Project title: Submergence Plane Oil Containment Technology

Principal Investigators:

M. Robinson Swift
Professor of Mechanical & Ocean Engineering
Mechanical Engineering, Kingsbury Hall
University of New Hampshire
Durham, NH 03824
Phone: (603) 862-1837
FAX: (603) 862-1865
e-mail: mrswift@christa.unh.edu

Barbaros Celikkol

Work Accomplishments

Tasks for the Period

The initial task was to investigate pump-out systems for recovering captured oil from the containment region of the Bay Defender II (BDII) flexible barrier. The flexible barrier had previously been tested for oil retention performance at Ohmsett before this project, and its practical capabilities were demonstrated in the CICEET-sponsored deployment off Dover Point during Fall 1999. During this work period, skimmer alternatives were to be considered and evaluated.

A field test would then be conducted in which BDII is deployed in the estuary and a selected skimming system is used to recover oil substitutes. The problem of positioning the skimming head within the containment region for best recovery would be addressed.
Later, during Summer 2000, a 100 foot flexible barrier (BDII is 40 feet) would be designed and a 1/5 scale physical model built for testing. Increasing the across-current length by a factor of 2 _ compounds the design problems associated with the flexible structure. The longer system must be designed for greater hydrodynamic forces, more severe strength requirements and the possibility of new modes of shape-retention failure.

Work Completed

A survey of pump-out equipment presently on-hand for the Great Bay system was conducted. All Piscataqua River Cooperative (Coop) and New Hampshire Department of Environmental Services (DES) skimmers and pumps were inventoried and inspected. Equipment suitable for flexible barrier containment region pump-out was brought to the UNH Ocean Engineering (OE) engineering tank and tested. A drum skimmer, a Waterous float/pump skimmer and a weir skimmer were operated and evaluated without oil. Oil testing had previously been done at Ohmsett with results summarized by Schulze (1998). The Coop also maintains a Trans-Vac 300DH – a large diesel-powered vacuum system which can be combined with a variety of skimming heads.

Pump capacity requirements were theoretically calculated for scenarios specified according to oil thickness, current speed and mouth width of the hybrid containment configuration. The resulting volume rate of flow varied over orders of magnitude. Thus no single system appears optimal over the full range of field situations, and different approaches need to be applied according to the extent of the spill. For thin slicks and sheens, an oleophilic system, such as the drum or disk skimmers presently in the Coop/DES inventory, would be the most efficient. For moderate spills, the DES Slurp weir skimmer would be the best match. In the case of a catastrophic spill, the Trans-Vac vacuum system would be required. Recovered oil would be stored temporarily in flexible, floating Sea Slug containers, which are also part of the local inventory.

The logistical aspects of removing oil from the flexible barrier were investigated in a field deployment. BDII was deployed with conventional boom lead-ins; a vessel was brought up next to the barrier, and a vessel-operated skimming head was positioned within the skimming system. The principal objective was to develop procedures for securing the vessel and positioning the skimmer within the containment region.

A joint decision was made with the DES and the Coop to carry out the deployment at the mouth of the Bellamy River during a flood tide. The lead-in booms would extend to the bridge jetties thus closing off the Bellamy entirely. There is considerable interest in being able to close off ecologically important tributaries as a backup line of defense. Though deflection booming strategies have been developed and implemented in exercises (see Swift et al., 1991), the deflection approach directs oil towards the shoreline. Using the centrally located BDII, on the other hand, oil is concentrated for recovery away from the shore. The Bellamy had also been subject to widespread damage during an oilspill in the 1970’s.

In preparation for the field deployment, a special skimmer was designed, built and tested. A skimming head that would recover the oil substitute (as well as oil) was needed. Popcorn had been selected as the oil substitute for its visibility, availability and negligible environmental impact. Thus the skimming system had to be able to handle large particulates (as well as liquids) and could not rely upon an oleophilic recovery mechanism. The skimming head shown in Figure 1 was developed for this application. The system is supported by four floats and consists of a standpipe with a variable height, omnidirectional, weir-type head. The disk shaped base induces inwards, horizontal surface flow and allows the intake holes to remain submerged. Dimensions were adjusted in the OE engineering tank trials for reliable recovery of the popcorn oil substitute. The head was coupled with a gas driven trash-pump vacuum system. It should be noted that this head could also serve as a recovery unit for catastrophic spills, either with the trash-pump or the Trans-Vac, though commercial heads for pure oil recovery are available (see Schulze, 1998).


Figure 1

Preparations also included site surveys where shore features, river bathymetry and flood tide currents were recorded. Though previously obtained data was available, the new bridge configuration had altered the mouth considerably. One important change was the increase in low tide width of the mouth from 600 feet to 1100 feet.

The deployment took place on July 20, 2000 with UNH, Portsmouth Towing, DES, the Coop, the U.S. Coast Guard and the Maine Department of Environmental Services participating. BDII was assembled on the beach on the west side of the mouth, while 900 feet of conventional boom was set on the east leg, and 500 feet was set on the west leg. BDII was then towed out and connected in the central apex position as shown in Figure 2. The inshore ends of the lead-ins were anchored just inside (upriver) of the jetties effectively closing off the mouth. The unequal lengths were necessary because the main channel is skewed with respect to the mouth. As set, BDII was at the apex and perpendicular to the flood current.

Figure 2

The Coop boom storage barge was then maneuvered aft of the containment region and was secured by two lines to the ends of the lead-in booms where they connected to BDII. As shown in Figure 3, the barge bow could be lowered to serve as a platform for setting out the skimmer. The barge was well-secured, did not interfere with the flexible barrier shape or functioning and was very stable as a work platform. The skimmer position was effectively controlled by lines from the skimmer out to pulleys on the two forward corners of BDII then back to the operating barge. The pump-out hose itself served as the third control line. Figure 4 shows the skimmer being positioned over the gap to scavenge popcorn coming in.

Figure 3

Figure 4

In general, all systems worked very well. The current, however, was somewhat slower than originally anticipated. Widening the mouth apparently reduced speed from over one knot to slightly less than a knot. The value of this approach may be greater at the mouths of other tributaries such as the Oyster, Lamprey and Squamscott rivers where currents are above one knot (the critical value for conventional boom leakage), but well within the operating range of BDII. The value of the planned 100 foot flexible barrier, over the 40 foot BDII, was also readily apparent.

The preliminary design for the 100 foot flexible barrier has been completed. Construction of the 1/5 scale physical model was nearly complete as of the end of this reporting period (7/31/00). Basic research carried out in this and in parallel studies included measurement of lift forces on the submergence plane and the use of a hydrofoil to resist lift forces for high speed applications. Recent testing at Ohmsett , sponsored by the U.S. Coast Guard, enabled submergence plane oil retention processes to be observed in the 2 – 4 knot range. Results of this supplementary work will be incorporated into the 100 foot barrier development effort.

As part of our information dissemination responsibilities, two papers were given at the Arctic and Marine Oilspill Program (AMOP) conference in Vancouver, British Columbia. The papers (Swift et al., 2000a and b) were peer-reviewed and appear in the published proceedings.

Concerns

The one-hour time required for assembly of BDII from its basic parts is of concern. This is being addressed in the 100 foot design through the use of air inflated buoyancy for all the inflation elements (instead of semi-solid foam). The system could then be stored fully assembled but deflated, possibly on a barge similar to that used in the Bellamy River deployment. Then deployment time could be a matter of minutes using a leaf blower to inflate the system.

Anticipated Success in Meeting Project Objectives in Scheduled Project Period

The project is on schedule.

Preliminary Observations

The hybrid BDII/conventional boom lead-ins concept is ideal for closing off tributaries in which mouth currents are in the range of one to two knots (as well as the Dover Point interception location tested Fall 1999). The 100 foot version will allow a greater portion of the mouth width to be occupied by the flexible barrier.

The docking of a barge aft of the containment region is not only feasible, but logistically straightforward. Use of lines enables good positioning of the suction head where necessary in the containment region.

Tasks and Activities for the Next Reporting Period

Tasks for the Reporting Period

Tasks for the next six-month period include finishing and testing the 1/5 scale physical model of the 100 foot flexible barrier. The full-scale design will then be completed and fabrication initiated.

Work Plan to Accomplish Tasks

The remaining finish work on the model will be completed. The 20 foot model will then be launched in the OE engineering tank to verify hydrostatic considerations. Testing in the field will include towing, anchoring and load cell measurement of critical forces. The ability of the system to maintain planform and cross-section shape and resist twisting will be evaluated. Model measurements will then be Froude-scaled to full size according to routine naval architecture procedures. Lessons learned will be incorporated into the full-scale design, and drawings for the system will be completed. Bid packages for component fabrication will be prepared and distributed. Awards will be made and vendors supervised during fabrication.

Concerns

None at this time.

Expenditures

The project is within budget.

References
Schulze, R. (1998) Oil Spill Response Performance Review of Skimmers, ASTM Manual Series: MNL34, ASTM, 100 Barr Harbor Drive, West Conshohocken, PA, 151 pp.
Swift, M.R., B. Celikkol, C.E. Goodwin, and John Chadwick (1991) Protective Oil Booming in Great Bay Part I: Tributary Protection, Final Report, New Hampshire Coastal Program, Office of State Planning 2 _ Beacon Street, Concord, NH, 03301.
Swift, M.R., B. Celikkol, R.R. Steen, W. DiProfio and S.E. Root III (2000) "A Flexible Submergence Plane Barrier for Fast Current Applications", Proceedings of the Twenty-Third Arctic and Marine Oilspill Program (AMOP) Technical Seminar, Environment Canada, Ottawa, 401-414.
Swift, M.R., J. Belanger, B. Celikkol, R.R. Steen and D. Michelin (2000) "Observations of Conventional Oil Boom Failure", Proceedings of the Twenty-Third Arctic and Marine Oilspill Program (AMOP) Technical Seminar, Environment Canada, Ottawa, 481-492.