Aquifers are permeable, underground rocks that hold water within their structure. This water flow underground to springs and rivers. Chalk is an example of a permeable rock that holds water. Permeable means that water can flow through the material. This water can be extracted for drinking water supply at pumping stations using wells. 

Chalk streams or chalk rivers are a type of lowland river that occur on chalk geology, where > 75% of the flow of the water comes from the chalk aquifer (i.e. is groundwater). Chalk streams are characterised by clear water, rich in calcium and magnesium carbonate with a high biological diversity including aquatic plants, invertebrates and fish.

Confluence is the location in a river where two streams meet or where a smaller river (termed a tributary) reaches a larger river.

Groundwater is the name given to the water in the ground where all the pore spaces in the rock are totally filled (termed ‘saturated’) with water.

Nutrient enrichment is the term given to increased concentrations of nutrients (chemicals which are food sources for plants and algae) in a river system. Nitrogen and phosphorus are examples of chemicals which are important nutrients in rivers.

Organic pollution occurs when organic compounds enter water and cause harm to the environment. Natural organic compounds are derived from plants, animals and microbes and contain a carbon-based structure.

Organic matter is the term given to the great variety of different carbon-based compounds derived from plants, animals and microbes in the environment. Large organic matter includes leaves, twigs, animal remains which are visible to the naked eye, but organic matter also includes carbon-based compounds which have decomposed, and and are so small that they are no longer visible.

Photosynthesis is the process by which plants and algae use sunlight to produce its own food from carbon dioxide and water. Photosynthesis produces oxygen as a by-product.

Respiration is a process in living organisms whereby energy is produced by taking in oxygen and complex organic molecules such as sugar. Carbon dioxide and water are released from the organism as products of the process.

River catchment is an area of land where water drains into a common outlet or body of water. Rain falling on this area of land will flow across the surface and through soils and rocks to the river or lake which drains the catchment.

Winterbourne is a stream, or section of a stream, which flows for only part of the year when the groundwater levels are highest.