Sediment traps are used to collect suspended matter in a wide variety of aquatic environments. A funnel-shape design, called the Anderson design, is typically used by the USGS Marine Science Centers for studies in the marine environment. The trap passively collects material settling both through the water column and from resuspension of bottom sediments and concentrates the material into a clear collection tube located below the funnel. The Partition Intervalometer, suspended inside the funnel, dispenses 20 disc-shaped partitions at programmable time intervals into the collection tube. The disc’s unique hydrodynamic shape allows the disc to descend vertically through the funnel and into the collection tube.

The discs settle onto the surface of the sediment and thereby provide a stratigraphic profile over time as the sediment accumulates in the collection tube.

The resulting sediment sample is separated into distinct segments  by a series of discs deposited at known time intervals and therefore can be analyzed and correlated with results from other oceanographic instrumentation on a finer scale than previously available.

The original Intervalometer designed by Roger Anderson (1977) has been re-fabricated, tested, modified, and deployed in the field by members of the technical staff at the USGS Woods Hole Science Center.

A review of the key findings and observations over the course of the development of this instrument at the USGS, as well as of the field results, is summarized as follows:

1. The integrity of the tubular Delrin pressure case has been successfully pressure tested to approximately 4500 psi (3200-m-equivalent water depth).

2. The operation of the Intervalometer was effectively pressure tested to approximately 1500 psi (1000-m-equivalent water depth). Minor water leakage was observed in a few of the instruments through the shaft of the manifold area; however, this flaw was corrected by remilling the shaft and installing a new dynamic O-ring seal on the shaft.

3. Laboratory test procedures and protocols were designed to evaluate the firmware and the operation of the Intervalometers. Employing the numerous combinations of programmable time settings and observing the subsequent mechanical operation of each instrument allowed assessment of potential mechanical or electrical problems.

4. It was found that initiating a user-defined program twice with a hand-held magnet would ensure stable functioning of the program.

5. The frequency of disc jams was significantly reduced by redesigning the rotor and disc configurations, establishing a loading protocol for the discs (concave upwards) into the manifold magazine, and reorienting the location of the end cap.

6. A new frame was designed to house the electronics boards and the 9-volt battery pack. This feature improves access to these components if a repair or a change of batteries is required.

7. A full complement of 20 discs may be loaded into the magazine of the Intervalometer.

8. Operational testing and program-scheduling verification for each Intervalometer are recommended prior to any deployments in the field. Similarly after recovery, each instrument should be assessed to determine if the programming schedule is still operating according to the original deployment schedule.

9. Results from the initial field deployment of five Intervalometers off the coast of Southern California indicated that all but one of the instruments operated as programmed. A rotor malfunctioned and the discs became jammed in one instrument after 110 days.

10. The amount of suspended material accumulated in the collection tubes by the near-bottom traps (30 mab) at the Hueneme Canyon and Mugu Canyon sites was 1.4 and 1.6 times the volume collected in each of the respective shallower traps  at 60 mab.

11. A larger volume of suspended matter was collected in the sediment traps from the Hueneme Canyon location. The Hueneme traps at 30 mab and 60 mab collected 1.5 and 1.6 times the volume of sediment as the Mugu Canyon traps, respectively. This difference probably reflects processes associated with longshore sediment transport, resuspension events, and the unique flow dynamics within the topographical settings of the Canyons.

12. See appendix 2 for a review of the field notes regarding the Intervalometer settings, site locations, and results from the deployments.