“This new type of lidar instrument should be able to give us a fresh look at our vegetation maps in Spring Lake and portions of the San Marcos River we’ve been restoring over the last several years,” said Christopher Riggins, a wildlife and fisheries biologist at the Meadows Center for Water and Environment in San Marcos (MCWE). “Routine sampling of Spring Lake includes species counts and surveys of specific sections of Spring Lake. With these bathymetric lidar 3-D data, we will have a much more detailed look at the lake bed, the amount of aquatic habitat, and the aquatic vegetation density and plant morphology (plant structure).”

Riggins’ team, the Ecological Research Group at MCWE, has two primary roles. One is habitat restoration which includes removing invasive, non-native plants from Spring Lake and San Marcos River. They also dislodge vegetation or algal growth that could be impeding springflows from the five major springs and more than 100 minor spring openings. Additionally, they plant native aquatic vegetation in those water bodies to replace and enhance aquatic habitat for other native species, primarily the endangered fountain darter fish. Spring Lake is critical habitat for five of the EAHCP’s covered species: fountain darter, Texas wild-rice plant, San Marcos salamander, Texas blind salamander, and a small population of the Comal Spring riffle beetle. 

Both the San Marcos River and Spring Lake are national tourist destinations due to the extremely clear and cool water that emanates from the San Marcos Springs. A critical part of the EAHCP programming is measuring the impacts of recreation on the San Marcos Springs ecosystem. The new bathymetric lidar images could also play into how the City of San Marcos and Texas State University teach people about water, the endangered species that thrive there and how people enjoying the San Marcos River can actively help protect those natural resources.

The drone-mounted bathymetric lidar equipment was provided by Frontier Precision and operated by Austin Rains, Frontier’s regional sales manager in the Southern U.S.

“What was so enticing about this project in Spring Lake is that the water here is so clear,” Rains explained. “Spring water is perfect for this type of technology because a LiDAR sensor can see all the way to the lake bed with no difficulty. We’ve done projects in Louisiana and other places with very turbid water which will not yield the level of detail for the client that this location will.  Lidar data is initially collected as a “point cloud” of millions of data points reflected from the land surface, river bottom, trees and other vegetation and even structures that might be there. Those data points are then assembled into detailed three-dimensional maps. The EAHCP program and professionals, like Chris, who are responsible for these mapping programs, can then assess trends over time. We’ll be very interested to learn how the higher-detailed maps this technology affords helps with upcoming Spring Lake assessments.”

To that end, Riggins noted that since this is the first time using bathymetric lidar in San Marcos, part of the learning process will focus on how they can use the technology. In the past, the team manually mapped the the aquatic vegetation of Spring Lake with 2-dimensional polygon shapefiles. That type of process will not yield a 3-D type of map. The orders of magnitude of data this lidar will provide over manual mapping will not only help save tremendous amounts of time in data gathering but provide a much more detailed assessment of aquatic habitat conditions.

“There are some specific points of interest we will be looking for,” Riggins said. “For example, the considerable amount of new data and associated map details of the open substrate in the lake will help us assess the status of the San Marcos salamanders which live in and near the spring openings. Also, the 3-D map will give us a better gauge of the volume of plants we are tracking.”

Traditional lidar is based on the machine’s laser sending out pulses from the air to the first hard object encountered on the ground. Those pulses reflect to the airborne receiver and vertical space data is captured. The type of bathymetric lidar Frontier employs is called “full wave lidar” or “green wave lidar.” There are two extremely strong lasers on board the drone which do not use pulses but are always connected to the targets on land or in water. Traditional lidar can work through tree canopies and other vegetation, but it will only measure the tops of water bodies. Full wave lidar is designed to penetrate water until it hits a hard object at the bottom of the water body.

“We’ve been doing vegetation mapping since 2010, but the level of data and the frequency of how often we collect that information has been increasing over time. The bathymetric lidar collection will be the most data we’ve ever collected in the shortest amount of time. In two hours of flying the drone, Austin was able to cover around 40 acres and gather much higher densities of data than we can using current methods. Also, we will now have a colorized, survey-grade representation of Spring Lake’s lake floor which we could not have produced with traditional mapping techniques. And that is a truly exciting type of development in our work to protect the unique ecosystem in San Marcos.”

You can learn from about Frontier Precision at this link.