BASIN SIDE HYDRODYNAMIC AND MORPHOLOGICAL MODELING
FOR THE DELTA BUILDING DIVERSION AT MYRTLE GROVE
Jeffrey G. Shelden, P.E., Moffatt & Nichol,
1616 East Millbrook Road, Suite 160, Raleigh, NC 27609
919 / 781-4626
jshelden@moffattnichol.com
Zhanxian Wang, Ph.D., Moffatt & Nichol, Raleigh, NC
zwang@moffattnichol.com
The Delta Building Diversion at Myrtle Grove (BA-33) project was initially proposed to be another
large freshwater diversion project in the Barataria Basin in addition to the Davis Pond Diversion
project. The Myrtle Grove Diversion project would involve installation of a diversion structure on
the west bank of the Mississippi River between Ironton on the south and the Alliance Refinery on
the north; a conveyance channel with parallel mainline flood control levees and an outflow channel
with guide levees.
As initial studies for the project progressed, it was decided to also analyze the land-building
potential if the project was modified to also act as a sediment diversion. Extensive data collection
efforts, sediment transport analyses, numerical modeling and physical modeling of the Mississippi
River; and a preliminary design of the diversion structure and conveyance channel were completed.
This presentation summarizes the basin side analyses of the Barataria Basin that have been
accomplished. Initially, an estuarine hydrodynamic model was developed for evaluating the
Barataria Basin effects due to operating both the Myrtle Grove and Davis Pond diversions at varying
and increasing flow rates. This work was then built upon to pre-screen Myrtle Grove diversion
flows for the State and other non-governmental organizations (NGO) in order to determine feasible
diversion flows for a sediment diversion. The RMA2 model was used to evaluate maximum
diversion magnitudes of 15,000 cfs; 45,000 cfs; 75,000 cfs; 150,000 cfs; 240,000 cfs and 300,000 cfs
on water level and velocity increases in the basin. The purpose of these runs was to establish the
upper limit of diversion magnitudes for further modeling by identifying the flows with significant,
insurmountable impacts. Next, the hydrodynamic effects of three pulsing diversions were
investigated. The pulsing interval was set at two weeks with the diversion operating and two
weeks with a minimum diversion flow of 5,000 cfs.
The Delft3D modeling system was then used to obtain a general understanding of the potential
land-building capacity within the Barataria Basin of the Myrtle Grove Sediment Diversion. The
Mississippi River 3D Model developed by others provided sediment loadings through the diversion
under different discharge conditions and was used as inputs for the Delft 3D model. The Delft
system was then applied to model the sediment transport and morphological changes due to the
sediment diversion over a period of 45 years. This allows for a better informed decision as to
whether enough sediment can be diverted at Myrtle Grove and delivered a significant distance into
the Barataria Basin to build land; or whether the primary benefit of this diversion will remain the
introduction of freshwater into the basin.
Jeffrey G. Shelden, P.E. is a senior coastal / hydraulic engineer with Moffatt & Nichol in Raleigh, NC.
He received a B.S. in Civil Engineering from the University of Virginia in 1984 and an M.S. degree
from North Carolina State University in 1985. He has been working on various ecosystem
restoration projects in Louisiana for the past dozen years, and his numerical modeling experience
includes the analysis of tidal flows, sediment transport, shoreline processes and pollutant transport
for estuary systems throughout the United States and internationally.