Implementation Tools and Methods
Certain tools, data, and approaches to determine jurisdiction will facilitate implementation of the Navigable Waters Protection Rule in the field. The agencies will typically consider all relevant sources of information when completing an approved jurisdictional determination, which may include on-site observations, field-based indicators of hydrological conditions, maps, remote tools, and reliable datasets that are available for the waterbody under evaluation. The availability, accuracy, completeness, reliability, and applicability of these various methods, tools, and sources of information may vary regionally and for site-specific reasons. The agencies are not mandating the use of specific data or tools to implement the rule. The agencies will continue the longstanding practice of evaluating waters based on the weight of evidence from the best available sources of information available for that waterbody.
The Antecedent Precipitation Tool (APT)
Under the Navigable Waters Protection Rule, determining the jurisdictional status of certain waterbodies is informed by understanding site conditions in a “typical year” (i.e., meaning when precipitation and other climatic variables are within the normal periodic range (e.g., seasonally, annually) for the geographic area of the applicable aquatic resource based on a rolling thirty-year period). In the absence of or with limited availability of site-specific flow or surface water connection data, the agencies will generally use the Corps’ Antecedent Precipitation Tool (APT) when assessing “typical year” conditions to inform a jurisdictional determination. The APT calculates precipitation normalcy using a standardized methodology and provides other relevant information such as drought indices to inform a decision of whether precipitation, drought and other climatic conditions are normal. Using the APT method can allow for reliable and predictable decisions as part of the approved jurisdictional determination process
Streamflow Duration Assessment Methods (SDAMs)
Long-term hydrologic data to assess streamflow duration are often limited, especially for streams that do not flow year-round. SDAMs are rapid field assessment methods that use hydrological, geomorphological, and/or biological indicators, observable in a single site visit, to classify streamflow duration as perennial, intermittent, or ephemeral at the reach scale. Regulators and water resource managers can use rapid, reach-scale methods to determine streamflow duration classifications (i.e., perennial, intermittent, ephemeral) and to help implement many federal, state, and local programs. Currently, EPA and partners are developing or modifying existing SDAMs for use across the U.S.