Watershed Boundary Dataset Research Articles

A graph-based modeling framework for tracing hydrological pollutant transport in surface waters

Anthropogenic pollution of hydrological systems affects diverse communities and ecosystems around the world. Data analytics and modeling tools play a key role in fighting this challenge, as they can help identify key sources as well as trace transport and quantify impact within complex hydrological systems. Several tools exist for simulating and tracing pollutant transport throughout surface waters using detailed physical models; these tools are powerful, but can be computationally intensive, require significant amounts of data to be developed, and require expert knowledge for their use (ultimately limiting application scope). In this work, we present a graph modeling framework – which we call HydroGraphs – for understanding pollutant transport and fate across waterbodies, rivers, and watersheds. This framework uses a simplified representation of hydrological systems that can be constructed based purely on open-source data (National Hydrography Dataset and Watershed Boundary Dataset). The graph representation provides a flexible intuitive approach for capturing connectivity and for identifying upstream pollutant sources and for tracing downstream impacts within small and large hydrological systems. Moreover, the graph representation can facilitate the use of advanced algorithms and tools of graph theory, topology, optimization, and machine learning to aid data analytics and decision-making. We demonstrate the capabilities of our framework by using case studies in the State of Wisconsin; here, we aim to identify upstream nutrient pollutant sources that arise from agricultural practices and trace downstream impacts to waterbodies, rivers, and streams. Our tool ultimately seeks to help stakeholders design effective pollution prevention/mitigation practices and evaluate how surface waters respond to such practices.

Assessment of Model-Derived Mass Flux Relative to Satellite Gravimetry via a Water Balance in North America

Abstract GRACE and GRACE Follow-On (GRACE-FO) mission data are utilized to assess mass flux derived from the North American Regional Reanalysis (NARR) and the NLDAS-2 Noah land surface model via multiple water balance formulations. Water balances are computed for 18 medium size basins in North America at the USGS Watershed Boundary Dataset HU2 level over the span of the GRACE and GRACE-FO missions (2002–21). Performance of model-derived mass flux is presented in the context of statistical agreement to changes in terrestrial water storage (ΔTWS) derived from Center for Space Research (CSR) GRACE RL06 mass concentrations (mascons), and GRACE and NARR uncertainty is estimated against comparable datasets. The land surface water balance method utilizing NLDAS-2 Noah consistently outperforms the total column method utilizing NARR, which is likely due to enhanced precipitation forcing and an updated Noah model version used in NLDAS-2. The surface approach to the calculation of atmospheric moisture flux divergence is carried through the presented analyses and is demonstrated to be comparable in performance to the more common volume approach. Mass balance methodology, basin characteristics, and ΔTWS signal characteristics are assessed to quantify effects on model performance and while factors such as basin size, basin average topography gradient, and ΔTWS annual amplitude are shown to have a measurable effect on model performance, no single factor exhibited a dominant or consistent effect. Drought conditions are shown to have a significant temporally localized effect on model-derived mass flux accuracy, with NARR being particularly susceptible to this effect. Significance Statement Measurements of Earth’s gravity field from the GRACE and GRACE-FO satellite missions are utilized to create estimates of water storage changes in 18 North American river basins that are compared to changes in water storage calculated from an atmospheric model reanalysis (NARR) and a land surface model (NLDAS-2 Noah). The resulting comparison demonstrates that certain basin characteristics can have a slight effect on model accuracy, while climatic conditions such as drought can have a major impact on model accuracy. This work provides useful quantification of when and where modeled water transport loses accuracy, which is integral to our understanding of the present and future distribution of this crucial resource and the natural processes that affect it.

Development of a Hydrologic Connectivity Dataset for SWAT Assessments in the US

Model-based water quality assessments are an important informer of conservation and environmental policy in the U.S. The recently completed national scale Conservation Effects Assessment Project (CEAP) is being replicated using an improved model populated with new and higher resolution data. National assessments are particularly difficult as models must operate with both a very large spatial extent (the contiguous U.S.) while maintaining a level of granularity required to capture important small scale processes. In this research, we developed datasets to describe the hydrologic connectivity at the U.S. Geological Survey (USGS) 12-digit Hydrologic Unit Code (HUC-12) level. Connectivity between 86,000 HUC-12s as provided by the Watershed Boundary Dataset (WBD) was evaluated and corrected. We also detailed a method to resolve the highly detailed National Hydrography Dataset (NHD) stream segments within each HUC-12 into vastly simplified representative channel schemes suitable for use in the recently developed Soil and Water Assessment Tool + (SWAT+) model. This representative channel approach strikes a balance between computational complexity and accurate representation of the hydrologic system. These data will be tested in the upcoming CEAP II national assessment. Until then, all the WBD corrections and NHDPlus representative channel data are provided via the web for other researchers to evaluate and utilize.

Inventory of Interbasin Transfers in the United States

AbstractInterbasin transfers (IBTs) are man‐made transfers of water that cross basin boundaries. These transfers are used to distribute water resources according to supply and demand. The objectives of this work were to quantify the number of IBTs that exist in the United States (U.S.) and to examine the distribution of IBTs and potential causes associated with any observed clustering of IBTs. Defining “basin” was important to enable determination of which transfers qualify as “interbasin.” A variety of definitions are employed by states, with no federal definition. The most recent national studies of IBTs were conducted by the U.S. Geological Survey (USGS) in 1985 and 1986 using USGS Hydrologic Unit Code (HUC) definitions of basins. To build a 2016 inventory of IBTs in the U.S., and to identify where they most commonly occur, the USGS National Hydrography Database (NHD) was utilized in conjunction with the Watershed Boundary Dataset (WBD). Transfers across HUC6 basin boundaries were considered interbasin. Geographical information analysis with the NHD and WBD databases revealed that there are a total of 2,161 man‐made waterways crossing HUC6 basin boundaries in the U.S. IBTs are somewhat concentrated: Florida, Texas, and North Carolina account for over 50% of the total identified IBTs. For some states, identified IBTs are locally clustered. Analysis of these clusters suggests a variety of reasons that IBTs have been built, including population, drainage, and agricultural factors.

How Misapplication of the Hydrologic Unit Framework Diminishes the Meaning of Watersheds.

Hydrologic units provide a convenient but problematic nationwide set of geographic polygons based on subjectively determined subdivisions of land surface areas at several hierarchical levels. The problem is that it is impossible to map watersheds, basins, or catchments of relatively equal size and cover the whole country. The hydrologic unit framework is in fact composed mostly of watersheds and pieces of watersheds. The pieces include units that drain to segments of streams, remnant areas, noncontributing areas, and coastal or frontal units that can include multiple watersheds draining to an ocean or large lake. Hence, half or more of the hydrologic units are not watersheds as the name of the framework "Watershed Boundary Dataset" implies. Nonetheless, hydrologic units and watersheds are commonly treated as synonymous, and this misapplication and misunderstanding can have some serious scientific and management consequences. We discuss some of the strengths and limitations of watersheds and hydrologic units as spatial frameworks. Using examples from the Northwest and Southeast United States, we explain how the misapplication of the hydrologic unit framework has altered the meaning of watersheds and can impair understanding associations between spatial geographic characteristics and surface water conditions.

The Road to NHDPlus — Advancements in Digital Stream Networks and Associated Catchments

AbstractA progression of advancements in Geographic Information Systems techniques for hydrologic network and associated catchment delineation has led to the production of the National Hydrography Dataset Plus (NHDPlus). NHDPlus is a digital stream network for hydrologic modeling with catchments and a suite of related geospatial data. Digital stream networks with associated catchments provide a geospatial framework for linking and integrating water‐related data. Advancements in the development of NHDPlus are expected to continue to improve the capabilities of this national geospatial hydrologic framework. NHDPlus is built upon the medium‐resolution NHD and, like NHD, was developed by the U.S. Environmental Protection Agency and U.S. Geological Survey to support the estimation of streamflow and stream velocity used in fate‐and‐transport modeling. Catchments included with NHDPlus were created by integrating vector information from the NHD and from the Watershed Boundary Dataset with the gridded land surface elevation as represented by the National Elevation Dataset. NHDPlus is an actively used and continually improved dataset. Users recognize the importance of a reliable stream network and associated catchments. The NHDPlus spatial features and associated data tables will continue to be improved to support regional water quality and streamflow models and other user‐defined applications.

The NHDPlus dataset, watershed subdivision and SWAT model performance

The Soil and Water Assessment Tool (SWAT) has been developed to evaluate the effectiveness of agricultural management practices on watershed water quality. Many studies have indicated that watershed subdivision can affect the accuracy of model predictions. Most of them used the minimum drainage area (MDA) to delineate sub-watersheds, and varied the value of MDA depending on the size of the watershed being modelled. Instead of MDA, we use the National Hydrography Dataset Plus (NHDPlus)—an integration of the best features of the National Hydrography Dataset (NHD), Watershed Boundary Dataset (WBD), National Elevation Dataset (NED), and the National Land Cover Dataset (NLCD)—to delineate the watershed. The Kaskaskia River watershed in Illinois, USA, was selected to investigate the individual effects of sub-watershed and hydrologic response unit (HRU) delineations on predicted streamflow, total suspended sediment (TSS) and total nitrogen (TN) losses at two USGS gauges. In addition, an MDA of 3000 ha, and four levels of stream (the 2nd, 3rd, 4th and 5th order) were evaluated. Three levels of HRU threshold (5%, 10% and 15%) were used for each stream order model. The results show that stream order had little effect on predicted streamflow, but a great impact on TSS and TN losses, and the impact of HRU delineation became greater when a higher stream order was used to delineate the watershed. For higher stream order, fewer streams were recognized in SWAT simulations, which resulted in less sediment routing and channel processes, which, in turn, led to less deposition in the channels; thus high sediment losses were obtained at the watershed outlet. However, fewer channel processes led to less in-stream N processes; thus lower TN losses. Overall, the SWAT simulations performed the best when the 2nd stream order was used for delineations comparing with USGS observed data, followed by the 3rd stream order. Therefore, to fully depict the watershed characteristics to perform SWAT simulations, a stream order higher than 3rd order is not recommended for watershed delineation.Editor D. Koutsoyiannis; Associate editor C. Perrin

Creating a Population of 12‐Digit Headwater Basins within the Albemarle‐Pamlico Estuary System

AbstractEcological research within the US Environmental Protection Agency's Office of Research and Development has recently changed its focus to quantifying and mapping ecosystem services provided to humans. Our local research group has been charged to develop a regional assessment of several ecosystem services in the Albemarle‐Pamlico Estuary System (APES). Time, data, and funding constraints precluded explicit modeling of the entire APES, so in Phase 1 of our research plan we chose to model ecosystem services in a random sample of headwater catchments. After observing numerous inconsistencies between the National Hydrography Dataset‐Plus (NHDPlus) stream network and the Virginia/North Carolina Watershed Boundary Dataset 12‐digit HUC coverage, we began by creating modified 12‐digit hydrologic units (HUCs) by aggregating smaller catchments delineated within the NHDPlus. In defining our population of interest (headwater 12‐digit HUCs with perennial, natural, wadeable pour points), we generally excluded HUCs that had multiple pour points, no pour points, or whose pour points were intermittent streams, artificial segments, ditches/canals, or lentic systems (lakes and reservoirs). After taking these actions, 318 HUCs remained and a stratified random sample (Omnerik ecoregions as strata) of 50 HUCs was chosen from this population.

A nationally consistent framework for identifying interstate waters with applications for the national listing of fish advisories

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.

MAPPING HYDROLOGIC UNITS FOR THE NATIONAL WATERSHED BOUNDARY DATASET1

ABSTRACT: In 2002, Wyoming became the first state to complete development of a statewide 1:24,000‐scale Watershed Boundary Dataset (WBD) under the new Federal Standards for Delineation of Hydrologic Unit Boundaries. The product was developed through the coordinated efforts of numerous state, federal, and local entities both within Wyoming and in neighboring states. Development of a comprehensive, standardized hydrologic unit boundary dataset in a “headwaters” state such as Wyoming poses a number of unique challenges. This paper details the WBD's development in Wyoming, highlighting technical methodology development and interagency coordination strategies. Evolution of the WBD standard is reviewed, addressing inconsistencies between definitions for hydro‐logic units and “true” watershed delineations. While automated methods are improving, manual and semi‐automated techniques continue to serve as valuable approaches to hydrologic unit boundary delineation given the quality of digital terrain models and the multijurisdictional nature of watershed based management. This case study provides insight on future development and maintenance of the WBD within and across other states and regions of the country and on opportunities for linking the WBD to related water resource geospatial data products like the National Hydrography Dataset.