The Freshwater System

Precipitation

The transfer of moisture (rain, snow, etc) to the earth's surface from the atmosphere.

Interception

The capture of raindrops by plant cover, which prevents direct contact with the soil.

Runoff

Precipitation that does not soak into the ground but flows over it into surface waters.

Groundwater

Water held underground in soil or porous rock, often feeding springs and wells.

Evapotranspiration (EVT)

The loss of water from vegetation and water surfaces to the atmosphere.

Potential evapotranspiration (pEVT)

The rate of water loss from an area if there were no shortages of water.

Maximum sustainable yields (MSY)

The maximum level of extraction of water that can be maintained indefinitely for a region.

Hydrological Cycle

The continuous movement of water on, above, and below the surface of the Earth.

Closed System

In a closed system, there is no exchange of matter with the surroundings, only energy.

Open System

In an open system, both matter and energy can be exchanged with the surroundings.

Precipitation

The initial stage where water vapor in the atmosphere condenses and falls back to Earth as rain, snow, sleet, or hail.

Interception

Before reaching the ground, precipitation encounters various surfaces like leaves, branches, and vegetation.

Infiltration

Water that doesn't evaporate penetrates the ground surface, entering the soil zone.

Runoff

Water that doesn't infiltrate either evaporates or flows over the land surface as runoff.

Evapotranspiration

The combined process involves the evaporation of water directly from soil and water bodies and the transpiration of water vapor from plants through their leaves.

Groundwater Recharge

A portion of infiltrated water percolates deeper into the soil, eventually reaching the saturated zone below, replenishing groundwater aquifers.

Water Balance

The relationship between the inputs and outputs of a drainage basin.

Soil moisture excess

When soil moisture and groundwater is replenished, leading to saturation and increased surface runoff.

Drainage basin

The area drained by a river and its tributaries.

Discharge

The volume of water passing a given point over a set time.

Peak rainfall

The highest rainfall (usually measured in mm) during a storm.

Erosion

The wearing away of the land as the water flows past the bed and banks of a river.

Transport

The movement of material by a river through solution, suspension, saltation, or traction.

Deposition

The dropping of material carried by the river when there is no longer sufficient energy to transport it.

Wetted Perimeter

The total length of the bed and the banks in contact with the river.

Cross-sectional area

The width of the river multiplied by the depth of the river.

Average Depth

The depth of a river is measured by taking an average reading across its width.

Velocity

The speed at which water in a river is flowing, measured in meters per second (m/s).

Channel Roughness

The roughness of a river's channel, which is influenced by the presence of angular boulders and affects the amount of friction and resistance to flow.

Regimes

The variations in a river's flow, which can have a seasonal pattern of discharge due to factors such as climate, geology, and human interaction.

Simple Regimes

River flow patterns characterized by high water levels followed by lower levels, often resulting from glacier melt, snowmelt, or seasonal rainfalls.

Complex Regimes

River flow patterns characterized by multiple periods of high and/or low water levels, more common in large rivers with varied relief and large tributaries.

Laminar Flow

Smooth flow of water in a straight channel, most common in the lower parts of a river.

Turbulent Flow

Flow characterized by variations in the shape of the river's channel, such as pools, meanders, and rapids, resulting in turbulence and disturbance of sediment.

Bradshaw Model

A framework developed by Dr. Anthony D. Bradshaw to understand the relationships between factors influencing the shape and form of river channels.

Discharge

The volume of water flowing through a river channel at a given time, a primary driver of channel morphology.

Sediment Supply

The amount and size of sediment entering the river channel, influencing channel morphology and leading to braided or meandering channels.

Channel Slope

The steepness of the channel bed, affecting flow velocity and depth.

Bank Material

The strength and cohesion of the material forming the riverbanks, influencing erosion, channel slope, and channel width.

Vegetation

The type and extent of vegetation along the banks and within the channel, stabilizing banks, reducing erosion, and influencing sediment transport.

Hydrographs

Graphs that show the variation in river discharge over time, influenced by the characteristics of the drainage basin and precipitation.

Impermeable Rock

Rock that does not allow water to infiltrate, resulting in more surface runoff and increased volume and speed of the river.

Permeable Rock

Rock that allows water to infiltrate, reducing surface runoff and volume in the river.

Base Flow

The normal day-to-day discharge of a river.

Rising Limb

The rapid increase in discharge resulting from rainfall.

Peak Flow

The maximum capacity of the river to hold water.

Recession Limb

The decrease in discharge and fall in river levels after the peak flow.

Basin Lag Time

The time difference between the peak of a rain event and the peak flow in the river.

Flash Floods

Sudden and intense floods caused by heavy rainfall, often resulting in short lag times and high discharge.

Land Use

The way land is utilized, including impermeable surfaces like concrete and tarmac, which can increase surface runoff and shorten lag times.

Deforestation

The removal of vegetation, reducing infiltration and interception, increasing surface runoff and speed of water.

River Management

The presence of dams, which can control river flow and affect discharge and lag times.

Advantages of Flooding

Benefits of floods, including replenishing groundwater reserves, providing nutrient-rich sediment for agriculture, and supporting fish populations.

Disadvantages of Flooding

Negative impacts of floods, such as destruction of agricultural land, damage to infrastructure, and displacement of populations.

Dams

Barriers constructed to hold back water and create reservoirs for various purposes, such as flood control, irrigation, and hydroelectric power generation.

Reservoir

A large natural or artificial lake used as a source of water supply.

Hydrological Changes

Changes to the water cycle resulting from the construction of dams and reservoirs, including increased evaporation, changes in river discharge, sedimentation, and water quality.

Aswan Dam

A dam complex on the River Nile in Egypt, providing flood control, irrigation, hydroelectric power, and improved navigation.

Aswan High Dam

A dam built in Egypt that supports the local fishing industry and provides jobs and new skills to local workers. It has an estimated value of $500m to the Egyptian economy each year.

Water losses

The dam provides less than half the expected amount of water, leading to water shortages.

Salinization

Crop yields have been reduced on up to ⅓ of the irrigated area due to salinization caused by the dam.

Groundwater changes

Seepage from the dam leads to increased groundwater levels and may cause secondary salinization.

Displacement of population

Up to 100,000 Nubian people have been removed from their ancestral homes due to the dam.

Seismic stress

The dam is believed to have caused an earthquake in November 1981. As water levels decrease, seismic activity also decreases.

Channel erosion

Clear water erosion beneath the channel has lowered the channel by 25mm over 18 years.

Increased sedimentation

Increased sedimentation may put stress on the dam, reduce lake depth, storage levels, and prevent nutrients from reaching farmland downstream.

Loss of nutrients

$100m worth of artificial fertilizers are used annually to replace nutrients trapped behind the dam.

Decreased fish catches

Sardine yields are down 90% and 3000 jobs in Egyptian fisheries have been lost due to the dam.

Spread of diseases

Stagnant water caused by the dam has led to the spread of diseases.

Erosion

The wearing away of the bed, banks, and load of a river. Types of erosion include attrition, hydraulic action, corrosion, and corrasion.

Transportation

The process of a river carrying eroded material. Types of transportation include traction, saltation, suspension, solution, and flotation.

Deposition

The process of a river putting down its load due to a decrease in velocity and energy. It leads to the formation of landforms such as floodplains, levees, and deltas.

Competence

The maximum diameter of a piece of load that a river can transport.

Capacity

The maximum amount of load that a river can transport.

Critical Erosion Velocity

The minimum velocity required for a river to start eroding and transporting material.

Settling Velocity

The velocity at which a river needs to fall below to start depositing its load.

Hjulstrom Curve

A graph showing the relationship between river velocity and particle size, determining whether a river will erode, transport, or deposit sediment.

Upper Course

The section of a river nearest to its source, characterized by vertical erosion and landforms such as waterfalls, gorges, and v-shaped valleys.

Middle Course

The section of a river between the upper and lower courses, characterized by horizontal erosion and landforms such as alluvial fans and meanders.

Lower Course

The section of a river closest to its mouth, characterized by flatter land, smaller and smoother load, and landforms such as meanders, oxbow lakes, braided rivers, levees, and deltas.

Meander

A curvy, bendy path that a river flows in, formed by erosion and deposition on the outer and inner banks.

Oxbow Lake

A meander that has become cut off from the main river channel.

Braided River

A river with multiple smaller channels separated by temporary islands called eyots, formed by variable flow and high quantities of load.

Delta

A landform formed at the mouth of a river where it meets a body of water, characterized by deposition of sediment.

Levees

Embankments found on the sides of a river channel, built naturally or by humans to reduce flood risk.

Floodplain

The floor of the valley that gets flooded when a river exceeds its bankfull discharge.

Bluff Line

The outer limits of the floodplain, marking the edge of the valley floor.

Strand Line

A line of load deposited at the limit of a flood.

Alluvial Deposits (Alluvium)

Load deposited by a river during a flood, composed of different-sized particles.

Floodplain Management

Techniques used to manage and mitigate the impacts of flooding, such as river walls, river training, channelization, embankments, raised buildings, controlled flooding, flood-proofing houses, and human modifications to floodplains.

Channel Enlargement

Making the width and depth of a river wider and deeper to increase its cross-sectional area and reduce flood risk.

Channel Straightening

Removing meanders from a river to make it straighter.

Meanders

Bends or curves in a river's course that can be removed to increase water velocity and reduce the risk of flooding.

Flood Relief Channels

Artificial channels built to divert excess water from a river during floods, reducing flood risk.

Artificial Stores

Reservoirs or lakes created to store excess water during floods, reducing pressure on the main river channel.

Flood Embankments (levees)

Raised banks along a river that increase its depth and reduce the risk of flooding.

Controlled Flooding

Allowing low-value land to flood in order to protect higher-value areas from flooding.

Afforestation / Reforestation

Planting trees in a drainage basin to increase interception, transpiration, and root uptake of water.

Flood Proofing

Measures taken to make properties less vulnerable to flooding or flood damage.

Insurance

Financial protection against flood damage and recovery costs.