Notes
Water cycle, groundwater and rivers
- The water cycle: evaporation, transpiration, condensation, precipitation, runoff and infiltration, driven by the Sun and gravity.
- Aquifers hold groundwater; the water table tops the saturated zone. Gravel is permeable; clay is not.
- Stream gradient $\displaystyle = \frac{\text{drop}}{\text{distance}}$ and discharge $= \text{width} \times \text{depth} \times \text{velocity}$.
Oceans
- Salinity averages 3.5%. Surface currents are driven by wind and the Coriolis effect; deep currents by density.
- Wave speed $\displaystyle v = \frac{\lambda}{T}$. Tsunamis come from seafloor disturbances.
Tides
- Tides come from the Moon's and Sun's gravity. Spring tides (new and full moon) have the largest range; neap tides (quarters) the smallest.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Evaporation turns liquid water to vapor.
The saturated zone supplies water.
$120 \div 40 = 3$ m/km.
Cold salty water is dense and sinks.
$35 \div 5 = 7$ m/s.
Neap tides occur at the quarter moons.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A river flows through a valley. At one point its channel is 15 m wide and 3 m deep, and the water moves at 2 m/s. Upstream the river drops 600 m in 150 km. A storm drives waves with a wavelength of 90 m and a period of 9 s toward a coast.
(a) Calculate the river's discharge at that point.
Show the answer and scoring guide
$15 \times 3 \times 2 = 90$ m³/s.
Check off the points you earned:
(b) Calculate the upstream gradient and say what that suggests about the valley shape.
Show the answer and scoring guide
$600 \div 150 = 4$ m/km. A steeper gradient means faster water, so more downcutting and a V-shaped valley.
Check off the points you earned:
(c) Calculate the wave speed and explain what happens to the waves as they reach shallow water.
Show the answer and scoring guide
$90 \div 9 = 10$ m/s. In shallow water the waves slow down, get taller and break.
Check off the points you earned: