Please enable JavaScript.
Coggle requires JavaScript to display documents.
Factors Influencing Fluvial Processes - Coggle Diagram
Factors Influencing Fluvial Processes
Natural Factors
Channel Roughness
Channel roughness is determined by bed and bank materials
Bed and banks which are composed of fine and cohesive materials cause less frictional drag between the moving water and channel bed and banks than large, angular rocks
Rougher channels cause a lower velocity flow
Channel Gradient
Local Influence
Influences flow velocity
A steeper channel gradient causes a higher velocity flow
Higher river velocities allow greater potential for erosion through hydraulic action
Higher river velocities increases channel competence, which allows transportation of coarser materials that increases chances of attrition and abrasion.
Only applies locally: downstream flows generally have higher velocity than upstream flows irrespective of channel gradient
due to
Increased discharge
Improves hydraulic radius, increasing channel efficiency to overcome frictional drag
Increased channel cross-sectional area
Reduced channel roughness downstream due to fining of particles, reducing frictional drag
Climate
Global/Regional Influence
Influences Discharge
Humid Tropics: intense rainfall (inputs) increases discharge
Seasonal Climates (Am/Aw): Variable precipitation (inputs) across seasons lead to seasonal changes in discharge
Geology
Influences both discharge and sediment regime
Local Influence
Discharge
Geological composition of basin affects infiltration capacity, which therefore affects the river's discharge as more water percolates vs surface flows
Drainage Basin with Impermeable Rocks (e.g. shale, granite)
Percolation into sub-surface is inhibited
Most water flows through surface flows, which increases discharge
Drainage Basin with Permeable Rocks (e.g. Limestone)
Percolation is encouraged due to presence of well-developed joint systems/bedding planes (high secondary permeability)
Most water flows through riverbed, decreasing discharge
Sediment Regime
Geological composition of channel affects its susceptibility to erosional processes
Soft, unconsolidated rocks like sand and gravel are easily eroded
Amount of sediment river is carrying (river's load) affects processes
Highly cohesive materials like silt and clay are more resistant to erosion
Human Factors
Influence discharge, river load and channel characteristics
Discharge
Human changes to landuse in the drainage basin can alter flow processes and therefore the inputs into and discharge of a river
Construction of dams affects discharge, either through withheld water that reduces discharge or releases of water that increases discharge
River Load
Deforestation or mining activites may loosen topsoil, increasing erosion during rainfall events. This causes excessive sedimentation, increasing the river load
Sand mining for land reclamation removes sediment from the river channel, reducing river load
Channel Characteristics
Channelisation of rivers concretises banks, precluding any downcutting or lateral erosion
Bradshaw Model
Lane's Balance Diagram