River Systems

A river system is an open system. An open system has inputs, processes and outputs. So unlike water in the hydrological cycle, where there is an endless cycle of rain, rivers, sea and evaporation, water in the river system enters the system, and eventually leaves it again. The Drainage basin

A river system operates inside a drainage basin (or river basin). A drainage basin is the area of land drained by a river and its tributaries. Any water falling inside the drainage basin will find its way into the main river channel (unless it is taken out of the system - for example by being piped to a factory). The boundary of a drainage basin is called the watershed. drainage basin tributaries river channel This diagram below shows a drainage basin. Make sure you know all the key terms used when talking about river systems.

Erosion

Transportation

Deposition

Erosional Processes Processes: Abrasion is the grinding of rock fragments carried by the river against the bed and banks of the river. This action causes the channel to widen and deepen. This grinding is most powerful in flood time when large fragments of rock are carried along in the river bed.

Erosional Processes Hydraulic action occurs as a river tumbles over a waterfall to crash onto the rocks below. It will lead to the formation of a plunge pool below the waterfall.

Erosional Processes Process: Attrition Attrition is the collision of rock fragments in the water against one another. The rock particles are broken into smaller pieces and become smoother the longer the process continues.

Stages in the Development of a River Valley

The river cuts downward to form a ‘V’shaped valley. The river starts to meander

River uses its meanders to cut from side to side eating into the valley Floodplain starts to form 1 2

1 2

Floodplain River bluffs River cliff Alluvial deposits

River Valley Development A river has a life cycle from source to mouth. The processes at work cause changes to the river valley and river features in the landscape that it passes over. Traditionally this cycle has been described in 3 stages, the Upper (Torrent) section, the Middle (Valley) section and the Lower (Flood Plain) section. The terminology's Youthful, Mature and Old have also been used to describe the sections. The stages are not clearly defined but merge from one to the other and rivers show individual characteristics. There are river features that can be defined within a broad pattern. upper middle lower

How are V-shaped valleys formed ?

Use this sketch to help explain how they form Vertical abrasion

Also known as ‘ Torrent ’ or ‘ Youth ’ stages Interlocking Spurs In the Upper Course, the river is fast flowing, but there is little water and load. The river is often called a stream and does not have the erosive power to remove the hillsides (spurs), but erodes downwards instead. EROSION TYPE: Vertical and Headward