US DOI Modified Water Deliveries to ENP (C)

May 2023


US DOI - Modified Water Deliveries to Everglades National Park
Construction (C)
Congressional Districts: 23, 24, 25, 26, 27


Public Law (P.L.) 101-229 authorized the 1989 Everglades National Park Protection and Expansion Act. A General Design Memorandum (GDM) describing the plan for modifying the flow of water to Everglades National Park (ENP) was completed in 1992 and approved in 1993. The Project Cooperation Agreement (PCA) was executed in 1994 with the South Florida Water Management District (SFWMD), and construction was initiated in 1995. In 2000, a General Reevaluation Report (GRR)/Supplemental Environmental Impact Statement (EIS) was completed for the 8.5 Square Mile Area (8.5 SMA), modifying the original plan, and in 2001, the first amendment to the PCA was executed. After a district court ruling stopped project implementation efforts, P.L. 108-7 was passed in 2003 directing the U.S. Army Corps of Engineers (USACE) to immediately proceed with efforts in accordance with the 2000 Report. In 2005, a Revised GRR/Supplemental EIS was completed recommending modifications to Tamiami Trail (U.S. Highway 41) to address the higher water levels under the authorized plan. The high costs of the 2005 plan led to a Limited Re-evaluation Report (LRR) of the Tamiami Trail project in 2007-2008. The second amendment to the PCA was executed in 2008. After a preliminary injunction stopped Tamiami Trail efforts, P.L. 111-8 was passed in March 2009 directing immediate construction of the 2008 LRR/EA plan with addendum. The preliminary injunction was dissolved in June 2009. The National Park Service funding cap imposed in November 2010 enables the completion of the 8.5 SMA, and modifications to the Tamiami Trail, implementation of 2 incremental tests (G-3273 Relaxation and S-356 Field Test) along with an operational plan that combines the constructed features of the MWD and Central and Southern Florida (C&SF) Canal 111 South Dade (C-111 SD) Projects. The third amendment to the PCA was executed in 2017.

The purpose of this project is to make modifications to the existing C&SF project to improve the natural water flows to Shark River Slough, the lifeline of the ENP. The project will enable restoration of more natural hydrologic conditions using three dimensions: timing, location, and volume of water. The project consists of four major components: 1) 8.5 SMA Flood Mitigation Plan; 2) Conveyance and Seepage Control Features; 3) Tamiami Trail Modifications; and 4) Project Implementation Support. The 8.5 SMA Flood Mitigation plan includes acquisition of approximately 4,320 acres of land (2,040 acres under the original authorization and 2,280 acres under the 8.5 SMA authorization) and construction of a levee, seepage canal, pump station, and detention area to prevent additional flooding due to construction and operation of the Modified Water Deliveries (MWD) project. The Conveyance and Seepage Control Features are necessary to facilitate flow through the system from Water Conservation (WCA) 3A and limit seepage eastward from ENP, including the reestablishment of the historic Shark River Slough flow-ways. Also included is raising the Tigertail Camp, part of the Miccosukee Tribe of Indians’ tribal lands, for flood protection. The Tamiami Trail Modifications component involves constructing a one-mile eastern bridge, allowing L-29 Canal stage to reach 8.5 feet National Geodetic Vertical Datum (NGVD), and reinforcing the road to mitigate for road impacts from the 8.5-foot stage. Project implementation support includes project and program management support, incremental testing, effort to develop a final operating plan, required stream gage monitoring, and necessary regulatory activities.


Estimated Total Authorized Cost $417,000,000
Estimated Federal Cost (USACE) $77,500,000
DOI Other Federal Agency $339,507,000
Allocation thru FY20 (USACE) $77,500,000
Allocation for FY21 $0
President’s Budget FY22 $0


South Florida Water Management District (SFWMD)
3301 Gun Club Road
West Palm Beach, Florida 33406

U.S. Department of the Interior (USDOI)
849 C St. NW
Washington, D.C. 20240

USDOI is not the non-federal sponsor; they are required to fund the project, so they are included in project activities and coordinated with.


(1) Flood Mitigation for the 8.5 Square Mile Area

All lands were acquired and initial construction was completed in 2008. The Corps has transferred all lands to the DOI and the SFWMD. The constructed features were turned over to the SFWMD for OMRR&R and are currently being operated under an Interim Water Control Plan. Initial operation of the features showed an area of concern in the southwest corner of the Las Palmas community. A construction solution to ensure the proper level of mitigation was identified. The construction contract for the S-357N Control Structure was awarded in September 2015. Construction and turnover to the SFWMD for OMRR&R were completed 2nd quarter FY18.

(2) Conveyance and Seepage Control Features

Available funds are fully allocated to other components of the Modified Water Deliveries Project. It is expected that no further modifications to levees and canals will be completed under the MWD project. The following conveyance and seepage control features as outlined in the 1992 GDM (approved 1993) were completed or constructed:

  • Spillway structures S-355A and B in the L-29 Levee
  • S-333 modifications
  • Tigertail Camp raised
  • Pump Station S-356 between L-31N Canal and L-29 Canal
  • Degradation of the L-67 Extension Canal and Levee (4 of 9 miles degraded)
  • S-331 Command and Control (complete – added telemetry & remote control of conveyance features)

With these features constructed, water will be delivered from WCA-3A to the L-29 canal, and then under Tamiami Trail (U.S. Highway 41) to Shark River Slough.

The following conveyance and seepage control features as, outlined in the 1992 General Design Memorandum, will not be completed:

  • Structures S-345 A, B, and C through the L-67A and C Levees
  • Structures S-349 A, B, and C in the L-567A Borrow Canal
  • Degradation of the L-67 Extension Canal and Levee (remaining 5 miles)

(3) Tamiami Trail Modifications

USACE issued a construction contract to Kiewit Southern on 25 September 2009. The notice to proceed was accepted on 11 November 2009, and a groundbreaking ceremony took place on 4 December 2009. Construction of the bridge and road reinforcement was completed in December 2013. Flowage easements for the properties along the Tamiami Trail and for the Tamiami Trail corridor were obtained 1st quarter of 2018. Project transfer to the Florida Department of Transportation was completed in February 2018.

(4) Project Implementation Support

This ongoing component includes project and program management support; hydrological stream gage monitoring and wildlife monitoring; operational plan development; and project closeout. USACE is currently working on project closeout. As part of the operational plan development, a series of field tests were performed to better understand the impacts to additional flows to North East Shark River Slough. Increment 1 of the G-3273 Relaxation and S 356 Field Test was implemented in October 2015. Increment 1 eliminated the constraint at the gage 3273 (G-3273) while the L-29 canal stage was limited to 7.5 feet NVGD. This test was planned for up to 2 years. To accommodate lessons learned from the 2016 High Water Emergency and additional operational constraints required by the Fish and Wildlife Service (FWS) Reasonable and Prudent Alternative in the 2016 Jeopardy Biological Opinion (BO) on the Everglades Restoration Transition Plan (ERTP), USACE implemented Increment 1 Plus (1.1/1.2) March 1, 2017. Increment 1 Plus raised the L-29 canal stage up to 7.8 feet NGVD. Increment 2 raised the L 29 canal stage up to 8.5 feet NGVD and was implemented on March 1, 2018. Construction of the critical features of the C-111SD Contract 8 and Contract 8a were necessary to raise the L-29 canal stage above 7.8 feet NGVD. These features were completed in August 2018. Increment 2 remained in place until implementation of Increment 3, the Combined Operational Plan (COP). COP incorporates both the MWD and C-111 SD projects constructed features. Development of the final COP alternative was completed, and the Record of Decision was signed August 28, 2020.

Mod Waters project area map