Mississippi Valley Division Engineer Research and Development Center

Old River Control Complex

Sedimentation Investigation

Mississippi River Geomorphology and Potamology Report No. 6

An investigation of the Old River Control Complex (ORCC) was conducted to determine 

current rates of sediment diversion, evaluate potential impacts on the stability of the 

Mississippi River, and identify options to increase sediment diversion rates. The 

investigation was conducted via a combination of field data collection and laboratory 

analysis, geomorphic assessments, and numerical modeling. 

The fraction of Mississippi River sediment diverted through the ORCC is a function of 

several factors, including the river discharge, the state of the river bed (i.e., bathymetry 

and bed material gradation), the shape of the hydrograph, and the distribution of flow 

allocated to each diversion structure: the Hydroelectric Station, the Low Sill Structure, 

and the Auxiliary Structure. This flow allocation among structures is of particular 

importance since each structure passes a different amount of sediment for the same 

diverted flow. Hence, changes in operations at the ORCC can have a significant impact 

on the amount of sediment diverted for a given water diversion.

Sediment diversion efficiency

Differences in the sediment diversion efficiency of each structure are due primarily to 

their relative locations in river bends. The Hydroelectric Station diverts water from the 

outside of a river bend, where the sediment concentration is at a minimum (bed material 

load tends to be higher toward the inside of a bend). The Low Sill Structure is located at 

the transition between bends, and the Auxiliary Structure is located at the inside of the 

next downstream bend.

AdH/SEDLIB numerical model

Bed material sediments, primarily sand in the Mississippi River, strongly influence the 

morphology of the channel; therefore, the diversion of bed material is the primary focus 

of this study. For a numerical simulation of January through September of 2010, the 

total mass of bed material diverted at the ORCC was 9.1 million tons. Based on an 

analytical estimate, the amount of bed material that must be diverted to maintain 

downstream equilibrium is 16.6 million tons. Hence, the excess bed material passed 

downstream for this simulation period is 16.6 – 9.1 = 7.5 million tons.

Screening tool

To allow water control personnel to apply the results of this study to practical 

operational decisions, a spreadsheet application that estimates the sediment diversion 

efficiency of the complex has been developed whereby the results of the numerical 

model analysis can be used to experiment with changes in the ORCC operations.
For More Information

To access the full version of Old River Control Complex 

Sedimentation Investigation report, click the following link: 

http://acwc.sdp.sirsi.net/client/en_US/search/asset/1045347.

Additional MRG&P reports, historic reports, and MRG&P 

information can be accessed from the MRG&P Publications 

and Technology Transfer website:

http://www.mvd.usace.army.mil/Missions/MississippiRiver

ScienceTechnology/MSRiverGeomorphologyPotamology/P

ublicationsTechTransfer.aspx.

Limited geomorphic assessment

Analysis of the comparative cross sections 

indicates a generally shallower river channel in 

2010 than existed in 1975 for the reach just 

upstream of the Hydroelectric Station to just 

downstream of the Auxiliary Structure.

Recommendations

To divert more sediment through the complex

within current operational constraints, the 

recommended operation of the ORCC is to divert 

as much flow as possible through the Low Sill 

Structure during the rising limb of the hydrograph. 

During the peak and falling limb of the 

hydrograph, full flow capacity can be restored to 

the hydropower structure with remaining flow 

passing through the Auxiliary Structure. Summary of Significant Findings

• In order to have any significant impact on 

sediment diversion at the Old River Control 

Complex (ORCC), it is necessary to alter 

the operation of the Hydroelectric Station.

• As currently operated, the Low Sill

Structure is the most efficient at 

transporting sediment to the Atchafalaya 

River side of the ORCC.

• The Auxiliary Structure is the most efficient 

at diverting sediment from the Mississippi 

River but tends to shoal as currently 

operated and therefore is less efficient at 

delivering sediment through the complex.

• The modeling analysis indicates that 

excess sediment is being passed 

downriver, and therefore, any mitigation of 

this excess sediment should either have a 

neutral or positive effect on flood stages.

Points of Contact

Ronnie Heath

Author

USACE ERDC-CHL

Ronald.E.Heath@usace.army.mil

Freddie Pinkard

MRG&P, Sr. Program Manager

USACE MVK

Freddie.Pinkard@usace.army.mil

Ty V. Wamsley, Ph.D.

MRG&P Technical Director

USACE MVD

Ty.V.Wamsley@usace.army.mil