Chip Groat

Coastal Watersheds and Sediment Management
Opportunities and Challenges in the Gulf of Mexico

Chip Groat
Director, US Geological Survey

     Coastal watersheds have a profound impact not only on coastal areas, but on oceans.  The health, sustainability, and evolution of coastal and ocean systems are intimately linked to watershed processes that deliver water, nutrients, contaminants and sediment.  The U.S. Commission on Ocean Policy report recognizes the critical role of human and natural processes across coastal watersheds and landscapes and embraces the concept of ecosystem-based management. The report also promotes sediment management and the importance of understanding sedimentary systems that link watershed, coastal, and ocean elements.   Sediment is the foundation of our coastal resources.  In deficit or excess, it impacts the health, function, and vulnerability of coastal ecosystems and communities.  Sediment must be viewed as a critical and limited resource and managed as such.
     Comprehensive sediment management must reflect the natural scales of sedimentary systems from sediment source to sink, must be grounded in understanding sediment transport processes and the evolution of sedimentary landforms, and must include an assessment of the resource value of sediment throughout the system. An adequate and appropriate model of sedimentary systems is one that links watershed and ocean processes. It provides the basis for understanding the evolution of coastal sedimentary processes and landforms over time scales ranging from short-lived storm events to relevant geologic time. Developing science-based models for sedimentary systems that can shape effective management practices, enhance local and regional resource management, and forecast future coastal responses to human and natural processes is a daunting yet achievable challenge.
     The physical framework of the coastal and ocean ecosystems of the Gulf of Mexico is the product of hydrologic and sedimentary processes, extensively impacted by human activities across the expanse of the Mississippi Basin and smaller coastal watersheds. The geologic processes of sediment delivery, transport, and regional subsidence are the persistent drivers that shape the coast.  They must be understood in the development of effective strategies to reduce hazard risk and protect and restore economically and ecologically critical habitats.  Alterations to land use across the Mississippi Basin have resulted in the growth of the notorious hypoxic zone.  Decreases in sediment delivery for delta nourishment and offshore deposition contribute to the loss of wetlands and barrier islands – impacting ecological function and increasing the exposure to coastal hazards. On a smaller scale, the reservoirs built on Texas’ rivers and soil conservation practices have impacted freshwater inflow into Texas bays and sediment delivery to the bays and longshore current systems that support barrier islands.
     There is no one-size-fits-all management unit definition if management is intended to utilize a natural or ecosystems approach.  Unless the regional management that the Commission on Ocean Policy report supports has the regions defined to coincide as closely as possible with the boundaries of natural systems, there will be complications related to two or more regions managing a system. Likewise, the research and monitoring that supports an ecosystems-based management must be organized on a systems basis. This will require close coordination among the state, federal, and university programs that provide the research and monitoring base for management.