HYDROLOGY (midterm coverage)

An earth science that refers to the scientific study of water and its properties, distribution, movements, and effects on Earth's surface, soil, and atmosphere.

• Comes from the Greek words hudor meaning water and logy meaning a study of.

• Has origins in the New Latin word hydrologia.

cloud condensation,

precipitation

snow accumulation

overland flow

river flow

lake storage.

infiltration,

soil-water storage,

groundwater flow.

evaporation,

transpiration,

sediment water exchange

Hydrologists field of interest also includes:

are traditionally concerned with the supply of water for domestic and agricultural use and the prevention of flood disasters.

Hydrological science has both pure and applied aspects. Understanding the engineering hydrology science is essential for:

has focused on providing freshwater resources to the needs of humans, livestock, commercial enterprises, agriculture, mining, industry, and electric power.

Theoretical approaches in hydrology have been increasingly developed due to the development of digital computers since

is used in engineering mainly in connection with the design and operation of hydraulic structures.

Two phases of the topics that Hydrology deals with:

Typical hydrologic problems involve:

• is found everywhere on the earth, is one of the most basic and commonly occurring substances.

• the only substance on earth that exists naturally in the three basic forms of matter, i.e., liquid, solid, and gas.

the constant interchange of water from the oceans to the atmosphere to the land and back to the ocean.

The effect of infiltration is to increase the_______.

If the moisture content becomes greater than the field capacity_____

moisture held by the soil after all gravitational drainage

The part of precipitation that falls into puddles and depressions can_____

Low places on the ground where water is held and is not available for overland flow or surface runoff.

• the flow path that must be filled with water before flow can occur overland and in the natural and/or manmade drainage systems.

• it is temporary since most of the water continues to run off after the rainfall ceases.

• in chemistry, it refers to material falling out of suspension.

• when studying weather and from meteorology, it refers to all forms of liquid or solid water particles that form in the atmosphere and then fall to the earth's surface.

the downward movement of water from the land surface into the soil profile.

is the transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere.

the primary source of energy for evaporation

• used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere.

• an important part of the water cycle

accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies.

accounts for the movement of water within a plant and the subsequent loss of water as vapor through stomata in its leaves.

an element such as a tree that contributes to evapotranspiration is called_____.

the transformation of water vapor to liquid water droplets in the air, creating clouds and fog.

the water which occurs in the saturated zone of variable thickness and depth below the earth’s surface.

Main elements of Hydrologic Cycle

Physical properties that are studied by hydrology:

Meteorological parameters that are used to study the hydrologic processes:

is measured by Thermometers located 1.25 m above the ground and sheltered.

measures maximum temperature

measures minimum temperature

the water vapor (moisture) content in the air or other gases

measures humidity

the air's capacity of absorbing moisture and can be expressed as a percentage

counts the number of rotations which is used to measures wind speed (W)

measured direction of wind

is measured by units of Knot or mph.

where: 1 Knot = 1.852 km/h 1 mph = 1.61 km/h

it expresses the relationship between wind speed and elevation.

the source of energy on the earth and it is measured by units of Watt/m2 and KJ/m2.

measures solar radiation in micro-meter 10−6 m

an important term used in some methods of estimating evapotranspiration.

Rainfall in the Philippines is brought about by different-causing weather patterns and among them— dominating causes are the

the seasonal change in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea.

Two monsoons in the Philippines:

• wind from the northeast

• it affects the country from the month of November to March

• wind from the southeast

• begins as early as mid of April and ends in November depending on location

• formed as a point where the trade winds converge forces the air up into the atmosphere.

• it appears as a band of clouds consisting of rain showers with occasional thunderstorms.

Trade winds move in southwesterly direction

Trade winds move northwesterly direction

• are characterized by a low-pressure center where winds of varying intensive blow around the center

• are classified according to maximum winds near the center

Classification of Tropical Cyclones

Various forms which Precipitation occurs:

• is precipitation that is in the liquid state when it reaches the earth.

• form of precipitation in which separate drops of water fall to the Earth's surface from clouds.

– liquid precipitation that reaches the surface in the form of drops that are less than 0.5 millimeters in diameter.

• a frozen water in a crystalline state.

• occurs when the layer of the atmosphere from the surface of the earth through the cloud is entirely below freezing.

• a frozen water in a 'massive' state.It is a product of very intense thunderstorms.

• is rarely seen when the surface air temperature is below freezing.

• forms as a byproduct of strong updrafts that exist in thunderstorms.

that are associated with thunderstorms can grow to heights where the temperature is below freezing. Drops of water will rise up with the upward directed wind as they collide with other droplets and grow larger. This will eventually result in the droplet freezing into a hailstone.

• a melted snow that is an intermixture of rain and snow.

• is nothing more than frozen raindrops.

• occurs when there is a warm layer of air above a relatively deep sub-freezing layer at the surface.

• usually doesn't last long and mainly occurs ahead of warm fronts during winter months.

Condensation may be attributed to one or more of the following causes:

most important cause of condensation

Condensation forms commonly associated with radiational and contact cooling are:

Types of storms:

Precipitation from ______storm results as warm moist air rises from lower elevations into cooler overlying air. Heating of air at the interface with the ground, the heated air expands with a result of reduction of weight and the air will rise

The characteristic form of convective precipitation is the

• it results as air is forced to rise over a fixed-position geographic feature such as a range of mountains.

• it is due to mechanical lifting of moist air masses over natural barriers such as mountains.

is caused by the rising or lifting of air as it converges on an area of low pressure.

occur at the boundaries of air of significantly different temperatures.

Type of Fronts:

Hurricanes, typhoons, or tropical cyclones develop over tropical oceans that have a surface water temperature greater than _______

has no trailing fronts, as the air is uniformly warm since the ocean surface from which it was spawned is uniformly warm

Rainfall Gauges:

• measure precipitation at or near the ground, and are observed at least once a day. The sizes of the gauges are made big enough to collect more than the average one-day or maximum 1-2 hours precipitation which differs according to various climatic conditions.

• are also commonly used to measure both rain and snow, and the latter affects fundamentally the form and dimensions of a particular national gauge (snow gauges are bigger).

• The height of the gauge orifice varies between zero and more than 1m above the ground.

An electronic rain gauges that measures rainfall and are also self-emptying and frost proof. The basic idea is the rain collector’s measuring spoon being automatically tipped and emptied when the pre-adjusted water weight has been reached.

that moves a pen downward with the rainfall accumulating in the collecting bucket.

have a row of collection funnels. In an enclosed space below each is a laser diode and a phototransistor detector. When enough water is collected to make a single drop, it drips from the bottom, falling into the laser beam path. The sensor is set at right angles to the laser so that enough light is scattered to be detected as a sudden flash of light. The flashes can be translated to amount of water and the rate of flashing can represent the time scale.

The bucket, 4" in diameter, measures each rain drop, displays it on the digital display with 3/8" numerals, and then empties itself. Simply place it outside on a hard, level surface and watch it record rainfall up to 99.999 in. Convenient one touch reset button lets you keep annual, monthly, or stormby-storm totals. The unit has no moving parts, gold-plated sensors for reliability, and is not damaged by freezing conditions.

Other types of modern rain gauges are:

• an object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain.

• was coined in 1941 as an acronym for Radio Detection and Ranging.

• was originally called Radio Direction Finder (RDF) in the United Kingdom, in order to preserve the secrecy of its ranging capability.

, transmits pulses of radio waves or microwaves which bounce off any object in their path.

Components of a radar:

• a type of radar used to locate precipitation, calculate its motion, estimate its type (rain, snow, hail, etc.), and forecast its future position and intensity.

capable of detecting the motion of rain droplets in addition to intensity of the precipitation.

• the first space borne instrument designed to provide three-dimensional maps of storm structure.

• has a horizontal resolution at the ground of about 3.1 miles (five kilometers) and a swath width of 154 miles (247 kilometers).

• One of its most important features is its ability to provide vertical profiles of the rain and snow from the surface up to a height of about 12 miles (20 kilometers)

• it can detect fairly light rain rates down to about 0.027 inches (0.7 millimeters) per hour.

• it can separate out rain echoes for vertical sample sizes of about 820 feet (250 meters) when looking straight down.

• it carries out all these measurements while using only 224 watts of electric power—the power of just a few households light bulbs.

• was built by the National Space Development Agency (JAXA) of Japan as part of its contribution to the joint US/Japan Tropical Rainfall Measuring Mission (TRMM).

is a type of satellite that is primarily used to monitor the weather and climate of the Earth.

Other types of environmental information collected using weather satellites:

an instrument used to measure the drop size distribution and velocity of falling hydrometeors.

can be used to analyze individual snowflakes.

• developed for measuring and recording in remote areas and it operates as a completely self-contained system.

• it includes Instrument shelter and needs no power and depend only on solar/battery supply.

• it has a RAM of a suitable size for storing data that can be downloaded.

should consist of adequate number of rain gauges evenly distributed all over the drainage basin.

Some of the common causes for inconsistency of record are:

• the simplest method of determining areal average rainfall.

• it involves averaging the rainfall depths recorded at several gauges.

• assumes that at any point in the watershed the rainfall is the same as that at the nearest gauge, so the depth recorded at a given gauge is applied out to a distance halfway to the next station in any direction.

• is generally more accurate than the arithmetic mean method, but it is inflexible, because a new Thiessen network must be constructed each time there is a change in the gauge network, such as when data is missing from one of the gages.

• it does not directly account for orographic influences on rainfall.

• is superior to the other two methods especially when the stations are large in number