Optimizing beach topographical field surveys: matching the effort with the objectives

In any study design, the surveying approach should match the objectives, thereby limiting the effort to focus on the purpose of the inquiry. Often, in beach geomorphological research, study design is based on expert judgment, that does not assure the optimization of the field surveys. In this study, several dimensions of survey strategies were evaluated to compare the outcomes and uncertainties associated with field data collection. The objective of this work is to assess the accuracy of the derived volumes achieved by different survey strategies, including cross- and alongshore lines, with varying density and spatial distribution, to optimize the field survey effort. A number of survey strategies are simulated, covering a range of data resolutions and configurations, replicating a number of possibilities for field data gathering. Topographical data from different field surveying approaches were analyzed for a 4 km long coastal stretch in Portugal. Measures of beach volume were computed from cross-shore as well as alongshore information, and the errors associated with each approach evaluated. Results show that beach volume varies with the adopted survey strategy. As an example, beach volume change can be adequately portrayed and survey effort minimized either through the surveying of 3 alongshore lines, or through 200 m spacing beach profiling. This work highlights the importance of the study design in beach contexts because of its inevitable influence on the results of volumetric change analyses.