Geography · Year 12 · The Water and Carbon Cycles · Summer Term

Drainage Basin as an Open System

Investigate the drainage basin as a hydrological system with inputs, outputs, stores, and flows.

• National Curriculum Attainment Targets
• A-Level: Geography - Water and Carbon Cycles
• A-Level: Geography - Hydrology and Drainage Basins

About This Topic

The carbon cycle is a critical system that regulates the Earth's temperature and supports life. Students investigate the major stores of carbon (the atmosphere, oceans, terrestrial biosphere, and lithosphere) and the processes that transfer carbon between them, such as photosynthesis, respiration, and combustion. This topic also explores the link between the carbon cycle and global energy consumption, particularly our reliance on fossil fuels.

At this level, students must understand the difference between the 'fast' and 'slow' carbon cycles and how human activity has accelerated the transfer of carbon from long-term geological stores to the atmosphere. This topic particularly benefits from hands-on, student-centered approaches where students can map the carbon footprint of different energy sources and model the impact of carbon sequestration strategies.

Key Questions

1. Explain how a drainage basin functions as an open system.
2. Analyze the various inputs and outputs within a drainage basin.
3. Differentiate between different types of water stores and flows within a basin.

Learning Objectives

• Analyze the drainage basin as an open system by identifying its boundaries, inputs, outputs, stores, and flows.
• Compare and contrast the different types of water stores (e.g., interception, surface storage, soil moisture, groundwater) within a drainage basin.
• Explain the key processes of water flow (e.g., overland flow, throughflow, groundwater flow) and their significance in a drainage basin.
• Evaluate the impact of varying climatic conditions and land use on the inputs and outputs of a drainage basin.

Before You Start

Weather and Climate

Why: Understanding different forms of precipitation and their spatial distribution is crucial for identifying inputs to a drainage basin.

Introduction to Systems Theory

Why: Students need a basic grasp of what a system is, including the concepts of inputs, outputs, and boundaries, to understand the drainage basin as an open system.

Key Vocabulary

Drainage Basin	An area of land where all surface water converges to a single point, usually an ocean, river, or lake. It is defined by its watershed or catchment boundary.
Input	Water entering the drainage basin system, primarily as precipitation (rain, snow, hail) and also as groundwater flow from adjacent basins.
Output	Water leaving the drainage basin system, mainly as river discharge (streamflow) and also as evaporation and transpiration from the surface and vegetation.
Store	Water held within the drainage basin at a particular time. This includes water intercepted by vegetation, held on the surface, in the soil, or underground in aquifers.
Flow	The movement of water within the drainage basin system. This includes surface runoff, throughflow (movement through the soil), and groundwater flow.

Watch Out for These Misconceptions

Common Misconception

The carbon cycle and the greenhouse effect are the same thing.

What to Teach Instead

The carbon cycle is the movement of carbon; the greenhouse effect is the warming caused by certain gases in the atmosphere. A 'concept mapping' activity can help students see how the two are related but distinct.

Common Misconception

Planting trees is the only way to remove carbon from the atmosphere.

What to Teach Instead

Oceans and soils are also massive carbon sinks, and technological solutions like Carbon Capture and Storage (CCS) are being developed. A 'sink sorting' task can help students identify the full range of carbon removal methods.

Active Learning Ideas

Inquiry Circle: The Carbon Budget Audit

Groups are assigned a specific 'store' (e.g., the oceans). They must research how much carbon it holds, how it enters and leaves the store, and whether it is currently a carbon 'sink' or 'source'.

50 min·Small Groups

Think-Pair-Share: The Future of Energy

Students compare the carbon intensity of coal, natural gas, and wind power. They discuss with a partner which energy mix is most realistic for the UK to reach 'Net Zero' by 2050 and share their plan.

25 min·Pairs

Simulation Game: The Sequestration Game

Students act as government advisors choosing between different carbon capture technologies (e.g., reforestation vs. CCS). They must weigh up the cost, scale, and permanence of each method to create a national strategy.

45 min·Small Groups

Real-World Connections

• Environmental consultants use drainage basin models to assess the impact of proposed developments, such as new housing estates or industrial sites, on local water resources and flood risk for communities near the River Thames.
• Water resource managers in regions like the Murray-Darling Basin in Australia analyze inputs and outputs to allocate water for agriculture, urban supply, and environmental needs, balancing competing demands during drought periods.
• Hydrologists working for the Environment Agency monitor river levels and flow rates across the UK, using data from gauging stations to predict flood events and manage water quality in river systems like the Severn.

Assessment Ideas

Quick Check

Provide students with a simplified diagram of a drainage basin. Ask them to label three distinct inputs, three distinct outputs, and two different water stores. Then, ask them to draw arrows indicating two types of water flow.

Discussion Prompt

Pose the question: 'How does the concept of an open system help us understand the challenges of managing water resources in a specific UK river basin, like the Ouse?' Encourage students to reference specific inputs, outputs, stores, and flows in their responses.

Peer Assessment

Students create a concept map illustrating the drainage basin as an open system. They then exchange maps with a partner. Each partner checks for the inclusion of all key components (inputs, outputs, stores, flows) and the clarity of connections, providing written feedback on one area for improvement.

Frequently Asked Questions

What is the difference between a carbon 'sink' and a 'source'?

A carbon sink absorbs more carbon than it releases (e.g., a growing forest), while a carbon source releases more carbon than it absorbs (e.g., a burning forest or a coal power station).

How do the oceans store carbon?

Oceans store carbon through the 'solubility pump' (CO2 dissolving in water) and the 'biological pump' (phytoplankton taking in CO2 through photosynthesis and then sinking when they die).

What is 'Carbon Capture and Storage' (CCS)?

It is a technology that captures CO2 emissions from industrial sources like power plants and pumps it deep underground into geological formations for long-term storage.

How can active learning help students understand the carbon cycle?

Active learning, such as the carbon budget audit or the sequestration simulation, helps students grasp the scale and complexity of the global carbon system. By working through the data themselves, they can better understand the magnitude of the challenge in balancing the global carbon budget.