Evaluating low-cost topographic surveys for computations of conveyance

Abstract. Rapid modern technological advancements have led to significant improvements in river monitoring using unmanned aerial vehicles (UAVs), photogrammetric reconstruction software, and low-cost real-time kinematic Global Navigation Satellite System (RTK GNSS) equipment. UAVs allow for the collection of dry bathymetric data environments that are difficult access. Low-cost RTK GNSS equipment facilitates accurate measurement wet bathymetry when combined with subaqueous measuring tools such as acoustic Doppler current profilers (ADCPs). Hydraulic models may be constructed from these data, which turn can used various applications water management, forecasting, early warning disaster preparedness by responsible authorities, construction rating curves. We hypothesise terrain UAV-based photogrammetry leads geometries particularly fit hydraulic understanding simulation models. This study sought (1) compare open-source commercial packages verify if authorities low resource availability option utilise without compromise on accuracy; (2) assess impact variations number ground control points (GCPs) distribution GCP markers quality digital elevation (DEMs), a particular emphasis characteristics hydraulics; (3) investigate reconstructions based different numbers conveyance slope. A novel method makes use simple tie line along edge measured but highly is presented so correct unwanted effect lens distortion (“doming effect”) enable concatenation geometric sources. Furthermore, we describe how merging achieved through gridding linear interpolation. tested our approach over section Luangwa River Zambia. Results indicate software package capable producing results comparable commercially available options. determined GCPs essential vertical accuracy, also an increase above limited five only moderately increases accuracy results, provided well spaced both horizontal dimension. insignificant differences among cross sections observed, corroborating fact well-spaced set enough establish hydraulically sound reconstruction. However, it appeared necessary make additional observation slope derived merely UAV survey was shown prone considerable errors caused distortion. Combination made suitable model setup.