DOTD — DOTD is implementing a plan that will provide broader observation and greater accuracy for DOTD’s monitoring efforts, especially along La. 70 and La. 69 near the Assumption Parish sinkhole area.
Currently, DOTD is conducting daily visual roadway inspections, weekly bridge inspections, and monthly GPS surveys of LA 70 and area bridges. They are also coordinating daily traffic control and signage, providing aerial photography as requested, and have developed a traffic contingency plan for LA 70.
In light of the most recent developments involving a second cavern located closer to LA 70, DOTD is moving forward with plans for enhanced and automated, continuous monitoring of LA 70 and the three area bridges (Bayou Corne, Grand Bayou and Bayou Choupique) for movement and subsidence.
These enhancements include the installation of tilt and accelerometer sensors on all three bridges, and Shaped-Accelerometer Arrays (SAA) located between the LA 70 right-of-way and the sinkhole, and at the two closest bridge locations to measure movement. (120 feet in length; measure vertically and horizontally)
Four Continuously Operating GPS Reference Stations (CORS) will be installed in the area for automated, continuous monitoring of subsidence. One will be located near the roadway, two will be located near the closest bridges, and one location is yet to be determined. (LSU conducting, higher accuracy, measuring with regional geographic perspective)
Additionally, DOTD is developing a detection and motorist warning system, which will use data from the monitoring systems and alert responders. Monitoring system will connect to DOTD’s Traffic Management Center in Baton Rouge. Notification process is in development.
DOTD is committed to having these enhancements in place no later than eight weeks from now.
Costs of automated monitoring and long-term plan
The initial capital cost of the enhancements is $1.7M: $1.2M for the detection and motorist warning system, and $500K for the feasibility study.
The annual operating and maintenance cost are $230,000, and includes daily, weekly, and monthly inspections; monthly surveys; traffic control and signage; and data collection and evaluation. These costs will be provided under the Secretary’s Emergency Fund, to be reimbursed by Texas Brine. Requested reimbursement from Texas Brine for cost to date is $216,000.
Feasibility Study of Alternative Alignments for LA 70
DOTD is conducting a feasibility study to determine if an alternate route could be built in the affected area in the event that La. 70 is compromised and help identify possible the cost. The study is expected to take 6 months. During this time, DOTD will hold public meetings to provide information about the proposed options.
Multiple alignments will be studied, including a local “run around” alignment, alignments around the salt dome cap, and alignments around the entire salt dome. The next step is the environmental assessment, which will take another 6 months.
Traffic Contingency Plan
The primary detour is intended for heavy truck traffic, and is 70 miles long (through Morgan City) - LA 70 South to US 90 East to LA 662 North, to LA 398 North to LA 1.
The local detour is intended for local traffic, and is 45 miles - LA 997 North to LA 75 North to LA 404 East, to LA 69 North, 45 miles (through Bayou Pigeon).
If detour routes are implemented, Variable Message Signs will be placed at the intersections of LA 1 and LA 70, LA 1 and U.S. 90, and LA 1 and at LA 70. Signs will be installed along the detour route to direct drivers to their ultimate destination.