The Submarine Groundwater Discharge is a process, consisting in the exchange of interstitial water across the sediment/water interface, which occurs across a land-sea interface.

Although overlooked for many years, the discharge of groundwater into the coastal zone has now been recognized as an important process in many areas. While the magnitude of such discharge may be relatively minor in areas dominated by river flow, recent studies have indicated that groundwater may occasionally account for a significant fraction of the fresh water inflow.

The implications of this process in the coastal zone are:

• SDG can be an important pathway for diffuse pollution to the Ocean, if coastal groundwater is contaminated with sewage or other materials (chemicals, pesticides).
• Its nature can determine the reliability and extent of potable water supplies, because it is responsible for limiting salt-water intrusion into the aquifer.
• SGD can affect coastal water quality and nutrient supplies to nearshore benthic habitats, coastal wetlands, breeding and nesting grounds because the fresh component of submarine water discharge interacts with and influences the recirculation of seawater.
• SDG can cause substantial loss of freshwater form arid regions.

Because SGD is essentially ‘invisible’, the problem that arises, from both a management and scientific standpoint, is determining how to avoid the error of ignoring an important process on the one hand, and wasting valuable resources on an unimportant issue on the other.

Where SGD is a significant factor in maintaining or altering coastal ecosystems (either terrestrial, estuarine, or marine), coastal zone managers will need to consider management of water levels and fluxes through controls on withdrawal or alterations in recharge patterns, as well as groundwater quality management (e.g. through control on land use, waste disposal, etc.).

Such major interventions in the coastal zone management system require a sound scientific justification and technical understanding that does not currently exist.  

Submarine Groundwater Discharge Project: Assessment and Management Implications of SGD

SDG Program is a five-year program, with inter-comparison experiments in different coastal environments in order to develop a standardized methodology for assessment of SGD that will provide both the scientific and the ICAM communities with the tools and skills necessary to evaluate the influence of SGD into the coastal zone. A central part of the project programme is to define and test the most appropriate assessment techniques via carefully designed intercomparison experiments:

• Site I, Cockburn, Australia, 29 November- 12 December 2000: the first intercomparison experiment was performed at Cockburn Sound, located in the southwest margin of continental Australia, near metropolitan Perth and Fremantle. Cockburn Sound is a marine embayment protected from the open Indian Ocean by reefs, a chain of islands including the dominant Garden Island, and a man-made causeway. 
  [Report: here]

• Site II, Eastern Long Island, USA, May 2002: the second intercomparison experiment was performed at Shelter Island, located in the Peconic Bay between the north and south forks of Long Island. The island is sparsely populated and only a small section in the northwestern area of the island has a storm drainage system.
  [Report: here]

As part of the IOC/IHP/IAEA Programme on Submarine Groundwater Discharges in the Coastal Zone, Guide has been published on SGD Management implications, measurements and effects. This guide was prepared by experts form the Scientific Committee on Oceanic Research (SCOR).
[Guide: here]

Partners involved

The SDG Project is implemented in collaboration with:

• LOICZ (Land-Ocean Interactions in the Coastal Zone of the International Geosphere-Biosphere Program)
• IHP/UNESCO (International Hydrological Programme of UNESCO)
• SCOR (Scientific Committee on Oceanic Research)
• IAEA (International Atomic Energy Agency)