Here are the answers to the knowledge test at the end of the currents chapter in book two.
1. What is the approximate time difference between high tide and low tide? (Assuming you’re in a region that experiences typical semi-diurnal tides.)
Six hours approx.
2. If it’s high tide now, what will the tide state be around this time next week?
Low tide
3. When are tidal currents typically are at their strongest (and therefore most dangerous) in an estuary or harbor?
Around mid tide
4. Name three benefits of paddling at high tide:
• Slack water
• Least distance to carry your gear
• The most water, so the greater area to paddle
5. Name three negatives of paddling at low tide:
• The longest walk to the water’s edge
• The least amount of water – it may even dry out completely
• There may be exposed rockpools, mud or soft sand to get across
6. Name three factors that could cause a river current to change:
• rainfall upstream
• a reservoir gate opening
• the river narrows
7. When are tidal currents typically at their minimum in an estuary or harbor?
Typically at or around the top and bottom of the tide, although this can differ considerably around the mouth of the estuary.
True or false?
8. Tidal currents are less strong at full moon and new moon.
False. Full moon and new moon means spring tides, with the greatest tidal range and strongest currents.
9. Tide times and current flows can behave differently around estuary mouths compared to other coastal locations.
True
10. As a general rule, a 1mb pressure change results in a 10cm sea level change.
Luckily, false. Otherwise a 50mb pressure change would cause a 5m sea level change, which would be catastrophic! The correct rule is 1mb pressure change equates to 1cm sea level change.
11. Half of all the tidal change happens in the middle two hours of a standard six-hour tide.
True
12. Rip currents can happen at any coastal location, even if there are no waves at all.
False. Rip currents are caused by waves. However, they don’t need to be particularly big or powerful – any waves big enough to be pushing white water into the beach can create rips.
13. River currents are constant along the whole length of the river at any given moment
False. Currents can vary wildly along a stretch of river, depending on its width, depth and other factors.