Non-navigable streams and adjacent wetlands:: addressing science needs following the Supreme Court's Rapanos decision

In June of 2006, the US Supreme Court ruled in two cases concerning jurisdiction under the Clean Water Act (CWA). The decisions suggest that hydrological permanence of non-navigable streams and adjacent wetlands (NNSAWs) and their effects on the chemical, physical, and biological integrity of navigable waters ("significant nexus") are relevant in determining CWA jurisdiction. This has increased the need for scientific information to support regulatory determinations and to inform future policies, rule making, and legislation. Here, we propose an approach for addressing these science needs. We define a metric - maximum duration of continuous flow - to assess hydrological permanence. We also define two metrics to evaluate significant nexus: proportion of total benefit to the navigable water contributed by an NNSAW class, and proportion of time that a navigable water receives benefit from an NNSAW. These metrics could be useful in implementing the Court's new legal standards.