Channelisation Key terms: 1. Uses Re‐alignment Transpiration Evaporation 2. E.gs Re‐sectioning Condensation Precipitation Drainage Basin 3. Ltms Bank Protection E.g. Dyes Infiltration Surface Runoff Watershed Vegetation Planting Ways to Hydrologic Parts of a River manage Cycle ‐River Source Upper rivers ‐Tributaries Waterfall, Gorge Valley River ‐River Mouth Formation of Middle River features Rivers System ‐Distributaries Meanders Courses of a River Lower River ‐Upper Meanders, River Energy ‐Middle Floodplains, Deltas Processes Volume of Flow ‐Lower ‐Duration of Speed of Flow Erosion Transportation Deposition Rainfall ‐ Gradient ‐Amount of ‐ Roughness of Hydraulic Traction Loses energy Rainfall river bed and action deposit Saltation ‐ Size of drainage bank load (heavier Attrition basin Suspension first, then ‐ Depth of riverAbrasion lighter load) ‐Type of soil Solution ‐ Wetted Solution ‐ vegetation cover perimeter
1.2 River Processes (Erosion)• Erosion (Hydraulic Action)Force of fast‐moving water surges into cracks & joints & breaks and loosens pieces of rocks and soil along river bed and banks.
1.2 River Processes (Erosion)• Erosion (Corrasion/ Abrasion)Rock fragments dragged along river bed or against river banks grind against channel walls. As a result, the river channel widens and deepens.
1.2 River Processes (Erosion)• Erosion (Attrition)Rock fragments and other materials carried by water collide with one another and break down into smaller pieces over time. Rough edges of large rocks get smoothened out.
1.2 River Processes (Erosion)• Erosion (Solution)Rainwater dissolve carbon dioxide in the atmosphere forming carbonic acid. As rainwater falls into rivers, the carbonic acid dissolves minerals in rocks on river beds and banks to form a solution. E.g. Limestone areas
1.4 River Processes (Transportation)• Transportation (Traction)Larger‐sized materials such as boulders, pebbles & gravel roll and slide along the river bed as they are too heavy to be lifted by river water.
1.4 River Processes (Transportation)• Transportation (Saltation)Smaller materials such as coarse sand particles, get lifted up and dropped onto the river bed over and over again as they are too heavy to be suspended all the time.
1.4 River Processes (Transportation)• Transportation (Suspension)Finer particles such as silt, clay & sand are carried along the river without touching the river bed by the turbulent flow of water. These form the greatest proportion of the river’s load & gives the river a murky appearance.
1.4 River Processes (Transportation)• Transportation (Solution)Minerals found in the rocks are dissolved by river water and carried downstream.
1.4 River Processes (Deposition)• Deposition – When a river does not have enough energy to either erode or transport its load put down/ deposit its load. – Factors causing Deposition: 1. Period with low precipitation Reduced River Volume 2. A river enters a lake or sea Reduced River Speed 3. A river flows along shallower side of river channel increased friction reduced River Speed 4. Sudden increase in load due to landslide, etc. 5. River channel is obstructed by aquatic plants or protruding bed rocks Reduced River Speed
1.5 River Energy e rg y r En R ive Volume (m3)As a river’s speed increases, its energy increases.As a river’s volume increases, its energy increases too.
1.5 River EnergyFactors affecting River Speed1. Gradient of channel2. Roughness of channel3. Wetted perimeterFactors affecting River Volume1. Size of drainage basin2. Presence of vegetation3. Permeability of rocks4. Climate
1.5 River Processes Factors affecting River Speed1. Gradient of Channel St ee p Gr Gen ad tle ie Gra nt die n t• Steep river gradient Greater gravitational pull Increased speed• Gentle river gradient Lesser gravitational pull Decreased speed
1.5 River Processes Factors affecting River Speed2. Roughness of Channel Rocks, boulders, vegetation Rough Channel Gentle Channel• Rough river channel more obstacles More friction Decreased speed• Gentle river channel less obstacles Less friction Increased speed
1.5 River Processes Factors affecting River Speed3. Wetted Perimeter: Part of river channel that is in contact with river waterSmall wetted perimeter Large wetted perimeter• Large wetted perimeter More channel area in contact with water More friction Decreased speed• Small wetted perimeter Less channel area in contact with water Less friction Increased speed
1.5 River Processes Factors affecting River Volume1. Size of drainage basin Large Small• Large drainage area More surface area to collect rainwater Increased volume• Small drainage area Less surface area to collect rainwater Decreased volume
1.5 River Processes Factors affecting River Volume2. Presence of Vegetation Dense vegetation Sparse vegetation• Dense vegetation increases interception of rain less surface runoff & more infiltration Smaller volume• Sparse vegetation decreases interception of rain more surface runoff Larger volume
1.5 River Processes Factors affecting River Volume3. Permeability of rocks Permeable rocks Less permeable rocks• Area of permeable rocks higher infiltration less surface runoff Lower volume• Area of less permeable rocks lower infiltration more surface runoff Higher volume
1.5 River Processes Factors affecting River Volume4. Climate – Area with distinct wet and dry seasons • River volume fluctuates – Dry areas • Low river volume throughout the year – Hot and wet equatorial areas • High river volume throughout the year
Stages of stream development: a youthful stream, mature stream, and old age stream .
The Life of A River Every river has its way,From Upper, Middle, and all the way, To the Lower courses of its end, It Erodes, Transports, then Deposits, Forming beautiful river landforms, Waterfalls, Valleys and Gorges,Meanders, Floodplains, along the way, Finally, ending its journey in a delta way.
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