Upper Mississippi River Navigation Structures

ERDC/CHL CHETN-IX-5

September 2001

harbor. The data is being utilized to determine the nearshore processes contributing to potential

shoaling. Wave height data is also being used to evaluate the success of the breakwater with

regard to wave height reduction. The hydraulic stability of the breakwater is also being

evaluated.

Upper Mississippi River Navigation Structures. Most training structures on the

Mississippi River were constructed over 100 years ago. Subsequent construction of locks and

dams submerged these structures which reduced their effectiveness and increased river-

floodplain connectivity. Both training structure submergence and river-floodplain connectivity

are a function of longitudinal pool position. Course sediment transport also varies because of the

longitudinal changes in submergence. A drawdown is being performed in Pool 8 to expose

mudflats, cause seed germination, and benefit fish and wildlife. In Pool 8, most dredging is done

in the middle of the reach of the pool between river mile (RM) 691 and 688, where a

combination of training structure submergence, floodplain conveyance, and coarse sediment

availability results in river deposition. It is unknown how the flow and sediment movement in

the vicinity of these structures will change during such a drawdown. In addition, training

structures in Pool 22 have recently been rehabilitated upstream of a lock and dam to maintain

sufficient navigation depth in the approach to the lock. The renovation was both numerically and

physically modeled and construction was completed in 1995.

The objectives of the monitoring effort are to evaluate hydrodynamic and sediment transport

processes before, during, and after the drawdown at Pool 8 as well as to evaluate the

effectiveness of the training structures in maintaining the channel in Pool 22. Monitoring at both

sites includes measurements to determine bathymetry changes, and to determine hydrodynamic

sediment transport changes. Suspended sediment samples and bed-load measurements also

would be obtained and analyzed. Monitoring is expected to improve the Corps predictive

capability and result in a more technically based, cost-effective, and ecologically sound

management of the Upper Mississippi River navigation system as well as other river systems.

Periodic Inspections. As previously stated, navigation structures are monitored in this work

unit on a periodic basis to gain a better understanding of their long-term responses to the

environment. Currently three project breakwaters in the Hawaiian Islands are being monitored.

These include breakwaters at Nawiliwili Harbor, Kauai; Kahului Harbor, Maui; and

Laupahoehoe, Hawaii. All these structures' primary armor layers are compromised of concrete

armor units. Base conditions were initially obtained for Kahului and Laupahoehoe breakwaters

in 1993 and Nawiliwili breakwater in 1995. Nawiliwili breakwater was constructed in 1922 and

has a long history of repair. Breakwater armor consists of 9,979.03- and 20,865.25-kg- (11- and

23-ton) dolosse and 5,896.70- and 16,147-89-kg- (6.5- and 17.8-ton) tribars. The breakwaters at

Kahului were initially constructed in 1900 and have undergone numerous repairs and

rehabilitations as well. The armor layers consist of 5,443.10-, 18,143.69-, and 27,215.54-kg-

(6-, 20- and 30-ton) dolosse, 5,896.70-, 8,164.66-, 9,979.03-, 17,236.51-, 22,679.62-, 31,751.47-,

and 45,359.24-kg (6.5-, 9-, 11-, 19-, 25-, 35-, and 50-ton) tribars, and 29,937.1-kg (33-ton)

tetrapods. The Laupahoehoe structure was completed in 1990 and includes 27,215.54-kg

(30-ton) dolos armor layers.