LNG Export Terminal

Stormwater drainage design for a Gulf Coast LNG export terminal, where a parish drainage channel ran through the site and had to be re-routed without changing the hydrology of the district around it.

The terminal sits behind a storm surge wall, and the wall splits the problem in two. While it is being built, runoff from inside the site is diverted to the ship channel through a temporary 48-inch pipeline and the design event is the 10-year, 24-hour storm. Once the wall closes, everything inside transitions to a buried pipe network discharging to a loop, the re-routed channel carries only what falls outside the wall, and the design events become the 25-year and 100-year, 24-hour storms. Two drainage regimes on one site, in sequence — and the temporary one has to keep working for as long as the permanent one takes to build.

What makes a job like this slow is rarely the hydraulics. It is the compliance stack: federal energy regulation, Army Corps Section 404 and Section 10 permits for impacts on waters of the United States, EPA water quality under the Clean Water Act through NPDES, and over the top of all of it a parish ordinance requiring culverts to be approved one by one, roads designed to a 25-year storm, and materials specified for a high-salinity environment. The inherited baseline model repaid a close reading too. It carried no tidal boundary condition, substituting a cut in the terrain to mimic the restriction, and it assumed the existing pump station was non-operational to hold the worst case. Both are defensible assumptions. Neither survives being forgotten by whoever picks the model up next.