Unit 1, hydrology and fluvial geomorphology Flashcards
Outputs of the drainage basin
Transpiration, evaporation, river channel flow.
Inputs of the drainage basin
Precipitation.
Stores of the drainage basin
Interception, surface storage, soil moisture storage, groundwater storage, channel storage.
Flows of the drainage basin
Overland flow, infiltration, percolation, throughflow, groundwater flow.
Components of hydrographs
Discharge, rising limb, falling limb, peak discharge, lag time.
Discharge definition
Amount of water passing every second.
Rising limb definition.
The rapid increase in resulting from rainfall causing overland flow.
Falling limb definition
When discharge decreases and the river’s level falls.
Peak discharge definition
Time of the highest river channel level.
Lag time definition
The amount of time between the peak amount of rainfall and the peak discharge in the river.
Influences on hydrographs
Shape of the drainage basin, heavy storms, snowfall, vegetation, rock type, deforestation, afforestation, urbanisation, reservoirs, agriculture.
How does climate and temperatures affect a storm hydrograph?
Hot, dry conditions and cold, freezing conditions result in hard ground, reducing infiltration and increasing surface runoff, this leads to a reduced lag time and peak discharge. High temperatures can also increase evapotranspiration, reducing the amount of water reaching the river channel and peak discharge.
Drainage basin characteristics
Size, shape, slope, rock type, soil type, drainage density, rainfall type and rainfall intensity.
Basin size
A large drainage basin will mean that water takes a long time to travel through tributaries or the ground to reach the channel.
Basin Shape
Circular basins mean shorter lag times and higher peak discharges and elongated basins, longer lag times and lower peak discharges.
Slope
A steeply-sided river valley means that gravity assists water in its descent towards the river channel, whereas gently sloping valleys tends to produce longer lag times and lower peak discharges.
Rock type
Permeable rocks such as chalk and limestone infiltrate water so longer lag times and lower peak discharges, and impermeable rocks such as granite and clay allow water to continue to move so this results in shorter time lags and higher peak discharges.
Soil type
Sandy soils have high rates of infiltration due to relatively large air spaces or voids between soil particles, whereas clay soils and silts have small pore spaces which allow very little throughflow.
Drainage density
Basins with impermeable rocks and soils are those with a high drainage density, whereas basins with permeable ones are those with a low drainage density.
Rainfall type
Snow intercepts water, long periods of rainfall leads to soil saturation and therefore overland flow and a basin with lots of vegetation will experience high rates of interception so therfore there would be a longer lag time and a lower peak discharge.
Rainfall intensity
Heavy rainfall may exceed the infiltration capacity of the soil, leading to surface runoff and a rapid increase in discharge.
Channel processes
Erosion, transportation and sedimentation.
Erosion
Four ways:
- Abrasion - large pieces wear away the river banks and bed.
- Attrition - sediment particles knock against the bed or each other and break, becoming more rounded and smaller.
- Hydraulic action - the force of water erodes softer rock.
- Corrosion - acidic water erodes rock.
Transportation
Four ways:
- Solution - minerals are dissolved and carried along.
- Suspension - fine, light material is carried along in the water.
- Saltation - small pebbles and stones are bounced along the river bed.
- Traction - large boulders and rocks are rolled along the river bed.
Sedimentation
Rock fragments produced by the weathering of geological features.
Channel types
Straight, meandering and braided.
Meandering
Rivers flowing over gently sloping ground begin to curve back and forth across the landscape.
Braided
A network of river channels separated by small, often temporary, islands.
Landforms
Potholes, rapids, waterfalls, meanders, levees, flood plains and deltas.
Potholes
Irregular hollow that is usually deeper than wide formed in the rocky bed.
Rapids
Sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence.
Waterfalls
An area where water flows over a vertical drop in the course of a stream or river. They are created when the riverbed changes suddenly from hard rock to soft rock.
Meanders
One of a series of regular sinuous curves in the channel of a river, They are formed as a river erodes the sediments comprising a bank and depositing this downstream.
Leeves
An elongated naturally occurring ridge or artificially constructed fill or wall that regulates water levels.
Flood plains
A flood plain is an area of flat land alongside a river. This area gets covered in water when the river floods.
Deltas
Wetlands that form as rivers empty their water and sediment into another body of water, such as an ocean, lake, or another river. The three main types of deltas are the arcuate, the bird’s foot and the cuspate.
Modifications to flows
Building dams to trap water from rivers, pumping water from the ground, and dredging for new sources of water.
Dams
A structure built across a river or stream to hold back water.
Causes of floods
Heavy rainfall, ocean waves coming on shore, melting snow and ice, dams or levees breaking.
Impacts of floods
Loss of human life, damage to property, destruction of crops, loss of livestock, non-functioning of infrastructure facilities and deterioration of health condition owing to waterborne diseases.
Forecasts
A process of estimating and predicting the magnitude, timing and duration of flooding based on known characteristics of a river basin, with the aim to prevent damages to human life, to properties, and to the environment.
Warnings
You should do all the actions for a flood alert but also: move vehicles to higher ground if it’s safe to do so. move family and pets to safety.
Hard engineering
Can involve raising the height of river banks by installing flood walls, bunds and levees which attempt to fix the river in place, stopping the natural process of the river overtopping and flowing onto the floodplain.
Soft engineering
Natural processes along the river to reduce the effects of flooding. Soft engineering warnings include flood warnings, preparation, flood plain zoning, and simply doing nothing.
