Attributes for NHDPlus Catchments (Version 1.1)for the Conterminous United States: Contact Time, 2002

This data set represents the average contact time, in units of days, compiled for every catchment of 
NHDPlus for the conterminous United States. Contact time, as described in Wolock and others (1989), 
is the baseflow residence time in the subsurface. The source data set was the U.S. Geological Survey's 
(USGS)  1-kilometer grid for the conterminous United States (D.M. Wolock, U.S. Geological Survey, 
written commun., 2008). The grid was created using a method described by Wolock and others (1997a; 
see equation 3). In the source data set, the contact time was estimated from 1-kilometer resolution 
elevation data (Verdin and Greenlee, 1996 ) and STATSGO soil characteristics (Wolock, 1997b).
		
The NHDPlus Version 1.1 is an integrated suite of application-ready geospatial datasets that incorporates 
many of the best features of the National Hydrography Dataset (NHD) and the National Elevation Dataset 
(NED). The NHDPlus includes a stream network (based on the 1:100,00-scale NHD), improved networking, 
naming, and value-added attributes (VAAs). NHDPlus also includes elevation-derived catchments 
(drainage areas) produced using a drainage enforcement technique first widely used in New England, 
and thus referred to as "the New England Method." This technique involves "burning in" the 1:100,000-scale 
NHD and when available building "walls" using the National Watershed Boundary Dataset (WBD). The 
resulting modified digital elevation model (HydroDEM) is used to produce hydrologic derivatives that agree 
with the NHD and WBD. Over the past two years, an interdisciplinary team from the U.S. Geological Survey 
(USGS), and the U.S. Environmental Protection Agency (USEPA), and contractors, found that this method 
produces the best quality NHD catchments using an automated process (USEPA, 2007). The NHDPlus 
dataset is organized by 18 Production Units that cover the conterminous United States.
		
The NHDPlus version 1.1 data are grouped by the U.S. Geologic Survey's  Major River Basins (MRBs, 
Crawford and others, 2006).  MRB1, covering the New England and Mid-Atlantic River basins, contains 
NHDPlus Production Units 1 and 2.  MRB2, covering the South Atlantic-Gulf and Tennessee River basins, 
contains NHDPlus Production Units 3 and 6.  MRB3, covering the Great Lakes, Ohio, Upper Mississippi, 
and Souris-Red-Rainy River basins, contains NHDPlus Production Units 4, 5, 7 and 9.  MRB4, covering 
the Missouri River basins, contains NHDPlus Production Units 10-lower and 10-upper.  MRB5, covering 
the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf River basins, contains NHDPlus Production 
Units 8, 11 and 12.  MRB6, covering the Rio Grande, Colorado and Great Basin River basins, contains 
NHDPlus Production Units 13, 14, 15 and 16.  MRB7, covering the Pacific Northwest River basins, 
contains NHDPlus Production Unit 17.  MRB8, covering California River basins, contains NHDPlus 
Production Unit 18.

Tags: cali, california, catchment, cogb, contact-time, conterminous-united-states, environment, geoscientificinformation, glmr, great-lakes-ohio-upper-mississippi-and-souris-red-rainy, inlandwaters, lmtg, lower-mississippi-arkansas-white-red-and-texas-gulf, major-river-basin, missouri, mori, mrb, mrb1, mrb2, mrb3, mrb4, mrb5, mrb6, mrb7, mrb8, nawqa, nema, new-england-and-mid-atlantic, nhdplus, pacific-northwest, panw, rio-grande-colorado-and-great-basin, sagt, south-atlantic-gulf-and-tennessee, sparrow, usgs-802df197-dacb-4061-befe-a10991a4cbd7
Organization: Department of the Interior