River Terminology

A list of key terms and definitions for the AS AQA rivers module

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Geo-Dictionary

Bank full discharge –The discharge of a river which is just contained within banks. This is maximum velocity in the channel.

Bed load – The material that is moved along the river bed by rolling and pushing and saltation.

Capacity - the ability to contain and hold sediment.

Channelization – Make or form channels by erosion.

Competence –The largest size of particle that a river can carry.

Cross sectional Area – view of the river and bed as a cross section.

Cumecs - The cumec is a measure of flow rate.

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Deltas (three types) - Deltas are the result of rivers and sea meeting.  But they can form anywhere a stream flows into shallower open water.

1.       Arcuate delta

2.       Digitate or bird foot delta

3.       Cuspate or tooth shaped delta

 Deposition – process of dropping sediment due to loss of energy, encountering vegetation.

 Discharge - River emptying into an ocean, lake, or other body of water and usually added by tributaries.

 

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Entrenched meander - A deepened meander of a river which is carried downward further below the valley surface in which the meander originally formed. Also known as inherited meander.

Erosion – Natural processes that wears material and sediment away from its original source. There are four dominant methods of erosion, attrition, abrasion, hydraulic action and corrosion

 Flash Flood – Sudden flood caused by heavy rainfall and a short lagtime, areas are flashy or slow flow depending on the gradient, soil type, rocky type, drainage density etc.

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Flood - When discharge exceeds bankfull capacity.

Flood Recurrence Interval - A tool used in cost benefit analysis to decide on what level of protection to provide.

Graded Profile - A theoretical concept where the long profile forms a small concave line indicating that all 3 river processes are in equilibrium and calibrated to current base level.

Groundwater/base flow - The lateral movement of water below the water table level.

Hjulstrom - A graph that relates sediment size to the velocity required for transportation and deposition.

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 Hydraulic Radius - It is a measure of channel efficiency which is calculated by dividing cross sectional area by the wetted perimeter.

Incised Meanders - A landform feature of rejuvenation in rivers that is provoked by a fall in base level caused by  eustatic sea level rise or isostatic rebound. There are two types of incised meanders. Ingrown meanders have an asymmetrical cross section and form when lateral erosion has time to occur too, as well as vertical erosion. This means that the valley floor is deepened whilst the channel only occupies a portion of it. Entrenched meanders form when base level drops quickly and so only vertical erosion has time to occur. This produces a symmetrical deep cut, gorge like cross section.

Infiltration - The process by which precipitation passes from the surface to the soil beneath the ground. It is measured mm per hour.

 

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Interception - When parts of vegetation get in the way of precipitation falling to the ground. The leaves hold the water in this store but it is very shallow and fills up quickly.

Lagtime - The difference, in time, between peak precipitation and peak discharge, short lagtime produces a flashy river.

Landforms - A natural feature that forms on the land due to the processes of erosion and deposition.

Long Profile - The study of how a river changes in gradient along its course.

Magnitude - The severity of floods with reference to the damage caused. It is used in the Weibull equation to help calculate the likelihood of a flood of a similar magnitude occurring again.

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Naturalisation  - The introduction of plants and/or animals to a place where they can flourish but are not indigenous.

Percolation – The ability of a liquid passing through a porous substance

River beach – Found on the inside bend of a river, where sediment is deposited due to energy within the water decreasing.

Rejuvenation - A river is said to be rejuvenated when the base level that it is flowing down to is lowered.

Soil water store -The ability to take in water and keep doing so until the soil is full or the rate at which the soil can transmit water into and through the pores is exceed.

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Solution – A method of transportation that carries dissolved substances in the flow of water.

Meander – is a bend in a sinuous watercourse. It forms when the moving water in a stream erodes the outer banks and widens its valley.

Potential/kinetic energy – potential energy is energy that is stored in an object, and kinetic energy is energy of motion. Potential energy is converted into kinetic energy for something to move.

River terrace - Part of an old flood plain that has been left perched on the side of a river valley. It results from rejuvenation, a renewal in the erosive powers of a river.

River cliff – forms on the outside of a meander, where erosion is the dominant process.

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Saltation – a type of transportation, when loose material from the river bed is picked up and then carried along by the river.

Sinuosity – is how much the river is meandering. It is the actual channel length divided by the shortest channel length.

Solute load – is the minerals and tiny particles of sediment that are dissolved in the water.

Surface run off – is the water flow that occurs when soil is infiltrated to full capacity and excess water flows over the land.

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Through flow

Water travels horizontally through gaps in the soil. For the process to be through flow, the water must come from land before it enters a body of water (stream, lake or pond.) 

Traction

Large particles such as pebbles, stones and boulders are rolled along the river bed by water moving downstream.

Transport

The movement of sediment along the river channel. This can include saltation, traction, suspension and solution.

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Vegetation store - The amount of water stored in vegetation. It is affected by the amount of vegetation that there is and the time of year it is.

Velocity - The speed at which water travels in a river.  It is measured in metres per second.

Water balance graph - A graph that shows the state of equilibrium in the drainage basin between the inputs and outputs which can be expressed as an equation P=Q + E +/- change in storage.

Weibull equation - An equation to work out the recurrence interval of flooding.  T= (n +1)/M (n=number of years in the record and M= magnitude ranking.)

 

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Wetted perimeter - Is the measurement of the line where the river’ cross section meets the river’ bed. It is related to the amount of water in the river channel.

Surface storage - The amount of water that is stored on the surface of the ground.  

Suspended load - Load that is caught within the flow of the river, it is normally sand and clays that are moving within the water as they are not connected to the bed.

Suspension - Very small particles of sand and silt carried along by the flow of the river. 

Through fall/stem flow - The flow of water down trunks and stems of vegetation after interception of rainfall.

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