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A Conceptual Model for Evaluating Hydrologic Connectivity in Geographically Isolated Wetlands
Citation:
Leibowitz, S. AND M. Rains. A Conceptual Model for Evaluating Hydrologic Connectivity in Geographically Isolated Wetlands. Presented at American Geophysical Union, San Francisco, CA, December 09 - 13, 2013.
Impact/Purpose:
As a result of the Rapanos US Supreme Court decision, certain water bodies, such as geographically isolated wetlands (GIWs), must have a significant nexus with a traditional navigable water if they are to be considered waters of the US under the Clean Water Act (CWA). Hydrologic connectivity between a GIW and downstream waters is one of the major ways by which a significant nexus can occur. Knowledge about hydrologic connectivity between GIWs and other aquatic resources is also important for understanding and managing watershed hydrology. GIWs mostly consist of depressions that typically lack surface water connections to other water bodies. However, GIWs may connect to downstream waters at a range of time scales through either surface water fill and spill events during flooding or through groundwater. Investigations of such connectivity are few, and have been limited to specific regional types of GIWs. An understanding of the general factors that control hydrologic connectivity of GIWs and downstream waters is lacking. Here we present a conceptual model that describes these general factors. By combining elements of the hydrologic budget with site and regional characteristics, we classify GIWs by type and magnitude of potential hydrologic connectivity. Combining this information with hydrologic landscape characteristics that are generally available throughout the US could allow GIW hydrologic connectivity to be evaluated. This could aid in evaluating whether a significant nexus exists, and could ultimately be useful in CWA jurisdictional determinations.
Description:
Knowledge about hydrologic connectivity between aquatic resources is critical to understanding and managing watershed hydrology and to the legal status of those resources. In particular, information is needed on the hydrologic connectivity and effects of geographically isolated wetlands (GIWs) on downstream waters. GIWs mostly consist of depressions that typically lack surface water connections to other water bodies. However, GIWs may connect to downstream waters at a range of time scales through either surface water fill and spill events during flooding or through groundwater. Investigations of such connectivity are few, and have been limited to specific regional types of GIWs. An understanding of the general factors that control hydrologic connectivity of GIWs and downstream waters is lacking. Here we present a conceptual model that describes these general factors. By combining elements of the hydrologic budget with site and regional characteristics, we classify GIWs by type and magnitude of potential hydrologic connectivity. Combining this information with hydrologic landscape characteristics that are generally available throughout the US could allow GIW hydrologic connectivity to be evaluated. For example, GIWs that occur in areas that have high rainfall and/or snowmelt relative to basin capacity, that have low soil permeability, and occur on a high slope would have a higher probability of fill and spill connectivity. For these same climatic and basin characteristics, high soil and aquifer permeability would favor groundwater connectivity. We illustrate the conceptual model with several case studies of different GIW types.