The Watershed Flow and Allocation model (WaterFALL®) provides segment‐specific, daily streamflow at both gaged and ungaged locations to generate the hydrologic foundation for a variety of water resources management applications. The model is designed to apply across the spatially explicit and enhanced National Hydrography Dataset (NHDPlus) stream and catchment network. To facilitate modeling at the NHDPlus catchment scale, we use an intermediate‐level rainfall‐runoff model rather than a complex process‐based model. The hydrologic model within WaterFALL simulates rainfall‐runoff processes for each catchment within a watershed and routes streamflow between catchments, while accounting for withdrawals, discharges, and onstream reservoirs within the network. The model is therefore distributed among each NHDPlus catchment within the larger selected watershed. Input parameters including climate, land use, soils, and water withdrawals and discharges are georeferenced to each catchment. The WaterFALL system includes a centralized database and server‐based environment for storing all model code, input parameters, and results in a single instance for all simulations allowing for rapid comparison between multiple scenarios. We demonstrate and validate WaterFALL within North Carolina at a variety of scales using observed streamflows to inform quantitative and qualitative measures, including hydrologic flow metrics relevant to the study of ecological flow management decisions.

The US Environmental Protection Agency's (EPA's) Total Maximum Daily Loads (TMDL) program promotes nationally consistent approaches for documenting the progress in restoring impaired waters. EPA's TMDL program provides tracking systems comprising both database and geographic information systems (GIS) mapping components. The GIS mapping is implemented using the National Hydrography Dataset (NHD). The EPA and the US Geological Survey have developed an enhanced NHD product (NHDPlus) that is applied in this study to define an interstate waters framework for the conterminous United States. This NHDPlus-based framework provides an efficient watershed-oriented approach for selecting interstate waters. Greater consistency in approaches for interstate waters is essential for providing improved techniques for integrated assessment and management programs. Improved analysis tools for interstate waters are clearly important from a federal perspective. Insights based on tools for federal interstate waters are also of interest for state water quality agencies when they deal with complicated interjurisdictional challenges that can require leveraging support from a wide range of stakeholders. Summaries are provided on the degree of consistency documented for inland waters where states have provided TMDL listing GIS information for shared interstate NHD reaches, and summaries are provided on the patterns for interstate assessments organized according to the ecoregions developed for EPA's Wadeable Streams Assessment. The relevance of this interstate waters framework in leveraging the TMDL program to provide enhanced support for watershed oriented management approaches is also explored.

Background: The mission of the United States Environmental Protection Agency (EPA) is to protect human health and the environment, including air, water and land. Understanding the extent of pollution in waters and identifying waters for protection has been based in part on water quality monitoring data collected and shared by parties (federal, state, tribal, and local) throughout the U.S. To date, this monitoring data has been largely represented by data collected as a water quality sample (data collected by a technician in the field or analyzed in a lab). EPA's "STORage and RETrieval" (STORET) and the Water Quality Exchange (WQX) have served as the repository for all this sampling data. However, these tools and systems were not designed to handle today's continuous water quality sensors. EPA has therefore embarked on the Interoperable Watersheds Network (IWN) project, which is focused on identifying a common set of formats and standards for data, and on testing and validating these standards as well as new ways of sharing data and metadata. The completed IWN will greatly expand the sharing of data and its use, thereby streamlining the assessment, restoration, and protection of surface water quality at all levels of government. Methods: Stakeholder workgroups were engaged to assist with developing requirements for the three major project components: required attributes and query capability for a centralized metadata catalog, technological and data requirements for data providers, and desired functionality for a web-based discovery tool that provides access to the catalog services and provider data. Results: The pilot implementation of IWN uses the Open Geospatial Consortium (OGC) Sensor Observation Service (SOS) 2.0 and WaterML2 standards as the foundation for a distributed sensor data sharing network. Data owners in locations across the United States have worked with EPA to publish their continuous sensor data and related metadata either through "data appliances" running the open-source 52°North implementation of SOS or using commercial software like Kisters' KiWIS product. Metadata are harvested into a centralized catalog that provides a REST Service API for sensor discovery. Users can discover data by querying for specific parameters, or using spatial boundaries such as HUC, county, a buffered point, or a user defined polygon. The sensor results are returned as GeoJSON, which can be used to create maps. The API also provides the service endpoints for the sensors, which can be used to access the continuous data to create charts or download the data for other analysis. Conclusion: The pilot IWN demonstrates that standards-based interoperability can provide a sound basis for a national-scale clearinghouse for continuous sensor data, though scalability of the approach will need further testing. Selected technical detail, lessons learned, and future plans for the IWN are included in the discussion.

Larger river systems in the western United States receive their base flow from snowpack in higher elevation areas. Extended drought episodes can reduce the release of water from the major snowpack zones, and climate change may lead to more chronic impacts on water availability. The enhanced National Hydrography Dataset (the NHDPlus) can be applied to provide a nationally consistent framework to define the extent of the western snowpack core areas. Once the periphery (or rim) of a core snowpack zone is defined within the NHDPlus, upstream and downstream analyses can be applied for units ranging from small local watersheds to large hydrological networks implemented for all U.S. western states. Examples are provided illustrating the methods for developing this NHDPlus-based snowpack framework and ways in which analytical data mining and modeling tools can assist in water quality and quantity management programs to address climate change impacts.

A 1988 survey, funded by the US Environmental Protection Agency (EPA) and conducted by the American Fisheries Society, identified the need to standardize the approaches for evaluating risks and developing fish consumption advisories that are comparable across different jurisdictions. A major tool for evaluating the progress in developing such nationally consistent information is EPA's web-based National Listing of Fish Advisories (NLFA) database, which has archived fish advisory information since 1993. The NLFA comprises both a database and Geographic Information System mapping components that are implemented using the National Hydrography Dataset (NHD). EPA and the US Geological Survey have developed an enhanced NHD product (NHDPlus) that is applied to define an interstate waters framework for the conterminous USA. This NHDPlus-based framework provides an efficient watershed-oriented approach for identifying interstate advisories from NLFA. We provide summaries of (1) the degree of consistency documented for inland waters where states have issued advisories for shared interstate NHD reaches and (2) the patterns for interstate advisories organized according to the ecoregions developed for EPA's Wadeable Streams Assessment. Approaches are also discussed for addressing interstate consistency issues for fish advisories in coastal waters making use of the NHDPlus combined with other nationally consistent frameworks, such as the 12-digit hydrologic unit code subwatersheds in the Watershed Boundary Dataset. Probability survey methods are recommended as a way to promote increased interjurisdictional consistency in the development of the monitoring and risk assessment conclusions reflected in NLFA, as well as in other EPA water quality-based programs.