Hydrology Midterm

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

• Has origins in the New Latin word hydrologia

• 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.

cloud condensation, precipitation

snow accumulation, overland flow, river flow, lake storage.

infiltration, soil-water storage, groundwater flow.

evaporation, transpiration, sediment water exchange

Hydrologists are traditionally concerned with the supply of water for domestic and agricultural use and the prevention of flood disasters. However, their field of interest also includes:

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 is less than the field capacity of the soil

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.

The precipitation that percolates down to ground water is maintained in the hydrologic cycle as

• 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.

has a defined capacity for infiltrating water. The capacity can be expressed as a depth of water that can be infiltrated per unit time, such as inches per hour.

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. Evapotranspiration is an important part of the water cycle.

an element such as a tree that contributes to evapotranspiration.

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:

The hydrologic cycle, illustrated in Figure 2, shows the pathways where water travels as it circulates throughout global systems by various processes. The components of this hydrologic cycle:

Meteorological parameters that are used to study the hydrologic processes:

These hydrologic processes are:

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

- the temperature at which 𝑒𝑣 reaches 𝑒𝑠 for the same conditions and water vapor starts to condense.

- It can be computed using eq. 1 if T is replaced by Td and the normal vapor pressure is considered as saturated one.

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

• relation between water volume in the globe that is considered to be constant but changes from a phase to another

• states that the change in the storage within a certain domain is equal to the summation of the inflow, outflow, underground flow, evaporation, and precipitation.

• is accounting of the volume of flow rate of water in all possible locations.

• in chemistry 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

• to the hydrologist, it is the general term for all forms of moisture emanating from the clouds and falling to the ground.

• the primary input parameter of the hydrologic cycle.

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. Hail 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:

The average annual precipitation on certain locations is a function of:

can be classified by the origin of the lifting motion that causes the precipitation. Each type is characterized by different spatial and temporal rainfall regimens.

Types of storms:

Precipitation from convective storms 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.

Air moves from areas of higher pressure toward areas of lower pressure. In the middle latitudes, cyclonic storms generally move from west to east and have both cold and warm air associated with them. These mid-latitude cyclones are sometimes called

occur at the boundaries of air of significantly different temperatures.

Type of Fronts:

type of air movement, where one has warm air being pushed into an area of cool air, while the other has cool air pushed into an area of warmer air.

shows a much steeper slope of the interface of warm and cold air usually resulting in rainfall of shorter duration and higher intensity. Some depressions are died-out cyclones.

Hurricanes, typhoons, or tropical cyclones develop over tropical oceans that have a

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

Measuring precipitation covers rain, hail, snow, rime, hoar frost, and fog, and is traditionally measured using various types of rain gages such as the

Limitations of Rain gauges:

The requirements for gauge construction are:

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.

There are 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.

These 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.