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Original SET
1) Design history of the SET
2) Components of the SET
3) Components of the Benchmark
Bombay Hook NWR, DE USA
Design of the SET

The original SET design of Boumans and Day (1993) has undergone three major modifications to improve precision and handling (Cahoon et al. 2002a).

Original SET

Version 1 - Original SET Design

The concept for the Boumans and Day (1993) SET was derived from an apparatus designed by Schoot and de Jong (1982) called the Sedi-Eros Table. This apparatus was used to measure elevation of exposed mudflats during low water in the Netherlands (Schoot and de Jong 1982; van Erdt 1985). The design of the Sedi-Eros Table is comparatively small and lightweight.

Boumans and Day (1993), using the general principle of the Sedi-Eros Table, designed a larger device they named the Sedimentation-Erosion Table (SET) to sample shallow water bottoms in Louisiana. The depth of the water required that the SET be taller and longer (> 1 m in length). The increased weight of the SET required a sturdier and deeper bench mark (up to 6 to 9 m). Boumans and Day (1993) designed a table with three plates and a remote release mechanism (sliding middle plate) for lowering the pins to the subtidal sediment surface in order to minimize disturbance of the bottom sediments created by a sampling platform. The platform is established on one side of the bench mark only and the long arm is deployed in a direction away from the platform. Pins with 5-cm diameter "feet" and floats are remotely released and lowered to the sediment surface, the pins locked in place by the remote mechanism, the SET removed from the bench mark, and the pins measured on the platform.

This version of the SET was also used in salt marshes in Georgia (Boumans and Day 1993), as well as in Maryland and South Carolina (Childers et al. 1993) where its larger size facilitated sampling in tall vegetation. The ends of the pins without "feet" were manually placed on the sediment surface, rather than remotely released, to accommodate the presence of vegetation. Thus the sliding-plate, remote-release mechanism, which allowed a substantial amount of "play" in the placement of the 90 cm long pins, was not needed in vegetated wetlands where (1) the sampling platform had little to no effect on sediment scouring because the vegetation canopy baffled water flows and plant roots bound the sediment particles, and (2) the pins had to be manually placed around the vegetation.

Version 1 Version 1
Version 2
The realization that the movable plate in Version 1 was not necessary, led to the development of a new version of the SET consisting of a single plate with collars around the pins to reduce "play", or movement when they are placed on the marsh surface. This single-plate version of the SET was originally built with 2.5 cm collars which were located on the topside of the plate.

a) Lighter design.
b) no movable plate
c) 2.5 cm (1 inch) Collars with set screws to hold pins in place.
Version 2
Version 2
Version 2 - Tijuana Slough NWR, CA USA
Version 2
SET- Version 2 Collars
SET - Version 2

Version 3
To further reduce the "play" in the pins, the 2.5 cm collars were replaced with longer (7.5 cm) collars which were attached to the underside of the plate to reduce the distance from the marsh surface to the pin hole. In addition, the pin hole was narrower to further reduce movement from side to side. Badge clips were used to hold the pins in place because they were easier and quicker to use than the set screws.

a) Longer collars with on the underside of the plate with smaller diameter holes.

Version 3
Version 3 - Delta NWR, LA USA
Version 4

Version 3 of the SET was modified by replacing the brass measuring pins with larger-diameter fiberglass rods that are less prone to bending. These pins, though larger in diameter (1/4" versus 1/8"), were considerably lighter and were much less likely to get bent from handling. This also decreased the weight of the instrument, especially when using longer 4 to 5' long pins in shallow water environments.

a) lighter pins which are flexible and not prone to bending.

Version 4
Version 4 - Sapelo Island, GA USA
Version 4
Version 4 - Blackwater NWR, MD USA
All 4 versions - diagram
Image from Cahoon et al. 2002a
Components of the SET

A) Instrument: The original SET (Version 4) is custom-built out of aluminum and stainless steel so it is not adversely affected by saltwater environments. The instrument weighs about 14-15 lb (6.5 kg) and measures about 53" long (135 cm), 24" (61 cm) high, and 10" (26 cm) wide. The instrument is custom built by a professional machine shop.

B) Pins: Pins for this version of the SET are constructed out of 1/4" diameter fiberglass rods. There are 9 pins needed for the instrument. For most emergent marshes pins of about 3' (or 1 meter) are adequate. For shallow ponds, longer pin lengths of 4 - 5' are common. In shallow ponds or mud flats where the mud bottom is often not visible, you may need pins with "feet" on the end. The foot is a circular disk, 1-2" in diameter, which distributes the weight of the pin and minimizes sinking into the substrate.

PIns with feet

C) Carrying Case: Because of the size of the instrument, a custom-built carrying case is needed to transport the SET safely and to keep the instrument when not in use. We use a custom-built case with the dimensions of 60"x18"x6". We also have the case custom foamed specifically for the instrument.

SET carrying case
Blackwater NWR, MD, USA
Components of the Benchmark

Benchmark Pipe
The SET attaches to an "insert pipe" which is in turn cemented into a long aluminum irrigation pipe which is sunk into the ground. The irrigation pipe is typically 3" in diameter and usually 20 or 25 feet in length.

Bayou Sauvage NWR, LA, USA
Jervis Bay, Australia

The pipe is driven into the ground using a vibracorer or a custom built "pounder" (pictured above). Any void space inside the pipe is filled with cement. An insert pipe is cemented into the top of the pipe.

Insert Pipe
The insert pipe is a 24" long piece of 2" diameter aluminum pipe (Schedule 40) which has 8 notches machined into one end. The SET rests in these notches, and therefore can repeatedly sample up to 8 fixed positions around the benchmark. The SET is attached only during sampling and then removed. The insert pipe is cemented into the the top of the 3" benchmark pipe. Holes are drilled in the pipe to allow cement to flow into the bottom half to ensure it is securely in place when the cement hardens. In addition, a metal disk is welded inside the insert pipe to keep the cement from traveling too far up the pipe (See below figure).

insert pipe drawing

Insert pipe photo

Top view of insert pipe

Top of SET pipe showing 8 notches. Note the disk in the center which keeps cement from rising up too far into the pipe.
U.S. Department of the Interior, U.S. Geological Survey,
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Last Updated: 12 January 2010
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