Tools for Managing Sediment for Coastal Restoration in Louisiana

Edward Haywood III, Syed M. Khalil, and Richard C. RaynieCoastal Protection & Restoration Authority of Louisiana

2012 COASTAL MASTER PLANThe 2012 Coastal Master Plan includes the nation’s largest investment, over $20 billion, in sediment mining and marsh creation projects over the next 50 years that will provide land building benefits for areas in dire need. At present, limited supplies of, or access to, renewable sediment constrains restoration efforts. Strategic management of sediment resources will be essential to ensure that sediment is used efficiently and cost-effectively.

LA SEDIMENT MANAGEMENT PLAN (LASMP)Broadly speaking, sediment management refers to the optimum use of various sediment resources (littoral, estuarine, and riverine) in an environmentally effective and economically feasible manner. The U.S. Army Corps of Engineers (USACE) has adopted Regional Sediment Management (RSM) on a national level so that in a very general sense it fits Louisiana’s sediment management actions into the context of a regional plan. In Louisiana, the USACE’s RSM effort forms an integral part of a broader LASMP being developed by CPRA. Basically, any sediment management plan in a given geological framework comprises sediment deposits on regional scales and encompasses understanding of regional sediment budgets along with records of dredging activities in the region.

CONTACT: Syed Khalil; Coastal Protection and Restoration Authority; Syed.Khalil@LA.gov; 225-342-1641

ABSTRACTSediment is critical to the sustainability of coastal Louisiana, and being sediment-limited, proper management of sediment resources is vital. Louisiana’s 2012 Coastal Master Plan prescribes billions of dollars in sediment diversion, barrier island and marsh creation projects. To meet the sediment needs of this ambitious plan, Louisiana has developed a comprehensive Louisiana Sediment Management Plan (LASMP) which facilitates the inventory of sediment resources, management of relevant datasets, and provides tools for project planners and managers to efficiently manage fluvial and offshore sediment resources. This plan has four primary components that direct State efforts toward a more formal Regional Sediment Management (RSM) approach: 1) sediment management 2); borrow area considerations; 3) policy and regulations; and 4) coordination with Federal, State, and other stakeholders. Various tools related to these components that have already been developed include a Delta Sand Search Model (DSSM), the Louisiana Sand Resource Database (LASARD), monitoring programs such as the Barrier Island Comprehensive Monitoring (BICM) program, and a set of regional sediment distribution maps identifying known sediment resources in coastal waters and the Mississippi River. Finding adequate quantities of restoration-quality sediments in the Mississippi and Atchafalaya Rivers, and within State and Federal OCS waters is fundamental to State implementation of RSM initiatives. The long-term goal for these tools is to enhance State planning capabilities to optimize sediment resources, capitalize on synergistic project opportunities, reduce project costs, maximize land-building potential, and ensure projects have the necessary sediment available for the 50-yr planning horizon of the 2012 Coastal Master Plan.

BOEM: Delineation of Significant Sand Resources In Coastal Louisiana, offshore sand resources are extremely scarce. Additionally, vast areas of these relatively small offshore sand resources are not extractable because of the presence of oil and gas infrastructure and archaeologically/biologically sensitive areas. Since the use of Outer Continental Shelf (OCS) sediment resources is authorized by the BOEM through its Marine Mineral Program, the bureau is implementing several measures to help safeguard the most significant OCS sediment resources, reduce multiple use conflicts, and minimize interference with oil and gas operations under existing leases or rights-of-way.

LOUISIANA SEDIMENT MANAGEMENT PLAN (LASMP)

Regional Sediment Management •Sediment Resources•Sediment Budget•Dredged sediment •Diversions

Sediment Evaluation• Delta Sand Search Model (DSSM) : Protocol &

Guideline of exploration • Evaluation of potential areas• Offshore/State & Federal Waters• Lower Miss River• Atchafalaya River

Sediment Data Management(LASARD)

• Protocol for standardization of data acquisition

•LCA Miss River Delta Mgmt Study•Atchafalaya Basin Sed Mgmt Plan•Others

•Prioritization of allocation•Federal Standard•Environment Issues

Pipeline/O&G

Sea Level Rise Policy

Coordination with StakeholdersState, Federal, NGO

SEDIMENTOCS Waters, State Waters, Coastal Zone Lower Mississippi & Atchafalaya River

Borrow Area Management & Monitoring (BAMM)

•Optimal Utilization •Location vs. project•Location vs. pipeline•Delineation of potential sand sources in OCS

• Infilling rate•Slope Stability Issues•Hypoxia

Monitoring Programs

• Barrier Island Comprehensive Monitoring Program (BICM)

•Bathymetric data•Sediment data

• Met-Oceanic Data - WAVCIS• Eustatic Sea Level Rise • Subsidence

Sediment Borrow Area

Policy/Regulation

Ship Shoal, long considered a depocenter of sand compatible for coastal restoration in Louisiana, is about 50 km (31 mi) long by 8 km (5 mi) wide in the center but narrows on the eastern and western margins. It is estimated that the entire Ship Shoal body contains an estimated 1.2 x 109 m3 of sand (Penland et al., 1988). However, much (80-90%) of the shoal’s sand resource is presently not available for extraction because of oil and gas infrastructure. Geotechnical investigation indicates about 13.2 x 106 m3 of clean sand is available in portions of Ship Shoal Blocks 88 & 89 and approximately 21.6 x 106 m3 was estimated to be available in three closely spaced potential borrows in South Pelto Blocks 12 & 13 (Khalil et al, 2007). A recent (2011) geological investigation in the Western Ship Shoal Area indicates that the total volume of mineable sand is 107.8 x 106 m3 with buffer considerations which increases to 168.0 x 106 m3 if pipelines are removed. Another important observation on the basis of comparison of existing NOAA bathymetric data collected in 2011 is that the whole ship shoal complex is migrating in a northwesterly direction at an average rate of 8.2 m/yr.

These sediment distribution maps and the sediment quantities/volumes along with the Louisiana Sand Resource Database (LASARD) are integral to the Louisiana Sediment Management Plan (LASMP), which conceptualizes systematic planning and better coordination of essential components of the extensive restoration and protection effort currently undertaken in Louisiana.

The 2012 Coastal Master Plan contains several sediment diversion projects as a major tool in creating a sustainable coast. The goal is to reconnect the river, re-establish deltaic processes and reduce saltwater intrusion. Diversions will be more successful if paired with other restoration strategies:• Diversions can reinforce marsh creation projects by

supplying new sediment.• Adding shoreline protection projects along with

marsh creation and sediment diversions can help restore sustainability to an area.

The Delta Sand Search Model (DSSM) was developed to provide guidance for a systematic and cost-effective methodology for exploration of sand in deltaic and fluvial environments. This model was developed on the basis of procedures and protocols (e.g. Khalil, 2004, 2008; Finkl and Khalil, 2005) which are based on high-resolution geophysical and geotechnical surveys to identify and recommend targets for further exploration by more detailed studies and cultural resource investigations. Several restoration-quality offshore sand and mixed sediment (sand, silt, and clay) deposits were explored and delineated on the continental shelf using these protocols as a guideline. These guidelines were also used to evaluate sand in the Lower Mississippi River. Also as Khalil et al. (2010) explained, this kind of understanding abbreviates the need to conduct random geophysical and geotechnical surveys over large expanses of continental shelf seabed and focuses on more detailed surveys that target potential deposits.

The main objective of BAMM is to understand the evolution of borrow pits over time, especially the infilling (rate and types of sediment) and gradient of the pit-slopes as well as the impact of dredging the potential borrow area on wave climate, sediment transport regime and on water quality. During the various phases of this program, geophysical and geotechnical surveys were conducted at eight borrow areas. Water quality (dissolved oxygen) was measured at six borrow areas. In addition, inventories of other existing borrow areas in coastal Louisiana and their respective design and water quality characteristics has been developed. Two of the six borrow areas surveyed for hypoxia are located offshore, but many of the current marsh creation and restoration projects in Louisiana specify that fill sediment will be obtained from borrow areas designed within interior lakes and bays. The use of “inland” borrow areas is governed by numerous restrictions and/or regulations.

LASARD is designed to archive historical and current geoscientific data relevant to sand/sediment resources that can be queried by state, federal, and private entities for planning and executing restoration projects (Khalil et al, 2005). The objective of LASARD is to centralize relevant data from various sources for better project coordination and to facilitate future planning by delineating sediment resources for restoration in coastal Louisiana (Khalil et al 2010). Relevant information consists predominantly of geophysical (seismic, sidescan SONAR, magnetometer, and bathymetry) and geological (vibracore, jet probe, grab sample, isopach) data. Oil and gas infrastructure data are also incorporated, since they affect the delineation of borrow areas and subsequent dredging. The database is available through the CPRA public website (http://coastal.la.gov/). LASARD is of significant value to coastal planners, scientists, engineers, and others interested in coastal restoration in the northern Gulf of Mexico. Sediment and related information is readily accessible to all the stakeholders thus helping to save money and time and avoid duplication.

To assist in planning coastal restoration projects for the 2012 Master Plan, surficial sediment distribution maps for Offshore Coastal Louisiana and the Lower Mississippi River were developed. The muddy deltaic coasts of the Mississippi River Delta Plain not only have complex sediment distribution patterns, but the classification and delineation of the surficial extent of various types of sediment are based on limited data. The boundaries of various sediment types are therefore, at best, tentative. Additionally, sand plays an important role in restoration of Louisiana’s barrier islands. Locating suitable sand sources in a muddy deltaic environment is challenging. The presence of a network of oil and gas infrastructure crisscrossing the entire coast is an impediment to fully utilizing the coastal sediment resources. This infrastructure requires safety buffers for their protection, which

BORROW AREA MONITORING & MGMT (BAMM)

LOUISIANA SAND RESOURCES DATABASE (LASARD)

DELTA SAND SEARCH MODEL (DSSM)

SHIP SHOAL SAND INVESTIGATION

SURFICIAL SEDIMENT DISTRIBUTION MAP

POLICY & COORDINATION WITH STAKEHOLDERS

REFERENCES:Finkl, C.W. and Khalil, S.M., 2005. Offshore exploration for sand sources: general guidelines and procedural strategies along deltaic coasts. In: Finkl, C.W. and

Khalil, S.M. (eds.), Savings America’s Wetland: Strategies for Restoration of Louisiana’s Coastal Wetlands and Barrier Islands. Journal of Coastal Research, Special Issue No. 44, pp. 203–233.

Khalil, S.M., 2004. General Guidelines: Exploration for Offshore Sand Sources. Baton Rouge: Louisiana Department of Natural Resources, CRM, Coastal Engineering Division. Version IV.

Khalil, S.M., 2008. General Guidelines: Exploration for Offshore Sand Sources. Baton Rouge: Louisiana Department of Natural Resources, OCRM, Coastal Engineering Division. Version V.

Khalil, S.M.; Finkl, C.W.; Andrews, J., and Knotts, C.P., 2007. Restoration-quality sand from Ship Shoal, Louisiana: geotechnical investigation for sand on a drowned barrier island. In: Proceedings of Coastal Sediments ’07 (New Orleans, Louisiana), pp. 685–698.

Khalil, S.M.; Finkl, C.W.; Roberts, H.H., and Raynie, R.C., 2010. New approaches to sediment management on the inner continental shelf offshore coastal Louisiana, Journal of Coastal Research, 26 (4), 591-604.

Penland, S., Boyd, R., and Suter, J. R., (1988). Transgressive depositional systems of the Mississippi River delta plain, Journal of Sedimentary Petrology, 58 (6), 932-949.

Most of these regulations focus on vertical and horizontal dredging limits. The impacts of these aspects of borrow area design on wave heights and energies, the surrounding marsh environment, and hypoxia are also not clearly understood. Therefore, the scientific basis of these restrictions and/or regulations needs to be investigated to determine whether these borrow area design constraints are justified. As the project progresses, borrow area modeling, and data processing and interpretation of measured dissolved oxygen concentrations will also be undertaken. The combined information gathered during these efforts will be analyzed and will be used to provide recommendations on borrow area design.

drastically reduces the volume of sediment/sand available for restoration and protection projects. To assess the distribution of sediments both offshore and within the Lower Mississippi River(LMR), existing geophysical and geotechnical data were examined. This information was used for the first time to develop sediment distribution maps and, based on these maps, approximate potential sediment volumes.