[Applause] [Music] please subscribe like and share it really helps us out and of course if you have any questions comment below and we will answer you as soon as we can [Music] welcome to another video in our series on igcse geography this is episode four in today's lesson we will be learning about rivers if you haven't seen our previous videos click on the card above [Music] water constantly cycles between the atmosphere and the earth's surface through a series of flows and stores the main flows are evaporation precipitation and rivers examples of stores are the sea glaciers and lakes when precipitation reaches the ground it gets into rivers in three ways direct flows straight from the atmosphere surface flow and flow through permeable rocks and the soil the area drained by a river and its tributaries is called the drainage basin or catchment the boundaries of the river basin or watershed separate one basin from another a river develops distinctive landforms as a result of erosion transportation and deposition the processes of river erosion are corrosion corrosion hydraulic action and attrition a river's load is transported by solution suspension saltation and traction depending on the size of the material a river's long profile or tall wake in its cross-section change from the river's source to its mouth moving downstream there is a decrease in the river's gradient an increase in water volume and an increase in the amount of sediment carried by the river these result in different processes and landforms developing in the river's upper middle and lower courses landforms in the upper cores form by erosion mainly potholing results in a v-shaped cross-section waterfalls retreat upstream leading a gorgeous result of headward erosion the river is small and inefficient so it is easily deflected by obstacles in its path this forms interlocking spurs [Music] in the middle course the river begins to erode sideways or laterally meanders begin to form the faster currents on the outside of the river bend undercut the bank forming river cliffs deposition takes place on slip-off slopes found on the inside of meanders where the current is slower the cross-section becomes asymmetrical the main features of the lower course are a broad shallow flood plain with oxbow lakes and levees the river enters the sea through an estuary or a delta deltas occur where a river splits into a series of distributaries this happens if the river flows into a sea where there are no strong tides or currents or if the river is carrying large amounts of sediment [Music] now let's look at flooding rivers flood when their discharge or flow is greater than the channel can cope with this often occurs when there is a large increase in precipitation or during spring snowmelt the river regime shows the seasonal variations in a river's flow the link between precipitation and discharge is shown in a flood hydrograph flooding is more likely when precipitation is heavy and intense if the soil is saturated water will run off quickly into rivers flooding is less likely if the main rock types are porous or permeable human actions can increase flood danger floodplains have dense populations because the fertile alluvial soils are good for farming and the river can be used for irrigation the flatland encourages industry and settlement the building of roads and houses increases surface runoff deforestation also increases surface runoff the impact of floods can be reduced by flood preventative measures these minimize runoff and use reservoirs to store excess water flood water can be confined to rivers by embankments and relief channels excess water can be removed by increasing the flow rate for example by widening deepening and straightening the river channel lastly let's look at human activities the most effective management of rivers is by a whole basin approach in addition to flood control measures irrigation and navigation can be improved dams and reservoirs can be used to generate hydro electricity as well as providing opportunities for recreation and leisure the upper parts of a river basin are used for sheep farming quarrying and water storage high precipitation and narrow valleys are suitable for dam and reservoir construction the slopes of the valleys can be forested there are greater opportunities for agriculture and industry further downstream estuaries are favorable sites for industry as they allow import and export facilities and in the flatland is suitable for building often there are large areas of mud that can be reclaimed and used for large industrial sites check out the description below we have included a quiz with answers to test your knowledge let's see how well you do thank you for watching our video please like subscribe and share and comment below so we can clarify things for you [Applause] you