Terrestrial Laser Scanning for Monitoring Streambank Retreat: Comparison with Traditional Surveying Techniques

Data concerning streambank retreat (SBR) rates are important for many different engineering applications such as stream restoration and total maximum daily load (TMDL) development. However, measurement of SBR can be time-consuming and is often characterized by large measurement and interpolation errors. These errors propagate into the calculation of sediment budgets for the development of TMDLs, creating uncertainty in source partitioning and overall load estimates. We compared two techniques for measuring SBR: (1) traditional surveying with a total station and (2) terrestrial laser scanning (TLS). An 11-m streambank on Stroubles Creek in Blacksburg, Virgina was surveyed six times over a 2-year period. The average SBR along the entire bank was estimated to be -0.15 m/year with TLS and -0.18 m/year with total station surveying. The resulting differences in median SBR estimates along five distinct cross sections between each of the survey dates ranged from -0.11 to +0.06 m. This error in SBR due to total station surveying would be significant when extrapolating to a reach- or watershed-scale estimate of sediment load due to SBR. In addition, TLS collects data across the entire streambank surface, rather than just at distinct cross sections, providing much more information concerning SBR volumes and spatial variability.