Year 4- Geographical background for section A
Site 1: Stream of the first order (no tributary) Catchment area: 9 km²
Geology: Limestone cliffs, consisting of permeable limestone with lots of bedding planes,
cracks and joints, allowing water to infiltrate (pass through it). This affects the volume of
water in the river channel as water doesn’t run off directly to the stream after rain + no
tributary = Small volume of water
High roughness of the channel
- Large boulders in the channel/ Vegetation  increase friction reduced velocity
Site 2: Stream of the second order (a few tributaries) Catchment area: 77 km²
Geology: The banks of the river and the sides of the valley are made of alluvium, which is a
material deposited by rivers. This is coarse sediment, gravel and clay that are permeable,
affecting the volume of water in the river channel, which decreases rapidly as water
infiltrates the surface and goes to the aquifer underground.
Human activity
Impact of agriculture on the
discharge of the river: people
abstract water from the river for
irrigation, decreasing its
discharge.
Roughness: Boulders and vegetation  friction affects velocity
Site 3: Stream of the third order (many tributaries) Catchment area (km²): 84
Geology: River channel made of coarse sediment, gravel and clay, that are permeable,
affecting the volume of water in the river channel, which decreases rapidly as water
infiltrates the surface and goes to the aquifer underground.
Human activity
Impact of agriculture on the volume of water in the river channel: people abstract water from
the river for irrigation.
Before the bridge: Increased roughness due to vegetation (Eutrophication). The channel
was widened 6 years ago, increasing friction.
After the bridge: Smaller channel than before the bridge, not affected by human impact.
Boulders in the river channel. Vegetation on the banks.