A drainage basin (or catchment area) is an area of land which is drained by a river and its tributaries.
A watershed is the boundary separating one drainage basin from another. It usually follows the ridge or crest of a hill or mountain. River starts at the source, flows along its course and ends or drains into a lake or sea.
Trellis Pattern -Develop in an area where the rocks are made up of alternate bands of resistant and less resistant rocks, dipping in the same direction and lying at right angles to the main river valley. Tributaries flow along the less resistant rocks and join the river at right angles.
Radial Pattern -Develop on volcanic cones or hills with rivers flowing out from a central high point in all directions.
FACTORS affecting river process River velocity River volume RIVER ENERGY
The first rainstorm peaked at 30mm of precipitation. True/False 1.2 The second rainstorm peaked at 12 mm of precipitation. True/False 1.3 The discharge of the river peaked at 74mm. TrueFalse 1.4 The lag times were two hours and then four hours. True/False
1.5 The rising limb was steep in storm 1 because run-off over the hard, dry surface was quick. True/False 1.6 The falling limb was more gentle because water reached the river gradually through the ground, after the rain had stopped. True/False 1.7 The second discharge peak was higher because the second storm had more precipitation than the first. True/False 1.8 After the rain has stopped, vegetation, soil and ground water discharge the excess water quickly through ground stores and underground streams and rivers. True/False
Corrasion (abrasion) : - The river uses its load to grind against the bed and sides The action would dislodge the materials and carry them away This process operates in 2 ways (verticle--> depth; lateral--> width) Potholes are the product of corrasion
Attrition: The loosened materials that are being carried away collide against the river sides and bed and against one another Over time, they would become smaller and eventually reduced to fine particles called silt
Solution (corrosion ): - The solvent action of water dissolves soluble materials and carry them away in solution
Hydraulic action : - The breaking down of rocks Removing and dragging rocks from the bed and banks of the river by the force of the running water (like a water jet) Usually there are lines of weakness like joints and cracks in the river The work of hydraulic action forms plunge pools (small lakes)
Potholes : Circular depressions on the river bed Formed by corrosion (abrasion) Most effective in flood conditions Pebbles which are trapped in hollows on the river bed are swirled about in turbulent/ fast flowing water
Waterfalls: - Vertical flows of fast moving water flowing from great heights Formed by 2 ways: - Due to unequal resistance of rocks or faulting Unequal resistance- less resistant rocks are eroded more rapidly than resistant rocks As a result, there is a change in gradient By faulting- displacement of rocks results in a difference in height between 2 rocks, water plunges downwards
Plunge pools: A large depression at the foot of a waterfall This depression is deepened by hydraulic action of the plunging water Condition: likely to form when the water plunges into less resistant rocks It may be further enlarged by rock debris swirling about by turbulent water at the base
--> A floodplain is a low-lying plain on both sides of a river that has repeatedly overflowed its banks and flooded the surrounding areas. When the floods subside, alluvium is deposited on the floodplain. The larger materials, being heavier, are deposited at the river banks while the finer materials are carried and deposited further away from the river. The larger materials at the river banks build up into embankment called levees.
Meanders are loop-like bends in a river. The water flows round the meander in a spiral manner. This causes erosion to take place on the outer bank and deposition on the inner bank.
Gradually, a steep river cliff is formed on the outer bank, making it concave in shape. On the inner bank, deposition of alluvial materials produces a gentle slip-off slope and the bank takes on a convex shape.
--> A delta is a flat piece of land built-up from layers of sediments deposited by a river where it enters a lake or calm sea. The river may have to branch into smaller distributaries to carry the water to the sea.
Types of deltas Arcuate delta ---> triangular in shape e.g. Nile Delta Bird's foot delta ---> e.g. Mississippi Delta
Conditions that favour the formation of deltas A large load of sediment Shallow sea at the river mouth Sheltered coast with weak tides and currents Absence of large lakes along the course of the