Freshwater Flashcards
Drainage basin
The total area drained by a river and its tributaries
Why is the drainage basin an open system?
Because water can enter the system via precipitation and also leave, moving across the watersheds of multiple drainage basins. Matter can leave the drainage basin.
Inputs, outputs and flows of drainage basin
Input: precipitation
Flows/transfers = infiltration, throughflow, groundwater flow, percolation, base flow
Outputs: Evaporation, transpiration
Stores
Vegetation Aquifers Soil Cyrosphere groundwater
Definition of precipitation
Transfer of moisture from the Earth’s atmosphere to the earth’s surface in the form of rain, hail, sleet, snow.
Definition of interception
The capture of raindrops by plant cover that prevents direct contact with the soil. If rain is prolonged, retaining capacity of leaves will be exceeded and water will drop to the ground (through fall)
Evaporation is a function of…
- Vapour pressure
- Air temp
- wind
- rock surface - bare rocks have greater evap rates
Potentail evapotranspiration
The water loss that would occur if there was an unlimited supply of water in the soil for use by vegetation.
Discharge definition + units?
The total volume of water flowing past a certain point per unit of time (cumecs)
Bradshaw model characteristics
Discharge increases Load size decreases Load angularity decreases Load amount increases Roughness decreases gradient decreases
5 river transport ways
Floatation - leaves and twigs carried on the surface of the river
Saltation - Heavier particles bounce or bump along the river bed
Attrition - particles collide with each other, becoming smaler and rounder
Solution - chemical ions are removed, dissolving particles in water
Traction - boulders are rolled along river bed
Factors affecting erosion
Rock type Vegetation Precipitation intensity Gradient Channel density Discharge Load angularity pH Urbanization
Explain the 4 types of erosion
Attrition - particles collide with each other, becoming smaller and rounder
Abrasion - particles scrape against river bed and banks and wear them away due to the friction
Hydraulic action - force of water directly weakens the rock or gets into cracks.
Solution - removal of chemical ions which dissolves rock
‘Capacity of a stream’ definition
The largest amount of debris a river can carry
‘Competence of a river’ definition
The diameter of the largest particle that can be carried.
Critical erosion velocity
The lowest velocity at which grains of a given size can move
Hjulstrom curve shows the relationship between…..
Debris diameter and velocity
3 main points about Hjulstrom curve
- Smallest and largest particles require high velocities to lift them (smallest is clay but requires big velocity because it is cohesive)
- Higher velocities required for entrainment than for transport
- When velocity falls below a certain level, deposition occurs
Factors affecting regime of a river (variation in the flow)
- Intensity of precipitation
- Porosity and permeability of rocks
- Amount of vegetation cover
Waterfall formation
- There are alternating layers of hard and soft rock
- Soft rock is more easily eroded than hard rock due to hydraulic impact
- This leaves the hard rock undercut
- It eventually collapses into a plunge pool due to lack of support by soft rock
- Abrasion occurs here, causing the waterfall to retreat.
- A gorge is formed
3 situations when deposition likely to occur?
- River floods
- River enters sea
- River enters behind a dam
Formation of a floodplain
They are flat areas found in the lower course, comprising of silt, clay and alluvium. Fertile lands.
Formation of levees
- When a river floods, it loses its velocity and thus energy and has to deposit some of its load
- It deposits the coarsest, heaviest material first
- This forms raised banks called levees at the edge of the river
- Build up over time as more deposition occurs
Factors affecting the formation of a delta?
- Salinity (salt makes particles more cohesive)
- size of load
- vegetation
- gradient of coastline