Middle and Lower Courses of a River

As we move downstream, the river's characteristics change significantly in the middle and lower courses. These changes are crucial for understanding the UK physical landscapes and answering GCSE Geography UK Physical landscape Past Papers.

Middle Course

In the middle course, the river becomes wider, deeper, and smoother. This is due to increased erosion and the addition of water from tributaries, which increases the river's discharge and reduces friction.

Vocabulary: Discharge refers to the volume of water flowing through a river channel at a given point.

The increased velocity and discharge lead to more erosion, particularly lateral erosion, which widens the valley floor. The bedload in this section consists of smaller, smoother particles like pebbles.

Example: Meanders are a characteristic feature of the middle course. They form due to the increased lateral erosion on the outside of bends where velocity is higher.

Lower Course

The lower course is where the river is at its widest, deepest, and smoothest. Velocity and discharge are typically at their highest in this section.

Highlight: In the lower course, the river's bedload consists of fine particles, often described as sludge-like due to extensive erosion upstream.

Significant landforms in the lower course include more pronounced meanders and oxbow lakes. These form when the neck of a meander is eventually cut through, leaving behind a curved lake separate from the main river channel.

Definition: An oxbow lake is a U-shaped body of water formed when a wide meander of a river is cut off from the main stream.

The lower course is also characterized by floodplains and levées. Floodplains are formed by lateral erosion widening the valley floor, while levées are natural embankments built up by sediment deposition during floods.

Example: The River Tees in Northern England provides an excellent case study of how a river's profile changes from upper to lower course.

Understanding these changes along the river's course is essential for answering questions about the long profile of a river and explaining why does the cross profile of a river change along its course.

Upper Course of a River

The upper course of a river is characterized by distinct features that set it apart from other sections. This part of the river is typically found in mountainous or hilly areas where the river begins its journey.

Vocabulary: Channel morphology refers to the shape and structure of a river channel.

In the upper course, the channel is narrow, shallow, and rough. This is primarily due to vertical erosion, which is the dominant process in this section. The bedload, or material carried by the river, consists of large and angular rocks.

Example: Interlocking spurs are a common feature in the upper course. These are formed when the river doesn't have enough energy to cut through hard rock and instead meanders around it.

The velocity of the river in the upper course is generally slow due to the channel characteristics and limited discharge. This results in reduced erosion and transportation capacity.

Highlight: Waterfalls and gorges are significant landforms found in the upper course of rivers.

Waterfalls form when the river flows over layers of hard and soft rock. The soft rock erodes faster, creating a step over which the water falls. Over time, the waterfall retreats upstream, leaving behind a steep-sided gorge.

Definition: Hydraulic action is the erosive force of water as it flows over and around rocks in the river channel.

The formation of waterfalls involves several processes, including hydraulic action, abrasion, and gravity. These processes work together to increase erosion and make the waterfall more pronounced over time.

Quote: "High Force waterfall on the River Tees is an excellent example of a waterfall in the upper course of a UK river."

Understanding the characteristics and processes of the upper course is crucial for answering Physical landscapes in the UK Exam questions and analyzing cross profile of a river changes.