AQA · A-Level · Geography
Course version: 7037 · Version from Sept 2018
Drainage basins as open systems – inputs and outputs, to include…
Full specification wording
The water cycle: Drainage basins as open systems – inputs and outputs, to include precipitation, evapo-transpiration and runoff; stores and flows, to include interception, surface, soil water, groundwater and channel storage; stemflow, infiltration overland flow, and channel flow. Concept of water balance.
A drainage basin operates as an open system with distinct inputs, outputs, stores, and flows.
Checked against the AQA 7037 specification (opens in a new tab) on .
- Point 3 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A drainage basin operates as an open system with distinct inputs, outputs, stores, and flows. Precipitation acts as the primary input, while evapo-transpiration and runoff form the main outputs. Water is held in various stores, including interception by vegetation, surface depressions, soil water, groundwater aquifers, and channel storage. Movement between these stores occurs via flows such as stemflow down plant stems, infiltration into the soil, overland flow across the surface, and channel flow within rivers. The water balance equation conceptualises the relationship between these components over time. By analysing this balance, geographers can predict periods of soil moisture surplus, utilisation, deficit, and recharge within a specific basin, illustrating the dynamic nature of the system.
What earns the marks
- Define a drainage basin as an open system with energy and matter crossing its boundaries.
- Categorise precipitation as an input, and evapo-transpiration and runoff as outputs.
- Differentiate between stores (interception, surface, soil water, groundwater, channel) and flows (stemflow, infiltration, overland flow, channel flow).
- Apply the water balance equation to explain seasonal variations in soil moisture and river discharge.
Common mistakes and how to put them right
Confusing infiltration with percolation.
Put it right: Infiltration is the movement of water from the surface into the soil, whereas percolation is the deeper movement from soil into groundwater.
Treating the drainage basin as a closed system.
Put it right: Explicitly state it is an open system because water and energy transfer across its watershed boundary.
Misunderstanding the water balance.
Put it right: The water balance accounts for changes in storage, meaning inputs do not always immediately equal outputs.
Exam tips
- Draw and label a systems diagram of a drainage basin to clearly illustrate the relationship between inputs, outputs, stores, and flows.
- Use the water balance graph to explain seasonal changes in a UK drainage basin, highlighting periods of surplus and deficit.
- Ensure you use precise terminology, distinguishing clearly between overland flow (surface runoff) and channel flow (river discharge).
Try the lesson
The start of the The water cycle: Drainage basins as open systems – inputs and outputs, to include precipitation, evapo-transpiration and runoff; stores and flows, to include interception, surface, soil water, groundwater and channel storage; stemflow, infiltration overland flow, and channel flow. Concept of water balance. lesson, made from checked teaching notes for this specification point.
Have a go first
In the context of a drainage basin system, which of the following components is classified as a flow rather than a store?
Listen
A drainage basin operates as an open system with distinct inputs, outputs, stores, and flows. Precipitation acts as the primary input, while evapo-transpiration and runoff form the main outputs. Water is held in various stores, including interception by vegetation, surface depressions, soil water, groundwater aquifers, and channel storage. Movement between these stores occurs via flows such as stemflow down plant stems, infiltration into the soil, overland flow across the surface, and channel flow within rivers. The water balance equation conceptualises the relationship between these components over time. By analysing this balance, geographers can predict periods of soil moisture surplus, utilisation, deficit, and recharge within a specific basin, illustrating the dynamic nature of the system. A strong answer earns marks for these points. Define a drainage basin as an open system with energy and matter crossing its boundaries. Categorise precipitation as an input, and evapo-transpiration and runoff as outputs. Differentiate between stores (interception, surface, soil water, groundwater, channel) and flows (stemflow, infiltration, overland flow, channel flow). Apply the water balance equation to explain seasonal variations in soil moisture and river discharge. A common slip: Confusing infiltration with percolation. Instead, infiltration is the movement of water from the surface into the soil, whereas percolation is the deeper movement from soil into groundwater. Exam tip: Draw and label a systems diagram of a drainage basin to clearly illustrate the relationship between inputs, outputs, stores, and flows.
Key words
Say what each word means before you turn the card.
Drainage basin
Try answering aloud or in your head before turning the card.
Water balance
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Stores
Try answering aloud or in your head before turning the card.
Flows
Try answering aloud or in your head before turning the card.
See every definition
- Drainage basin
- An open system in which energy and matter cross its boundaries, with inputs and outputs, stores and flows.
- Water balance
- A concept that accounts for changes in storage, meaning inputs do not always immediately equal outputs, and that explains seasonal variations in soil moisture and river discharge.
- Stores
- Interception, surface, soil water, groundwater and channel storage, between which movement occurs via flows.
- Flows
- Stemflow, infiltration, overland flow and channel flow, which move water between the stores.
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