USGS SET website - Read the SET

Taking your SET readings

This page provides detailed instructions for reading the SET. All designs of the SET are read in the same manner.

The first measurement with the SET is called the "baseline" reading which is subtracted from all subsequent readings.

Step 1 - Choose your directions -

From a single SET benchmark pipe you will normally have a choice of 8 directions from which to sample (unless you have an insert pipe with only 4 notches). NOTE: The shallow benchmark platforms usually provide only 4 directions once installed. We normally take readings at 4 of the 8 possible directions. Typically, the 4 directions are chosen so they are 90 degrees from each other, although other spatial patterns may be required for a particular site or experiment.

For example, we would use directions 1,3,5 and 7 or 2,4,6 and 8 for the SET readings. Having extra directions is helpful should a problem arise. For example, suppose you step in one of the sampling plots and there is now a footprint. You could start another baseline using one of the four remaining directions.

Step 2 - Place instrument on benchmark -

Original SET - Place the two pins on opposite sides of the lower (vertical) portion of the SET firmly in the notches of the insert pipe in the direction you want to sample.

Rod SET - Slide the SET onto the rod being sure to align the 2 pins on the base of the instrument with the holes of the collar for the direction you want to sample. Clamp the SET to the collar once in place.

All SET's have a bubble level on them. Be sure to level the instrument.

Original SET	Deep RSET	Shallow RSET
Delta NWR, LA USA	Blackwater NWR, MD USA	Old Oyster Bayou, LA USA

Step 3 - Lower the pins to the surface -

If you are working on a marsh site or tidal pond, it's helpful if the surface is dry when taking your readings. If the site is flooded most of the time so that you cannot see the sediment surface when placing the pins, its best to use pins with feet. The feet help pin placement by keeping the pin from "piercing" the sediment.

The pins are held in place by badge clips. Unclip a pin and lower it until it touches the surface. Place the clip back on the pin to hold it in place. Repeat this for the other 8 pins. Placing the pins on a dry surface is mainly accomplished visually. If the surface is underwater, you may have to place the pins by feel (i.e. resistance).

NOTE: At most marsh sites you may have to push the vegetation aside while placing pins. In addition, some sites will undoubtedly have detritus, leaves and other materials on the surface. You will need to make a decision on what to remove and what to leave in place.

We normally move away any materials which are not attached to or incorporated into the sediment. For example, we would push aside dead leaves and twigs which are loose on top of the soil surface. We would NOT remove something like a mussel shell or branch which is buried in the sediment. If a pin rests on an unusual surface, such as a branch or crab hole, make a note in the data book.

SET with badge Clips	Lowering SET pins	Pins with feet
RSET - Blackwater NWR, MD USA

Where's the surface?:

Determining the actual sediment surface can be a subjective call, depending on the environment you are working in.

In general, tidal saline wetlands (Spartina alterniflora, Juncus roemerianus, mangrove forests) and more mineral sediment sites are straightforward and easier for pin placement. Sites with more organic sediments (fresh and brackish marshes), can be more difficult for pin placement due to the uneven nature of the surface. Shallow ponds or waterways are generally easy since you have the "feet" on the pin and the bottom is relatively uniform.

Regardless of the environment you are working in, it's important that you are consistent from sampling to sampling in how you determine pin placement. Establish a protocol and follow it.

Step 4 - Read the nine pins and record the values -

The pins will stick up above the level aluminum plate or arm on the instrument. You will need to measure the distance from the plate or arm to the top of the pin.

It's important to record any specific information on individual pins. It's very useful to record if a pin falls in a hole, on a mussel shell, on a tree root, etc. Some of these values may not be used in calculations based on this information so it's important to document this as you take the readings.

Below is a sample table showing how we organize our databook (Four directions from a single pipe). Values are in millimeters.

Marsh Site 1 - Pipe 1 - February 14, 2003
Direction	Pos 1	Pos 2	Pos 3	Pos 4
Bearing	NE 40°	SE 130°	SW 220°	NW 310°
Pin 1	121mm	132	122	134
Pin 2	120	129	140	121
Pin 3	120	133	125	119
Pin 4	123	133	122	128
Pin 5	125	132	141	115
Pin 6	119	126	139	149 Shell
Pin 7	128	101 hole	133	119
Pin 8	131	122	126	125
Pin 9	130	121	123	128
SET read by: Jim Lynch, SET ID#=2002-1

Step 5 - Repeat for the other directions -

Don't forget to level the instrument prior to placing the pins at each of the positions.

Who reads the SET?

We recommend that the same person read the SET from sampling to sampling. This approach will maintain a consistent sampling protocol when taking the readings and minimize sampling errors.

Double Reading the SET:

If you need to switch readers, we recommend that you "double-read" the SET during one of the samplings. For example, suppose SET READER #1 has been reading the data since the project started, but is leaving for a new job. SET READER #2 is going to replace him/her. The best situation would be for both readers to go and sample the site together. READER #1 would take their final set of readings with the SET. Then READER #2 would take a repeat set of readings.

You should also double read if you are switching pins. For example, if you wanted to swap out your pins for longer pins with feet you could double read the sites with the two sets of pins. A final reading with the original pins and a baseline reading with the new pins.

This can make for a lot of work, but it will ensure a smooth transition of data collection.

Step 6 - Marker Horizons:
If you are establishing Marker Horizons you should put them out when you are taking your first SET readings. This way the values from the SET and the marker horizon have the exact same starting date. If the dates vary you may have some problems interpreting the data in the future.

If Marker Horizons are already established and you need to sample them, click here.