Bathymetric Mapping: Modern Methods Yielding Better Data, Better Outcomes
When balancing functionality, safety, and design aesthetics against time, cost, and legal constraints, you can never have too much data. The role of the surveyor is critical in this regard as the data gathered—from boundary lines to the relevant shape and contour of a specific site—provides the foundation for how a project can move forward.
In the pursuit of highly accurate and reliable data, a familiar balancing act is at play: safety, cost, and time. This is especially true in hydrography and bathymetry mapping where access to waterways can be challenging or dangerous to survey crews and additional equipment and personnel may be required. Advancements in sonar imaging technology, coupled with remote data collection capabilities, is making this balancing act and the collection of reliable and accurate data much easier. It is this last piece of the puzzle, remote data collection, that has the survey teams at Otak pretty excited.
“We now have an easy way of collecting a significant amount of accurate data for mapping channel bottoms to aid in our fish passage and stream restoration work, as well as construction and engineering projects that are either abutted against bodies of water or submerged,” Nathan Dasler, Otak Water Resources Engineer, states. What Nathan is referring to is the capabilities of the single beam sonar unit Otak’s survey teams now employ via an unmanned surface vessel (USV).
Remote Data Collection
Utilizing single beam sonar echo sounding, mounted on an unmanned surface vessel (USV), Otak’s survey crews are able to collect detailed data of stream, river, and lake beds and precisely map the underwater topography. Portable sonars, like the one Otak uses, quickly measure and log depths with a high degree of accuracy, providing a seamless transition between land and bathymetric survey. The USV essentially extends the capabilities of traditional survey equipment, enabling remote data collection in otherwise challenging or inaccessible environments. GPS tracking and an autonomous control system also allow the USV to be pre-programmed to follow specific, repeatable track lines. This increases data acquisition consistency and efficiency. In situations where multiple surveys are needed over time, reliable data can be collected efficiently in the same location, and with extreme precision.
In addition to more complete data, Jon Yamashita, Otak Director of Land Surveying also points out the added cost savings as the USV can be operated by one person. “Whereas in certain situations we might have had to work with three people doing the work previously for safety and logistical reasons, we now only need one person. This significantly reduces our costs to do certain types of survey work, which of course reduces the costs for our clients.”
The application and use of the technology and equipment in the field are proving to be beneficial in a number of settings and project types.
In the state of Oregon, certain property lines are based on an elevation and, for sites immediately adjacent to tidal bodies of water, those elevations may be underwater and not always accessible during much of the year. Depending on the time of year, shoreline accessibility and water flow can vary significantly. With remote data collection capabilities, water level, and flow, for example, no longer matter. “We can still find and follow the contour of the land beneath the water and accurately determine property lines, even during high flow seasons,” Jon states. “We no longer have to wait for low flows which may only be at certain times of the year.”
In addition to shoreline validation, projects and developments that border or cross bodies of water need accurate hydraulic modeling. “Any construction work that is performed within a floodplain requires hydraulic modeling to verify flooding impacts from the project and, right now, we’re starting to see state agencies require more data-intensive models,” Nathan states. “Agencies are requiring 2D hydraulic models, which really need a full map of what the bottom of a river looks like and not just sections spaced at your typical 100 feet.” With remote access, Otak’s hydraulic surveyors are able to efficiently collect more refined data and provide highly accurate terrain for models.
“This level of data is key for the hydraulic modeling necessary in our bridge and culvert work,” Jon adds. As Nathan explains, “if you’re going to restore a riverbank or protect a bridge abutment, you need a hydraulic model to know how fast and how deep the water is flowing there. You don’t know those hydraulic characteristics without having good detail of what the channel looks like. The USV is what we’ll use to get that detailed information.”
Understanding sedimentation levels in rivers, lakes, and reservoirs is also key to understanding, predicting, and managing depths for river passage, aquatic habitats, floodwater capacity, and the integrity of structures like levees, bridges, and pier footing. Remote access and a pre-programmable auto-drive system, like the one Otak is using, is extremely useful when collecting sedimentation data over time. As Jon explains, “we can run a pre-programmed route to map the exact same points over and over again and this allows us to reliably quantify bed changes.”
Otak has long been at the forefront of survey and mapping processes and electronic data collection. Staying abreast of the latest advancements in mapping methods and equipment assures Otak’s surveyors are able to provide the highly accurate and reliable data necessary for successful project design and engineering outcomes. Single beam sonar echo sounding coupled with an unmanned surface vessel is the latest example of how Otak is able to balance data collection needs against time, safety, and cost constraints. As Jon puts it, “we want our maps to depict what all the surfaces look like as accurately as possible. This technology and equipment give us the ability to easily and efficiently obtain a lot of data—we’re able to just get more data in the same amount of time.”
The technology and the data it yields removes some of the unknowns and this, in turn, allows designs to be more efficient, and ultimately more cost-effective. In the end, as Jon reminds us, “it’s not just about the new technology or even the data, it’s about how accurate data can be used for better outcomes.”