Leveling rod base required for surveying gravel river bed surface elevations

Consistent surveying of bed elevations in natural channels containing grave l and cobble substrates is subject to measurement error if a leveling rod i s placed indiscriminately between or on top of individual particles. The in fluence of surface microtopography decreases with increasing leveling rod b ase diameter, while the influence of bed form topography increases. Field t ests were performed to identify a rod base diameter that minimizes these su rvey errors. A leveling rod base diameter of 127 mm (5 inches) is suggested to be most appropriate for consistent bed surveys.