Application of Portable Traps for Obtaining Point Measurements of Sediment Transport Rates in the Surf Zone

Abstract

This paper describes a portable trap developed and applied to measure the vertical and lateral distributions of the longshore sand transport rate in the surf zone. Both bedload and suspended load transport rates can be measured. The trap consists of long rectangular bags of polyester sieve cloth vertically mounted on a stainless steel rack. An operator standing downcurrent attends the trap during- a sampling interval typically lasting- 5 to 10 minutes. Presently, use of the trap is restricted to surf zones with wave heights less than about 1m. Traps successfully functioned in a major field experiment on the Atlantic Ocean coast involving approximately 150 trap deployments, and yielding more than 500 sand samples. In reproducibility tests performed by using pairs of traps in close proximity, measured vertical distributions of the sand transport rate were found to be in fair to good agreement. Examples of field results of reproducibility tests and data on the lateral and vertical distributions of the longshore transport rate are presented. The utility of the trap is put in perspective in a critical review of available methods for measuring long-shore sand transport rates. It is concluded that, at present, traps provide the only practical method for making short-term point measurements of sand transport rates in the surf zone.