Background

The City of Hamilton must constantly monitor 130 stormwater management facilities with 70 ponds and wetlands designed to contain specific volumes (permanent pool) of stormwater as regulated by the Ministry of the Environment, Conservation, and Parks. Accurate data collection from these ponds is essential for compliance and informed decisions regarding dredging, the process of removing accumulated sediment to maintain capacity.

The city surveys these facilities on a three-year cycle to check for sediment buildup and water quality protection for its watersheds. Sediment accumulation is a crucial measure of the stormwater facilities' performance.

Challenges

Traditional methods of surveying these ponds involved manual measurements using a GNSS receiver rod from a rowboat, a time-consuming and labor-intensive process. The need to balance the timing of dredging operations posed a significant challenge. Dredging too frequently leads to unnecessary expenditures, while insufficient maintenance could result in flooding.

The existing method for sediment surveys involves two city workers manually measuring pond depths by boat, which requires loading a boat onto a large vehicle and launching it into various city ponds. This task becomes particularly challenging and hazardous at hard-to-reach sites like the ponds near Red Hill Valley Parkway, where space is limited off a busy highway. The process is time-consuming, demands adherence to safety protocols, and involves navigating steep or slippery banks, handling heavy equipment, and dealing with potentially variable conditions.

Additionally, the present method for sediment surveying has limitations that can impact its accuracy. City workers use a GPS receiver on an extended-range pole to measure sediment elevation at 10 different points within the facility. However, thick underwater vegetation can artificially raise the measured pond base level, while the survey rod's bottom plate may compress the sediment, giving a deeper measurement than intended. Windy conditions can also cause the boat to drift, reducing precision in pinpointing pond measurement locations.

Solution

The above mentioned conditions were the perfect opportunity to test a drone-based echo sounder.

A flight plan was created for each pond using UgCS, Flight Planning, and Control Software to set up flight paths in a grid pattern over the stormwater management facility (SWMF). The team operated a DJI M300 RTK drone to fly over the facility, using SPH Engineering system with an Echologger ECT 400S single-beam echo sounder to gather sound measurements. The echo sounder, suspended just below the water’s surface, was attached to a drone flying about 2 meters above the water, stabilized by a radar altimeter. The depth soundings were pinpointed using the drone’s real-time kinetic (RTK) global navigation satellite system (GNSS) positioning. The sonar data were processed with Hydromagic software, which produced a 3D model of the SWMF bottom and calculated the volume of water above it. Additionally, a second drone equipped with photogrammetry was used to capture a 3D model of the site above the water level, enhancing the survey’s comprehensiveness.

The project involved extensive data collection across various phases of the dredging process. The team employed a drone-based echo sounder to survey the wet operational ponds while using LiDAR, photogrammetry, and traditional surveying methods to gather data from dewatered ponds. This multifaceted approach allowed for thoroughly comparing and validating the new technology against established methods.

Outcome

The comparative review revealed minimal deviation in calculated volumes between the drone-mounted echo sounder and other survey technologies, confirming the reliability and accuracy of the new system. The increased efficiency and precision facilitated by the echo sounder system enables the City of Hamilton to optimize their maintenance schedules, ensuring that dredging investment can occur at the most opportune times to balance the cost and risk of non-compliance with legislation due to lack of water quality treatment capability of the stormwater infrastructure.

The volumetric data was collected pre- and post-dredge (with and without water) across three different technologies. The chart shows the correlation between the different volumetric calculations from all three technologies.

Conclusion

The successful deployment of drone-mounted echo sounder technology for surveying wet ponds in Hamilton significantly enhances stormwater management practices. This case study demonstrates the potential of unmanned autonomous SONAR solutions to transform traditional environmental management and compliance strategies, offering a more efficient, accurate, and cost-effective approach to maintaining crucial stormwater infrastructure.

The introduction of drone-mounted echo sounder technology provided an additional reliable solution. By utilizing this advanced system, the team could conduct more comprehensive surveys in less time, significantly increasing the accuracy of volumetric measurements essential for effective pond management while minimizing health & safety risk to workers associated with working around water.

Rather than basing the facility's capacity on ten measurements, this technology offers high-resolution mapping of the stormwater management facility (SWMF) and enables precise calculations of its current storage capacity. This accuracy eliminates the need for guesswork in planning SWMF maintenance schedules. It also conserves the natural ecosystems within each SWMF and saves money by preventing premature maintenance expenditures.