Лекция: Supply, Renewal and Use of Water Resources

Worldwide Supply and Renewal. The world's fixed supply of water in all forms (vapor, liquid, and solid) is enormous. If we could distribute it equally, there would be enough to provide every person on earth with 292 trillion liters (77 trillion gallons). However, only about 0.003% of the world's water supply is available as fresh water for human use, and this supply is unevenly distributed.

About 97% of the earth's total supply of water is found in the oceans and is too salty for drinking, growing crops, and most industrial purposes except cooling. The remaining 3% is fresh water, but over three-fourths of it is unavailable for use by plants, human beings, and other animals, because it lies too far under the earth's surface or is locked up in glaciers, polar ice caps, atmosphere, and soil. This leaves 0.5% of the earth's water available as fresh water in rivers, lakes, and economically recoverable underground deposits (groundwater) to a depth of 1,000 meters (1.6 miles). However, when we subtract the portion of this water that is highly polluted or too difficult and expensive to tap, the remaining supply amounts to about 0.003% of the world's water. To put this in measurements that we can comprehend, if the world's water supply were only 100 liters (26 gallons), our usable supply of fresh water would be only about 0.003 liter (one-half teaspoon).

That tiny fraction of usable fresh water still amounts to an average of 879,000 liters (232,000 gallons) for each person on earth. The supply is continually collected, purified, and distributed in the natural hydro-logic (water) cycle. This natural purification process works as long as we don't pollute water faster than it is replenished or add chemicals that cannot be broken down by bacterial action.

Surface-Water Runoff. The fresh water we use comes from two sources: groundwater and surface-water runoff. Precipitation that does not infiltrate into the ground or return to the atmosphere is known as surface water and becomes runoff – water that flows into nearby streams, rivers, lakes, wetlands, and reservoirs. This flow of water is renewed fairly rapidly (12 to 20 days) in areas with average precipitation. The land area that delivers runoff, sediment, and water-soluble substances to a major river and its tributaries is called a watershed or drainage basin. Surface water can be withdrawn from streams, rivers, lakes, and reservoirs for human activities, but only part of the total annual runoff is available for use. Some flows in rivers to the sea too rapidly to be captured, and some must be left in streams for wildlife and to supply downstream areas. In some years the amount of runoff is reduced by drought.

Упражнение 3.

(Парная работа) Выберите из текста Supply, Renewal and Use of Water Resources 10–15 ключевых слов. Определите, к какой части речи они относятся.

Упражнение 4.

(Парная работа) Передайте содержание Surface Water Runoff
в 5 предложениях.

Упражнение 5.

Вставьте предлоги: AT • IN • FOR • TO • OF • WITH.

1. Although they have normal motor activities, people suffering from somnambulism are not aware … their surroundings.

2. Contrary to what most people think, musicians are not particularly good … languages.

3. The virus responsible … Ebola fever comes from animal sources.

4. What he told the police is incompatible … the facts.

5. Satellite images are capable … detecting objects less than 15 cm across.

6. One of the effects of aspirin is to make patients less liable … heart attack and thrombosis.