooling the body by reducing the rate of ev aporation of moisture from the skin. Water Vapor: Source of all condensation and precipitation; Most important gas in the atmosphere for understanding

atmospheric processes; Zero to 4% by volume Relative Humidity: is a measure of the amount of moisture in the air compared with the amount of moisture the air can hold. Relativ e humidity is expressed as a percentage of how much moisture the air could possibly hold at the temperature it

happens w hen you measure it. If the air is at 90% relativ e humidity, sweat will not evaporate into the air. As a result, we feel much hotter than the actual temperature w hen the relativ e humidity is high.

If the relativ e humidity is low, we can feel much cooler than the actual temperature because our sweat evaporates easily, cooling the body .

Dew Point: The temperature at w hich one parcel of air w ould need to be cooled in order to reach saturation If the air w as cooled further it w ould condense, this would cause dew, fog, and clouds

Absolute Humidity: the total amount of w ater vapor present in a giv en volume of air. Instrument Used To Measure Humidity: Hygrometer: is an instrument used for measuring the moisture content in the atmosphere.

Types of Hygrometer:

• Metal Paper Coil Type Hygrometer: The metal-paper coil hygrometer is very useful for giving a dial indication of humidity changes

• Hair Tension Hygrometer: These devices use a human or animal hair under tension. • Pyschrometer: consists of tw o thermometers, one which is dry and one which is kept moist with distilled water

on a sock or w ick • Sling Psychrometer: where the thermometers are attached to a handle or length of rope and spun around in

the air for a few minutes, is sometimes used for field measurements, but is being replaced by more convenient electronic sensors.

• Chilled Mirror Dew Point Hygrometers: Dew point is the temperature at w hich a sample of moist air (or any other w ater v apor) at constant pressure reaches water vapor saturation.

• Gravimetric Hygrometer: measures the mass of an air sample compared to an equal v olume of dry air. V. GEOGRAPHIC DISTRIBUTION OF TEMPERATURE

Geographic Distribution of Temperature In general, surface air temperature tends to be highest at low latitudes and to decrease pole-ward. Geographical Distribution of Surface Temperature and Salinity The distribution of temperature at the sea surface tends to be zonal, that is it tends to be independent of longitude

This trend is greatly distorted by the influence of:

Landmasses- Land heats and cools about four times faster than w ater.

Topography- Climates over land may vary radically within very

short distances because of the elev ation and variations in landforms. Vegetation- refers to assemblages of plant species and the ground cover they provide.

Term of vegetation like:

o Coastal mangrove stands o Primev al redwood forests o Sphagnum bogs o Desert soil crusts

o Roadside w eed patches o Wheat fields o Cultiv ated gardens and lawns

The Variation of Temperature In continental regions the w armest and coldest point of the annual temperature cy cle lag behind the solstices by about 1 month.

Temperature Variations: The amount of solar energy received by any region varies with time of day , with

seasons, and with latitude.

Diurnal Variation: Is the change in temperature from day to night brought about by the daily rotation of the Earth.

Seasonal Variation: In addition to its daily rotation, the Earth rev olves in a complete orbit around the sun once

each y ear.

Variation with Latitude: The shape of the Earth causes a geographical variation in the angle of incident solar

radiation.

Variations with Topography: Not related to movement or shape of the earth are temperature v ariations induced

by w ater and terrain.

Variation with Altitude: We learned that temperature normally decreases with increasing altitude throughout the

troposphere.

VI. WINDS

Winds are caused by differences in air pressure. They move from areas of high pressure to low pressure. Differences in air pressure are caused by unequal heating of the atmosphere. Cool air has higher air pressure so it flow s underneath the w arm, less dense air.

Parameters of Wind:

Wind speed: speed is measured using an anemometer; Wind speed is given in miles per hour, metres per second

or knots(1 knot = 1.151 miles/hr). Wind run

Wind direction: is measured with a wind vane.

Instruments Used to Measure Wind Parameters:

Anemometer: is the cup anemometer made up of 3 or 4 cups arranged in a circular form rotating around a

v ertical axis. The w ind speed is the speed of rotation of the cups w hile the w ind run, which is the distance a particular parcel of air is mov ing through in a given time, is given by the total rev olutions around the ax is of the cups.

Wind Vane: A wind vane measures wind direction. The name tells where the wind is coming from. i.e. – north

w ind blows from the north to the south. Types of Wind:

Local Winds: Winds that blow over short distances and are caused by unequal heating of Earth’s surface within a

small area. Sea Breeze – a w ind that blows from an ocean or lake onto land.

Land Breeze – the flow of air from land to a body of w ater.

GROUP 3: Precipitation

I. Introduction to Precipitation II. Occurrence of Precipitation

III. Measurement of Precipitation IV. Interpretation of Precipitation Data V. Variations in Precipitation

PRECIPITATION I.INTRODUCTION TO PRECIPITATION

Precipitation: is any product of the condensation of atmospheric water vapor that falls under gravity. Forms of Precipitation:

1. Rain : liquid deposits falling from the atmosphere to the surface with a diameter 5mm to 7 mm

2. Drizzle: are rainfall which is less than 5mm in diameter

3. Freezing rain: when falling liquid water droplets reaches a surface with a temperature below freezing point so, the rain droplets quickly turn into ice.

4. Sleet / ice pellets: transparent / translucent spheres of frozen w ater with a diameter > 5 mm; develop first as raindrops in relativ ely warm atmosphere then raindrops descend into a colder layer of the atmosphere (Temp:<0oC) causing the freezing into ice pellets while reaching the ground surface

5. Snow: commonly found in the mid- and high- latitudes; it develops when water vapor deposits itself directly to a

six -sided (hexagon) deposition nuclei as a solid crystal, at temperature below freezing. -Snow is usually associated with frontal uplifting w ith mid-latitude cyclones

-Snow occurs from the Bergeron process, riming, and aggregation -The nature of snow flakes depends on temperature and moisture content

6. Hail: a frozen form of precipitation w ith a diameter > 5 mm; hailstones: concentric shells of ice with alternating.

They are white cloudy appearance & those that are clear cloudy white: contain partially melted. Snowflakes that freeze on to the to the surface of the grow ing hailstone clear shell: develops when liquid water freezes onto the hailstone

Shape of Raindrops:

II. OCCURRENCE OF PRECIPITATION Cause of Occurrence of Precipitation:

1. Cyclonic or Frontal Activity: Stratiform or dynamic precipitation occurs as a consequence of slow ascent of air in sy noptic systems (on the order of cm/s), such as over surface cold fronts, and over and ahead of w arm fronts. It is the result from the lifting of air conv erging into a low pressure or cyclone. Cyclonic precipitation may be either:

• Frontal Precipitation: it results from the lifting of w arm and moist air on one side of a frontal surface ov er colder, denser air on the other side

• Non-Frontal Precipitation: air will flow horizontally from the surrounding area, causing the air in the low -pressure area to lift. When the lifted w arm-air cools down at higher attitude, non-frontal cyclonic

precipitation w ill occur

2. Convection: Convective rain, or showery precipitation, occurs from convective clouds, It falls as showers with rapidly changing intensity.

Conv ective precipitation falls over a certain area for a relativ ely short time, as convective clouds have limited horizontal ex tent. Most precipitation in the tropics appears to be convective; however, it has been suggested that stratiform precipitation also occurs. It is caused by the rising of warmer, lighter air in colder, denser surroundings. The difference in

temperature may result from unequal heating at the surface, unequal cooling at the top of the air lay er, or mechanical lifting w hen the air is forced to pass over a denser, colder air mass or over a mountain barrier.

3. Orographic Effects: Orographic precipitation occurs on the w indward side of mountains and is caused by the

rising air motion of a large-scale flow of moist air across the mountain ridge, resulting in adiabatic cooling and condensation.

In mountainous parts of the w orld subjected to relativ ely consistent w inds (for example, the trade w inds), a more moist climate usually prevails on the w indward side of a mountain than on the leew ard or dow nwind side

It is the result from the mechanical lifting ov er mountain. In rugged terrain the orographic influence is so marked that storm precipitation patterns tends to resemble that of mean annual precipitation.

Purpose of Precipitation:

1. As air rises it cools 2. As air cools clouds form and precipitation occurs

Necessary Conditions for Precipitation to Occur:

1. cooling of air (e.g. convectional / orographic / cyclonic (frontal) uplifting) 2. condensation and cloud formation 3. an accumulation of moisture 4. the grow th of cloud droplets

Kinds of Clouds Subject to Precipitation:

Warm Clouds: clouds with only liquid water above 0oC

Causes of Warm Cloud Precipitation: 1. Collision: when cloud droplets collide with each other. Collision efficiency depends on relative size of a

collector drop and droplets below: - Low efficiency for v ery small drops - Low efficiency for same-size drops - High efficiency for drops in between these size 2. Coalescence: – w hen colliding cloud droplets stick together. Coalescence efficiency is assumed to be near

100% (all drops stick together if they collide)

Cold Cloud: a cloud entirely below 0oC that may contain supercooled water, ice, or both

Cool Cloud: a cloud with regions both above and below 0oC

Mechanism of Precipitation Development: 1. Collision - Coalescence theory

- A droplet may continue to grow by diffusion beyond 20 micrometers in diameter, however, once a droplet attains this size, growth is slow and inefficient.

- Droplets this large begin to collide and coalesce with other droplets as they fall through the cloud, meaning they w ill bump into and bond to one another and form larger drops.

2. Bergeron-Findeisen Process - Also know n as the cold rain or ice crystal process - As the formation of precipitation in the cold clouds of the mid and upper latitudes by ice crystal growth.

- The equilibrium v apor pressure over water is greater than the saturation v apor pressure over ice, at the same temperature. - Therefore in a mix ed phase cloud, the liquid water will be out of v apor pressure equilibrium and will evaporate to

reach equilibrium. - The w ater droplets w ill move toward the lower pressure over the ice and diffuse onto the ice crystals.

- The v apor w ill be condensed and freeze onto the ice crystal, causing it to grow larger. For air with both supercooled water and ice: 1) Amount of w ater v apor is in equilibrium with water (saturated) 2) Amount of w ater v apor is not in equilibrium with ice (supersaturated)

3) Water v apor deposits onto ice, lowering the amount of w ater vapor, causing ev aporation of w ater 4) The cy cle continues – ice grows and water vanishes

Effects of Precipitation: 1. Effects on Agriculture: a regular rain pattern is usually vital to healthy plants, too much or too little rainfall

can be harmful, ev en devastating to crops. Drought can kill crops and increase erosion, while overly wet

w eather can cause harmful fungus growth. Soil nutrients diminish and erosion increases during the wet season. Animals have adaptation and surv ival strategies for the w etter regime.

III. MEASUREMENT OF PRECIPITATION Instruments for Measuring Precipitation:

Cylindrical Rain Gauges: As this ty pe of rain gauge can also be used to measure snow, it is alternatively known

as a cy lindrical rain/snow gauge. It consists of a cylindrical vessel with a uniform diameter from top to bottom and an orifice at the top.

Ordinary Rain Gauges: Ordinary rain gauges are the ty pe used at non-automated observatories. With such

dev ices, the observer takes measurements using a rain-measuring glass at regular intervals.

Siphon Rain Gauges: This ty pe of rain gauge consists of a receptacle to collect precipitation and a measuring

part to measure and record its amount. The measuring part consists of a float w ith a recording pen attached, a storage tank w ith a siphon to drain a fix ed amount of w ater, and a clock-driven drum.

Tipping Bucket Rain Gauges: This type of rain gauge generates an electric signal for each unit of precipitation

collected, and allows automatic or remote observation with a recorder or a counter. The only requirement for the instrument connected to the rain gauge is that it must be able to count pulses. Thus, a wide selection of configurations and applications is possible for this measuring system. Solid precipitation can also be measured if a heater is set at the receptacle.

Windshields: Wind ex erts a significant influence on the observation of precipitation with snow and rain gauges,

and there is no w ay to avoid its effects. However, accurate collection of precipitation in a rain gauge is possible w hen the w ind around the receptacle is horizontal and its speed is equal to that at ground lev el or w hen no

v ortices develop near the gauge. IV. INTERPRETATION OF PRECIPITATION DATA Interpretation of missing precipitation data includes:

1. Estimating Missing Precipitation Data at a Station Arithmetic Mean Method: is used when normal annual precipitation is within 10% of the gauge for w hich

data are being reconstructed. This method is least accurate however. Normal Ratio Method (NRM): is used when the normal annual precipitation at any of the index station

differs from that of the interpolation station by more than 10%. In this method, the precipitation amounts at the index stations are weighted by the ratios of their normal annual precipitation data.

2. Checking Inconsistency in Particular Data at a Station: by a technique called Double Mass Analysis. It is used to check the consistency of many kinds of hy drologic data by comparing date for a single station with that of a pattern composed of the data from sev eral other stations in the area. The double-mass can also be used to adjust inconsistent precipitation data

3. Averaging Precipitation over an Area: It is the amount of precipitation w hich can be assumed uniform over an

area. If the av erage precipitation over an area is known than total rain v olume of water can be computed for that area.

There are some w idely used methods to compute average precipitation over an area, but the most common of these used are: Arithmetic Mean Method

Theissen Polygon Method: (otherwise known as Voronoi polygons or Voronoi diagrams), are an essential method for the analy sis of prox imity and neighborhood.

Isohytal Method Depth-Area-Duration Curve Analysis: DAD curves exhibit the depth and the area cov ered by the rainfall

w ith a particular duration. There is a definite relation among depth, area and duration of rainfall. The longer duration rainfall

cov ers a wider area. Short time rainfalls normally cover small areas. Rainfall rarely occurs uniformly over a large area.

IV. VARIATIONS IN TEMPERATURE

1. Geographic Variations: In general, precipitation is heaviest near the equator and decreases with increasing latitude. There are four recognized climate types in the Philippines, and they are based on the distribution of

rainfall 2. Time Variations: The seasonal distribution of precipitation varies widely which shows typical seasonal

distributions. Distribution v ary with storm type, intensity and duration. There is no ty pical distribution that is applicable to all situations. The time distribution of rainfall w ithin storms is important for estimating flood

hy drographs. 3. Record Rainfalls: rainfalls amount are not met by existing data from past rainfalls therefore setting up a new

record for rainfall

GROUP 4 – 5: Stream Flow

I. Introduction to Stream Flow II. Measurement of Stream Flow

III. Ice, Snow Pack and Snow Fall on Streams

IV. Stream Flow Discharge V. Water Years

VI. Presentation of Stream Flow Data a. Hy drographs

b. Mean Annual Run-Off c. Mean Daily Flows

VII. Adjustment Of Stream Flow Data a. Factors that affect Stream Flow data

b. Factors that Causes Inaccuracy to Stream Flow Data VIII. Variation Of Stream Flow IX. Precipitation- Run Off Relation

STREAM FLOW I. INTRODUCTION Stream flow or Channel runoff: is the flow of water in streams, rivers, and other channels, and is a major element of

the w ater cycle. Stream flow is the main mechanism by which water moves from the land to the oceans or to basins of interior drainage Purpose of documenting and monitoring stream flow:

1. Dev eloping w ater budgets 2. Conducting loading calculations 3. Ev aluating the relationship betw een groundwater and surface water 4. Critical in ev aluating impacts from urban runoff

5. Essential part in the hy drologic cycle II. MEASUREMENT OF STREAM FLOW

Stream flow measurement methods:

1. Non recording stream gauge:

a. Staff b. Wire or String c. Crest Staff

2. Recording stream gauge:

a. Float ty pe b. Digital Gauge

Two Type of Gauges used in Measurement of Stream Flow:

1. Manual Gauges a. Staff gauges are used for a quick visual indication of the surface level In reservoirs, rivers streams,

irrigation channels, retention ponds, and wherever accuracy and readability are important. b. Crest-Stage Gage is a device for obtaining the elev ation of the flood crest of streams. The gage is

w idely used because it is simple, economical, reliable and easily installed

2. Recording Gauges: They have advantages over the manual ones a. Float Gauge: Float movement fluctuates with change in stage and this is recorded by a chart. In

hy drologic measurements, both the big and low flows are measured within the chart b. Digital Recorders: they have clocks and used when for ex ample hourly measurements are desired

usually where stages do not increase and decrease steeply. The recorder should be placed at a height more than the ex pected peak stage. To know the maximum stage expected, an ordinary

gauge can be used for some time Location of the Gauge:

1. Gauges should not be located in riv ers with scouring characteristics. 2. The locations should stir clear of river bends because the water surface is inclined and there is turbulence making

the stage measurement inconsistent. 3. The upstream of a natural control eg. a rapid should be used, not downstream. 4. A uniform channel helps good stage measurement. Irregular cross sections should be avoided.

III. ICE, SNOW PACK AND SNOW FALL ON STREAMS

Snow Hydrology: is a scientific study in the field of hy drology which focuses on the composition, dispersion, and movement of snow and ice.

Snow Pack: It forms from lay ers of snow that accumulate in geographic regions and high altitudes where the climate includes cold w eather for ex tended periods during the year. Snowpack are an important w ater resource that feed streams and rivers as they melt. Therefore snow packs are both the drinking water source for many communities and a potential source of flooding

(in case of sudden melting). Snow packs also contribute mass to glaciers in their accumulation zone. The freezing of w ater also temporarily affects stream flow by suddenly increasing friction and thus causing the flow to decrease. When Ice conditions exist, it is necessary to make periodic measurement through holes in the ice.

Types of Ice Formation on Streams:

1. Frazil Ice: is a collection of loose, randomly oriented needle-shaped ice crystals in water. It resembles slush and has the appearance of being slightly oily when seen on the surface of w ater.

2. Anchor Ice: forms in large quantities on the beds of riv ers or on obstacles under the water surface 3. Ice Sheet: forms due to insufficient turbulence in the stream.

Measurement of Snow on Streams:

• Terrestrial Measurements

• Remote Sensing • The Landsat-MSS

IV. STREAM FLOW DISCHARGE

Measurement of Stream Flow Discharge:

1. Current meter: is oceanographic device for flow measurement. For measurement in deep w ater, the meter is

suspended from a cable. For measurement in shallow water, the meter is mounted on a rod, and the observer w ade the stream. Current Meter Measurement:

A. Div ide channel section into numerous sub sections.

B. Determine the area of each sub sections by directly measuring the w idth and depth C. Determine the w ater v elocity of each sub section using current meter. D. Av erage Velocity = (Velocity @2/10th ) + (Velocity @8/10th ) for Deep w ater

2

Av e. Velocity for shallow water = Velocity @6/10th depth E. Discharge (n) = Av e. Velocity in a vertical x Area

F. Total Discharge = Σ Discharge in each vertical 2. Price Meter: is the most common current meter consists of six conical cups rotating about a v ertical axis. 3. Acoustic Doppler Current Profiler (ADCP): a device mounted on a small watercraft. It is used for measuring the

discharge of a riv er that release acoustic beams to probe the riv er bed and its geometric feature and span of the riv er to determine the discharge.

V. WATER YEARS

Water Years is a term commonly used in hydrology to describe a time period of 12 months for w hich precipitation totals are measured. A 24-hour counterpart to this is called w ater-day

Purpose: • To compare precipitation one year to another • To be used in the determination of surface-w ater supply

Purpose in Relation to Engineering:

• Projection of w ater supply for domestic and industrial uses • Used in the design of bridges • Used in the design of w ater systems • Used in the design of flood prev ention and alleviation systems

• Projection of Foundation Plans of Structures Definition of Terms:

• Flood – when the capacity of a river to transport w ater is exceeded and water flow s over its banks.

• Base flow - The base flow of the riv er represents the normal day to day discharge of the riv er and is the consequence of groundwater seeping into the riv er channel.

• Storm flow - storm runoff resulting from storm precipitation involving both surface and through flow. • Bank full discharge - the maximum discharge that a particular riv er channel is capable of carrying without

flooding. • Peak discharge – the point on a flood hy drograph when river discharge is at its greatest. • Peak rainfall - the point on a flood hy drograph when rainfall is at its greatest. • Lag time – period of time betw een the peak rainfall and peak discharge

VI. PRESENTATION OF STREAM FLOW DATA: A. HYDROGRAPHS

Hydrograph is a graph showing the rate of flow (discharge) versus time past a specific point in a riv er called station, or other channel or conduit carrying flow. The rate of flow is typically expressed in cubic meters or cubic feet per second (cms or cfs).

It can also refer to a graph show ing the volume of water reaching a particular outfall, or location in a sewerage network. These are commonly used in the design of sewerage, more specifically, and the design of surface water sewerage systems and combined sewers.

A.1. TYPES OF HYDROGRAPHS:

There are different methods of plotting hydrographs, depending on the purpose of the chart: • Storm Hydrographs - These can be used to show annual discharge patterns of flow in relation to climate. • Direct Run-off or Unit Hydrograph Run-off- are a ty pe of storm hydrographs. They cover a relatively short time

period, usually hours or days rather than weeks or months. They are used to measure the run-off or rate of

discharge of a certain storm or rainfall. • Flood hydrographs – These are used to show the rate at w hich normally dry areas are infiltrated by water

because of the ov erflow of nearby bodies of water • Annual Hydrographs aka Regimes – are used for reservoir studies and power-generation studies if ev er a

pow er plant is situated in a certain body of water. Shows the discharge rate and the changes in discharge a body of w ater produces over a period of 1 y ear.

• Other hydrographs – used to determine storage opportunities in the drainage network.

A.2. FLOOD SCALES Flood Stage: term used to describe a point at w hich water level as read by gauge for a particular body of water

threatens liv e, property commerce or trav el.

Five Levels of Flooding: 1. Action Stage: at this point, there are no man-made structures flooded but water level passes slightly

bey ond its normal levels. 2. Minor Flood Stage: minor flooding is expected at this lev el. 3. Moderate Flood Stage: flooding reaches higher than minor level. Roads and some areas may be cut

off. Buildings are ex pected to be flooded.

4. Major Flood Stage: this stage is significant to catastrophic. 5. Record Flood Stage: this is the highest or the peak w ater level that it’s been since records began

B. MEAN ANNUAL RUNOFF

Mean Annual Runoff is the total quantity of w ater that is discharged ("runs off") from a drainage basin in a year. Data reports may present annual runoff data as v olumes in acre-feet, as discharges per unit of drainage area in cubic feet per second per square mile, or as depths of water on the drainage basin in inches.

C. MEAN DAILY FLOW Mean Daily Flow is the stream flow date published from midnight to midnight. It result in a mean daily flow is expressed in cumecs/water-day or volume of discharge in cubic meter per seconds of a time span of midnight to midnight.

VII. ADJUSTMENT OF STREAMFLOW DATA

a. Factors Affecting Stream flow Data

• Physical factors: a. Shape and Size of Drainage Basins b. Drainage Basin Gradient - Drainage basins with steep sides tend to hav e shorter lag times

than shallow er basins.

c. Stream Network - Basins that have many streams (high drainage density) drain more quickly so hav e a shorter lag time.

d. Degree of Saturation - If the drainage basin is already saturated then surface runoff increases due to the reduction in infiltration.

e. Permeability of Rock Type Within the Basin – the permeability or the porosity of the bed of the body of w ater.

f. Amount of Vegetation - If a drainage basin has a significant amount of v egetation this will hav e a significant effect on a storm hy drograph.

g. Amount of Precipitation – increase the rate of discharge.

• Human Factors: a. Existing Man-made Drainage Systems - Drainage systems that have been created by

humans lead to a short lag time and high peak discharge as water cannot evaporate or infiltrate

into the soil b. Urbanization - Area that hav e been urbanized result in an increase in the use of impermeable

building materials. This means infiltration lev els decrease and surface runoff increases. This leads to a short lag time and an increase in peak discharge.

b. Factors That Causes Inaccuracy in Stream Flow Data

1. Changes in the location of the station- changes in the location of the station affects v olume and rate of discharge readings.

2. Unaccounted Diversion – causes of w ater diversion which decreases run-off or flow rate. 3. Deforestation and Reforestation of Area – certain areas may have changes in the v egetation that causes shifts in

the flow record.

VIII. VARIATIONS OF STREAM FLOW These are the v ariations or the changes that occur in the rate of discharge and amount of run-off in a body of w ater caused by natural phenomena.

1. Variations in Total Run-off – changes observed every year from the annual total run off published.

2. Seasonal Variations in Run-off – changes in run-off caused by changes in climate or seasons. 3. Variations of Daily Rate - day-to day changes in the stream flow.

IX. PRECIPITATION-RUN OFF RELATION

Phenomena of Run-Off:

1. Surface Retention: is the state w hen the w ater comes from the rain, hail, snow or any kind of precipitation is being retained in or abov e the ground surface and act like a basin in the ground surface. Includes the ff.:

a. Interception Storage Capacity: refers to precipitation that does not reach the soil, but is instead intercepted by the leav es and branches of plants and the forest floor. It occurs in the canopy and in the forest floor or litter lay er. Interceptometer: A rain gage which is placed under trees or in foliage to determine the rainfall in that

location; by comparing this catch with that from a rain gage set in the open, the amount of rainfall w hich has been intercepted by foliage is found.

b. Depression Storage Capacity is the ability of a particular area of land to retain w ater in its pits and depressions, thus preventing it from flow ing. The study of land's depression storage capacity is important in

the fields of geology , ecology, and especially hydrology. Roughness Clinometer: measure surface roughness, slope and depression storage in the field. Designed for digitizing the surface of the landscape at 3.8 cm intervals, it is capable of estimating depression storage up to 1 meter in length.

2. Runoff Mechanisms: includes the ff.:

a. Infiltration: is the process by which water on the ground surface enters the soil. b. Saturation Overland Flow: occurs primarily at the base of slopes marginal to stream channels.

c. Subsurface Storm Flow: is a runoff producing mechanism operating in most upland terrains. In a humid env ironment and steep terrain with conductive soils, subsurface storm flow may be the main mechanism of storm runoff generation.

3. The Runoff Cycle: The part of the hy drologic cycle involving water between the time it reaches the land as precipitation and its subsequent ev apotranspiration or runoff.

GROUP 5-6: Evaporation and Transpiration

I. Ev apotranspiration

II. Factors Controlling Evaporation III. Instruments Used In Ev aporation Rate Determination IV. Transpiration

EVAPORATION & TRANSPIRATION

I. EVAPORATION AND TRANSPIRATION (EVAPOTRANSPIRATION) Evaporation is the continuous exchange of w ater molecules to and from the atmosphere.

Transpiration is the process of w ater movement through a plant and its ev aporation from aerial parts, such as from leaves but also from stems and flow ers. II. FACTORS CONTROLLING EVAPORATION

A. Meteorological Factors A.1. Solar Evaporation: it is the ev aporation caused by the radiation from the sun. A.2. Wind Speed: higher wind speeds tends to extract heat from the w ater at a more rapid rate. A.3. Vapor Pressure: If the air already has a high concentration of the substance evaporating, then

the giv en substance will evaporate more slowly. A.4. Temperature: temperature is directly proportional to ev aporation. A.5. Surface Area of Basin: Large surface areas have faster evaporation rates.

B. Nature of Evaporating Surface The rate of ev aporation of w ater depends on the surface in which it is suspended, or the kind of substance that is subject to ev aporation. C. Effects of Water Quality

The w ater quality or any foreign material which tends to seal the water surface or change its vapor pressure or albedo w ill affect the ev aporation.

III. INSTRUMENTS USED IN EVAPORATION RATE DETERMINATION

1. Atmometers or Evaporimeter: is an instrument that measures the loss of water from a wetted, porous surface.

2. Pan and Tank Evapotranspirometer: a kind of Atmometer that uses pan and tanks. 3. Lysimeter or Evapotranspirometer: is a measuring device which can be used to measure the amount of

actual ev apotranspiration which is released by plants, usually crops or trees.

IV. METHODS IN MEASURING EVAPORATION RATE: A. Water-Budget Determination: the most obvious approach in evaporation determination which involves the

maintenance of w ater budget. Water-budget determination includes the amount of precipitation, seepage, inflow and outflow in the computation of ev aporation. *Note: If quantity of w ater is large in comparison with evaporation losses, water-budget results are of questionable accuracy.

B. Energy-Budget Determination: This includes the amount of radiation absorbed by the water body, amount of heat-transfer to the atmosphere or conduction, the energy stored in the w ater body, and the adverted energy or energy content of inflow and outflow elements to compute for the rate of ev aporation.

C. Aerodynamic Determination: This approach includes the determination of v apor pressure, winds speed,

and height at w hich data w as taken from the water surface to compute the net ev aporation. This approach y ields the most satisfactory results of all the approaches but it is considered as seasonally biased which means this approach also depends on atmospheric stability like the energy-budget determination approach.

IV. TRANSPIRATION

Definition of Terms:

1. Transpiration: is the process by which moisture is carried through plants from roots to small pores on the

underside of leav es, where it changes to vapor and is released to the atmosphere. 2. Senesce: Premature ageing, which can result in leaf loss 3. Hydrophytes: Aquatic plants such as reeds or cattails 4. Phytometer: is a large vessel filled with soil in which one or more plants are rooted.

5. Xerophytes: a plant evolved to withstand very dry environmental conditions 6. Phreatophytes: Deep rooted plants that obtain significant portion of w ater that it needs from the phreatic zone. 7. Mesophytes: terrestrial plants which are adapted to neither a particularly dry nor particularly wet environment

Factors Affecting Atmospheric Transpiration; 1. Temperature: An increase in temperature increases the rate of transpiration. 2. Relative Humidity: High humidity surrounding the leaves reduces the rate of transpiration. The higher the

humidity of the surrounding atmosphere, the lower is the rate of transpiration.

3. Wind-air Movement: An increase in air movement increases the rate of transpiration. 4. Soil Moisture Availability: When moisture is lacking, plants can begin to senesce and transpire less water. 5. Type of Plant 6. Light Intensity: An increase in light intensity increases the rate of transpiration.

IV.a. COMPUATION OF EVAPOTRANSPIRATION Determination of Evaporation:

1. Water-Budget Determination of Mean Basin Evapotranspiration: Assuming that storage and all items of inflow and outflow ex cept evapotranspiration can be measured, the volume of w ater (usually expressed in units of depth) required to balance the continuity equation for a basin represents evapotranspiration. The reliability of a w ater-budget computation hinges largely on the time increments considered.

Formula: E = P – R + ΔS Where: P = Precipitation

ΔS = Change in soil moisture storage R = Runoff

2. Field-Plot Determination of Evapotranspiration: Field Experimental Plots The different elements of the w ater budget (other than ET) in a know n interval of time are measured in special ex perimental plots established in the field. ET is then estimated as:

Formula: ET = (P + I) – R – ΔS – Q Where: P = Precipitation I = Irrigation Input

R = Runoff

Q = Ground w ater or ΔS = Change in soil moisture storage percolation losses

3. Lysimeter Determination of Evapotranspiration

4. Estimating Potential Evapotranspiration from Meteorological Data

Potential evapotranspiration (PET): is the amount of w ater that w ould be evaporated and transpired if there w ere sufficient w ater available.It is higher in the summer, on less cloudy days, and closer to the equator, because

of the higher lev els of solar radiation that prov ides the energy for evaporation. It is also higher on w indy days because the ev aporated moisture can be quickly moved from the ground or plant surface, allow ing more evaporation to fill its place.

Equations used in determining evapotranspiration rate: 1. Penman’s Equation: Penman’s equation is based on sound theoretical reasoning and is obtained from a

combination of the energy balance and mass transfer approach

Formula: Where: m = Slope of the saturation v apor pressure curve (Pa K-1) Rn = Net irradiance (W m-2)

ρa = density of air(kg m-3) cp = heat capacity of air (J kg-1 K-1) ga = momentum surface aerodynamic conductance(m s-1)

δe = v apor pressure deficit (Pa)

λv = latent heat of v aporization (J kg-1)

γ = psy chrometric constant (Pa K-1)

2. Blaney-Criddle Equation: is a method for estimating reference crop evapotranspiration. It is recommended that it

is used to calculate ET for periods of one month or greater. Formula: ETo = p (0.46 T mean +8) Where:

ETo = Reference crop ev apotranspiration (mm/day) as an average for a period of 1 month T mean = mean daily temperature (°C) p = mean daily percentage of annual daytime hours

3. Thornthwaite Formula: Uses only mean monthly temperature along with an adjustment for day length.

Formula:

Where PET = is the estimated potential ev apotranspiration (mm/month)

= is the av erage daily temperature (degrees Celsius; if this is negative, use ) of the month being calculated N = is the number of day s in the month being calculated

L = is the av erage day length (hours) of the month being calculated

= is a heat index w hich depends on the 12 monthly mean temperatures .

4. Lowry -Johnson Method: found out that there w as a high correlations between consumptive use and

accumulated degree-days during the growing season.

Formula: CU=o.00185 HE +10.4 Where: CU= annual consumptive use, in inches; and HE =effectiv e heat, in degree-days above 32 °F

IV.b, ESTIMATING ACTUAL FROM POTENTIAL EVPOTRANSPIRATION

Some inv estigators contend that ev apotranspiration from homogeneous plot continues at an undiminished rate until moisture content.

Other cite ex perimental results to show that the rate is approx imately proportional to the remaining available later.

The rate is a complex function of available water but limited to potential rate. The assumption that the ratio of actual to potential ev apotranspiration is promotional to the remaining available

w ater. A key element in the design of any irrigation system is the determination of the total w ater requirements.

The most w idely used techniques for estimating consumptive use rely largely on the transposition of data deriv ed from tanks, field plots or irrigated v alleys. IV.c. CONTROLLING EVAPOTRANSPIRATION

Mono-Molecular Film Techniques: experiments were undertaken to reduce transpiration from plants by mixing fatty alcohols into the soil

GROUP 6-7: Sub-surface Water, Groundwater and Aquifers I. Sub-Surface Water II. Groundw ater

III. Aquifers IV. Equilibrium Hy draulic of Wells V. Non-Equilibrium Hydraulic of Wells

VI. Utilizing Underground Water Reservoirs

VII. Seaw ater Intrusion

SUB-SURFACE WATER, GROUNDWATER AND AQUIFERS

I. SUB-SURFACE WATER

Soil water: 75% precipitation in temperate climates enters surface of soil and becomes,

• Soil moisture – in unsaturated soil, or

• Ground w ater – in saturated soil and rock Occurrence of Sub-Surface Water:

The saturated zone ex tends from the upper surface of saturation down to underlying impermeable rock. In the

absence of ov erlying impermeable strata, the water table or phreatic surface, forms the upper surface of the zone of saturation. Field Capacity: is defined as the moisture content of soil after grav ity drainage is complete. The volumetric soil moisture

content remaining at FC is about 15 to 25% for sandy soil, 35 to 45% for loam soils, and 45 to 55% for clay soils. Colman – field capacity is essentially the w ater retained in soil at a tension about 30 kPa.

For Veihmeyer and Hendrickson – found that the moisture equiv alent, water retained in a soil sample, 9.5mm

deep after being centrifuged, also nearly fine-grained soils. Specific Yield: Ratio of the w ater which will drain freely from the material to the total v olume of the formation Wilting Point: Represents the soil moisture level when plants cannot extract water from soil. The water content of a soil w hen most plants grow ing in that soil wilt and fail to recov er their turgor upon rewetting. Volumetric soil moisture content at the w ilting point w ill have dropped to around 5 to 10% for sandy soils, 10 to 15% in loam soils, and 15 to 20% in clay soils.

Available Water Capacity: The total av ailable water capacity (holding capacity) is the portion of w ater that can be absorbed by plant roots. Measurement of Soil Moisture: The standard determination of soil moisture is the loss in weight when a soil sample is oven-

dried. - Tensiometer: Consists of a porous ceramic cup which is inserted in a soil, filled w ith water, and connected to a

manometer. It can indicate soil-moisture tension from saturation to a tension of about 100kPa.

Typical Moisture Values for Various Soil Types:

Percent Dry Weight Soil

Soil Type Field Capacity Wilting Point Available

Water Density

Kg/m3 dry

Sand 5 2 3 1520

Sandy Loam 12 5 7 1440

Loam 19 10 9 1360

Silt Loam 22 13 9 1280

Clay Loam 24 15 9 1280

Clay 36 20 16 1200

Peat 140 75 65 400

Porosity: The ratio of pore v olume to the total v olume of the formation.

Original Porosity: It is the porosity which existed when the material was formed.

Secondary Porosity: Results from fractures and solution channels.

Permeability: is the ability to transmit the w ater

Permeameters: It is a Laboratory equipment used to measure the permeability.

II. GROUNDWATER Groundwater: is water that ex ists in the pore spaces and fractures in rocks and sediments beneath the Earth’s surface. It originates as rainfall or snow , and then moves through the soil and rock into the groundwater system, where its way back to

the surface streams, lakes, or oceans. Origin of Groundwater:

1. Meteoric Water: Groundwater derived from rainfall and infiltration w ithin the kind of water is called meteoric w ater. The name implies recent contact with the atmosphere.

2. Connate Water: Groundwater encountered at great depths in sedimentary rocks as a result of w ater having been

trapped in sediments at the time of their deposition

3. Fossil water: if fresh may be originated from the fact of climate change phenomenon.

4. Juvenile Water: formed chemically within the earth and brought to the surface in intrusiv e rocks, occurs in small quantities. It is the w ater found in the cracks or crevices or porous of rocks due to condensation of steam emanating from hot molten masses or magmas existing below the surface of the earth. Some hot springs and gey sers are clearly derived from juvenile water.

Water table / Phreatic surface - the level below which the ground is saturated with water. • Perched water table: the top of a body of ground water separated from the main water table beneath it by a

zone that is not saturated

Vadose Zone - the position at w hich the groundwater (the water in the soil's pores) is at atmospheric pressure. Movement of Groundwater:

• Most ground w ater moves relatively slowly through rock underground • Because it mov es in response to differences in water pressure and elevation, water within the upper part of the

saturated zone tends to mov e downward following the slope of the w ater table • The direction of groundw ater flow normally follows the general topography of the land surface.

• Is described by Darcy’s Law

Where:

Q= Volume of w ater A = Cross sectional Area K= Permeability or the Hy draulic Conductivity h= v ertical drop

l= flow distance Groundwater Discharge:

Effluent steams – Streams intersecting the water table and receiving groundwater flow.

Spring – any natural occurrence where water flow s to the surface of the earth from below the surface

Type of springs:

a. Contact spring b. Sinkhole Spring c. Faulty Spring d. Depression Spring

Groundwater issues • Recharge areas • Inorganic pollutants

Soil trafficability

• Location of roads and skid trails • Operating seasons

Groundwater Problems:

• Pesticides, Herbicides, Fertilizers: chemicals that are applied to agricultural crops that can find their w ay into ground w ater w hen rain or irrigation water leaches the poisons downward into the soil

• Rain: can also leach pollutants from city dumps into ground-water supplies • Heavy metals: such as mercury, lead, chromium, copper, and cadmium, together with household chemicals and

poisons, can all be concentrated in ground-water supplies beneath dumps • Liquid And Solid Wastes: from septic tanks, sewage plants, and animal feedlots and slaughterhouses may

contain bacteria, v iruses, and parasites that can contaminate ground water • Acid Mine Drainage: from coal and metal mines can contaminate both surface and ground water • Radioactive Waste: can cause the pollution of ground w ater due to the shallow burial of low-level solid and liquid

radioactiv e wastes from the nuclear power industry

• Pumping Wells: can cause or aggravate ground-water pollution III. AQUIFERS

Aquifer: a body of saturated rock or sediment through which water can move easily. Good aquifers include sandstone, conglomerate, well-joined limestone, bodies of sand and gravel, and some fragmental or fractured volcanic rocks such as columnar basalt Aquiclude: A formation which contains water but cannot transmit rapidly enough to furnish a significant supply to a well or

spring. Auifuge: A formation that has no interconnected openings and cannot hold or transmit water.

Aquitards: when the porosity of a rock is 1% or less and therefore retards the flow of ground water Types of Aquifers:

1. Unconfined Aquifers – is one w/c a water table varies undulating form and in slope. It is a partially filed aquifer ex posed to the land surface and marked by a rising and falling water table

2. Confine Aquifers – w here groundwater is confined under pressure greater than atmospheric. They are also called artesian aquifer. It is an aquifer completely filled with pressurized water and separated from the land

surface by a relatively impermeable confining bed, such as shale 3. Leaky Aquifers – where a permeable stratum is overlain by semi-previous aquitard or semi- confining layer.

Characteristics of Aquifers:

Transmissivity (T) is the rate of flow through a v ertical strip of aquifer (thickness b) of unit w idth under a unit

hy draulic gradient Storage Coefficient (S) is storage change per unit volume of aquifer per unit change in head

Radius of Influence (R) for a w ell is the maximum horizontal extent of the cone of depression when the w ell is in

equilibrium w ith inflows Pump Wells/ Observation Wells : are used to determine the properties of an aquifer

• The number of w ells depends on test objectives and available resources for test program.

– Single w ell can give aquifer characteristics (T and S). Reliability of estimates increases with additional observ ation points.

– Three w ells at different distances are needed for time-distance analysis

– No max imum number because anisotropy, homogeneity, and boundaries can be deduced from response

IV. EQUILIBRIUM HYDRUALIC OF WELLS Well - a hy draulic structure that is designed and constructed to permit economic withdrawal of w ater from an aquifer

Cone of depression - occurs in an aquifer w hen groundwater is pumped from a well. Drawdown - depressed water level (or potentiometric surface)

Formation of a cone of depression in the water table:

Equilibrium flow to well: Occurs when aquifer is pumped for a v ery long time. Water lev el (or potentiometric surface) does not change w ith time. We can use darcy’s law to calculate “K” OR “T” if w e know Q and hydraulic heads at tw o locations (i.e.

called “pumping test”)

Theim Equation:

V. NON- EQUILIBRIUM HYDRAULIC OF WELLS Well Hydruialics: A water well is a hydraulic structure that is designed and constructed to permit economic withdrawal of w ater from an aquifer

Water well construction includes: Selection of appropriate drilling methods

Selection of appropriate completion materials

Analy sis and interpretation of w ell and aquifer performance

Theis Solution: The Theis (1935) solution (or Theis non-equilibrium method) is useful for determining the hydraulic properties (transmissivity and storativity) of confined aquifers.

Formula:

w here: s = draw down [L] Q = pumping rate [L³/T]

T = transmissivity [L²/T] R = radial distance from pumping well to observation well [L] S = storativ ity [-] t = elapsed time since start of pumping [T] V. UTILIZING UNDERGROUND WATER RESERVOIR

Safe yield (or optimal yield): Amount of w ater that can be withdrawn from a groundwater basin annually without producing an “undesired” result

- w ithdraw al in excess of safe y ield is known as overdraft

- undesired results - mainly depletion of reserves - also intrusion of w ater of undesirable quality - contrav ention of w ater rights

- deterioration of economic advantages of pumping - ex cessive depletion of stream flow by induced infiltration and subsidence

Overdraft: removal of water beyond safe or normal suggested amounts from reservoirs

- Safe y ield has to be balanced against socioeconomic demand for the w ater - At sometimes it may be necessary to “mine” groundwater to depletion

- Other cases may call for complete conservation - Some hav e suggested that safe y ield is the annual extraction of groundwater that does not ex ceed annual recharge

- Remov al of water changes regime/recharge Groundwater Extraction:

Groundw ater is the main source of - Drinking w ater in many coastal areas, and extraction has increased over time. - Groundw ater extraction can also lead to well contamination by causing upwelling, or upcoming, of saltwater from

the depths of the aquifer.

Time effects in Groundwater: Flow rates in the groundwater are normally extremely slow, and considerable time may be involved in

groundw ater phenomena. A critical lowering of the w ater table adjacent to a coast may not bring immediate saltwater intrusion because of the time required for the salt w ater to mov e inland.

Retaining the Potential of Underground Reservoirs:

Artificial Recharge: If transmissibility is not a problem, the yield of an aquifer may be increased artificially by introducing w ater into it. In most cases this is equivalent to reducing the surface runoff from the area. The methods employed for artificial recharge are controlled by the geologic situation of an area and by economic

considerations. Some possible methods include: 1. Storing floodw aters in reservoirs constructed over permeable areas. 2. Storing floodw aters in reservoirs for later release into the stream channel at rates approximating the percolation

capacity of the channel.

3. Div erting stream flow to spreading areas located in a highly permeable formation. 4. Ex cavating recharge basins to reach permeable formations. 5. Pumping w ater through recharge wells into the aquifer. 6. Ov er irrigating in areas of high permeability.

7. Construction of w ells adjacent to a stream to induce percolation from stream flow. VI. SEAWATER INTRUSION IN AQUIFERS/UNDERGROUND WATER RESERVOIRS

Saltwater intrusion is the movement of saline water into freshwater aquifers, which can lead to contamination of drinking w ater sources and other consequences.

Ghyben-Herzberg Relation:

Causes of Saltwater Intrusion: 1. Canals: The construction of canals and drainage networks can lead to saltwater intrusion. Canals provide

conduits for saltw ater to be carried inland, as does the deepening of existing channels for nav igation purposes. 2. Drainage networks: Drainage networks constructed to drain flat coastal areas can lead to intrusion by lowering

the freshw ater table, reducing the w ater pressure exerted by the freshwater column. Effects of Saltwater Intrusion on Water Supply:

• Many coastal communities are experiencing saltwater contamination of water supply wells, and this problem has

been seen for decades. • The consequences of saltwater intrusion for supply wells vary widely, depending on extent of the intrusion, the

intended use of the w ater, and w hether the salinity exceeds standards for the intended use.

GROUP 8: Run-Off

I. Surface Run-Off II. Storm and Storm Run-Off

III. Snow melt Run-Off

RUN-OFF

I. SURFACE RUN-OFF Surface runoff (also known as overland flow) is the flow of water that occurs when excess water from rain, or other sources

flow s ov er the earth's surface. This might occur because soil is saturated to full capacity. Pollutants that are carried to streams and lakes by surface runoff are a major contribution to water pollution.

Wash off materials include sediment, mineral salts, heavy metals, nutrients, Pesticides, biodegradable organics, and microbial pollution. Transport of Materials through the Soil Profile

A. Fine-Textured Soils with High Clay Content - Do not drain w ell - Retain large amounts of w ater for long periods - Aeration in these soils is limited

- Processes such as organic decomposition, ammonia, volatilization, and nitrification are retarded B. Coarse-Textured Soils - Conduct large quantities of air and w ater, and oxidative processes are - encouraged

- At the same time the rates of ev aporation, lateral transmissibility - Percolation are higher.

As a rule, passage through the soil profile results in purification of water because of:

- Adsorption: process entails the removal of chemicals at solution and retention on the surface of soil particles by

chemical or physical bonding. The quantity of a chemical that can be adsorbed by soil depends on concentration of adsorbate and soil temperature. Adsorption usually assures that chemicals remain in the soil long enough for processes such as decomposition and plant uptake to occur.

- Volatilization: The loss of a chemical from the soil-water system by vaporization into the atmosphere. Certain

chemicals move to the soil surface by diffusion or mass flow. Volatilization can remove large quantities of chemicals such as ammonia and pesticides from the soil, particularly during the initial period after application.

- Decomposition or degradation: Organic materials in the soil break down to form carbon dioxide, water,

inorganic elements such as nitrogen and chloride. Degradation rates depend on soil temperature, moisture, strength of binding by soil, soil type, and soil microorganisms. In many soils the combined processes of

adsorption and degradation can remove 99 percent or more of the organic content of heav ily polluted water.

- Nitrification: The two-step process in which ammonia (NH₂) or ammonium (NH₄) is oxidized to Nitrite (NO₂) and

then to nitrate (NO₃). This is an important reaction in the soil-water system because a largely immobile form of nitrogen (ammonia) is converted to a highly mobile form (nitrate) which may be absorbed by plants or lost by leaching and denitrification.

- Denitrification: involves the conversion of nitrate to gaseous nitrogen species such as element nitrogen gas,

nitrous ox ide, or nitric acid

- Plant uptake: In soils with heavy vegetal cover, the major mechanism for removal of inorganic Nitrogen and phosphorous is uptake by plants. Flow of water toward roots in response to transpiration results in the transport of non-adsorbed nutrients w ith high solubilities, such as nitrate. Diffusion is the most active mechanisms for transporting adsorbed species (e.g. phosphorous, potassium, iron) to plant roots

II. STORM AND STORM RUN-OFF Storm water is water originates during precipitation.

Characteristics of Storm: 1. Rainfall amount 2. Rainfall intensity

3. Rainfall duration Storm Analysis:

In any statistical correlation, it is extremely important that the basic data be as consistent and reliable as possible.

The consistency test for precipitation data should be applied whenever the normal annual precipitation varies appreciably over the catchment.

Runoff also depends upon rainfall amount, intensity, and duration, but for basins of 250km² or more, an average intensity as reflected by amount and duration is usually adequate.

Estimating the Volume Of Storm Runoff

Despite the complex nature of the rainfall-runoff process, the practice of estimating runoff as a fix ed percentage of rainfall is the most commonly used method in design of urban storm-drainage facilities, highway culverts, and many small

w ater-control structures. Computer simulation techniques offer the most reliable method of computing runoff from rainfall because they

permit a relativ ely detailed analysis using short time intervals.

1. Infiltration Approach To Runoff Estimates: The infiltration approach that the surface runoff from a giv en storm is equal to that portion w hich is not disposed of through:

- interception and depression storage - ev aporation during storm

- infiltration If the rainfall intensity is alw ays above the infiltration-capacity curve the problem is merely one of defining the

infiltration curv e which is a function of the antecedent moisture conditions.

2. Infiltration Index: Difficulties with the theoretical approach to infiltration led to the use of infiltration index es. The

simplest of these is the ф index , defined as that rate of rainfall abov e which rainfall volume equals the runoff v olume. Formula:

Where:

W = av erage infiltration rate during the time rainfall intensity ex ceeds the capacity rate P = total precipitation corresponding to t t = time during w hich rainfall intensity exceeds infiltration capacity F = total infiltration

Qs = surface runoff S = effectiv e surface retention

Initial Moisture Conditions The quantity of runoff from a storm depends on the moisture conditions of the catchment at the onset of the storm.

In humid areas, where streams flow continuously, groundwater discharge at the beginning of the storm has been found to be a good index to initial moisture conditions.

The rate at w hich moisture is depleted from a particular basin under specified meteorological conditions is roughly

proportional to the amount in storage. In other w ords, the soil moisture should decrease logarithmically with time during periods of no precipitation.

It = I0kt

Where I0 is the initial v alue of antecendent-precitation index, It is the reduced value t days later, and k is a recession factor ranging normally between 0.85 and 0.98. letting t is equal one gives…

I1=kI0 The index for any day is equal to that of the prev ious day multiplied by the factor k. if rain occur on any day, the

amount of rain is added to the index . III. SNOWMELT RUN-OFF

Estimating Snowmelt Run-off: The storage and melting of snow plays an important role in the hy drology of some areas. In such areas, reliable

predictions of the rate of melt and release of liquid w ater from a snow pack are requisite to the efficient design and operation of w ater resources projects and the issuance of river forecasts and warnings

Physics of Snowmelt Snow melt and evaporation (including sublimation) are both thermodynamic processes, and both are amenable to the energy -balance approach in applying the energy balance to a snowpack, the rate melt and release of liquid water are primary concern. Heat ex change with the soil is more important when treating snowmelt than in the case of lake evaporation,

but the ex change at the snow-air interface dominates the melt process. Heat ex change between a snowpack and the atmosphere is also affected by conduction, convection, condensation and ev aporation. Although it is readily shown that conduction in air is very small, convective exchange can be an

important factor. The transfer rates by both processes are proportional to w ind velocity v. Since the latent heat of v aporization is about 7.5 times the latent heat of fusion, condensation of unit depth of w ater v apor on the snow surface produces 8.5 units of

liquid w ater, including condensate. The tw o processes can be described by similar equations for melt:

Mh = kh (Ta- T0) v Me=ke (ea - e0 ) v Raindrop temperatures correspond closely to the surface wet-bulb temperature. As the drops enter a snowpack,

their temperature is reduced to 00C and an equiv alent amount of heat is imparted to the snow . Melt (millimeters) from rain is given by

Mr = 4.19

Where:

P= is the rainfall in millimeters, Tw =is the w et-bulb temperature in degrees Celsius,

334 =is the latent heat of fusion in joules per gram, 4.19= is the specific heat of w ater in joules per gram per degree Celsius. Estimating Snowmelt Rates and Consequence Runoff

Air temperature is the single most reliable index to snowmelt. It is completely reflects radiation, wind, and humidity that residual errors are usually not materially correlated with these factors. Since snowmelt does not occur with temperatures appreciably below freezing the temperature data are commonly converted to degree-days or degree-hours above some base. A v ariety of different relationships have been mean temperature of 100C and a minimum temperature below freezing suggested for forecasting snowmelt. Most commonly, however, a degree-day factor or the ratio of snow melt to

concurrent degree-days is utilized. If the actual rate of snow melt were known, the degree-day factor might well be substantially

constant. Actually , the rate of runoff must be used in lieu of rate of melt, and a plot of accumulated snowmelt runoff v ersus accumulated degree-days tends toward an olive shape.

Snow Survey The application of snow -survey data to the preparation of w ater-supply forecasts is appealing because of the rather simple relation env isioned. If the seasonal flow results primarily from melting a mountain snowpack, measurements of the w ater in the snow pack before melt begins should indicate the v olume of runoff to be ex pected.

Although there is good correlation betw een snow-survey data and seasonal runoff, it is now recognized that reliable w ater-supply forecasts cannot be made from snow surveys alone. Runoff subsequent to the surveys is also dependent upon:

1. Groundw ater storage 2. Antecedent soil- moisture deficiency 3. Precipitation during the runoff period.

It has been found that snow -survey data can best be treated as an independent measure of winter precipitation in a multiple, or as a check on simulated snow cover.

GROUP 9: Erosion, Weathering and Sedimentation I. Erosion, Weathering and Sedimentation and its Effects of the Riv er Basin II. Streams and Stream Patterns III. Flood Plains

IV. Erosion Process V. Sedimentation

EROSION, WEATHERING AND SEDIMENTATION

I. EROSION, WEATHERING AND SEDIMENTATION AND ITS EFFECTS OF THE RIVER BASIN

Definition of Terms:

1. Sediment:settled matter at bottom of liquid. 2. Catchment: rainwater receptacle. A structure, reservoir, or container for collecting rainwater. 3. Reservoir: lake or tank for storing water.

4. Erosion is a process of detachment and transport of soil particles by erosive agents Factors That Affect Production of Sediments:

1. Climate 2. Soil Ty pe 3. Land Use 4. Topograpy

5. Presence of Reservoir The rate at which the capacity of a reservoir is reduced by sedimentation depends on: 1. The quantity of sediment inflow.

2. The percentage of this inflow trapped in the reservoir 3. The density of the deposited sediment. Physical Descriptors of Catchment Form:

- Stream Order - Drainage density - Length of ov erland flow - Area relations

- Basin shape Stream Order: Horton suggested a classification of stream order as a measure of the amount branching within a basin.

Law of Stream Numbers: relates number of streams of order to the number in the nex t low est order.

Law of Stream Lengths

Law of Stream Areas

Law of Stream Slopes

Drainage Density: the total length of streams w ithin a catchment divided by the drainage area defines drainage density, the length of channels per unit area.

D = total L/A Characteristics of high and low-density drainage basins:

1. High density: (+2km per km2)Impermeable land surface, steep slopes, limited vegetation cover, limited rainfall, gentle slopes, large channel frequency (tributaries).

2. Low density (-2km per km) Permeable rock, for example, chalk, much vegetation cover, limited rainfall, gentle slopes, lower channel frequency.

Length of Overland Flow: The average of overland flow may be approximated by,

Area Relations: Data for a number of the larger riv ers of the w orld seem to conform to the equation

Basin Shape: the shape of a catchment affects the stream flow hydrograph and peak-flow rates.

Descriptors of Catchment Release:

• Channel slope: the slope of the channel affects v elocity of flow and must play a role in hydrograph shape.

• Land slope: The slope of the ground surface is a factor in the ov erland flow process and hence a parameter of hy drologic interest, especially on small basins where the ov erland flow process may be a dominant factor in determining hy drograph shape.

• Area-elevation data: an area-elevation ( or hypsometric ) curve can be constructed by planimetering the area

betw een contours on a topographic map and plotting the cumulative area above (or below) a given elevation v ersus that elevation

• Aspect: The aspect of a slope is the direction tow ard which the slope faces.

II. STREAMS AND STREAM PATTERNS Stream: is body of water confined within a bed and stream banks. Branch, beck, burn, gill, lick, rivulet, streamage, wash or run. Streams are v ital geologic agents. Streams carry most of the w ater that goes from land to sea (essential part of the

hy drologic cycle). Streams transport billions of tons of sediment to the oceans each year. Load: is the sediment and dissolved matter the stream transports. Load is expressed in kilograms per cubic meter. It is dissolv ed matter generally does not affect stream behavior.

Types of Stream:

1. Brook: Stream smaller than creek, shallow and it’s bed composed of primarily rocks 2. Creek: small to medium sized natural stream, a small inlet or bay narrower than a cove

3. River: A large natural stream which may be a waterway, usually freshwater flowing towards the sea, lakes or ocean.

4. Tributary: Contributory stream which does not reach the sea but joins another river(parent river) also called a branch

Patterns of Stream: 1. Meandering Stream: characterized as an irregular waveform. Flows in large, more or less symmetrical loops, or

bends. Usually occur in a region of a riv er channel with shallow gradients, a well-developed floodplain & cohesive floodplain material.

Median length-about 1.5 times the v alley length Wavelength- ranges from 7-11 times the channel width Radius of Curvature- 2-3 times the channel width

2. Braided Stream: Consist of many intertwined channels (anabranches) separated by islands. Tend to be v ery

w ide and relativ ely shallow with coarse bed material. Occur when bed material is coarse and heterogeneous, banks are easily erodible and has a high stream gradient.

Total width of Branches- 1.5 to 2 times that of an unbraided 3. Straight Stream: defined as one with a sinuosity of less than1.25 are found in the most tectonically incised /

activ e areas at alluvial fans. III. FLOOD PLAINS

Flood Plains: An area of land adjacent to a stream or river that stretches from the banks of its channel to the base of the enclosing v alley walls.

Formation-made by meander eroding sideways as they travel downstream. When a riv er breaks its banks and floods, it leav es behind layers of alluvium (silt).these gradually build up to create the floor of the floodplain IV. EROSION PROCESS

The Erosion Process:

1. Splash Erosion: starting w ith the detachment of soil particles by impact of raindrops 2. Sheet Erosion: relatively uniform degradation of the soil

3. Gully Erosion: Dislodge soil is carried by the flow ing water 4. Mass Movement: Breakdown and transport of w eathered materials 5. Landslide: Ground movement such as rockfallsdeep failure of slopes & shallow debris flow

The Mechanism of Erosion: 1. Detachment 2. Transport 3. Deposition

Erosion by Running Water Erosion by water before a distinct channel has formed occurs in two ways:

– By impact as raindrops hit the ground.

– By ov erland flow during heavy rains, a process known as sheet erosion. The effectiv eness of raindrops and overland flows in eroding the land is greatly diminished by a protective cover of v egetation. Factors Controlling Erosion:

1. Rainfall Regime

2. Vegetal Cov er 3. Soil Ty pe 4. Land Slope

Erosive Agents:

1. Raindrop impact

2. Ov erland flow surface runoff from rainfall 3. Bed and bank turbulence in streams

Effects of Erosion:

1. Degrades soil resource a. Reduces soil productivity b. Reduces soil organic matter c. Remov es plant nutrients

2. Causes downstream sedimentation 3. Produces sediment w hich is a pollutant 4. Produces sediment that carries pollutants

V. SEDIMENTATION Sediment Transport: mechanics of sediment erosion, transport, and deposition by water. Sediment is transported in rivers and streams by two components:

1) Suspended load: sediment moves through the fluid 2) Bed load: sliding, rolling, saltating Effects of Scarce/Abudance of Sediments:

A. Problems with too much sediment – Raised flood profiles – Reduced underwater light

– Decreased capacity of hydraulic structures B. Problems with too little sediment

– Incision (channel lowering) – Delta loss

– Scour at hy draulic structures Sediment Size:

Clay < 0.004 mm - Clay and silt are considered fine sediments

Silt 0.004 - 0.0625 mm

Sand 0.0625 - 2 mm - Sand and grav el are considered coarse sediment

Grav el > 2mm

GROUP 10: Hydrology and Water Quality

I. Water Quality

HYDROLOGY AND WATER QUALITY

I. WATER QUALITY

Falling precipitation carries gases and particulate matter from the atmosphere. As it strikes the ground it may dislodge sediment which overland flow transports to a stream together with material dissolved from the land surface. Infiltrating

w ater undergoes chemical exchange with the soil, giving up some materials and dissolving others. Thus surface runoff, interflow , and groundwater have chemistries characteristic of the rocks and soils encountered along their paths of flow .

Hy drologic factors play a major role in determining the concentration, rate of movement, and final disposition of

pollutants. Prediction of w ater quality and of the changes which might result from control measures requires an understanding of the hy drologic, physical, chemical and biological processes in water bodies. Unique Property of Water:

- Solv ent Action - Dissociation - Transparency

1. Solvent Action of Water:

The polarity of charge in the w ater molecule favors the disruption of ionic crystals by reducing the interionic attractiv e forces. Sodium chloride and salts of potassium are readily dissolved in water. Water can also solvate separated ions.

- Solvation entails the surrounding of charged solute particles by solvent molecules in response to attractiv e forces.

- Cations, positively charged ions, are effectively solvated by compounds of elements in the first row of the periodic table that hav e unshared electron pairs.

- Anions, negatively charged ions, are easily solvated by a solvent in which a strongly electronegative element such as oxygen is bonded to hy drogen.

- Water molecules are capable of forming hydrogen bonds to molecules containing oxygen atoms

2. Disassociation: Water is not only a solvent for other substances but is itself capable of dissociating into tw o charged ions. Hence water acts as both a base and an acid .

3. Transparency: Solar radiation arriving at the earth’s surface is characterized by wavelengths between 0.3 and

1.3 µm. Nearly all radiation outside the range of v isible wavelengths (0.4 to 0.8 µm) is absorbed in the first meter of w ater. Radiation with wavelengths greater than 0.8 µm (infrared) results in significant heat transfer to w ater. The v arious spectral bands of v isible radiation are absorbed differentially. The red component penetrates no more than 4m of w ater w hile some of the blue component penetrate 70m or more.

Beer’s Law:

Fomula: qz = q0e ̂ nz Where:

qz – light intensity at depth z q0 – intensity of light at the w ater surface n – v arious wavelengths

Quality of Precipitation:

Precipitation contains dissolved substances largely determined by the air quality and wind patterns of the region.

In areas w here there is heavy air pollution the atmosphere is a complex chemical system controlled by dozens of chemical and photochemical transformations

Atmospheric water in such areas accumulates carbon dioxide, nitrates, and inorganic forms of phosphorus and sulfur. This moisture becomes chemical-laden precipitation hundreds of kilometers from the original pollution source.

Reported annual deposition rates of nitrogen and phosphorus from precipitation range from 5 to 10 kg/hectare and 0.5 to 0.6 kg/hectare, respectively.

Data from areas relativ ely unaffected by human activity indicate that much of the in-stream burden of nitrogen comes from precipitation, while only a small portion of the in-stream burden of phosphorus is precipitation-borne

Water Temperature:

The density and viscosity of water, and the solubility and diffusivity of gas in water are dependent upon water temperature. Both w ater density and viscosity decrease as temperature increase. Even the slight changes in density can result

in stratification of lakes and impoundments, resulting in the w ater quality problems outlined in the preceding section. As temperature increase, the ability of water to carry suspended materials decrease according to stokes’ law.

The v elocity of water below which particles settle out of suspension, the settling v elocity, is directly related to

w ater density and inversely proportional to viscosity. The net result of an increase in tem (above 4°C is an increase in settling v elocity and increased sedimentation in sludge deposits.

All biochemical reactions are sensitive to variations in temperature. Organisms consist of heat-sensitive proteins and enzy mes which control the grow th, respiration, reproduction, and death rate of each species. Within the range of tolerance

for a species. An increase on temperature increase metabolic reaction rates. A generalized expression for the v ariation of a reaction-rate constant w ith temperature has been derived from the van’t hoff-arrhenius law. Biochemistry of Natural Water:

The discussion of nonliving material is divided categorically into inorganic and organic chemicals. Organic chemicals are further div ided into biodegradable and non-biodegradable substances.

- Inorganic chemicals: the inorganic chemicals of most importance to the aquatic environment include dissolved ox y gen, free hydrogen ions, and compounds of carbon, nitrogen and phosphorus. The survival of many aquatic organisms and the aerobic decomposition of waste materials depend on the maintenance of adequate dissolved ox y gen in water.

- Organic chemicals: Organic materials - found in the aquatic environment include natural compounds such as

sugar, starch, fat, and oil and synthetic compounds such as surfactants, phenols, and pesticides. o Biodegradable - is the decay or breakdown of materials that occurs when microorganisms use an

organic substance as a source of carbon and energy. o Non-biodegradable

Ph of Water: The availability of free hy drogen ions in water is measured by the рH, defined in terms of hy drogen-ion concentration.

- Pure w ater has ph of 7 - Low er than 7 acidic water - Higher then 7 alkaline w ater

Acid in Natural Water: Acid in natural waters combines with the basic carbonate ion to form bicarbonate. If ex cess acidity remains after neutralization of all carbonate, bicarbonate is driven back into the carbonic acid form and, and finally carbonic acid breaks down into water and free carbon dioxide.