ACCESS NUMBER: 30660-19943 

STUDY TITLE: An Observational and Predictive Study of Inner Shelf Currents over the 

Louisiana-Texas Shelf

REPORT TITLE: Observational and Predictive Study of Inner Shelf Currents over the 

Louisiana-Texas Shelf

CONTRACT NUMBER: 14-35-0001-30660-19943 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREA: Central & Western Gulf of Mexico 

FISCAL YEARS OF PROJECT FUNDING: 1997-2005 

COMPLETION DATE OF REPORT: November, 2004 

COSTS: FY ’97: $216,500 

CUMULATIVE PROJECT COST: $216,500 

PROJECT MANAGERS: William J. Wiseman, Jr., Lawrence J. Rouse 

AFFILIATION: Louisiana State University 

ADDRESS: Department of Oceanography& Coastal Sciences, Louisiana State 

University, Baton Rouge, LA 70803 

PRINCIPAL INVESTIGATORS: Lawrence J. Rouse, Jr., William J. Wiseman, 

Jr., Leslie C. Bender, Norman L. Guinasso, Jr., F. J. Kelly, David A. Brooks, YaoTsi Lo, J. She, and A. Valle-Levinson 

KEY WORDS: Physical Oceanography, Gulf of Mexico, wind forcing, coastal currents, 

Louisiana-Texas Shelf, TABS buoys 

BACKGROUND: Upon exiting the Mississippi and Atchafalaya River Deltas, the 

relatively fresh river waters flow westward along the coast to form the Louisiana Coastal 

Current (Wiseman and Kelly, 1994). The waters of this current system move downcoast 

(in the sense of phase propagation of Kelvin waves) most of the year and are readily 

identifiable along the Mexican coast of the Gulf of Mexico during the late fall, winter, and 

early spring. The flow is highly responsive to wind forcing, the most important synoptic 

wind pattern being cold air outbreaks (Huh et al., 1984), which occur on time scales of 3 

to 10 days during the winter season (DiMego et al., 1976; Fernandez-Partagas and 

Mooers, 1975). Driven by such events, the current may reverse direction for a brief 

period of time and flow upcoast. During summer, when winds are weaker, the coastal 

waters of Louisiana are highly stratified and the surface flow may be incoherent with the 

near-bottom currents on sub-tidal time scales. Along the south Texas coast, the winds 

become upwelling favorable in late spring and the mean flow reverses direction and 

moves upcoast. For periods of a month or longer the direction of the mean current over 

the western Louisiana inner shelf may be eastward (Cochrane and Kelly, 1986). 
ACCESS NUMBER: 30660-19943 

An understanding of the currents within this coastal system is important to a number of 

environmentally important processes. Not the least of these is oil spills, since any spill 

in nearshore waters is immediately transported by the waters of this current system and 

any spill in Outer Continental Shelf waters must transit this current system before 

impacting the highly productive marshes and estuaries of coastal Louisiana and Texas. 

Much of this country’s imported oil is lightered from super tankers offshore Louisiana 

and Texas. Offshore production contributes an important but significantly smaller 

amount than lightering. The volume of oil lightered last year from Southwest pass to 

Corpus Christi was about 275 million barrels; equivalent to almost 200 EXXON VALDEZ 

loads (Larry Smith, Calero Refining; personal communication). The volume continues 

to increase. 

OBJECTIVES: The objective of the modeling and data analysis was to verify previous 

findings and to explore new features of the subtidal circulation over the Texas-Louisiana 

inner shelf and its response to wind forcing. 

DESCRIPTIONS: TABS buoy data obtained from April 1995 to March 1998 were 

among the data used to study subtidal circulation over the shelf. The principal objective 

of the modeling effort was to investigate the basic physical mechanisms responsible for 

the development of the Mississippi-Atchafalaya River plume associated with surface 

wind forcing on the Texas-Louisiana continental shelf.

SIGNIFICANT CONCLUSIONS: Interaction between the Mississippi-Atchafalaya river 

plume and the Mississippi Canyon was demonstrated through circulation modeling. The 

results of data analyses indicate both significant spatial and temporal variability in the 

response of currents along the Texas-Louisiana inner shelf to wind forcing, and the fact 

that a local, linear relationship between the alongshore wind field and cross-shelf flow 

field does not explain all the observed variability in the currents. The role of upstream 

river discharge and local flow convergence has been suggested as important 

contributors to this variability. The importance of local upwelling/downwelling was 

confirmed. 

STUDY RESULTS: Steps towards development of a fully three-dimensional model of 

circulation on the Louisiana-Texas shelf were presented. Data analyses have confirmed 

the seasonal coherence between local winds and currents. Cross-shore flow patterns 

were consistent with upwelling theory. Marginally significant signatures of longshore 

propagating flow features consistent with coastally-trapped wave theory were identified. 

An hypothesis was developed that there exists a seasonal geopotential high near 93o 

W, forced by the convergence of wind-driven flows from the southwest and riverinedriven flows from the east, which is used to explain the very low frequency patterns of 

flow. 

STUDY PRODUCTS: Lo, Y.-T. Modeling the Buoyancy-Driven Flow Due to River 

Discharge On the Texas-Louisiana Continental Shelf of the Gulf of Mexico. Unpublished 

Ph. D. Dissertation. Department of Oceanography. Texas A&M University. College 

Station, TX. 154 pp. 
ACCESS NUMBER: 30660-19943 

D Brooks and Y Lo. Interaction of the Mississippi River Plume with the Mississippi 

Canyon, 2000 Ocean Sciences Meeting, January 24-28, 2000, San Antonio, Texas.