Junior Cert Geography: Rivers Revision

River Source: The place where a river begins.
Watershed: The area of land where rainwater collects and drains into the river.
Tributary: A smaller stream or river that joins the main river.
Confluence: The exact spot where two rivers or a tributary and a river meet.
Estuary: The wide part of the river near the sea where fresh river water mixes with salty sea tides.
River Mouth: The end of the river where it empties into the sea.

The Youthful Stage:
- Steep slope.
- Fast, powerful water.
- Carves out steep V-shaped valleys.
The Mature Stage:
- Gentle slope.
- Slower-moving water.
- Wider valley with gentle slopes on the sides.
The Old Age Stage:
- Almost completely flat slope.
- Very slow water flowing through flat lowlands.

Hydraulic Action: The force of rushing water slamming against the riverbed and banks, breaking pieces away. Faster water causes more erosion.
Abrasion: Rocks, stones, and pebbles carried by the river scraping along the river floor like sandpaper, wearing it down and making it deeper.
Attrition: Rocks and boulders carried in the river colliding with each other, smashing into smaller, smoother, and rounder pieces.
Solution: River water dissolving soluble rocks along the riverbed through chemical reactions.

Rolling and Dragging (Traction): Heavy boulders and big rocks rolled along the riverbed by the water.
Bouncing (Saltation): Medium-sized pebbles skipping and hopping along the riverbed.
Suspension: Fine sand, silt, and tiny stones floating in the water without touching the bottom.
Solution: Dissolved minerals carried invisibly within the water.
Floatation: Light materials like leaves and twigs floating on top of the water's surface.

Interlocking Spurs:
- Ridges of hard rock that stick out into the valley.
- Because the youthful river lacks the energy to cut straight through them, it bends and winds around them.
V-Shaped Valleys:
- Formed as the river cuts straight down into the ground (vertical erosion).
- Weathering weakens the valley sides, causing loose rock and soil to fall into the river, leaving behind a sharp V shape.
Waterfalls:
- How they form: Occur when a river flows over a layer of hard rock situated next to softer rock downstream.
- Erosion: The softer rock wears away much faster, creating a sudden drop.
- Plunge pool: Rushing water and swirling pebbles carve out a deep pool at the bottom.
- Collapse and retreat: The hard rock overhang above the pool loses support and collapses. Over many years, this repeats and the waterfall slowly moves upstream.
- Examples: Powerscourt, County Wicklow.

Meanders:
- Large bends and loops that form along the middle part of a river.
- Outside bend: Water moves fastest here, eroding the bank and making the bend wider.
- Inside bend: Water moves slowly, dropping its carried load (deposition) and building up a gentle bank.

Oxbow Lakes:
- Horseshoe-shaped lakes cut off from the main river.
- Flooding: Heavy floods increase the river's speed and volume.
- Short cut: The river bursts through the narrow neck of a meander to take the straightest, easiest route.
- Sealing off: The abandoned curve receives slow water, deposits mud at both ends, and eventually gets completely sealed off into a standalone lake.
Levees:
- Naturally raised banks of mud and silt (alluvium) along the edges of an old river.
- When the river floods, it carries silt onto the flat land.
- As the water recedes, it loses energy and drops the heaviest material right along the banks.
- Repeated floods build these deposits into elevated ridges.

Location: Ardnacrusha on the River Shannon in Ireland.
Operator: The ESB (Electricity Supply Board).
Purpose: Generating hydroelectric power (clean electricity) using river energy.
The Project: A large concrete dam was built across the river valley, creating an artificial lake behind it.
Advantages: Produces clean, renewable, and free electricity.
Disadvantages: Flooded fertile farmland upstream to make room for the reservoir.