A few weeks ago, the MĀKI team invested in a new piece of kit - a CHIRP MEGA SI GPS scanner - for advanced underwater scanning and mapping. In true MĀKI spirit, we wouldn't call testing complete without actually going for a spin on water, so took to a local lake, lake Ngaroto, to both test out the kit and find out what interesting insights we might discover about this local lake.
Background on Lake Ngaroto
According to Waikato Regional Council, Lake Ngaroto is the largest of the Waipa peat lakes. It is located south of Hamilton city and north-west of Te Awamutu. The lake is hypertrophic - meaning it suffers poor water quality with:
A vey high level of nutrients
Over abundance of microscopic algae (including algae-blooms)
Lots of suspended sediment
As well as low water clarity.
A major effort had been launched by Waipa District Council since 1995 to return this lake to a more natural state, so while the catchment around the lake is mainly pastoral the council has created marginal strips of land around the lake that are fenced and replanted with native vegetation.
Find out more direct form the Waikato Regional Council website HERE.
The Scanning Process
Method
As the lake is around 108ha in area and motorboats are not permitted, in order to scan the lake efficiently, we decided to use the MĀKI inflatable e-kayak as the vessel. The advantage for using this inflatable vessel is that it's light yet rigid making it ideal for navigating around navigate with reeds, marginal plants surrounding the lake while able to handle the impact if we hit any submersed logs.
The sonar scanner was mounted on at the side of the vessel and a MĀKI autopilot e-kayak controls was was used as the main method of controlling the vessel. After estimating the depth of the water, we set the path and waypoints to maintain a consistent width apart in order maximize the quality of the scan by avoiding blind spots but also to minimize the number turns needed to completely scan the lake.
The combination of the MĀKI autopilot e-kayak controls with the MĀKI inflatable drop-stitch kayak was perfect for the job - it meant only one man is needed to transport and control the kayak for this scanning - and with a few tweaks the system can be turned into an automated "no-man" job in the future.
Video and photos of MĀKI e-kayak system.
Day 1
We started from the the north end of the lake, wind was mild which helped as we needed to turn sharply in some corners. Maybe due to the lack of human activity on the day, many big fish (Orange & White - most likely Koi Carp) could be seen. They were so large that they could even be seen on the FPV camera mounted on the kayak.
Day 2
This day we focused on the middle section of the lake with had the widest width. Wind was a little stronger (up to 15-18km/hr) but it caused no issues for the vessel. This day I decided to sit in the kayak to enjoy the ride and sunset while the kayak was doing its job. Other than fish, an interesting structure was found in the middle of the lake with a length of 55m. We have no idea what it might be but we are not going to disturb it. Day 2 ends with sundown and I struck conversation with a local person who recognized me from my social posts and had seen the work I was doing.
Day 3
The final day, and the weather was beautiful for scanning again. This time it was for southern end of the lake. We think we've found a number of what I assume to be small sunken boats (based on the shapes) however we can't be 100% certain. The scanning was successful and we used a manual control run to get as close as possible to the edge of the lake. I couldn't wait to get home and see the data.
Insights and Results
Topographical Layout
Using software we combined all the data into one project and a full bathymetric map was produced from it along with a 3D model. We also stitched all the side scan images into one image to get a better view of all the detailed structures at the bottom of the lake. As expected, the deepest part of the lake is in the middle with the current depth at 3.2m. The east end of the lake seems to be steeper than the west side. The volume of the lake was also calculated by using modelling.
Side-scanning clarity
As you can see in the images below, the side-scanning is high quality with lots of details and a high resolution result - even in such shallow water. To get results like this, the setting used while determining the scan path and any waypoints were crucial. By using the light weight kayak without a human in it, it can reach to the edge of the lake without worrying about it hitting the substrate. There is a GPS implemented to the scanner which allows us to match the images and videos its exact GPS location.
Features of interest
Below are some of the features of interest that we found during the scan:
A large spoked structure that was 55m in length.
Plants could be detected in the edges and shallows of the lake, however they may be debris and marginal plants rather than aquatic species.
There was essentially no plant life or other structures at the deeper areas of the lake (beyond 1.2-1.5m depth).
Some sunken objects could be seen for example a boat shaped object as well as some shapes that were most likely carp as many could be seen from the water surface during the scan
The water clarity was very low, it looked almost black, could barely see into the water except for the brightly coloured carp as they swam by.
Next Steps
With this scan as an example, we are hoping to be able to offer our skills towards improving on existing methods of environmental monitoring. Starting off with scanning and recording, our aim is to move towards monitoring and reporting, and subsequently implementation of maintenance systems in order to help maintain water quality and prevent future algae blooms at this and other lakes around NZ.
Scan & Recording
By simplifying the scanning process. MĀKI believes our system can do the job more efficiently and make regular scanning more viable. With regular scanning on a routine basis, we would be able to record any changes to the lake, and better track long term trends and any affects of seasonality.
Monitoring & Reporting
MĀKI has already started the investigation into water monitoring equipment and sampling. The next step will be the design of continuous monitoring equipment and reporting of the data so that environmental experts and analysts will be able to take the information to form new insights on lake health. Using data to narrow down the issues at each lake, identify the causes, and possible remedies.
Maintenance & Restoration
Once the core issue has been identified, with the expertise of the MĀKI team in software and robotics we can design and implement robotic systems for maintenance and systemize the restoration work at each lake. One specific example, might be to selectively cull pest species like carp. Through automation, there is potential to minimise the damage caused by nutrient run-off or pests, so that we can slow the effect, or perhaps even improve the lake quality in a sustainable way.
References
This scanning process was designed and refined by the MĀKI through the research and information we found on the Waikato Regional Council, Department of Conservation as well as the NIWA website.
Although this project was not commissioned by any of the above entities, we are thankful for the ongoing work each of these parties provide towards a better New Zealand - the care for our land, our water, as well as all the knowledge and in-depth information that they each chose to share widely with the public so that we can learn and appreciate the work that they've done over the decades.
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