Geography rivers

• Formation of potholes: Currents and turbulence of fast moving waters swirl pebbles and cobbles in the hollows of the river bed, drilling holes, forming potholes. The potholes get wider and deeper as more erosion occurs, and some may join together. As more potholes are formed and joined together, the river bed is deepened.
• Formation of waterfalls: Firstly, the soft rock erodes quicker than the hard rock, undercutting the hard rock and forming a plunge pool. This creates an overhang of hard rock which eventually collapses. Next, the overhang falls into the plunge pool, increasing abrasion, making the plunge pool deeper. As erosion continues to occur and this process repeats, the waterfall retreats upstream.
• Formation of meanders: Water flows fastest on the outside of the river bends, leading to erosion, which undercuts the riverbank, forming a river cliff. The river flows slowest on the inside of the river bends, leading to deposition. The deposits form a slip off slope. Deposition on one side and erosion on the other leads to the meander migrating across the valley.
• Formation of oxbow lakes: (formation of meander) This forms a meander neck, which gets narrower as more erosion occurs. During floods, the river may cut through the neck of the meander forming a straighter course for the water, causing the flow of water at the entry and exit of the meander to become slower, leading to deposition. As more material is deposited, the meander becomes cut off from the main river channel, forming an oxbow lake.
• Formation of floodplains and levees: Heavy rain leads to high discharge which causes the river to overflow its banks and flood surrounding areas. Once out of the channel, the wetted perimeter increases, so water encounters more friction, slows down, and deposition occurs. Larger and coarser material is deposited at the river banks first because it is heavier, forming the levee. Smaller and finer material is deposited further away because it is lighter, forming floodplains.
• Delta: When a river enters a larger body of water, it slows down, causing deposition. Gravel and sand are deposited first as they are heavier, followed by silt. Fine clay is transported by suspension and deposited further out. The saltwater causes the clay to flocculate, become heavier, and sink to the sea bed. As layers of alluvial material are deposited, it forms a platform which eventually rises above the water, which is the delta. Ss the main river channel in a delta gets silted up and its bed rises, water overflows its banks into different channels called distributaries.
• Hydrological cycle: An open cycle involving the continuous circulation of water in the earth-atmosphere system
• Evaporation: Heat from the sun causes water in water bodies to evaporate and rise through the air as water vapour
• Condensation: As water vapour rises, it cools and condenses into water droplets
• Precipitation: Water droplets gather to form clouds, which release water back into the earth's surface when they get too heavy
• Interception: The movement of water onto the earth's surface is interrupted by obstructions such as plants, buildings...
• Interception loss: Water is retained by plant surface and is later evaporated or absorbed by the plant
• Stemflow: Flow of intercepted water down the trunk or stem of a plant
• Throughfall: Water that flows through gaps in the vegetation
• Infiltration: Process which by some of the water that falls onto the ground seeps into the soil
• Percolation: Water flows through the soil and into underlying rock layers
• Surface runoff/overland flow: Water that does not infiltrate into the ground flows over the earth's surface down mountains and hills
• Transpiration: The movement of water from the soil to the atmosphere through plants
• Groundwater storage: A permanently saturated layer, where the upper layer is known as the water table
• Aquifers: Permeable rocks that store water
• Drainage basin: An area of land where water from rain or snow melt drains downhill into a body of water such as a river or lake
• Drainage divide/watershed: The line that seperates different areas that are drained by different river systems
• Tributaries: Smaller rivers that join a large river
• Confluence: Point where a smaller river branches into channels at a delta
• Floodplain: Land areas adjacent to rivers that often flood
• Source: Beginning of a river
• Mouth: Where the river empties its water
• Course: Path the river takes from source to mouth
• River discharge: Volume of water flowing through a point in the river at a given time
• Attrition: Rocks that are carried in the river collide against each other, making them smaller, rounder, smoother
• Abrasion: Rocks hit against the side and bottom of the river bed, dislodging rocks and carrying them away
• Corrosion: Acidic water (acid rain, carbonic acid) causes some types of rocks (limestone) to chemically react and dissolve
• Hydraulic action: Water and air are forced into cracks of rocks, causing them to break away
• Traction: Large rocks and material are rolled along the river bed
• Saltation: Rocks are bounced along the river bed
• Suspension: Lighter material being carried within the river flow
• Solution: Materials dissolved in water are transported along the river
• Long profile: Shows changes in the river gradient from source to mouth
• Cross profiles: Cross section of a river from one bank to another
• Soft engineering: Using the natural environment to prevent flooding