Rivers

waterfalls

'Step' in the long profile of a river characterised by water cascading over a rock lip of harder rock into a deep plunge pool.

Solid storage

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surface storage

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delta

A river delta is a landform that forms at the mouth of a river, where the river flows into an ocean, sea, estuary, lake, or reservoir. Delta form from deposition of sediment carried by a river as the flow leaves its mouth.

tributary

A smaller river that joins a larger one.

flood plain

An area of low-lying ground adjacent to a river, formed mainly of river sediments and subject to flooding.

water budget

An equation used to describe the flow of water in and out of a system.

Char

An island in Bangladesh in the middle of the river caused by braiding.

magnitude-frequency analysis

Analysis of the magnitude and frequency of events such as floods, which are often characterised by 'high magnitude, low frequency' events (negative association).

thalweg

Area in river cross-section where current flows the fastest, and the channel is the deepest.

drainage basin

Area of land, bordered by a watershed, drained by a river and its tributaries.

diversion spillways

Artificial channels that a river can flow into when its discharge rises. These channels move water around an area at risk of flooding and send it either back into the river(but further downstream) or into another river. They generally have floodgates on them that can be used to control the volume of water.

interlocking spurs

As the river descends from the highland, it begins to meander between these that interlock down the valley.

water balance

Audit of water based on the equation: precipitation = runoff + evapotranspiration +/- soil moisture.

eustatic

Changed in sea level induced by variations in the amount of water in the oceans.

isostatic

Changes in sea level resulting from the rise and fall of land masses.

potholes

Circular hollow or depression formed by erosion in bedrock on a river bed. Caused when pebbles caught in eddies in the river drill the river bed.

hard engineering

Commonly, built structures such as concrete walls designed to resist natural processes.

helicoidal flow

Cork-screw-like flow of water in a meander. It is one example of a secondary flow. It is a contributing factor to the formation of slip-off slopes and river cliffs in a meandering section of the river.

deposition

Deposition is the geological process in which sediments, soil and rocks are added to a landform or land mass. Wind, ice, and water, as well as sediment flowing via gravity, transport previously eroded sediment, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of sediment.

solution

Dissolving of chemicals as water flows over soluble rock.

inputs

Enters a river, e.g. energy from the sun and precipitation like rain and snow.

floodplains

Extensive, flat land immediately adjacent to a river that is prone to periodic inundation.

cuspate delta

Formed when a river drops sediment onto a straight shoreline with strong waves. Waves force the sediment to spread outwards in both directions from the river's mouth, making a pointed tooth shape with curved sides by regular opposing, gentle water movement.

slip off slope

Forms on the inside of a meander bend as a result of deposition in the slower flowing water.

hjulstrom curve

Graph showing the relationship between the velocity of a river and the critical velocity needed to pick up (erode) or deposit an individual particle. The graph comprises of two curves, one showing the critical erosion velocity, the other the critical deposition velocity.

riffles and pools

In a flowing stream, a sequence of these develops as a stream's hydrological flow structure alternates from areas of relatively shallow to deeper water. These are only present in streams carrying gravel or coarser sediments.

corrosion

Includes the dissolving of carbonate rocks (e.g. limestone) in sea water and the evaporation of salt crystals which expand on formation and help the rock to disintegrate.

flooding

Inundation of land not normally under water e.g. river floodplain.

saltation

Is a specific type of particle transport in fluids. It occurs when loose material is removed from a bed and carried by the fluid before being transported back to the surface.

wetted perimeter

Length (in metres) of river channel in contact with water at a river cross-section.

storm hydrograph

Line graph showing the discharge of a river over a period of time as it responds to an individual storm event.

soft engineering

Management approaches that have minimal impacts on the environment and aim to work with natural processes(e.g. planting trees in a river basin to reduce the risk of flooding).

straightening

Managing a river by doing this so that water can travel faster along the course.

traction

Material rolled along the bed of the river.

Channel roughness

Measurement of the smoothness of the wetted perimeter and the extent to which rocks protrude into the flow of a river. A smooth profile will result in little turbulence and a high velocity.

knick point

Point in the river's long profile, often marked by a waterfall, that represents the extent to which a river has re-graded its profile following rejuvenation. Over time a knick point will gradually migrate upstream due to waterfall retreat.

rapids

Series of relatively small 'steps' in the long profile of a river forming a stretch of turbulent white water.

cross profile

Shows you a cross-seciton of a river's channel and valley at certain points in the river's course. This changes as it moves from the upper to lower course as a result of changed in the river's energy and the processes that the river carries out.

sediment calibre

Size of sediment.

suspension

Small particles carried in water e.g. silts and clay, which can make the water look cloudy.

graded profile

Smooth concave long profile of a river that has achieved a state of equilibrium with its environment.

falling limb

Sometimes referred to as the recession limb is when discharge decreases and the river's level falls.

velocity

Speed of flow of a river. The line of fastest flow in a river is called the thalweg.

incised meander

Steep-sided meander formed during a period of significant down-cutting rejuvenation.

gorges

Steep-sided narrow valley often found immediately downstream from a waterfall.

flood alleviation

Stopping flooding e.g. walls etc or trying to stop the problems of flooding e.g. warning etc.

potential energy

Stored energy in a still body of water that has potential to do 'work'.

Channelisation

Straightening, deepening, widening, clearing or lining existing stream channels.

Braiding

Sub-dividing of a river channel, splitting the river into shallow interconnecting channels, a characteristic of a river with a variable discharge.

meanders

Sweeping bend or curve in a river, characterised by having a depositional slip-off slope on the inside bend and an erosional river cliff on the outside bend.

Base level

The base level of a river or stream is the lowest point to which it can flow, often referred to as the 'mouth of the river'. For large rivers, sea level is usually the base level, but a large river or lake is likewise the base level for tributary streams.

hydraulic radius

The cross sectional area of a river channel divided by its wetted perimeter. The higher the value, the less energy lost by friction, so the greater the efficiency.

plunge pool

The deep pool below a waterfall that retreats with it.

groundwater flow

The deeper movement of water through underlying rock strata.

salinisation

The deposition of salts on or close to the ground surface commonly associated with high rates of evaporation in arid environments.

infiltration

The downward movement of water into the soil.

Closed and open systems

The drainage basin hydrological cycle may be defined as a single river basin bounded by its own watershed and the sea. The drainage basin hydrological cycle is an open system. This means it has inputs and outputs.

percolation

The gravity flow of water within soil.

erosion

The group of natural processes, including weathering, dissolution, abrasion, corrosion, and transportation, by which material is worn away from the earth's surface.

watershed

The highland separating one river basin from another.

recurrence interval

The interval at which particular levels of flooding will occur.

evapo-transpiration

The loss of water from a drainage basin into the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants.

land use management

The management and modification of natural environment or wilderness into built environments such as settlements and semi-natural habitats such as arable fields, pastures, and managed woods.

Bedload

The material carried by a river by being bounced, rolled, or carried in suspension along its bed.

upper course

The mountain stage of a river with steep gradients and much erosion.

throughflow

The movement of water down slope within the soil layer.

Channel flow

The movement of water within the river channel.

Confluence

The point at which rivers meet.

interception

The prevention of rain from reaching the Earth's surface by trees and plants.

permeable

The property of rock or soil permitting water to pass through it.

Attrition

The reduction and rounding of particles of sediment carried in water by repeated collision with each other and the shore.

wetland restoration

The rehabilitation of degraded or destroyed wetlands. Takes place in places that are of have been wetlands.

transportation

The river moves material as bedload, suspended load or dissolved load(in solution). Bedload can be moved by saltation or traction,

middle course

The section of the river between the mountains and the lowland, where transport of eroded material is important and the river begins to cut sideways due to the reducing gradient.

lower course

The section of the river near the sea, where deposition is the most important process and the valley becomes wider and flatter.

ground storage

The storage of water underground in permeable rock strata.

lag time

The time difference between the peak of the rain event and the peak discharge.

river capacity

The total amount of sediment a river is able to transport.

soil moisture

The total amount of water, including the water vapour, in an unsaturated soil.

cross sectional area

The total length of the bed and the bank sides in contact with the water in the channel.

interception storage

The total volume of water held on the surface vegetation.

river discharge

The volume of water flowing through a river channel. This is the total volume of water flowing through a channel at any given point and is measured in cubic metres per second(cumecs).

Abrasion (corrasion)

The wearing away of the shoreline by sediment carried by the waves.

relief channels

These allow flood water to by-pass land which needs to be protected in times of flood.

point bar

These are found in abundance in mature or meandering streams. They are crescent-shaped and located on the inside of a stream bend, being very similar to, through often smaller than, towheads, or river islands.

floodplain zoning

These are zones that has determined to be a flood risk to nearby communities and property. These zones are rated for their severity of risk.

lateral erosion

This concurrent process refers to the widening of a stream channel or valley. When a stream is high above its base level, downcutting will take place faster than this but as the level of the stream approaches its base level this will increase.

the Environmental Agency

This is a non-departmental public body sponsored by the UK government's DEFRA relating to the protection and enhancement of the environment.

surface run off

This is a term used to describe when soil in infiltrated to full capacity and excess water, from rain, snowmelt, or other sources flow over the land.

soil recharge

This is a time when water is added to soil moisture storage. It occurs when precipitation exceeds potential evapotranspiration but the soil has yet to reach its field capacity.

ingrown meanders

This is a type of incised meander that is asymmetrical and form when the river downcuts at a less rapid pace giving the river opportunity to erode laterally as well as vertically.

soil deficit

This is the amount of rain needed to bring the soil moisture content back to field capacity.

soil moisture budget

This is the balance between water inputs and water outputs.

stem flow

This is the flow of intercepted water down the trunk or stem of a plant.

flood mitigation

This is the managing and control of flood water movement, such as redirecting flood run-off through the use of floodwalls and flood gates, rather than trying to prevent floods altogether.

river competence

This is the maximum particle size that a river is able to transport. This increases with velocity.

entrainment

This is the process by which surface sediment is incorporated into a fluid flow(such as air, water or even ice) as a part of the operation of erosion.

risk analysis

This is the process of prioritising risks for further analysis by assessing and combining their probability of occurrence and impact.

realignment

This is the straightening of the river channel. This is to remove meanders and reduce the length of the river. Thus increasing the speed o the river.

peak rainfall

This is the time of highest rainfall.

peak discharge

This is the time when the river reaches its highest flow.

soil moisture utilisation

This is the time when water is drawn from soil moisture storage. It occurs when potential evapotranspiration exceeds precipitation but soil storage is yet to reach 0.

flood prediction

This is the use of real-time precipitation and streamflow data in rainfall-runoff and streamflow routing models to forecast flow rates and water levels for periods ranging from a few hours to days ahead depending on the size of the watershed or river basin.

Cost benefit analysis

This is what people do to decide whether to pay to defend a place or not - I.e. what are the costs of the costs of the scheme (money, costs to people and the environment) and what are the benefits.

outputs

This leaves the river system in the form of water.

vertical erosion

This makes a river channel deeper. It happens more in the upper stages of a river.

soil surplus

This occurs when precipitation exceeds potential evapotranspiration and the soil has reached its field capacity. Any additional water applied to the soil runs off. If this water runs off into nearby streams and rivers it could cause flooding. It can be used to predict the severity of potential flooding.

rising limb

This represents on a hydrograph the rapid increase in water resulting from rainfall causing surface runoff and then later throughflow.

long profile

This shows how a river's gradient changes as it flows from its source to its mouth.

porous

Used in geology, hydrogeology, soil science and building science, this describes the fraction of void space in the material, where the void may contain: air or water.

storm flow

Water that reaches the channel largely through runoff. This may be a combination of overland flow and rapid throughflow.

Base flow

Water that reaches the channel largely through slow through-flow and from permeable rock below the water table.

drilling

What stones do to form pot holes.

kinetic energy

When water moves downhill, potential energy is converted to kinetic energy and used to do 'work'.

mouth

Where a river ends, at a lake or the sea.

stores

Where water is found or stored e.g. soil, aqufers, surface etc.

distributaries

finger-like river channels which branch away from a main river channel in a delta.

eutrophication

high nitrate levels combined with phosphates cause excessive plant and algae growth, a deteriorating process that results in loss of oxygen and the biological death of a the river.

sinuosity

the curving nature of a meander described as: actual channel length divided by straight-line distance

estuary

the tidal mouth of a river, with large, flat expanses of mud exposed at low tide.

dams

A barrier constructed to hold back water and raise its level, forming a reservoir used to generate electricity or as a water supply.

Bluff

A bluff is a steep cliff, or wall of rock or soil. Most bluffs border a river or its flood plain. Bluffs may form along a river where it meanders, or curves from side to side. Water on the outside of the curve flows faster.

Arcuate delta

A bowed or curved delta with the convex margin facing the body of water. Also known as fan-shaped delta.

culverts

A culvert is a structure that allows water to flow under a road, railroad, trail, or similar obstruction. Typically embedded so as to be surrounded by soil, a culvert may be made from a pipe, reinforced concrete or other material. A structure that carries water above land is known as an aqueduct.

river cliff

A cut bank that makes up the outside bank of a water channel, which is continuously undergoing erosion.

Bird's foot delta

A delta with long, projecting distributary channels that branch outward like the toes or claws of a bird.

entrenched meander

A form of incised meander that is symmetrical and form when the river downcuts particularly quickly. Due to the speed which the river downcuts, there is little opportunity for lateral erosion to occur giving them their symmetrical shape.

hydrograph

A graph showing for a given point on a steam the discharge, stage(depth), velocity, or other property of water with respect to time; a graphical representation of stream discharge(volume/time) during a storm or flood event.

flashy hydrograph

A hydrograph is described as this when it depicts sharp vertical jumps and equally vertical declines.

efficiency

A large hydraulic radius increases this because it means that a smaller proportion of the river's water is in contact with the bed and banks so there is less friction. To maximize this a large hydraulic radius with a narrow and deep channel.

ox-bow lake

A meander which has been cut off from the main river channel and abandoned.

roughness

A measure of the resistivity offered by the material constituting stream channel margins to the flow of water.

spur

A narrow neck of highland extending into a river valley, often forming the divide between two tributaries.

flood

A temporary excess of water which spills over onto land.

Bund

A wall or embankment usually protecting a building or place e.g. the hospital in Keswick is protected by one of these.

river terraces

Abandoned floodplain left perched above the current floodplain following a renewed period of erosion(rejuvenation).

precipitation

All forms of moisture that reach the Earth's surface e.g. rain, snow, dew

levee

Raised river banks formed by deposition when, in flood, a river spills over the sides of its channel.

particle size

Range from clay (0.001mm), through silt, sand, gravel, pebbles. cobbles, and boulder (500+mm).

impermeable

Relating to a material such as rock through which substances, such as liquids cannot pass.

rejuvenation

Renewed period of river erosion resulting from a fall in base level(often sea level). As the river cuts down into its channel characteristic features form including incised meanders and river terraces.

river restoration

Restoring a river channel to its natural course following earlier intervention, e.g. channel straightening. River restoration usually involves soft engineering and aims to improve natural habitats and the amenity value of the river.

hydraulic action

River erosion involving the sheer force of flowing water.

dynamic equilibrium

Rivers are constantly changing over time to reach a state of balance with the processes that determine their form. As the flows of energy and materials passing through a river system vary, the river changes to move towards this equilibrium.

Alluvium

Rock particles (clay, silt, sand and gravel) deposited by a river.