On Monday, 13th March, the Y13 Geography class travelled to Dunedin to investigate the Leith Stream. They spent the day investigating the spatial variation of the stream; in particular, did the river channel get wider from its upper to lower reaches? Where was it the deepest and fastest flowing? Where was the largest sediment (rocks) found? What were the human modifications, and how did this impact channel morphology?
Students visited various sites down the river, unfortunately, the heavy rainfall earlier that morning meant that the flow was too fast, high, and dirty to physically enter the river. Students had to problem-solve how they could safely gather their data, including modifying the float method to use the age-old method of “Pooh” sticks and the more digital tech options of phone Aps to measure the width.
On the second day, we wandered down Castle Street with the flow of students going to 9 am lectures and spent the morning in a Geography lab finding out about the high-tech equipment the university students use to gather data. Professor Tom Redpath talked to us about the digital approach. This is called Velocimetry. It involves taking photos of the river and tracking the velocity with dye, then using computer software to track the images and determine the velocity. The students got to see the various other equipment, such as flow trackers, current meters, and the Acoustic Doppler Current Profiler (ADCP), which is mounted to a remote control boat. This technique involves sending sound waves into the water and measuring the frequency shift of the waves as they bounce back off the moving particles in the stream to measure the speed and direction of water currents.
We then meet with Dr. Raphael Krier-Mariani at St Clair beach to learn about the impact of coastal processes, and the issue of coastal erosion. He outlined the various methods used for the management of coastal erosion. He discussed the options available to the Dunedin City Council in their Coastal Plan for St Clair / St Kilda beach. It was very interesting to learn about the various methods and apply them to the erosion issues in North Otago.
A big thank you to Mrs. Williams who gave up her time to accompany us on this trip.