Water

Importance of water

Water is the most abundant and useful substance on earth. Water covers more than 70 % of the earth's surface and also exists as vapor in the earth's atmosphere.

Water is essential to life and has vast influence on weather and climate. It seems to be necessary in almost all chemical reactions. Water furnishes hydroelectric and steam power. In rivers, lakes and oceans, it forms important avenues of transportation. As rain and ice it wears down hills and mountains, causes erosion, and helps convert rocks into soil. We drink water, and use it in cooking, washing, heating, putting out fires, treating diseases and in many other ways.

Water Cycle

The water cycle refers to the movement of water through the hydrosphere, atmosphere, lithosphere and biosphere of the earth.

The heat of the sun vaporizes water from land and sea. Water vapor is given off also in the transpiration of plants and in the breathing of human being and animals. In the colder regions of the upper atmosphere, water vapour condenses and forms clouds. Under certain conditions, the clouds condense to form rain, snow, hail or sleet which gravity pulls down to the earth.

Part of the water that falls on the land flows along or wear the surface of the ground to rivers, ditch which carry it to the sea. This water, called 'run off' is the water absorbed by the soil. Part of this water is evaporated by the sun, part is used by plants and part steps down to become ground water.

Groundwater is a great natural reservoir, sands, gravel, porous rocks and cavities under the ground, The upper level of this reservoir is called the WATER TABLE. Ground water feeds springs, wells, rivers and the ocean. Most of it finds it's way to the sea eventually to be evaporated.

This endless circulation of the earth's water, powered by the heat of the sun and the pull of gravity, is called the WATER CYCLE or HYDROLOGICAL CYCLE. It is vitally important to life and climate. Without it, parts of the land would consist of swamps and the remainder would be deserts, lakes and oceans would stagnate, and the earth could be uninhabitable.

Complete this Practical Activity on the Water Cycle in your portfolios.

Sources of Water

On planet earth, and within Guyana, there are basically three ways in which water can initially exist.

These being:-

1. Atmospheric Water

2. Surface Water

3. Underground Water

(1) Atmospheric Water

• Rain

• Dew/Fog

• Snow

• Sleet

Atmospheric water is generated as a result of precipitation, in the form of rain, snow, dew, etc. Since Guyana is below the sea level and is located in the Tropical regions, snow is not a source of atmospheric water for us: rain, dew and fog are the dominant sources within the country.

As shown in the illustration of the Water Cycle, a great percentage of the Earth's water is obtained from precipitation. During the day, the sun causes water from oceans, lakes, plants and in the air, to evaporate as vapour. This vapour forms rain clouds which, after becoming too heavy, falls as precipitation, i.e. rain, dew, snow, etc. Rain and dew are the main sources of water for agricultural purposes in Guyana.

(2) Surface Water

• Rivers

• Lakes

• Oceans

• Ponds

• Creeks

• Trenches

This is water that can be found at the Earth's surface. Within Guyana, all these sources are used for agricultural purposes except water from the Ocean and this because of its salinity.

Rivers, lakes and man-made reservoirs are often used as the main sources of surface water for agriculture.

Let us look more in-depth at these two sources:

Rivers

Rivers are used all over the world as sources of surface water. The most typical quality defining a river is that it has a source, a mouth and possibly tributaries and it flows; it is not a reservoir which contains a fixed amount of water. At each movement a new amount of water is passing in any given location along the river. The flow of a river fluctuates overtime. With the flow of small local rivers fluctuating greatly over relatively short periods of time in response to rainfall in their catchment area.

A catchment area is the area from which a particular river or lake receives both surface flow and drainage water originating from precipitation.

Other rivers show little fluctuation or vary only over a long period of time. These are mainly rivers with a large catchment area, where the main tributaries are spread over a greater area and/or a larger period of time. River flows vary considerably, not only within a given year, but also from one year to the next. In a year with little rain during the rainy season the river flow will be small; sometimes the river flow will cease altogether during the dry season. The river flow will be far more in years with heavy rainfall during the wet season.

Lakes and Reservoirs

Lakes are natural depressions of land which are filled up with water. Fresh water lakes have a natural outlet through which the lake discharges superfluous water.

Lakes are supplied with water via the run-off of rainfall from the adjacent land, from small streams or by ground water that seeps through the soil to the lowest point, which is the lake. Lakes lose water via evaporation from the lake's surface, via the lake's natural outlet (overflow), or through percolation from the bottom of the lake to the surrounding ground water.

A reservoir is an artificial lake. It can be formed by building a dam across a valley, by excavating the land or by surrounding a piece of land with dykes.

(3) Underground Water

• Springs

• Artesian Wells

• Geysers

• Aquifers

This is another source of water. It is only available below ground level. It must therefore be lifted, or pumped before it can be used. Pumping underground water from wells is a well know method of utilizing underground water the world over.

To understand how underground water functions, think of it as a series of lakes below the surface of the earth. The earth is built up of different layers - sand, gravel, clay, rock, etc. The layers of coarse sand and gravel, on the other hand, contain many pores and cracks, which allow rainfall to enter the soil and percolate from the surface. These porous layers filled with water are called acquifers. Underground water flows, in most cases, slowly to the lower parts. Where the acquifer meets the surface, the underground water flows out of the soil into, for instance, a river or spring.

Underground water may be found close to the surface or at profound depths. In coastal plains the underground water is often brackish or saline due to the proximity of the sea. Inland underground water may also be brackish in places where the soil contains many soluble salts.

Complete the following Practical Activity on Water Salinity Testing.

Complete the following Practical Activity on Water Alkalinity Testing.

(N.B.: These activities are not yet available and will need to be done within the school laboratory. They cannot be done at home...)

Discussion

Let's do a review of the lesson...

Post under the appropriate topic in the Forums what you learnt, what you would like to learn and what you do not understand.

References

• Grade 9 SCCP Curriculum Guide

• Image of Water Availability <https://i.pinimg.com/originals/3a/a8/60/3aa8608fa94741327be48a21ed717229.jpg>

• Water Cycle Infographic <https://visual.ly/community/Infographics/environment/water-cycle-0>

• Rain image <https://images.pexels.com/photos/1463530/pexels-photo-1463530.jpeg?auto=compress&cs=tinysrgb&dpr=1&w=500>

• Dew Image <https://media.nationalgeographic.org/assets/photos/000/204/20420.jpg>

• Fog Image <https://m.economictimes.com/thumb/msid-66121137,width-1200,height-900,resizemode-4,imgsize-235781/iit-scientists-develop-material-that-can-harvest-water-from-fog.jpg>

• Major Rivers of Guyana Image <https://www.researchgate.net/profile/Shawn_Lehman/publication/228782720/figure/fig4/AS:300845250957319@1448738505404/Locations-of-major-rivers-tested-for-relationship-to-variations-in-primate-diversity-in_Q320.jpg>

• Image of River Catchment Area <https://sncyear7geography.weebly.com/uploads/5/7/7/8/57782431/1907510_orig.png>

• Image of Linden Blue Lakes <https://i.pinimg.com/originals/ba/df/d2/badfd2678fce6f73331ade5332eded3b.jpg>

• Image of Nappi Reservoir <https://scontent.fogl3-1.fna.fbcdn.net/v/t1.0-9/67685535_2487208977967075_2509404465971331072_n.jpg?_nc_cat=108&_nc_sid=110474&_nc_ohc=rajeQLh8FGIAX9azQBb&_nc_ht=scontent.fogl3-1.fna&oh=f81eea2ed1eff37a5e5268dc5d605ac0&oe=5F8AAFFB>

• Image of Aquifers and Wells <https://s3-us-west-2.amazonaws.com/courses-images-archive-read-only/wp-content/uploads/sites/459/2015/06/21062450/aquifersandwells.gif>

• <Saline Groundwater <https://www.researchgate.net/profile/Paramsothy_Jeyakumar/publication/227366583/figure/fig4/AS:302362351685637@1449100210762/Conceptual-sketch-of-fresh-brackish-and-saltwater-under-a-strip-of-land-bordered-by-a.png>