ACCESS NUMBER: M11AC00013

STUDY TITLE: Shelf-Slope Sediment Exchange in the Northern Gulf of 

Mexico: Application of Numerical models for Extreme Events

REPORT TITLE: Shelf-Slope Sediment Exchange in the Northern Gulf of 

Mexico: Application of Numerical models for Extreme Events

CONTRACT NUMBER: M11AC00013

SPONSORING OCS REGION: Gulf of Mexico

APPLICABLE PLANNING AREA(S): Northern Gulf of Mexico

FISCAL YEAR(S) OF PROJECT FUNDING: 2012, 2013, 2014, 2015

COMPLETION DATE OF REPORT: October 10, 2015

COSTS: $990,000

PROJECT MANAGER(S): Hernan G. Arango

AFFILIATION: Rutgers, The State University of New Jersey

ADDRESS: DMCS, 71 Dudley Road, New Brunswick, New Jersey, 08901-8521

PRINCIPAL INVESTIGATOR(S)

*

: H. G. Arango, C. K. Harris, E. H. Meiburg, 

J. P. M. Syvitsky

KEY WORDS: Northern Gulf of Mexico; sequentially coupled numerical 

models; Mississippi River delta and canyon; sediment transport; turbidity currents; 

ROMS; ROMS-CSTMS; seabed failure and Flow Ignition models; LES/RANS 

TUBINS.

BACKGROUND: The Gulf of Mexico Outer Continental Shelf (GOM OCS) 

region is a mature offshore oil and gas production area with many producing leases 

generating more than 1.7 million of barrels of oil per day, through more than 3,500 

oil platforms. Production on many of these leases is expected to continue into the 

next decade thus carrying into the future the associated risk of an oil spill. A large 

number of oil-rigs and other manmade structures, e.g., pipelines and platforms, are 

located on the continental slope where sudden and powerful turbidity currents are 

more likely to occur than elsewhere. Over the last decade there has been a 

significant increase in the number of oil platforms operating in deep waters. The 

northern GOM currently has more than 28,000 miles of underwater pipes, which 

are all exposed to risks of various types of structural damage, most of them 

associated with extreme oceanic and atmospheric events. Of all damaged 

underwater pipes, about 5% are broken or damaged by sudden and violent 

 

* P.I.’s affiliation is different than that listed for Project Manager(s).
ACCESS NUMBER: M11AC00013

cascading of sediments. The transport, burial, and impact of contaminated 

sediments within the GOM environment are of interest to many.

OBJECTIVES: The primary goal of this study is to provide a comprehensive 

understanding of the factors that trigger significant across-isobath sediment fluxes 

in the mid- and outer-continental shelf and slope in the northern Gulf of Mexico.

The objectives to accomplish this primary goal are: (1) to develop the capability to 

numerically model sediment fluxes from inner continental shelf or fluvial sources 

to the continental slope; (2) to explore the conditions that trigger episodes of 

sediment flux on the continental slope where gas and oil infrastructure exist; (3) to 

study the sediment transport scenarios due to idealized extreme atmospheric 

forcing events (storms and hurricanes of various intensities and different paths);

and (4) to study the sediment transport response to high discharge and ambient 

oceanic forcing (Loop Current eddy shedding, mesoscale and sub-mesoscale 

eddies, meanders, waves, etc).

DESCRIPTION: The approach for achieving the project goal and objectives is to 

utilize loosely coupled numerical simulations using hydrodynamic, wave, sediment 

transport, and turbidity models. Several state-of-the-art models were linked to 

address the various land-sea pathways for sediment routing from terrestrial and 

coastal sources, across the continental shelf and ultimately down the continental 

slope and canyon systems of the northern GOM. Coupled model simulations were 

designed to represent a range of conditions and climatologies that might impact the 

generation of turbidity-current triggering mechanisms (i.e. extreme storms, high 

discharge, eddy shedding from the Loop Current, cumulative sediment deposition).

SIGNIFICANT CONCLUSIONS: The suspended sediment transport model 

indicates that episodic suspended transport down features like the Mississippi and 

De Soto Canyons is fed principally by sediment fluxes generated by wave 

resuspension. In particular, while hurricane conditions only lasted for two brief 

episodes during the one-year model run, they accounted for about 30% of the 

sediment delivered from the continental shelf to the slope. Delivery of sediment 

directly from settling from the freshwater river plume at the canyon head or over 

the continental slope was not a significant source of sediment delivery for the study 

period from 1-Oct-2007 to 30-Sep-2008. During the two Hurricanes modeled (Ike 

and Gustav), suspended sediment fluxes were predominantly offshore in the 

vicinity of the Mississippi and De Soto Canyons. Peak suspended sediment fluxes 

coexisted with the occurrence of the highest wave–induced bed stresses on the 

continental shelf, but showed increasingly long delays relative to this timing with 

distance down the canyon or continental slope. On the continental slope, turbidity 

currents can be triggered by slope failure when storm driven supply forces 

accumulation sediment to deep water.
ACCESS NUMBER: M11AC00013

STUDY RESULTS: The suspended sediment fluxes across the shelf break from 

model calculations of depth-integrated flux were analyzed for five cross-slope 

transects in the northern GOM (see Fig. 7.6 of the Final Report). These data

highlight the dominant role of the hurricanes in delivering large fluxes of 

suspended sediment from the continental shelf to the slope. Cross-slope fluxes 

were small during and after Hurricane Gustav west of the Mississippi Canyon, but 

created some of the largest sediment fluxes over the De Soto Canyon area. In 

contrast, Hurricane Ike produced suspended sediment fluxes at all studied 

transects, but the magnitude of the suspended fluxes generally increased toward the 

west. During both storms, the suspended sediment flux was directed toward the 

southwest for water depths from 92 – 700 m, i.e. roughly across the Mississippi 

Canyon with a slight offshore component. For the shallowest location analyzed 

(92 m) at the head of the Mississippi Canyon, the suspended sediment flux peak 

coincided approximately with the presence of storm waves on the shelf. The peaks 

in sediment flux calculations down the Mississippi Canyon, however, lagged 

behind the passage of the storms, being delayed by 1–5 days relative to the 

occurrence of peak wave energy on the shelf at ~700 m water depth. Sediments 

resuspended on the shelf during the hurricanes were transported across the shelf 

break after the hurricanes began to cause relatively high resuspension on the west 

side of the Mississippi delta. As winds and along-shelf currents relaxed and 

changed direction, and sea-surface heights lowered, sediments were then 

transported down-slope, sometimes days after the hurricane. For the transect 

located in the DeSoto Canyon, however, the model estimated net downslope flux 

towards the south to southeast during the hurricanes. The apparent increase in flux 

downslope (between 643 and 754 m) during and after the passage of hurricane 

Gustav (Aug25-Sep3) suggests possible contributions from suspended sediment 

transported over the sides of the canyon. Short periods (hours long) of transport 

apparently upslope, reflect the complex currents of the area, which occasionally 

form a gyre. Sediment transport in the DeSoto Canyon during Hurricane Ike 

appeared to begin at the 1115 m and then later at shallower depths. This occurred 

because a large suspension of sediment over the DeSoto Canyon was shifted to the 

east after Hurricane Ike passed through the area, and winds began blowing from 

the northwest.

STUDY PRODUCT(S): H.G. Arango, C.K. Harris, J.J. Birchler, T.A. Kniskern, 

J.P.M. Syvistski, C.J. Jenkins, E. Hutton, E.H Meiburg, and S. Radhakrishman, 

2015: Shelf-Slope Sediment Exchange in the Northern Gulf of Mexico: 

Application of Numerical models for Extreme Events. A final report for the U.S.

Department of the Interior for the Bureau of Ocean Energy Management. Contract 

Number M11AC00013.
ACCESS NUMBER: M11AC00013

It is very likely that several papers will be written and published in the scientific 

literature. Currently, we have the following synthesis draft paper:

J.P.M. Syvitski, H.G. Arango, C.K. Harris, E.H. Meiburg, C.J. Jenkins, E.W.H. 

Hutton, G. Auad, S. T.A. Kniskern3, and S. Radhakrishnan, 2016: A Multi-model 

workflow to understand of the Influence of Hurricanes on Generating Turbidity 

Currents in the Gulf of Mexico.