ABSTRACT:

The Watershed Boundary Dataset (WBD) is a comprehensive aggregated collection of hydrologic unit data consistent with the national criteria for delineation and resolution. It defines the areal extent of surface water drainage to a point except in coastal or lake front areas where there could be multiple outlets as stated by the "Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD)" “Standard” (http://pubs.usgs.gov/tm/11/a3/). Watershed boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. This dataset represents the hydrologic unit boundaries to the 12-digit (6th level) for the entire United States. Some areas may also include additional subdivisions representing the 14- and 16-digit hydrologic unit (HU). At a minimum, the HUs are delineated at 1:24,000-scale in the conterminous United States, 1:25,000-scale in Hawaii, Pacific basin and the Caribbean, and 1:63,360-scale in Alaska, meeting the National Map Accuracy Standards (NMAS). Higher resolution boundaries are being developed where partners and data exist and will be incorporated back into the WBD. WBD data are delivered as a dataset of polygons and corresponding lines that define the boundary of the polygon. WBD polygon attributes include hydrologic unit codes (HUC), size (in the form of acres and square kilometers), name, downstream hydrologic unit code, type of watershed, non-contributing areas, and flow modifications. The HUC describes where the unit is in the country and the level of the unit. WBD line attributes contain the highest level of hydrologic unit for each boundary, line source information and flow modifications.

ABSTRACT:

Authors:
Naomi DetenbeckAlyssa Le
Owners: Naomi Detenbeck
Type: Resource
Storage: The size of this resource is 53.7 MB
Created: May 27, 2025 at 1:35 p.m.
Last updated: May 27, 2025 at 3:38 p.m.
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Abstract
We created a baseline SWAT model for 1995-2015 (including a 2-year warm-up period) at the HUC12-scale using the HAWQS v1 system. We used default data included with the HAWQS v1 system, including land-cover derived from NLCD 2006 and the Cropland Data Layer (2011-2012) and weather inputs from the HAWQS PRISM database. We updated the SWAT model to include point source inputs from wastewater effluent that were derived from (a) the EPA ECHO database (https://echo.epa.gov/trends/loading-tool/get-data/watershed-statistics) for TSS and (b) the Hypoxia Task Force database for TP (https://echo.epa.gov/trends/loading-tool/hypoxia-task-force-nutrient-model) We assumed 57% of TP effluent from wastewater is soluble reactive P, 2.8% is organic P and 40% is particulate mineral P (total of 97% mineral P and 3% organic P). For the Potawatomie treatment plant, modeled discharge values were used in place of measured values because violations had been reported due to inadequate flow calibrations at the facility. We also added initial groundwater concentrations of 0.1 mg N/L for NO3-N and 0.0433 mg P/L for soluble P to replace default SWAT values of zero.
The baseline SWAT model from HAWQS was modified to represent existing agricultural management activities. Information on existing agricultural conservation practices in the USC (cover crops, residue and tillage management, contouring, terraces, filter strips, controlled stream access for cattle, managed grazing), as of 2015 were compiled from KDHE (Andrew S. Lyon, KDHE, pers. comm.). To model the effects of cattle grazing and associated BMPs, we used methodology described in Sheshukov et al. (2016)]; See Supplemental Material 2)). Following guidance in Waidler et al. (2009), cover crops were implemented using the land use update (lup) table in SWAT and modifying HRU fraction (HRU_FRC) to simultaneously convert area from converted crop land (CORN or SOY or CORNSOY combinations) to SOYWW (soy/winter wheat) or WWSY (winter wheat/soy) sequences. The baseline SWAT model for USC, including existing BMPs (Contouring (736 acres treated), Grassed waterways (2965 acres), No till (966 acres), Terracing (966 acres), Vegetative filter strips (848 acres), Created agricultural wetlands (36 acres treated) and cattle grazing, was calibrated using the SUFI-2 (Sequential Uncertainty Fitting version 2 using SWAT-CUP.] This model set-up includes the swat670-WMOST version which formats output for use in US EPA's Watershed Management Optimization Support Tool.