Ground Survey Methods for Mixed Sand and Gravel Beaches in Intertidal Environments: A Comparison

Abstract

An assessment of variation in beach volumes is needed to better understand beach behaviour and to monitor changes in an attempt to manage beach volume distribution through targeted intervention. Mixed sand and gravel beaches, as well as gravel beaches, are distinct from sandy beaches in that they often have multiple steep (>20° or 1 : 4) berms on the upper part of the beach and short-wavelength (<20 m) longshore variations in the form of beach cusps or in close proximity to groynes. This paper discusses a range of ground survey and remote sensing methods for surveying mixed beaches, methods of point collection in relation to the different methods, and subsequent interpolation to calculate beach volumes. Particular emphasis is given to high-density surveys by Global Positioning System (GPS) with a rover attached to a wheel. Results show that average surface elevation changes greater than ±0.04 m can be reliably detected and that the method, if carried out using cross-shore profiles, provides a useful tool for beach monitoring in scientific projects interested in inferring processes from the surveys and that have a temporal resolution from tides to weeks. For surveys predominantly interested in monitoring total beach volume, GPS surveys with a quad bike (all-terrain vehicle) might be more economical while providing only marginally poorer results if surveys coincide with minimum cross-shore variation during spring tide. Comparisons between ground surveys with GPS and remote sensing methods like LIDAR or airborne photogrammetry are also discussed.