This is an EarthCache, there is no physical cache to find, to log a find, visit the location and complete all the questions at the bottom of the page, and message the answers to me via my profile, I will respond to you saying if you have given me the right answers or not.
This EarthCache is about flooding and sedimentation. It is at the Royal Park/Seaport area, best visited at high tide when the silt isn't visible. The two signs at the two waypoints have the information you will need to complete this EarthCache.
The Tamar River is not technically a river, it is an estuary, this means the tide impacts the level of the water, but they are protected from the full force of the ocean, and are usually surrounded by reefs, barrier island, sand or mud.
Sedimentation: Sedimentation is the word to describe the process of sediments gathering at the bottom of a fluid. In the Tamar River, sediments flow into the estuary, flocculate (clump together) and then flow further into the Tamar, getting bigger along the way. But when the tide goes out, not very much sediment flows back out into the ocean. The sediments in the Tamar is mostly made of top soil with fine particles of clay and silt. Over time, this causes big problems, with silt building up so eventually, it would be too shallow for boats. The only solution is for ships to collect the silt, and move it out of the Tamar (dredging).
Sedimentation in an estuary diagram.
Flooding: Flooding can be caused by heavy rainfall, storm surges or tsunamis, in Tasmania, floods are typically caused by heavy rainfall. Major floods usually cause lots of damage and can be fatal. The 1929 flood was the biggest flood in Launceston on record, about 2,000 homes were damaged or washed away and 14-22 people were killed. This was a major flood (you can see the flood markers all around Invermay).
In June 2016, historic major floods lashed Tasmania. Floodwaters at Royal Park reached as far as the top of the first step on the flood levee. The deaths of three people were among the tragic consequences of the floods. There was an estimated $100 million damage, coming mostly from farms. Over 60 homes were damaged, including 20 at Latrobe which were left severely damaged, and in Launceston, homes at Newstead were inundated.
Flooding at Royal Park in June 2016.
Flooding at the Seaport near WP2.
1929 Launceston floods.
Questions:
1. At the time of your visit, was the tide high or low, and was it on the way in or out?
2. Describe the turbidity (cloudiness) of the water at your visit.
3. (Sedimentation) according to the sign at WP1, up to how deep is the lower estuary?
4. (Sedimentation) on average, how many cubic metres of sediment is deposited in the Tamar each year? (see WP1)
5. (Flooding) in a 1-in-200 year flood, significant dredging would lower the flood level by about how many centimetres?
6. (Flooding) according to the sign at WP2, how may significant floods have occurred since records began?
7. (Optional) Photos you took at the location are most welcome.
A few things you should know:
Message these answers to me via my GC profile.
Do not put answers in your log.
If you wish, I will let you log a find before I reply to keep finds in order, but you must complete and send the answers to me within a timely matter (2-3 weeks)
Please only give answers or hints to anyone who was with you on the day.
I may delete your log if:
You have put answers/spoilers in your log.
You have not sent the answers to me within timely matter (1-2 weeks) or you have not completed all of the answers.
I hope you enjoy 'finding' this EarthCache!
Ref: QVMAG Douglas Ewington 28/10/08