Geography: All Topics

The area of land drained by a river and its tributaries. Also called a river basin or catchment.

The place where a river starts, usually in an upland area (e.g. a spring, lake, marsh or melting glacier).

The place where a river ends, flowing into a sea, ocean or lake (sometimes through an estuary or delta).

A smaller river or stream that flows into a larger (main) river.

The point where two rivers meet, e.g. where a tributary joins the main river.

The boundary of a drainage basin. It is usually a ridge of high land that separates one drainage basin from the next.

The course the river flows along, made up of the bed (bottom) and the banks (sides).

The volume of water passing a point in a river each second. It is measured in cumecs (cubic metres per second, m³/s).

The speed of the water's flow, measured in metres per second (m/s).

The distance across the channel from one bank to the other, measured at the water surface.

The distance from the water surface down to the river bed. It is usually given as a mean (average) of several measurements taken across the channel.

How the gradient (height) of a river changes from its source to its mouth, shown side-on as a graph of height against distance downstream.

The shape of the valley (or channel) seen as a cross-section from one side to the other.

A smooth concave curve: steep near the source (upper course), gentler in the middle course and almost flat near the mouth (lower course). There can be irregular steps (knick points) at waterfalls or rapids where the rock hardness changes.

Upper course: narrow, steep-sided V-shaped valley. Middle course: wider valley with gentler sides. Lower course: very wide, flat valley floor (floodplain).

The total length of the bed and banks that are in contact with the water in a cross-section of the channel. The water surface is NOT included.

Discharge (cumecs) = Cross-sectional area (m²) x Velocity (m/s).

Cross-sectional area (m²) = Width (m) x Mean depth (m).

The bigger the wetted perimeter compared with the amount of water, the more water is in contact with the bed and banks. This means more friction, so more energy is lost and the water flows more slowly.

The channel is where the water actually flows (bed and banks). The valley is the whole landform the river flows through, including the valley floor and valley sides.

In the centre of the channel, just below the surface. This is furthest from the friction of the bed and banks. Flow is slowest next to the bed and banks.

Width: stretch a tape measure across the river from bank to bank at the water's edge. Depth: use a metre ruler at regular intervals across the channel (e.g. every 50 cm), then work out the mean depth.

Float method: time a float (e.g. an orange or a dog biscuit) over a measured distance (e.g. 10 m). Velocity = distance ÷ time. Repeat at least 3 times and take an average. Alternatively, use a flowmeter (impeller) for more accurate readings.

Hydraulic radius = Cross-sectional area ÷ Wetted perimeter. A higher hydraulic radius means a more efficient channel: less of the water is slowed by friction, so the river can flow faster.

Cross-sectional area = 6 x 0.5 = 3 m². Discharge = 3 x 0.4 = 1.2 cumecs (m³/s).

Wetted perimeter = 1 + 4 + 1 = 6 m (bed + both banks). Cross-sectional area = 4 x 1 = 4 m². Hydraulic radius = 4 ÷ 6 = 0.67 m (2 d.p.).

Channel A: wetted perimeter = 8 + 0.5 + 0.5 = 9 m, hydraulic radius = 4 ÷ 9 = 0.44. Channel B: wetted perimeter = 6 m, hydraulic radius = 0.67. Channel B is more efficient because less water is in contact with the bed and banks, so it loses less energy to friction and is likely to flow faster.

Floats only measure surface speed, which is faster than the average speed. They can get caught in eddies, vegetation or the bank, be pushed by wind, and stopwatch reaction times cause errors. To improve: repeat and average the readings, use the same float each time, or use a flowmeter.

How the characteristics of a river change downstream, from the source to the mouth.

Discharge, occupied channel width, channel depth, average velocity and load quantity.