Determination of Geographically Isolated Wetland Bathymetry with a Low-Cost Commercial Sonar Scanner and Evaluation of Geometric Bathymetry Methods

Geographically isolated wetlands, a common feature of many landscapes, provide valuable ecosystem services such as wildlife habitat, water storage, and nutrient processing. Accurate depth-area-volume relationships based on wetland bathymetry are needed for analysis of hydrology and related functional processes. However, existing methods for determining wetland bathymetry are either costly and labor intensive or have large associated uncertainty. In this study, we developed a simple, field-based method to characterize geographically isolated wetland bathymetry using a low-cost Deeper Smart Sonar CHIRP 2 + fish finder and demonstrated the method in three seasonally inundated wetlands. Using sonar-derived measurements of depth, we created a high spatial resolution (1 m) bathymetry map via interpolation. We assessed the accuracy of sonar bathymetry with terrestrial lidar scans when the wetlands were dry. The depth-area-volume relationships from the novel sonar method were shown to correspond to the terrestrial lidar scans with Nash-Sutcliffe Efficiency values above or equal to 0.85. The results from the sonar method were also compared to a parameterization of a geometric bathymetry equation, which is a common approach in larger scale studies of geographically isolated wetlands. This geometric equation provided good accuracy when parameterized directly to terrestrial lidar data, and the sonar depth method performed similarly. The sonar depth method offers a quick and cost-effective way to obtain precise depth-area-volume relationships for small wetlands. These results will improve wetland science and management by allowing more precise quantification of bathymetry-dependent ecosystem processes and services.