Mobile Harbor - Thin Layer Placement TLP/Maintenance
Learning from the Past
The U.S. Army Corps of Engineers (USACE) is charged with maintaining Federal navigation channels for commerce, national security, and recreation. The USACE, Mobile District must perform maintenance dredging events to keep the Mobile Harbor channel navigable. Maintenance dredged material from the Bay channel was historically placed within Mobile Bay along the channel prior to the 1980s. Environmental concerns of this in-Bay placement method were identified in the 1980s resulting in the Water Resources Development Act (WRDA) of 1986 requiring the maintenance material from the Bay channel be taken to the Gulf of Mexico and placed in Mobile-North Ocean Dredged Material Disposal Site (ODMDS). Placing the Bay channel’s dredged material in the ODMDS removed the sediment from Mobile Bay’s natural system. The environmental soundness of removing material from the Bay’s sediment system was questioned in the 1990s. Subsequently, WRDA of 1996 authorized the consideration of in-Bay placement as long as the placement does not negatively impact the environment. From 1996 to 2014, the Bay channel maintenance material continued to be placed in the ODMDS since the environmental impacts of in-Bay placement had not been studied. The only exceptions to this were to support emergency actions to re-open the channel in 1998 and 2005, after Hurricanes Georges and Katrina, and in 2012 due to excessive material deposition.
Partners in Progress
An Interagency Working Group (IWG) was established to prioritize identifying environmentally acceptable in-bay placement alternatives in 2010. The IWG consisted of numerous federal and state resource agencies with scientific experts as well as several local environmental non-governmental organizations (NGOs). The focus of this group was to evaluate and provide guidance pertaining to in-Bay placement practices that kept the sediment in the natural system and were environmentally acceptable. The IWG quickly recognized additional research was needed to better understand the impacts and make better decisions.
An Emergency Full of Opportunity
In 2012, an emergency event required the placement of material within the Bay to allow ships to access the channel. The USACE quickly worked with the IWG to develop requirements of the dredged material placement to avoid or minimize impacts to the Bay. The IWG and USACE agreed to place the material in a thickness no greater than one foot, a practice commonly known as thin layer placement. The fast-acting coordination and decision making allowed the USACE to meet its mission while providing an invaluable opportunity to study the practice of thin layer placement in Mobile Bay. The USACE collected data before, during, and after the placement activities. This data was used to measure how the dredged material moved within the Bay. Maybe more importantly, the data was used to develop a model that can accurately predict the material’s behavior for typical seasonal conditions and in extreme weather events such as hurricanes.
Data Driven Decisions
The results of the year-long study were presented to the IWG in 2014 and published in the Modeling of Thin Layer Placement of Dredged Material in Mobile Bayreport. The monitoring and modeling analyses indicated that material placed using the thin layer method is not transported along the bottom as a large sediment mass. Rather, the material is remobilized into the water column by waves and currents and returned into the Bay’s natural sediment transport system. Approximately 65% of material was widely dispersed by the natural waves, winds, and currents, while 35% of the placed material returned to the channel. The modeling also indicated the dredged material placed in thin layers is less erodible (~ 45%) than native sediment.
The Mobile Bay National Estuary Program developed a sediment budget for Mobile Bay during the same time. The Sediment Dynamics in Mobile Bay, Alabama: Development of an Operation Sediment Budget documented the Mobile Bay system did not have a balanced sediment budget. In fact, more material was being removed from the Bay by dredging operations than what was being put into the Bay by the natural system. This study recommended in-Bay placement of dredged material would be the most natural solution to the un-balanced sediment budget.
These studies provided the research needed to better understand the impacts of in-Bay disposal and how to do it better. The IWG recommended the USACE conduct in-Bay, thin layer placement of dredged material as a long-term solution for Mobile Bay. They also recommended the USACE place material further away from the channel to allow more material to be re-introduce naturally into the system instead of being moved back into the channel.
Better Today Than Yesterday
The USACE pursued in-Bay, thin layer placement for Bay channel maintenance material at the recommendation of the IWG. A Statement of Findings for the Modification to Mobile Harbor Operations and Maintenance Additional of a Long Term Open Bay Thin-Layer Disposal Optionswas approved in 2014. These findings were coordinated with resources agencies including the Environmental Protection Agency (EPA), U.S. Fish and Wildlife Service (USFWS), and Alabama Department of Environmental Management (ADEM). The plan for the Open Bay Thin-Layer placement included the following: (1) placing material at least 2,500 feet away from the channel, (2) placing material in thicknesses of less than one foot, and (3) rotating placement sites on a 4-6 year schedule, to the greatest extent possible. The resulting wholistic plan provides flexibility for better management of the channel by optimizing the use of thin-layer open bay sites, taking advantage of additional beneficial use opportunities, and continuing the use of the ODMDS.
Better Tomorrow Than Today
The USACE is one of the largest managers of dredged material in the nation and its responsibility to better manage this valuable resource is a national priority. In January 2023, Lieutenant General Scott Spellmon (the 55th Chief of Engineers for USACE) issued a “Beneficial Use of Dredged Material Command Philosophy Notice” outlining the organization’s goal to beneficially use at least 70% of its dredged material by the year 2030. The Mobile District is committed to achieving this goal through innovation, commitment, and collaboration with our partners and stakeholders. We routinely partner with local governments, federal and state agencies, and other organizations to restore the environment through the beneficial use of dredged material, reduce flood risk, and maintain our navigable waterways. Currently, we are working on projects with the Alabama State Port Authority, Alabama Department of Conservation and Natural Resources, Mobile County, Town of Dauphin Island, USFWS Bon Secour National Wildlife Refuge, Mobile Bay National Estuary Program (MBNEP), the Nature Conservancy, and other federal and state agencies to improve the environmental and economic resilience of coastal Alabama. We are also actively engaged in the forum provided by the MBNEP that allows all organizations and community members to be heard and we welcome dialogue and feedback on ways we can partner to meet the needs of the community.
Mobile Dredging FAQ
HOW IS THE STUDY FUNDED?
The Mobile Harbor General Reevaluation Report study is authorized under Section 201 of the Water Resources
Development Act of 1986, Public Law 99-662 (WRDA). In accordance with the 1986 WRDA, the project is
cost-shared between the federal government and the local sponsor (Alabama State Port Authority) with the
federal portion being 75% of the cost of the study and the Alabama State Port Authority funding the other 25%
of the cost.
HOW MUCH WILL IT COST AND HOW LONG WILL IT TAKE?
The project is anticipated to take 48 months to complete (starting from November 2015) with an estimated study
budget of $7.8 million.
WHY DOES THE STUDY PROCESS TAKE SO LONG?
The Corps of Engineers process for the General Reevaluation Report is very thorough. The study includes a
significant amount of information gathering, data collection, and modeling to help better understand the
economic benefits derived from the project and the environmental impacts caused by channel modifications.
The study process also includes public, technical, policy, legal and independent external peer reviews at various
stages of the project.
WHAT ARE THE EXISTING AND PROPOSED CHANNEL DIMENSIONS?
The General Reevaluation Report will study the feasibility of increasing the depth and width up to the authorized
limits of the project. Per the 1986 WRDA and the 1981 Chief's Report for Mobile Harbor, Alabama, the project is
authorized to increase the depth and width of the Mobile Bay Channel from the mouth of the bay to south of the
Mobile River to 55 feet by 550 feet, a distance of about 27.0 miles (Currently 45 feet by 400 feet) and to increase
the depth and width of the entrance channel over the bar to 57 feet by 700 feet, a distance of about 7.4 miles
(Currently 47 feet by 600 feet).
WHEN WILL THE DRAFT REPORT BE RELEASED FOR PUBLIC COMMENTS?
The draft report is scheduled to be released for public comment in the summer of 2018.
WHAT IS THE RECOMMENDED PLAN (TENTATIVELY SELECTED PLAN)? IF WE DON'T KNOW YET THEN
WHEN WILL WE KNOW?
A recommended plan to modify the existing dimensions of the Mobile Harbor channel has not yet been developed.
Currently, the Tentatively Selected Plan (TSP) is scheduled for public review in summer 2018.
WHEN AND HOW CAN THE PUBLIC PARTICIPATE?
Preparing an Environmental Impact Statement (EIS) under the National Environmental Policy Act (NEPA) assures
public participation, which includes the identification and evaluation of project-specific issues. Public participation
includes effective communication between all federal, state, local agencies, tribal governments; and other
persons or organizations who may have an interest in the project. The Public Involvement Management Strategy
(PIMS) for the study is available for download on the website http://www.sam.usace.army.mil/Missions/Program-
and-Project-Management/Civil-Projects/Mobile-Harbor-GRR/. The PIMS highlights several channels of
communication including publications, web pages, public meetings, public notices, and news releases that will
be used to communicate with the general public and stakeholders as the study moves through the EIS process.
WILL THERE BE MORE TRAFFIC OR SHIPS USING THE HARBOR IF THE PROJECT MOVES FORWARD?
Due to the impending increase in the number of Post Panamax vessels in the world fleet and the opening of the
Panama Canal expansion, the transition of larger vessels to the U.S. Gulf Coast is anticipated to occur with or
without the proposed channel deepening. However, previous navigation analyses have demonstrated that
channel improvements alone will not have an impact on the forecasted demand of commodities handled at a
particular port. The sponsor asserts that the proposed channel improvements at Mobile Harbor would allow for
those commodities that are transported through the harbor to move more efficiently. If the project is approved
and the modifications allow vessels calling on the harbor to transit more efficiently (carrying additional cargo per
call), the total number of vessels required to meet the anticipated demand at Mobile Harbor during the period of
analysis would most likely decrease compared to the current channel configuration.
DOES THE GULF COAST REALLY NEED ALL THESE PORTS AND COULD A MORE CENTRALIZED LOCATION
(SUCH AS HOUSTON OR NEW ORLEANS) ALSO SERVE THOSE AREAS?
Many factors influence the growth of a particular harbor including land side development and infrastructure,
location of distribution centers for imports, source location for exports, population and income growth and
location, port logistics and fees, business climate and taxes, carrier preferences, labor stability, and business
relationships. Mobile Harbor handled just over 64 million tons in 2014. This is a 10.3 percent increase from the
tonnage handled in 2005. Houston and New Orleans have respectively grown 9.7 and 22 percent during that
time period as well.
COULD AN EXISTING ADJACENT PORT TAKE CARE OF THE FUTURE INCREASED PORT TRAFFIC WITHOUT
DEEPENING THIS PORT?
As stated above, there are many reasons why a carrier chooses to call on a particular harbor. The proposed
channel improvements are not anticipated to impact that decision. Channel improvements at Mobile Harbor
would theoretically allow for more efficient movement of cargo through the port.
DOES THE STUDY CONSIDER ENVIRONMENTAL IMPACTS CAUSED BY THE EXISTING CHANNEL?
The study will characterize the environmental conditions associated with the existing channel conditions of the
area. These conditions will serve as the baseline for comparison of all future potential conditions associated with
a modified channel (i.e. wider and/or deeper).
WILL CHANGES TO SHIP TRAFFIC IMPACT SUBMERGED AQUATIC VEGETATION AND MARINE LIFE
(TURTLES, DOLPHINS, WHALES, MANATEES)?
Potential impacts to the bay’s natural resources and protected species resulting from changes in the bay’s
hydrodynamics, including potential increase in ship wake, will be investigated. The resources evaluated will
include wetlands, submerged aquatic vegetation, oysters, fish, and benthic macro-invertebrates and their
potential effects on the marine mammals that utilize the bay. The difference in effects between the current level
of traffic and future conditions associated with a modified channel will be evaluated and presented in the
Supplemental Environmental Impact Statement which will be provided for public review and comment in
summer 2018.
WILL DEEPENING RESULT IN INCREASED SALINITY IMPACTS TO THE ENVIRONMENTAL RESOURCES
OF THE STUDY AREA?
Potentially, however the extent and magnitude of the effects will not be known until the amount of deepening
that can be economically justified is determined, and the proper analyses are completed to quantify relative
changes in the hydrodynamics (i.e. water levels, waves, and currents) and water quality (i.e. salinity, temperature,
dissolved oxygen, nutrients, etc.). The results will be presented in the Supplemental Environmental Impact
Statement, which will be available for public review and comment in summer 2018.
HOW WILL INCREASED SHIP TRAFFIC AND THE ASSOCIATED SHIP WAKE IMPACT ADJACENT SHORELINES?
Potential changes in ship traffic and the associated wake could have an impact on adjacent shorelines and
habitats. The difference in effects between current traffic and future conditions associated with a modified
channel will be evaluated and presented in the Supplemental Environmental Impact Statement for public review
and comment in summer 2018.
WILL DEEPENING THE HARBOR HAVE AN ADVERSE IMPACT ON STORM SURGE?
Deepening is not anticipated to have an adverse effect on storm surge, however, this will be fully evaluated
through detailed modeling and analyses. The results will be presented in the Supplemental Environmental
Impact Statement, which will be available for public review and comment in summer 2018.
109 St. Joseph St., Mobile, AL 36628-0001 • 251-690-2505 • CESAM-PA@usace.army.mil • https://www.sam.usace.army.mil
IS BENEFICIAL USE OF DREDGED MATERIAL BEING CONSIDERED?
Expanding the Mobile Harbor navigation channel will potentially involve dredging and disposal of millions of
cubic yards of sediment. Disposal considerations for this material will be a significant component of the study
which will identify and examine realistic beneficial use opportunities associated with the proposed widening and
deepening activities. Beneficial use considerations will include, but are not necessarily limited to:
• Shoreline protection measures such as living shorelines
• Oyster reef restoration
• Creation of islands
• Thin-layer placement in strategic areas to reduce hypoxia
• Thin-layer placement for marsh conservation and restoration
• Raising bottom elevation in strategic locations to promote productivity
• Strategic placement of berms for shoreline protection
WHAT TYPE OF MATERIAL WILL BE DREDGED IF THE PROJECT MOVES FORWARD?
The type of material depends on where the deepening and/or widening will take place. The soils north of the
bay entrance are predominantly silts and clays. The soils south of the bay entrance are a mixture of silts, clays,
and sands. A detailed analyses will be performed to quantify the types and amount of material to be dredged
once the extent of deepening and widening that can be economically justified is determined.