Alternative D1 ("One Lake") Dam and Excavation
Dam
Alt D1 includes construction of a new dam at River Mile 286.5 to create a "Lake Surface Area" of 1,556 acres. The dam would be built to an elevation of 256 ft, six feet higher than the current weir at J.H. Fewell Drinking Water Plant. Portions of the dam would be submerged during normal flow allowing excess water to pass downstream and a low flow structure is included in the design. Water would pass over the weir or through the low flow structure with inflow into the lake approximately equaling outflow at any given time. The new dam would not provide any flood control benefits but would create a permanent lake impoundment.
2025 USACE RDEIS, Appendix I
Alternative D1 "One Lake" Dam:
- Top at EL (elevation above Mean Sea Level): 256 feet (6 feet higher than the current weir)
- Length: 2,200 feet (0.4 miles)(for comparison, the Pool's Bluff sill in Louisiana is 350 feet long)
- Bottom width: 15 feet plus 10 feet concrete extension and 10 feet long sheetpile on the backside to reduced potential erosion during overtopping events since the structure will sit directly on exposed alluvial sands that are highly erodible
- Includes fish passage and low flow gate
- Estimated cost of dam $58 million
- Estimated cost of new pumping station $54 million
*Notes
- The proposed dam "does not provide any flood control benefits, and construction of the weir necessitates additional pumping needs at existing levees as well as seepage protection in the form of berms and slurry walls on existing levee segments" (2025 USACE RDEIS, App I, p 36)
- "The proposed weir in Alternative D1 meets USACE and State criteria to be defined as a dam based on the height of the structure and water storage. As a result, the dam will need to be designed and constructed to meet higher USACE and State criteria for a dam." (2025 USACE RDEIS, App I, p 30)
- The $58 million dam cost will be solely the responsibility of the Rankin-Hinds Pearl River Flood and Drainage Control District and will not be cost-shared with the USACE (2025 USACE RDEIS, App I, p 37)
2025 USACE RDEIS, Appendix I
River Plug:
- The river will need to be plugged during construction for any weir option selected
- The plug is a reinforced part of the dam foundation in the original river channel
- Includes the need for a temporary cofferdam during construction
- Excavation for the plug will remove all alluvial soils above the Tertiary clays within the river bottom
- Plug will extend 325 feet wide along the channel bottom at EL 234 ft and slope up to a 50 foot wide crest at EL 252 ft
2025 USACE RDEIS, Appendix I
2025 USACE RDEIS, Appendix I
Low Flow Structure
- Allows for passage of flow downstream when weir is not being overtopped
- 12ft x 12ft reinforced box culvert 60 feet long
- Regulated by a sluice gate
- Bottom set at EL 234 feet, which is the estimated elevation of the bottom of the existing river channel
- Average depth estimated to be 18 feet
- Lined with riprap in the bottom and along the entire sides
- May take 2 years to construct
2025 USACE RDEIS, Appendix I
2025 USACE RDEIS, Appendix I
Fish Passage (conceptual):
- 5,000-6,000 feet in length
- Ties into the Conway Slough which connects to the Pearl River 0.8 miles downstream of the CN Railroad Bridge
- Even if diverting the entire river through the fish passage, during much of the calendar year, there will not be sufficient water available to support its use
2025 USACE DEIS "Proposed Weir (Black) and Fish Ladder (Blue)"
2025 USACE DEIS, Appendix I
Armoring to protect JH Fewell Drinking Water Plant and Mayes Lake:
- Current weir at the JH Fewell Drinking Water Plant will remain in place
2025 USACE RDEIS, Appendix I
Excavation
954 acres would be excavated along the Pearl River from River Mile 285 to River Mile 294 to improve water conveyance. The width of excavation would range from 500-2,600 feet and depth from 0-13 feet. The USACE predicts that excavation would provide reduction of flood elevations within the excavation area and for over 8 miles upstream.
- Excavation will be completed over a 3-year period.
- 9.11 MCY (million cubic yards of material) will be excavated from the floodplain and channel overbanks
- Excavated fill would be placed in designated disposal areas on the protected and unprotected side of existing levees as well as other locations within the flood plain.
- The disposal fill areas would impact 523 acres with up to 9.38 MCY (million cubic yards) of excavated fill.
- The excavated fill material would be used to create land areas ranging from 3-93 acres. The newly created areas could allow for expanded riverfront access, natural areas, along with recreational opportunities.
- Up to 1.6 MCY of fill (100 acres of fill 10 feet high) would be provided to the Rankin-Hinds Pearl River Flood and Drainage Control District for additional usage within the project area. (2025 USACE RDEIS, Appendix E, p 48-49)
- Some excavation is located near areas of concern for Hazardous Toxic Radiological Waste (HTRW). The Rankin-Hinds Pearl River Flood and Drainage Control District will be solely responsible for the performance and cost of HTRW cleanup and response, including the costs of any studies and investigations. If HTRW limits excavation, project improvements just upstream would be reduced by 0.8 feet at 100-year flood level and the Canton Club levee design would need to be refined.
- Induced flooding will occur due to water being able to move through the Pearl River more quickly. 81 acres outside of the regulatory floodway would experience water stages more than 0.25 feet higher due to the project and up to 11 structures would experience additional water added above ground floor elevations. Any structure experiencing new or added water due to the project would have to be mitigated (i.e. construction of a feature, raising of a structure, acquisition of a right of way, or acquisition in fee).
2025 USACE RDEIS, Appendix I
Adverse Impacts
Water Quality and Drinking Water Supply: Adding a large weir could increase sediment loads enough to alter the river water chemistry and induce failure at the existing J.H. Fewell Drinking Water Plant. (source: 2024 DEIS, PDF page 201) The new weir and channel improvements could disturb the known Hazardous Toxic Waste Sites (HTRW) enough to cause probable exposure to toxic contaminants within the ponded area at the inflow to J.H. Fewell Drinking Water Plant. (source: 2024 DEIS, PDF page 201). "Additional study could be needed to determine the best methods of design and construction to limit the impact to potable water throughout the system in respect to contaminant retention due to pooling and sediment loading prior to treatment." 2024 DEIS, PDF page 202
Mitigation: A USACE 2023 internal presentation states: “Identification of lands ongoing for terrestrial mitigation, extremely challenging (if not impossible) to mitigate riverine impacts of this proportion. Experts agree that restoring large systems such as this or even compensating for such great function and habitat loss to a truly desirable condition (as existed pre-disturbance) is impossible to achieve. Impoundment removal seems to be the national trend, due to significant adverse impacts of impoundments on river systems for natural resources and humans.” The USFWS estimated in its Fish and Wildlife Coordination Act Report: "Preliminary analysis shows total mitigation costs (based on bank credit purchase) for forest types and palustrine habitat could exceed $1 billion, which excludes riverine mitigation costs. We expect riverine mitigation to be costly since both function and habitat loss need to be compensated. Therefore, costs would greatly exceed $1 billion." (source: 2024 USACE DEIS, Appendix J, PDF page 44)
Induced Flooding: Floodwaters will move more quickly through the excavated project area, adding additional induced floodwater to the area south of the new dam. Induced flooding caused by Alternative D1 includes:
Relocations or Removal Actions Required:
High Cost of Alt D1:
Mitigation: A USACE 2023 internal presentation states: “Identification of lands ongoing for terrestrial mitigation, extremely challenging (if not impossible) to mitigate riverine impacts of this proportion. Experts agree that restoring large systems such as this or even compensating for such great function and habitat loss to a truly desirable condition (as existed pre-disturbance) is impossible to achieve. Impoundment removal seems to be the national trend, due to significant adverse impacts of impoundments on river systems for natural resources and humans.” The USFWS estimated in its Fish and Wildlife Coordination Act Report: "Preliminary analysis shows total mitigation costs (based on bank credit purchase) for forest types and palustrine habitat could exceed $1 billion, which excludes riverine mitigation costs. We expect riverine mitigation to be costly since both function and habitat loss need to be compensated. Therefore, costs would greatly exceed $1 billion." (source: 2024 USACE DEIS, Appendix J, PDF page 44)
Induced Flooding: Floodwaters will move more quickly through the excavated project area, adding additional induced floodwater to the area south of the new dam. Induced flooding caused by Alternative D1 includes:
- 11 structures receiving additional flooding in the ground floor during 100-year flood
- 97 structures receiving additional flooding in the ground floor during 200-year and 500-year floods
- 81 acres receiving additional flooding in the ground floor during 100-year flood
- 5,822 acres receiving additional flooding during 200-year and 500-year floods
Relocations or Removal Actions Required:
- Relocating 4-5 utility transmission lines
- Bridge countermeasures
- Mitigating potential HTRW (Hazardous, Toxic, Radiological Waste Sites) and other hazardous waste sites within the floodplain. USACE is prohibited from undertaking HTRW work on behalf of the Rankin Hinds Pearl River Flood and Drainage Control District (the Non Federal Sponsor). "Consideration may be given to designating an HTRW avoidance alternative as the National Economic Development plan when costs and risks of response actions are uncertain." 2024 DEIS, PDF pages 94-95.
High Cost of Alt D1:
- Projected First Cost for Alt D1: $873-$917 million
- Total Project Cost (accounting for inflation and interest): over $1 billion (2025 USACE RDEIS, Appendix R)
- Maximum Project Cost Limit: $475 million (*An increase in the authorized project cost would require approval from Congress)
- Current Federal Cost Share Appropriation: $221 million (appropriated in Oct 2022)
TOTAL PROJECT COST |
D1 (High Cost) |
D1 (Low Cost) |
Local Cost Share |
Relocations |
$7 million |
$7 million |
35% |
Dams |
$58 million |
$58 million |
100% |
Fish and Wildlife Facilities |
$159 million |
$112 million |
35% |
Channels and Canals |
$351 million |
$351 million |
35% |
Levees and Floodwalls |
$125 million |
$125 million |
35% |
Pumping Plant |
$54 million |
$54 million |
100% |
Recreation Facilities |
$6 millon |
$6 million |
50% |
Bank Stabilization |
$99 million |
$99 million |
35% |
Lands and Damages |
$109 million |
$109 million |
35% |
Planning, Engineering, & Design |
$62 million |
$59 million |
35% |
Construction Management |
$53 million |
$50 million |
35% |
TOTAL* |
$1 billion ($1,088, 438,000)* |
$1 billion ($1,035,003,000)* |
- |
source: 2025 USACE RDEIS, Appendix R
Costs to Rankin Hinds Pearl River Flood and Drainage Control District, the Non Federal Sponsor (NFS):
Harm to endangered and threatened species: The USACE notes that, despite having a smaller footprint that the original "One Lake" project design, this alternative "will still cause major long-term negative impacts to fisheries and aquatic resources.” Threatened, endangered, and protected species that will by negatively impacted by Alternative D1 include the Gulf sturgeon, Pearl River map turtle, ringed sawback turtle, alligator snapping turtle, LA pigtoe mussel, tricolored bat, monarch butterfly, and bald eagle.
- The local Drainage District, Rankin-Hinds Pearl River Flood and Drainage Control District, shall contribute 35 percent of total project costs. (Source: 2024 Commander's Report, pages 13 and 14) The Drainage District has not indicated how they will pay for their portion of the project costs.
- The local Drainage District is solely responsible for 100% of the costs for remediation of the Hazardous, Toxic, Radiological Waste (HTRW) Sites in the project area, including the costs of any studies and investigations.
- The local Drainage District shall acquire the real property interests that the Government has determined are required for the construction, operation, and maintenance of the Project.
- The local Drainage District shall perform or ensure the performance of the relocations necessary for construction, operation, and maintenance of the Project
- In addition, the local Drainage District will be responsible for Estimated Annual Operation and Maintenance Costs of $700,000/year. Local Drainage District revenues are obtained through a 4.75-mil tax assessment on properties protected by the levee system. The majority of the tax revenue comes from properties located in Rankin County. The state-owned properties on the Jackson side of the Pearl River do not pay taxes.
Harm to endangered and threatened species: The USACE notes that, despite having a smaller footprint that the original "One Lake" project design, this alternative "will still cause major long-term negative impacts to fisheries and aquatic resources.” Threatened, endangered, and protected species that will by negatively impacted by Alternative D1 include the Gulf sturgeon, Pearl River map turtle, ringed sawback turtle, alligator snapping turtle, LA pigtoe mussel, tricolored bat, monarch butterfly, and bald eagle.
2024 USACE DEIS, PDF page 216, LeFleurs Bluff State Park
Loss of Public Lands: 78 acres, 16% of LeFleur’s Bluff State Park, Jackson’s only public access to the Pearl River and a popular recreation area, would be excavated and permanently under water, according to the map published in the 2024 USACE DEIS.
LeFleurs Bluff State Park has been the recipient of $1,422,999 in Land Water Conservation Act grant funding. (not adjusted for inflation) A condition of the grant is that: "No property acquired or developed with assistance under this section shall, without the approval of the Secretary, be converted to other than public outdoor recreation uses."
LeFleurs Bluff State Park has been the recipient of $1,422,999 in Land Water Conservation Act grant funding. (not adjusted for inflation) A condition of the grant is that: "No property acquired or developed with assistance under this section shall, without the approval of the Secretary, be converted to other than public outdoor recreation uses."
Pearl Riverkeeper asks that everyone make his or her own decision regarding the Pearl River Flood Risk Management Project using sound science and engineering. We encourage the review and thorough analysis of all available information. We welcome comments and feedback. Please email Pearl Riverkeeper or visit our Facebook for comment space. Our publishing, or re-publishing, of anyone else's research or opinions is not an endorsement on our part of those conclusions.
