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Hydrology: Some interesting facts and Terminologies - Anitha Manivasagam

by Arul Aram last modified 2009-10-26 19:33

Hydrology: Branch of earth science that deals with water as it occurs in the atmosphere, on the surface of the ground, and underground.

Land-Water Proportion: Water covers about three quarters of the earth’s surface, either as oceans (salt water) or as fresh water and this forms the hydrosphere. Most of the earth’s surface water is in the oceans (97 per cent). Of the remainder, 2% is frozen in glaciers and polar ice caps, only one per cent is fresh water with a salt content under 1/5% found in either lakes or ponds (still water) or in rivers and streams (running water). Fresh water becomes available in the form of snow, snowfall, dew, etc.

Sea: Either a very large lake that contains salt water or a portion of an ocean (can be surrounded by water or surrounded by land.

Ocean: The largest bodies of water on the planet.

Bay: Any wide indentation of the land. Larger than a cove but smaller than a gulf.

Creek : A body of water that flows with gravity; larger than a brook but smaller than a river. Creeks are often called streams.

Estuary : The wide end of a river when it meets the sea; salty tidal water mixes with the fresh water of the river here.

Canyon – a large-scale, steep-sided valley, which is deeper than it is wide.
Cliff – a tall, vertical, or near vertical, rock face.
Gulf: A large inlet of water surrounded by land; usually surrounded on three sides by land. Larger than a bay.
Gorge: is a deep valley between cliffs often carved from the landscape by a river.
Geyser: a geothermal feature of the Earth where there is an opening in the surface, that contains superheated water and periodically erupts in a shower of water and steam.

Grey water: wastewater from clothes washing machines, showers, bathtubs, hand washing, lavatories and sinks.

Water hardness: Indicator of the concentration of alkaline salts in water, mainly calcium and magnesium, as a measure of water quality.

In stream Water Use: Water that is used, but not withdrawn, from a surface-water or groundwater source for such purposes as hydroelectric power generation, navigation, water-quality improvement, fish propagation, and recreation, sometimes called non-withdrawal use or in-channel use.

Surface Water: Open bodies of water, such as lakes, rivers, or streams. All non-marine waters on the surface of the earth, including fresh, brackish, and salt water are surface water sources.

Run Off: When rain or snow falls onto the earth, it just doesn't sit there -- it starts moving according to the laws of gravity. A portion of the precipitation seeps into the ground to replenish Earth's ground water. Most of it flows downhill as runoff. Runoff is extremely important in that not only does it keep rivers and lakes full of water, but it also changes the landscape by the action of erosion. Flowing water has tremendous power -- it can move boulders and carve out canyons.
Have You ever Thought???…………
If fresh water flows out to the sea, why is the sea still salty?
The Mississippi, Amazon, and Yukon Rivers empty respectively into the Gulf of Mexico, the Atlantic Ocean, and the Pacific Ocean, all of which are salty. The saltiness of the ocean is the result of several natural influences and processes, the salt load of the streams entering the ocean is just one of these factors.
Safe Water: Safe water means water that will not harm you. It refers to drinking water, but it could also apply to water for swimming and other purposes. Safe water must have sufficiently low concentrations of harmful contaminants to avoid sickening people who use it. The list of harmful contaminants includes disease-causing microbes such as bacteria, viruses, and protozoans; cancer-causing chemicals such as many pesticides, organic solvents, petroleum products, chlorinated byproducts of the disinfection process, and some metals and metalloids; nitrates and nutrients, endocrine-disrupting compounds, strong acids, strong bases, radionuclides, and any other acutely toxic substance.

Defining safe water is a matter of risk assessment, in which you consider the chance of illness or injury from drinking the water; in comparison to the risk of illness or injury from the many hazards in our lives, say, riding in a car, or breathing the air, or shaking hands, or exposure to radiation from the sun, or to contaminants in the food we eat.

In comparison to such activities, drinking public tap water, or any of the bottled waters, or water from most domestic wells, is very safe indeed. These waters might come from wells or springs that tap shallow or deep aquifers*, from rivers or lakes, or glaciers, or even from rainwater collectors, fog collectors, or from desalinated seawater. Most of these waters are filtered and treated to kill microbes and contaminants at safe levels.

*Aquifer-underground layer of water bearing permeable rock from which ground water can be extracted.

The amount of ground water that can flow through soil or rock depends on the size of the spaces in the soil or rock and how well the spaces are connected. [The amount of spaces is the porosity. Permeability is a measure of how well the spaces are connected.]

Ground Water: When rain falls to the ground, the water does not stop moving. Some of it flows along the land surface to streams or lakes, some by plants, some evaporates and returns to the atmosphere, and some seeps into the ground. Water seeps into the ground much like a glass of water poured onto a pile of sand.

Ground water Resources: Out of 0.6% of ground water, only 0.3% is economically extracted.

Importance of groundwater: It is the largest source of fresh water that can be economically extracted. If not replenished, this will become unattainable.

At least some ground water can be found almost everywhere. The water table may be deep, such as under a hillside, or shallow such as under a valley. The water table may rise or fall depending on several factors. Heavy rains or melting snow may increase recharge and cause the water table to rise. An extended period of dry weather may decrease recharge and cause the water table to fall.

We can run out of ground water if more water is discharged than recharged. For example, during periods of dry weather, recharge to the aquifers decreases. If too much ground water is pumped during these times, the water table can fall and wells may go dry.

Ground water can become unusable if it becomes polluted and is no longer safe to drink. In areas where the material above the aquifer is permeable, pollutants can seep into ground water. Ground water can be polluted by seepage through landfills, from septic tanks, from leaky underground fuel tanks, and sometimes from fertilizers or pesticides used on farms.

Bottle water is prized 1.5$ which is 80INR. The chemical Bisphenol-A is carcinogenic.It leaches into water from bottles. This chemical is also found in mobile phones, baby bottles and CD's. It is estimated that accumulation of bottles is at the rate of 1500/sec. Overall, 100 billion$ is spent on bottled water, leading to plastic accumulation. Ditching bottled water can alone keep Mother Earth and the wallet ‘Green’

Traditional Water Conservation: Water is a ‘Public good’, a natural asset. The best and right solution to conservation of water is to save precious drops from the sky. It can be used for drinking or for groundwater recharge.

Need for conservation:

• Smooth out variations in availability/rainfall
• Shortage of water within distance of its place of use
• Have good quality water for all
• Mitigate floods/droughts

Water shed(drainage area) Management: Controlling and directing the resources and activities associated with the land and streams of a drainage  basin  to maintain the supply and quality of  water and prevent floods, erosions and destructive  conditions like

• Establishing Green cover
• Sustaining forests that check infiltration and runoff
• Developing gardens and ponds
• Upcoming buildings in the city will have to include a water harvesting plan in their design for government approval.
• Rainwater harvesting in both rural and urban areas
• Collecting water on roofs and underground storage will help augment underground water table
• Protection of drinking water supply sources

Has it ever caught your imagination?

What causes rainfall?

Not all cloud has rain pouring out!! This is how the formation of a cloud leads to actual rain!!

The water condensing in the clouds has to become heavy enough to fall to Earth. The tiny droplets just are not heavy enough to fall, they go whichever way the wind blows them, or they just hang suspended in the air.
 These droplets need to grow into large heavy drops. Some will collide with other droplets and become larger while others will grow as water condenses in the air. It is like watching drops of rainwater on a window. This process will be happens to millions of tiny droplets, all growing at the same time, but at different speeds.
Eventually, if the droplets keep growing, they will reach a mass where they cannot remain floating in the cloud because they are too heavy and will finally start to fall. Some are caught in upward blowing winds and are blown back into the clouds for a while, but once they are heavy enough to overcome the force of the wind, they will fall to earth as rain! It will keep raining as long as the conditions are right to make the clouds and let the water droplets grow heavy enough to fall.


Textbook: Principles of Ecology, Verma P. S, Agarwal. V. K

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