Rivers and Environments Chapter 10 PDF

# Rivers and Environments ## Chapter 10 ### A Cleaner River The Singapore River that we see today is vastly different from that in the early 1970s. The river then was badly polluted and littered with rubbish. It was only after the clean-up campaign organised by the government from 1977 to 1987 t...

# Rivers and Environments ## Chapter 10 ### A Cleaner River The Singapore River that we see today is vastly different from that in the early 1970s. The river then was badly polluted and littered with rubbish. It was only after the clean-up campaign organised by the government from 1977 to 1987 that the Singapore River becomes what we know of today. #### You Will Learn * To describe the features along a river course * To identify river features on topographical maps * About the positive and negative impact of rivers on people * To examine the interrelationship between River Nile and human activities (Special/Express streams only) ___ ## Environments ### Distribution of water on the Earth Almost three-quarters of the Earth's surface is covered with water. However, 97 percent of the water on the Earth's surface is salt water contained in the seas and oceans. This salt water cannot be used for drinking or for industrial purposes unless it is processed. The remaining 3 percent of the Earth's water is fresh water. Even then, 70 percent of this fresh water is frozen in the form of glaciers and ice sheets. Glaciers are huge masses of snow and ice in mountainous areas. Antarctica contains most of the world's fresh water. The remaining amount of fresh water is contained underground and on the surface of the Earth. Only 1 percent of the Earth's fresh water is contained in streams, rivers and lakes. Fresh water is very important to people. People use fresh water for drinking, farming, industry and other activities. In fact, many civilisations, some dating back thousands of years, began along rivers. For example, ancient Egyptian civilisation started along the banks of River Nile. The Egyptians have depended on River Nile for survival for the past 3 000 years. ### The Hydrologic Cycle Water is continuously moving from the Earth's surface into the air, and from the air back onto the Earth's surface. This continuous movement of water is called the hydrologic cycle, or water cycle. Water exists in three states: solid, liquid and gas. In the hydrologic cycle, water goes through a cycle of changes in these states. Water also moves from one part of the Earth to another through the hydrologic cycle. During the day, the Sun heats up the surface of the Earth and changes some of the water from the oceans, lakes, rivers and ground into water vapour. This process is called evaporation. Plants also give out water vapour into the air through their leaves. This process is called transpiration. When warm air rises, the water vapour in the air is carried up in it. As the warm air rises, it cools. As a result, the water vapour in the saturated air changes into very small water droplets. This process is called condensation. ___ ## The River System A river is a body of water flowing in a channel. The place at which a river begins is called the river source. This is usually found in mountainous areas or the highlands. The source may be melting snow from the top of a mountain, or a lake with a stream flowing out from it. Due to the pull of gravity, a river flows downhill from its source. The path which the river flows along is called the river course. As a river flows along its course, other streams or rivers may join it. The streams and rivers that join a main river are known as its tributaries. The river ends when it flows into a lake or sea. This part of the river is called the river mouth. The main river and its tributaries form a river system. This system can be compared to a tree. Just as the branches and the trunk make up the frame of the tree, the main river and its tributaries make up the river system. ### The Drainage Basin Rivers 'drain' the surrounding land by collecting the surface runoff and directing it to the lakes and seas. The area that is drained by a river and its tributaries is called the drainage basin. The boundary of a drainage basin is marked by the tops of the surrounding highland and is known as a watershed. The watershed is an imaginary line that separates one drainage basin from another. This is why the watershed is also known as a divide. ### Features formed by Rivers A river is powerful as it shapes the land over which it flows. Through erosion, it is capable of creating features and changing its surroundings. Let us now learn about a few common features that are formed by rivers. #### Valleys One common feature formed by the action of rivers is a valley. A valley is a low area between hills or mountains. An example of a valley is the Grand Canyon in northeast Arizona, the United States of America. #### Waterfalls A waterfall is a vertical flow of fast-moving water falling from a great height. It usually forms when a river flows over a horizontal layer of hard rock overlying soft rock. The soft rock is eroded more quickly than the hard rock. A ledge is formed over which the water falls. #### Meanders As a river flows over flat land, it forms curves and bends which become more and more noticeable along the river course. These bends are called meanders. Meanders are formed when the river erodes sideways and deposits the sediments it carries on the opposite banks (or sides) of the curves. #### Floodplains As a river flows through a flat valley floor, it deposits most of the sediments it is carrying. As a result, the river bed, or the bottom of the river, is raised. Whenever it rains heavily, the river will overflow its banks and flood the surrounding low-lying land. This land is called a floodplain. #### Deltas At the river mouth, the river deposits its sediments into a lake or sea. There, the sediments build up slowly and obstruct the flow of the river to the sea. When this happens, the river has to flow along alternative channels called distributaries. Remember that tributaries join a river whereas distributaries branch out from a river. Where layers of sediment have been deposited at the river mouth, a delta is formed. A delta will form only under certain conditions. First, a river must be carrying a large amount of sediment. Second, the waves along the coasts must not be so strong that they remove the sediments faster than the river can deposit them. Over time, the delta grows upwards and outwards, and pushes the coastline farther out to sea. Deltas come in various shapes and sizes. The Nile Delta of Egypt is an example of a fan-shaped delta. ___ ## Identifying River Features on Topographical Maps River features are represented on topographical maps using contours and symbols. ### Valley - The contours are closely spaced and are bent towards the highlands in the shape of a 'V'. Usually, a river runs down the middle of the 'V'. ### Delta - A delta can be found at the river mouth, where the river branches into distributaries. ### Floodplain - A floodplain can be identified by the widely spaced contours next to a river. The land is very low too. ### Meander - The meander of a river is easily identified by its bend. ### Waterfall - Waterfalls are represented on maps with the symbol: W ___ ## How Do Rivers Affect People? We have seen the power of rivers in changing the Earth's surface. Now, we will look at how rivers affect people and their activities. ### Positive Impact Of Rivers #### Water Supply For Farming - Rivers are an important source of water for growing crops. As much 70 percent of the world’s fresh water from rivers and lakes is used in growing crops, such as rice and vegetables. For example, the water in the Chao Phraya River in Thailand has enabled the growing of rice on a large scale. Singapore buys a lot of rice from Thailand, we should be thankful for that river! - In areas which receive little rain, fresh water from a river is sometimes channelled to provide water to farms. This method of supplying water to farms through man-made canals is known as irrigation. In Israel, such a method has enabled fruits and vegetables to be grown even in the desert! #### Fertile Soil For Farming - When a river floods its banks, it deposits sediments that help to increase the fertility of the soil. Thus, farmers are attracted to plant their crops along the river course where flooding occurs frequently. The Ganges Plain along the Ganges River in India is one such example. #### Water Supply For Industry - It is estimated that 23 percent of all water drawn by people is used in industries. The industries use water for various purposes, such as for cooling machines to prevent overheating and for the manufacture of food products. #### Recreation and Tourism - Rivers can also be used for recreation. Recreational activities that take place at rivers include rafting, canoeing and fishing. Like landforms, rivers beautify a place, making it a tourist attraction. That is why many hotels and resorts are built alongside rivers. - The Singapore River, for example, is a popular tourist attraction because it forms an important part of Singapore's history. The river is also used for dragon boat races during the annual Singapore River Regatta where over 2 000 participants meet to compete. ### Negative Impact Of Rivers #### Loss Of Lives and Property - Flooding occurs when the water in a river overflows its banks. Floods can take lives and cause serious damage to property and crops. For instance, the flooding of the Ganges River in Bangladesh during August and September 1988 affected 80 percent of the country. It was estimated that 25 million people made homeless, and rice crops thousands of kilometers of roads were destroyed. As a result, it was nearly impossible to deliver food and medical supplies to the victims. - A river floods easily when it carries a lot of sediments. As the sediments are deposited along the course, the river bed is raised. This in turn causes the water level of the river to rise. Hence, whenever it rains heavily, the river overflows its banks and floods the surrounding land. For example, the Yellow River in China regularly overflows its banks during heavy rains because it carries lot of sediments. As a result, towns and cities along the Yellow River that do not have proper flood-control measures face the risk of losing lives and property ___ ## Case Study: River Nile Rivers are important to many civilisations because they provide fresh water. One of the most important rivers that has sustained the lives of millions of people since ancient times is River Nile in Africa. River Nile got its name from the Greek word neilos, meaning ‘river valley’. At 6 695 kilometres long, River Nile is the world’s longest river. It is almost 900 times longer than the Singapore River! River Nile begins its flow from near the middle of Africa and ends in the Mediterranean Sea north of Africa. When River Nile flows into the sea, sediments build up at the river mouth to form the Nile Delta. River Nile and its three tributaries – the White Nile, the Blue Nile and the Atbara – flow through ten countries. The ten countries are Tanzania, Congo, Burundi, Rwanda, Kenya, Uganda, Ethiopia, Sudan, Eritrea and Egypt. Out of these ten countries, Egypt depends most heavily on River Nile. Since Egypt is a dry country which receives hardly any rainfall, almost all the water the people of Egypt need comes from River Nile. The parts of the desert near River Nile flourish with life thanks to the water from the river. Let us now look at how important River Nile is to people living along its banks, and how people have made changes to it. ### Uses Of River Nile The drainage basin of River Nile makes up approximately 10 percent of the African continent. All the countries drained by River Nile depend on its water for various purposes. #### Fertile Land For Farming Every year, from June to October, River Nile floods the surrounding land along its banks at the lower course of the river. When it floods, sediments are deposited onto the land, making the soil fertile for farming. As the lower course of River Nile is located in Egypt, its annual flooding has benefited the people of Egypt greatly. Hence, for t e past 3 000 years, people in Egypt have chosen to live along the banks of River Nile mainly because they can grow crops on the fertile land. #### Source Of Food People depend on River Nile as a source of food. Fishing is the main human activity in some countries, such as Tanzania and Congo. Lake Victoria, one of the main sources of River Nile, provides fish for the countries around the lake. #### Means Of Transport River Nile has always been an important transport route for the people living along the river. People travel along River Nile by boats, commonly known as feluccas. A felucca is a long, narrow boat moved by sails or oars, or both. People also use River Nile to transport goods, such as bricks and sugar cane, to the marketplace. #### Source Of Water As the settlements along River Nile grew, more land was needed to grow food crops. Thus, the people decided to grow crops in areas beyond the banks of River Nile. However, since the areas farther from River Nile are very dry, the people built canals to direct water from the river to the farms. For example, in the early 1900s, the people built a network of canals in Egypt to direct the flow of the water from River Nile. This network of canals irrigates about 4 050 square kilometres of land. People have also built dams along River Nile to control the supply of water. Water is stored in reservoirs behind the dams. This water is then released when needed by the people, especially in times of drought. One of the more successful dam projects is t e Aswan High Dam in Egypt, which was built in 1970. Let us now learn more about the Aswan High Dam. #### The Aswan High Dam The Aswan High Dam in Egypt is an important dam for the people in Egypt because it provides them with a steady supply of water throughout the year. Although the Aswan High Dam has brought many benefits for t e Egyptians, it has also brought some problems. The table on the following page summarises the benefits and problems brought about by the construction of the Aswan High Dam. ### Benefits and problems brought about by t e construction of the Aswan High Dam #### Benefits Of The Aswan High Dam * **Steady supply of water** The reservoir behind t e dam stores water. During t e dry season, t e water in t e reservoir is released to increase t e amount of water flowing in t e lower course of River Nile. * **Availability of hydroelectric power** The Aswan High Dam is used for generating hydroelectric power. The number of people living in Egypt increased from 25 million in 1960 to 50 million in 1987. This caused t e country’s need for electricity to increase. * **Travelling along River Nile** Before the Aswan High Dam was built, boats could not travel along River Nile during the annual flood. * **Since water is now made available throughout the year, farmers living along t e lower course of River Nile no longer have to depend on t e annual flood for water to irrigate their crops.** #### Problems Caused By The Aswan High Dam * **Loss of soil fertility** The sediments and nutrients t at flow from t e sources of River Nile are now trapped in t e reservoir behind the Aswan High Dam. This causes t e soil in areas along t e lower course of t e river to become less fertile. * **Decrease in the supply of fish** At t e mouth of River Nile is t e Nile Delta. The delta provides not only fertile land for farming, but also nutrients for t e fish living in t e Mediterranean Sea. * **Loss of land for farming** Water and fertile soil are essential for farming. After the building of t e dam, t e volume of water in River Nile is reduced. This, coupled with less sediments being deposited at the Nile Delta, has decreased the area of land available for farming. ___ ## Rivers Of Life Rivers bring life to places and people. In Singapore, we are more fortunate than many people in Egypt because we are not as dependent on rivers for our daily activities. However, we too have a limited supply of potable water. If our consumption and usage of water increase, or if we face a prolonged period of dry weather, we may face water shortage. Through studying how people in other places are dependent on rivers, let us keep in mind how precious water is in our country and take care not to waste it. ___ ## What It Means * **Condensation** is the process through which water vapour in the saturated air changes into very small water droplets. * **A delta** is formed where layers of sediment are deposited at the river mouth over time. * **A distributary** is an alternative channel that branches out from a river at the river mouth. * **A drainage basin** refers to the area that is drained by a river and its tributaries. * **Evaporation** is the process through which water from the oceans, lakes, rivers and ground is changed into water vapour. * **A floodplain** is low-lying land that becomes flooded when a river overflows its banks. * **The hydrologic cycle** is the continuous movement of water from the Earth's surface into the air, and from t e air back onto t e Earth's surface. * **A meander** refers to a curve or bend in a river. * **Rainfall** refers to the amount of rain that an area receives over a period of time. * **The river mouth** is the place where the river ends its flow, usually at a sea or lake. * **The river source** refers to the place at which a river begins. * **Runoff** refers to the water that does not seep into the ground but flows on the surface from highlands to lowlands. * **Transpiration** is the process through which plants give out water vapour into the air through their leaves. * **A tributary** is a stream or river that joins a main river. * **A valley** is a low area between hills or mountains. * **A waterfall** is a vertical flow of fast-moving water falling from a great height. * **A watershed** is an imaginary boundary of a drainage basin, marked by the tops of the surrounding highland. ___ ## Got It Covered **Water On The Earth** * **Formation** * **Hydrologic Cycle** * 97% salt water in seas and oceans * **Distribution** * 3% fresh water * **How Rivers Affect People** * **Positive** * water supply for farming * fertile soil for farming * water supply for industry * recreation and tourism * source of drinking water and food * production of hydroelectric power * means of transport * **Negative** * floods - loss of lives and property * **Case Study Of River Nile** * **Aswan High Dam** * **Benefits** * steady supply of water * availability of hydroelectric power * travelling along River Nile * **Problems** * loss of soil fertility * decrease in the supply of fish * loss of land for farming * **River Features** * **Valley** * **Waterfall** * **Meander** * **Floodplain** * **Delta** * **River System** * **River Source** * **Tributary** * **River Mouth** * **Distributary** * **Drainage Basin** * **Watershed**