New River pump station into the Mississippi explained by HNTB

Upper Manchac, Bluff Swamp and Spanish Lake encompasses three parishes with only one outlet for Bayou Manchac

HNTB’s John Monzon was on hand Monday to update EA Drainage District on the ongoing effort to produce a Floodplain Master Plan.  The presentation shifted focus to a new project aimed at pumping New River’s water from its western terminus into the Mississippi.  Monzon enumerated the substantial benefits to Ascension Parish along with four other parishes which, hopefully, will appeal to the decisionmakers doling out the necessary millions from the pot-o-gold that is Louisiana Watershed Initiative.

HNTB, along with CSRS engineers, have been collecting data and surveying floodplains since February when the contract to undertake the Plan was approved.  Starting from scratch it appears, the first task is to Identify Problems.  No area of Ascension (along with Iberville and East Baton Rouge) has caused more consternation for residents than the Bluff Swamp/Spanish Lake/Bayou Manchac area (see above).


2016 saw backwater flooding from the Amite River after localized rainfall of 13″ in less than 24 hours. (Tropical Storms can cause a rise of 4′ (Ida-2021)

  • Under high water conditions in Bluff Swamp (more than 12′ elevation), water crosses Hwy 74 and flows toward Morgan Swamp and vice versa.

Reconnecting Spanish Lake to New River with new box culverts and gates at Hwy 74 is part of a solution, digging a new channel.  Spanish Lake once had a hydrologic connection to New River.  According to Monzon it would “improve New River from Interstate 10 to the pump station to be built at the Mississippi River.”

It would “manage levels in Bluff Swamp/Spanish Lake.  If New River cannot handle additional flows the control structure will prevent water from flowing toward Gonzales.”

Marvin Braud Pumps pull water from New River’s western terminus…

But, water from Geismar and Dutchtown has to travel 18 miles to get there.

When Bluff Swamp is not flowing towards New River (normal conditions) and other areas to the east need capacity, a pump at the Mississippi can assist with flow into New River.  Thus, the project can reduce the amount of water that Marvin Braud PS has to handle.  That, according to Monzon, equals improved drainage in the vicinity of Geismar and Dutchtown with less impact on Gonzales and St. Amant.

It all sounded very promising, and there would be other benefits:

  • Reduction in the amount of water that flows from Spanish Lake and Alligator Bayou in to Bayou Manchac (helping EBR and the Upper Manchac Basin)
  • Reduction of water levels in Spanish Lake to benefit Iberville Parish
  • Lessening of the impact on the City of Gonzales and St. Amant with flood waters being pumped into the Mississippi
  • Potential to reduce the amount of water pumped at Marvin Braud into Blind River (benefiting Livingston and St. James parishes

That makes five parishes which stand to benefit, which renders the project eligible (and hopefully, attractive) for Louisiana Watershed Initiative funding.