Lesson 1 - Introduction to Hydrology

Hydrology

the science of water

Hydrology

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

Hydrology

(as a branch of earth science) is concerned with the water in streams and lakes, rainfall and snowfall, snow and ice on the land and water occurring below the earth’s surface in the pores of the soil and rocks

Hydrology

is basically an applied science

Classification of Hydrology

Scientific Hydrology and Engineering/Applied Hydrology

Scientific Hydrology

the study which is concerned chiefly with academic aspects

Engineering/Applied Hydrology

a study concerned with engineering applications

Engineering/Applied Hydrology

deals with (i) estimation of water resources, (ii) the study of processes (precipitation, runoff, evapotranspiration, and their interaction), and (iii) the study such as floods and droughts, and strategies to combat them

• help solve local and global problems related to the overabundance, scarcity, or quality of water

• undertake a wide range of activities in order to monitor, manage and protect the water environment

Role of Hydrologists

• design and operation of hydraulic structures

• water supply

• wastewater treatment and disposal

• irrigation

• drainage

• hydropower generation

• flood control

• navigation

• erosion and sediment control

• salinity control

• pollution abetement

• recreation use of water

• fish and wildlife protection

Tasks of Hydrologists

• hydrologic design provides a service

• level of service must be defined and acceptable risk of failure must be determined (local drainage ordinances)

• cost and site characteristics are typical constraints

• occurrence, timing, and amount are the key aspects of hydrology from an engineering perspective

• problems are created by lack of water or too much water in a location at a moment in time (e.g., flood)

Importance of Hydrologic Engineering Design

observations, practice

Much of hydrology is based on _____ that are generalized to _____

Hydraulics

tends to start from basic physical principles, then make approximations for practice

Hydraulics

tends to work with manmade systems

surface water hydrology, max flow rate, hydraulics

Often, _____ provides inputs (_____) for _____.

[oversimplified explanation]

Water Cycle/Hydrologic Cycle

a cycle that involves the continuous circulation of water in the Earth-atmosphere system

• Evapotranspiration

• Transpiration

• Condensation

• Precipitation

• Runoff

most important processes involved in the water cycle

constant, continually changing

Although the total amount of water within the cycle remains essentially _____, its distribution among the various processes is _____.

evaporates, solar radiation, upward, clouds, condense, fall back, rain, winds, condense, precipitate, precipitation, evaporate, move down

Water in the oceans _____ due to the heat energy provided by _____. The water vapor moves _____ and forms _____. While much of the clouds _____ and _____ to the oceans as _____, a part of the clouds is driven to dry land areas by _____. There they _____ and _____ onto the land mass as rain, snow, hail, sleet, etc. A part of the _____ may _____ back to the atmosphere or _____ to the ground surface.

Infiltration

A portion of the water that reaches the ground enters the earth’s surface through _____, enhance the moisture content of the soil and reach the groundwater body.

Vegetation, transpiration

sends a portion of the water from under the ground surface back to the atmosphere through the process of _____

precipitation, filtration, evaporation

The _____ reaching the ground surface after meeting the needs of _____ and _____ moves down the natural slope over the surface through a network of gullies, streams and rivers to reach the ocean.

Runoff

the portion of the precipitation which by a variety of paths above and below the surface of the earth that reaches the stream channel

stream flow

Once it enters a stream channel, runoff becomes _____.

• transportation of water

• temporary storage

• change of state

Aspects of Each Path of the Hydrologic Cycle

water budget equation/hydrologic equation

The quantities of water going through various individual paths of the hydrological cycle in a given system can be described by the continuity principle known as _____.

Evaporation

occurs when the physical state of water is changed from a liquid state to a gaseous state

Evaporation

can occur on raindrops, and on free water surfaces (seas, lakes)

Evaporation

can even occur from water settled on vegetation, soil, rocks and snow

Condensation

process by which water vapor changes its physical state from a vapor, most commonly, to a liquid

Water vapor

condenses onto small airborne particles to form dew, fog, or clouds

Condensation

brought about by cooling of the air or by increasing the amount of vapor in the air to its saturation point

Precipitation

the process that occurs when any and all forms of water particles fall from the atmosphere and reach the ground

Interception

the process of interrupting the movement of water in the chain of transportation events leading to streams

Interception, vegetal cover, depression storage, rills, furrows

can take place by _____ or _____ in puddles and in land formations such as _____ and _____

Infiltration

the physical process involving movement of water through the boundary area where the atmosphere interfaces with the soil

Water transfer, porosity, permeability

_____ is related to the _____ of the soil and the _____ of the soil profile.

Percolation

the movement of water through the soil, and its layers, by gravity and capillary forces

Transpiration

the biological process that occurs mostly in the day

water vapor, transpire, upper, cool, cooler

Water inside of plants is transferred from the plant to the atmosphere as _____ through numerous individual leave openings. Plants _____ to move nutrients to the _____ portion of the plants and to _____ the leaves exposed to the sun. Leaves undergoing rapid transpiration can be significantly _____ than the surrounding air.

Runoff

flow from a drainage basin or watershed that appears in surface streams

Runoff

generally consists of the flow that is unaffected by artificial diversions, storages or other works that society might have on or in a stream channel

Runoff

is made up partly of precipitation that falls directly on the stream, surface runoff, subsurface runoff and groundwater runoff

Surface Runoff

flows over the land surface and through channels

Subsurface Runoff

infiltrates the surface soils and moves laterally towards the stream

Groundwater Runoff

from deep percolation through the soil horizons

• water is stored in the atmosphere

• water is stored on the surface of the earth

• water stored in the ground

Three Basic Locations of Water Storage that Occur in the Planetary Water Cycle

Meteorology

science that deals with the study of the atmosphere and its phenomena especially with weather

Weather

mix of events that happen each day in our atmosphere

Weather

is different in different parts of the world and changes over minutes, hours, days and weeks

Weather

most happens in the troposphere

Troposphere

the part of Earth’s atmosphere that is closest to the ground

Weather

condition of the atmosphere at a particular place over a short period of time in terms of:

• wind

• precipitation (rain, snow)

• temperature

• sunshine

• humidity

• pressure

• cloud

• visibility

Sun

causes all our weather because it heats the Earth unevenly

contrast, powerful engine, air pressure

The _____ between Earth’s hot parts and cold parts turns the atmosphere into a _____. This engine keeps the cold and warm air moving, thus makes changes in _____.

• sunshine

• air pressure

• wind

Air pressure changes cause:

Climate

an average portrait of weather conditions in a specific place over a long period

Climate

considers the average weather conditions and its variability to give a long-term view of the weather being experienced by a certain area (ISDR, 2008)

Climate

the average weather patterns for an area over a long period of time (20 - 1, 000, 000 years)

Climate

determined by rainfall and temperature

• latitude

• elevation

• ocean currents

What are rainfall and temperature influenced by?

• where people live

• how people live

• what they grow and eat

What do rainfall and temperature affect?

tropical and maritime

climate of the Philippines

Climate of the Philippines

is characterized by relatively high temperature, high humidity and abundant rainfall

Climate of the Philippines

is similar in many respects to the climate of the countries of Central America

• temperature

• humidity

• rainfall

Most Important Elements of the Country’s Weather and Climate

26.6 degrees Celsius

What is the mean annual temperature of the Philippines based on the average of all its weather stations?

January, 25.5 degrees Celsius, May, 28.3 degrees Celsius

The coolest months fall in _____ with a mean temperature of _____ while the warmest month occurs in _____ with a mean temperature of _____.

Latitude

an insignificant factor in the variation of temperature

Altitude

shows greater contrast in temperature

18.3 degrees Celsius

What is the mean annual temperature of Baguio with an elevation of 1, 500 m?

Summer Capital of the Philippines

• Its temperature is comparable with those in the temperate climate.

What is Baguio known as? Why?

Zamboanga, Laoag, insignificant

The difference between the mean annual temperature of the southernmost station in _____ and that of the northernmost station in _____ is _____.

no difference

There is essentially _____ in the mean annual temperature of places in Luzon, Visayas or Mindanao measured at or near sea level.

Humidity

refers to the moisture content of the atmosphere

high relative humidity

Due to high temperature and the surrounding bodies of water, the Philippines has a _____.

71 percent, 85 percent

The average monthly relative humidity varies between _____ in _____ and _____ in September.

high sensible temperature, March, May, temperature, humidity

The combination of warm temperature and high relative and absolute humidities give rise to _____ throughout the archipelago. It is especially uncomfortable during ______ to _____, when _____ and _____ attain their maximum levels.

Rainfall

the most important climatic element in the Philippines

Rainfall distribution, direction, moisture-bearing winds, location of the mountain systems

_____ throughout the country varies from one region to another, depending upon the _____ of the _____ and the _____.

965, 4,064

The mean annual rainfall of the Philippines varies from _____ to _____ millimeters annually.

• Baguio City

• Eastern Samar

• Eastern Surigao

Who receives the greatest amount of rainfall?

Southern Portion of Cotabato

Who receives the least amount of rain?

General Santos City, 978

At _____ in Cotabato, the average annual rainfall is only _____ millimeters.

• rainy season; June to November

• dry season; December to May

What is the two major seasons of the Philippines and when do they occur?

• cool dry season; December to February

• hot dry season; March to May

What is the dry season further subdivided into and when do they occur?

• Type I

• Type II

• Type III

• Type IV

What are the four climate types?

Type I

two pronounced season: dry from November to April and wet during the rest of the year

Type I

maximum rain period is from June to September

Type II

no dry season with a very pronounced maximum rain period from December to February

Type II

there is not a single dry month

Type II

minimum monthly rainfall occurs during the period from March to May

Type III

no very pronounced maximum rain period with a dry season lasting only from one to three months, either during the period from December to February or from March to May

Type III

resembles type I since it has short dry season

Type IV

rainfall is more or less evenly distributed throughout the year

Type IV

resembles type II since it has no dry season

Fr. J. Corona; 1920

Who devised the system of climate classification? When was this classification devised?

November - April, rest of the year

When is the dry season and wet season of Type I?

No dry season, maximum rain period from December to February; minimum rainfall during the period from March to May

When is the dry season and wet season of Type II?

short dry season either during the period from December to February or from March to May, no very pronounced maximum rain period

When is the dry season and wet season of Type III?