Analysis of Georeferenced Sonar-Based Thalweg and Cross-Sectional River Depth Profile Measurements

Depth is a physical river characteristic that is important for habitat classification, river health analysis, and hydrologic/hydraulic modeling. Recent studies have shown that sonar can be an accurate way of measuring river depth, when compared to traditional techniques, but more study is necessary. The main objective of this research was to evaluate the utility of the CruzPro ATU120S and the Lowrance LMS-350A sonar depth units as tools for collecting river depth measurements along longitudinal (thalweg) and cross-sectional profiles. This included analyzing and evaluating the georeferenced commercially available sonar units for accuracy, precision, and response time under controlled lab and river test conditions. The CruzPro sonar unit is capable of accurately measuring dynamic depths greater than 0.5 m with average absolute percent error (AAPE) and average root mean square error (RMSE) values less than 8.9% and 0.08 m, respectively. Cross-sectional profile mapping utilizing sonar yielded RMSE values from 0.01 to 0.06 m and AAPE values from 2.06% to 4.23% at depths greater than 0.5 m. Sonar mapping systems were successful at collecting thalweg and cross-sectional depth profiles on the Driftwood River. A thalweg depth comparison between the two sonar units yielded no statistically significant difference in measured depths. Maximum cross-sectional depth and the cross-sectional area of a river were predicted using thalweg depth and river width with R² values of 0.49 and 0.69, respectively. Georeferenced sonar is an excellent tool for collecting large-scale accurate river depth in relatively short amounts of time as compared to traditional methods.