From Spring to Estuary

In the picture

1. 1The ridge crest — the watershed boundary that separates this catchment from the next one.
2. 2The spring in the mossy rock notch — where groundwater reaches the surface and the channel begins.
3. 3The gravel bar at the confluence — where tributaries join the main channel and its discharge grows.
4. 4The sand bank inside the river bend — sediment dropped where the current slows on the inside of the curve.
5. 5The mudflat in the estuary — where the river meets the tide and releases its finest sediment.

Examples

• Rain falling on your roof runs into the gutter, then a drain, then a local stream — the same gathering pattern at a tiny scale.
• The Thames in London is still tidal near its mouth, so the water level rises and falls twice a day.

Quiz: From Spring to Estuary (Age 15)

1. 1

   A high ridge runs along the edge of a river catchment. What does that ridge decide?

   • Which river system the rain falling on each side will drain into
   • Where underground water first breaks out of the rock as a spring
   • How far inland the tide can push salt water up the channel
2. 2

   Sand and gravel often pile up on the inside of a river bend. Why does the river drop its load there?

   • The water is deepest on the inside of the curve, so sediment sinks out of reach of the flow
   • The current is slower on the inside of the curve, so the water can no longer carry the sediment
   • The bank on the inside of the curve is being eroded, so its material falls into the water
3. 3

   What makes the estuary at the end of a river different from the stretches further upstream?

   • The river flows fastest there, so it scours out a deep, clean channel
   • Tributaries stop joining there, so the river’s discharge falls sharply
   • Fresh water meets the incoming tide there, and the river releases its finest sediment

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.