ABSTRACT
Accurate determination of the water surface slope (WSS) is essential for hydraulic calculations, yet it remains challenging in lowland rivers with gentle gradients, particularly over short reaches. Existing methods such as leveling, satellite data, TLS, or photogrammetry show significant limitations in small streams. This study presents a novel tachymetric approach that employs a robotic total station to continuously track a specially designed floating target drifting with the current. Field tests conducted on the Ślęza River demonstrated that the method enables continuous WSS profiling and achieves high precision, with measurement accuracy up to 2.5 mm. Compared to the reference method, the approach offered superior accuracy and eliminated the need for an operator holding a staff on the water surface. The results confirm the potential of this technique for precise WSS determination in lowland streams over short distances. The developed technique is potentially very useful in mining damage areas where, over short distances, the subsidence of the ground surface also causes a change in the slope of the streams.
