6The Upper Courseis the highest section which is found in the mountains or hillsHere the river erodes a v-shaped valley, the path is fairly straight and it flows downhill steeplyThe landforms that are common in this course of the river are waterfalls and gorges
7V-shaped valleysWith time the river directs its energy into eroding the valley laterally. The whole process then repeats itself.The river uses its load to cut down into the bedrock causing vertical erosion.Loosened material is washed into the river increasing the load and therefore the ability to erode.
12In its upper stage theriver erodes verticallyrather than laterally.Interlocking spurs areridges producedwhen the young rivertwists and turns roundobstacles of hard rockalong its downwardpathway.These ridges interlockwith one another likethe teeth of a zip fastener
13Interlocking spurs (Lake District) Slopes attacked by weatheringV-shaped valleyEroded materials transported by riverRiver erodes downwards (vertical erosion)Interlocking spursGravity and rainwater move material downwards (slope transport)River source
25The Middle Coursethe gradient that the river flows down is less steep, the river begins to meander and the valley sides are also less steep.Common landforms here are a wider river valley – slightly U shape, meanders
28The genesis of a Meander Pool……are areas of deeper water where the flow of water is convergent. In a pool the erosion is greater due to reduced friction.Riffle……An area of a river which is wide and shallow, with the water flowing over a pebble bed with protruding rocks. Friction is high due to the shallow depth and rough bed.
40Floodplain formationFloodplains and levees are formed by deposition in times of river flood. The river’s load is composed of different sized particles. When a river floods it deposits the heaviest of these particles first. The larger particles, often pebble-sized, form the leveés. The sands, silts and clays are similarly sorted with the sands being deposited next, then the silts and finally the lightest clays. This deposition makes up the floodplain.
41This is a cross section of a meander bend This is a cross section of a meander bend. Sketch the diagram and mark on the following:river clifffastest velocityslip off slopeundercuttingarea of deposition
43Landforms are primarily caused by: processes of erosionprocesses of depositiona mixture of erosion and depositionWhich of the following landforms are the result of a mixture of erosion and deposition?deltasmeandersfloodplainswaterfallsleveésoxbow lakesrapidsv-shaped valleysinterlocking spurs
45The Lower Coursehas the gentlest slopes - both in long profile and across the valley floorThis almost flat land is known as the flood plain.The river may have very large meanders and ox-bow lakes. TThe mouth of a river is when it reaches open water - either a lake or the sea.Under certain conditions a delta can be found here
46Oxbow lakes new course of the river Meander neck becomes smaller When the river floods it breaks through the thin meander neck and the river takes the easier, straight course. This leaves the meander loop ‘cut off’ as an oxbow lake. Over time, the oxbow lake will become colonised by vegetation.new course of the riverMeander neck becomes smalleroxbow lake
47Types of FlowLaminar Flow - at low velocities the fluid particles follow the streamlinesTurbulent Flow - at higher velocities the flow breaks up into a fluctuating velocity pattern or eddies
48Types of Rivers Perennial Rivers – flow all year round Permanent RiversExotic RiversNon Perennial Rivers – flow in rainy seasonPeriodic RiversEpisodic Rivers
50Exotic Rivers Flow all year round Reflect the characteristics of sourceNot of the region they are flowing throughNile River flows all year yet it runs through a desert region – source is the Ethiopian HighlandsOrange River also flows through driest areas of South Africa – source is the Drakensberg
51Episodic Rivers Flow only after an episode of rain After a thunderstorm a river may only flow for a few hoursA river may flow for a few days or weeks after an extended episode of rainFor much of the year, the Fish River is barely a stream, and in parts it dries up completely. When the short wet season arrives, however, torrential rains run off the rock-hard soils. In a few hours the river swells into a raging torrent
52Periodic Rivers Only flow after a period of rain Is a seasonal flow – winter, summerRivers may flow for 3 to 6 months
54The Flood PlainThe Flood Plain is a flat region of a valley floor located on either side of a river channelA floodplain is built of sediments deposited by the river that flows through it and is covered by water during floods when the river overflows its banks.Floodplains tend to develop on the lower and less steep sections of rivers.
55Meandering and Braided Streams River channels in floodplains form two kinds of patterns: meandering and braidedMeandering rivers consist of a single main channel that bends and loopsBraided rivers have numerous distinct channels that repeatedly divide and then merge again downstream
56Oxbow LakesIn meandering rivers, sediment is eroded on the outside of bends (undercut banks) and deposited on the inside of bends (slip off slope)Over time, this causes meander loops to migrate downstreamIf the movement of one meander loop overruns the next one downstream, then a meander cut-off is formedThis causes the course of the channel to be shortened as the two meander loops joinThe abandoned meander loop is gradually isolated as sediment is deposited at each end by the water flow in the main channel. This process eventually leads to the creation of an ox-bow lake
60DeltasDelta (geologic formation), deposit of soil or silt formed wherever a swift stream or river empties into a lake, ocean, or slower river, so called because its triangular shape resembles the Greek letter (delta)The triangular shape and the great width at the base are due to blocking of the river mouth by silt, with resulting continual formation of distributaries at angles to the original course. Deltas are usually characterized by highly fertile soil
61Requirements for the formation of a Delta Constant supply of silt and sandShallow lake or seaLittle or no tidal action, wave action or current action
62Types of Deltas Arcuate delta – Nile river Cuspate delta – Elbe River Bird’s Foot delta - MississippiEstuarine delta -
72Stream OrderHierarchical ordering system based upon the degree of branching(A second-order stream is formed by the joinig of two first order-streams; the junction of two second-order streams forms a third order stream
75The peak rainfall is the time of highest rainfall The peak rainfall is the time of highest rainfall. The peak discharge (the time when the river reaches its highest flow) is later because it takes time for the water to find its way to the river (lag time) .The normal (base) flow of the river starts to rise (rising limb) when run-off, ground and soil water reaches the river.Rock type, vegetation, slope and situation (ie is this an urban river?) affect the steepness of this limb. The falling limb shows that water is still reaching the river but in decreasing amounts.The run-off/discharge of the river is measured in cumecs - this stands for cubic metres per second. Precipitation is measured in mm - this stands for millimetres.