Sara Brandt Peter Steeves 2009 vector digital data Data Series 451 (1 of 3) DS-451 Reston, VA U.S. Geological Survey http://water.usgs.gov/lookup/getspatial?ds451_subbasins U.S. Geological Survey 2009 Data Series 451 DS-451 http://ma.water.usgs.gov/publications/ds/default.htm Impervious surfaces such as paved roads, parking lots, and building roofs can affect the natural streamflow patterns and ecosystems of nearby streams. This data set summarizes the percent of impervious surface for subbasins in Massachusetts using a newly available statewide 1-m binary raster dataset of impervious surface for 2005. Subbasin boundaries include the entire upstream drainage area and are nested such that polygons for headwater basins and tributary streams will overlap with basin polygons delineated further downstream. This is one of three data layers in this data series publication. This data layer was created in cooperation with the Environmental Protection Agency (EPA) to assist local communities in environmental planning and stormwater run off studies. The purpose of this data layer is to provide basin boundaries and impervious surface data at a more discretized scale than is available with current Watershed Boundary Dataset (WBD) subdivisions. For the purpose of this data set, a subbasin is defined as the entire drainage area upstream of an outlet point. For multiple outlet points on the same stream, subbasins are nested. That is, a large downstream subbasin polygon will overlap with the smaller upstream subbasin polygon. A hydrologic unit is the intervening drainage area between a given outlet point and the outlet point of the next upstream unit. Hydrologic units subdivide basins into discrete, non-overlapping areas. Each subbasin in this data layer has a corresponding hydrologic unit delineated from the same outlet point and which shares the same unique identifier attribute in the data layer Massachusetts Hydrologic Units which is also published in this data series. Because the same set of outlet points were used for the delineation of subbasins and hydrologic units, the linework for both data layers is identical however polygon attributes may differ because for a given outlet point, the subbasin polygon area is the summation of all the upstream hydrologic units. Subbasin boundaries were delineated from a 10-m digital elevation model (DEM). A primary reason from using DEMs in delineation is that it enables automated batch processing from many stream points, a process that would have been cost-prohibitive had it been done manually from topographic maps. Subbasins were delineated by an automated procedure using ArcHydro Tools in ArcGIS 9.2. The 10-meter DEM was created by re-sampling the 30-meter National Elevation Dataset (NED) to a 10-meter resolution. (http://ned.usgs.gov). Prior to basin delineation, the elevation data was further enhanced with a series of hydrologic conditioning steps (http://nhd.usgs.gov/watershed/watershed_tool_inst_TOC.pdf) that enforce the drainage flow path in the DEM to match the stream network. In addition, ridge lines from the WBD were used to force the DEM to recognize these divides. There were several steps in choosing the delineation points. The high-Resolution National Hydrography Dataset (NHD) (http://nhd.usgs.gov/) stream layer (NHDFlowline) was preprocessed to remove arcs in braided streams and eliminate divergent stream paths, to produce a purely dendritic stream network. Strahler stream order was calculated by applying an existing USGS Arc Macro Lanugage (AML) computer routine to the dendritic stream layer. Strahler stream order is a simple hydrology algorithm used to define stream size based on a hierarchy of tributaries. Stream order increases with stream size, with headwater streams recieving a value of one. Delineation points were placed near stream confluences. Stream nodes were selected at the junctions of any two third-order or higher streams. A 2 mi2 minimum area was chosen for subbasins in order to avoid the includsion of intermittent streams. A preliminary analysis showed that basins for third order streams in Massachusetts generally fit this minimum area criteria. An unavoidable artifact of using DEM data to delineate watersheds is that the delineation points cannot be placed directly on the confluence as this will often give unintended results. For example, a watershed delineated from a point right on the confluence could result in a watershed which includes both confluent streams where the user was intending to get a delineated watershed for either one or the other. To correct for this, point locations must be chosen slightly upstream or downstream of the true confluence; upstream to get the watershed area of one or the other confluent streams and downstream to get the entire watershed area of both confluent streams. Since the DEM data used to delineate watersheds was 10-meter in resolution, a 25-meter distance from the confluence was chosen to verify the intended delineation. Delineation points were placed on each upstream reach of the junction using a 25 meter buffer around the junction. Delineation points were also placed at the outlet of streams along coastlines and estuaries. For coastal areas, the stream layer was extended past the shoreline and subbasins were delineated from an offshore pour point and clipped with a 1:25,000 shoreline layer. Coastal areas in this data layer are not true subbasins as they may contain the drainage of small streams or direct ocean drainage. They are kept in the data layer for continuity between this data layer and the MA hydrologic units data layer. The dendrite stream layer includes centerlines through water bodies and wetlands, which include centerline junction points inside the waterbodies. Delineation points which fell within the boundary of lakes 0.5 mi2 or greater were moved along the centerline to the edge of the lake. Delineation points which created headwater subbasins less than 2 mi2 were removed in order to prevent the inclusion most intermittent-stream basins. In addition, a few delineation points were added to coincide with the outlet points of published 12-digit Hydrologic Units from the National Watershed Boundary Dataset (WBD) (http://www.ncgc.nrcs.usda.gov/products/datasets/watershed/). Subbasin linework generally conforms to previously published basin boundaries at the 12- and 8- digit HUC levels, however minor discrepancies exist at the HUC-12 level due to the difference in base layers used for these delineations. The percent impervious cover was calculated as an attribute for each subbasin. Impervious surface for a subbasin represents the average percent impervious cover for the entire basin. For large basins, there may be a large degree of variation between upstream and downstream impervious cover. Two gridded impervious surface data layers are available for Massachusetts. The National Land Cover Dataset (NLCD) is derived from Landsat satellite imagery and ancilliary data that provides estimates of the percentage of impervious surface at a 30-m grid cell resolution for the entire United States for the year 2001 (http://www.mrlc.gov/index.php). Another impervious surface data layer is provided by the Massachusetts Office of Geographic and Environmental Information (MassGIS), (http://www.mass.gov/mgis/laylist.htm). This data is a 1-m binary impervious surface grid based on 2005 infrared orthoimagery for the Commonwealth of Massachusetts. To compare the data layers, both the MassGIS and the NLCD grids were overlayed onto the subbasin polygons. Percent impervious in each watershed was calculated using both impervious surface data layers. Although the data from both sources are comparable, there are notable differences, particularly at the high and low ends of the perviousness scale. The MassGIS data are more recent and at a finer spatial scale, however it cannot be used for basins which extend past the border of Massachusetts. Based on data from watersheds entirely within MA, a regression equation was developed relating the percent impervious as calculated with the 1-m MassGIS impervious data layer to that calculated with the 30-m NLCD dataset. Natural log transformations were used to linearize the relationship. Results of the regression analysis are shown below. The regression equation was calculated with 1283 independent data points. The coefficient of determination (R2) for the regression is 93.9% and regression coefficients were significantly different from zero at the 0.05 significance level. Ln (Imp_1m) = 1.15 + 0.592 * Ln (Imp_30m) Where, Imp_1m is the percent of area that is impervious for a subbasin calculated with the 1-m MassGIS impervious grid Imp_30m is the percent of area that is impervious for a subbasin calculated with the 30-m NLCD impervious grid For subbasins partially outside of MA, percent impervious was calculated with the NLCD grid and then transformed by using the above relationship. 2009 publication date Complete None planned -73.666836 -70.531999 45.302523 41.463959 ESRI inlandWaters U.S. Geological Survey Massachusetts, except Cape Cod and Plymouth - Carver None The distributor shall not be held liable for improper or incorrect use of this data, based on the description of appropriate/inappropriate uses described in this metadata document. It is strongly recommended that this data is directly acquired from the distributor and not indirectly through other sources which may have changed the data in some way. These data should not be used at scales greater than 1:24,000 for the purpose of identifying hydrographic watershed boundary feature locations. Digital data files may be periodically updated. Files are dated, and users are responsible for obtaining the latest version of the data from the source distributor. U.S. Geological Survey Ask USGS -- Water Webserver Team mailing address

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Reston VA 20192 1-888-275-8747 (1-888-ASK-USGS) http://answers.usgs.gov/cgi-bin/gsanswers?pemail=h2oteam&subject=GIS+Dataset+ds451_subbasins Funding for this dataset was provided by the Environmental Projection Agency and the U.S. Geological Survey. Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 3; ESRI ArcCatalog 9.3.1.1850 This dataset was developed as a polygon feature class within the ESRI personal geodatabase model. The completeness of the data reflects the content of the sources, which most often are the published USGS topographic quadrangle maps. The USGS topographic quadrangle is usually supplemented by Digital Orthophoto Quadrangles (DOQs). Features found on the ground may have been eliminated or generalized on the source map because of scale and legibility constraints. In most cases DEM data were derived from these topographic maps. Office of Geographic and Environmental Information (MassGIS), Commonwealth of Massachusetts Executive Office of Environmental Affairs Unknown raster digital data none none Office of Geographic and Environmental Information (MassGIS), Commonwealth of Massachusetts Executive Office of Environmental Affairs Office of Geographic and Environmental Information (MassGIS), Commonwealth of Massachusetts Executive Office of Environmental Affairs http://www.mass.gov/mgis/impervious_surface.htm online unknown ground condition MassGIS impervious surface See Supplemental Information U.S.Geological Survey Unknown http://ned.usgs.gov/ online unknown ground condition NED See Supplemental Information U.S. Geological Survey (USGS) Water Resources Division (WRD) U.S. Department of Agricultural (USDA) Natural Resources Conservation Service (NRCS) Unknown http://nhd.usgs.gov online unknown publication date NHD See Supplemental Information U. S. Environmental Protection Agency Unknown http://www.epa.gov/mrlc/nlcd-2001.html online unknown ground condition NLCD See Supplemental Information See Supplemental Information. 2009 Dataset copied.T:\SubHUC12\ds451_subbasins2009060912074000 Vector G-polygon 1510 State Plane Coordinate System 1983 2001 41.716667 42.683333 -71.500000 41.000000 200000.000000 750000.000000 coordinate pair 10 10 meters North American Datum of 1983 Geodetic Reference System 80 6378137.000000 298.257222 unknown 0.000100 unknown Explicit elevation coordinate included with horizontal coordinates ds451_subbasins vector attribute table U. S. Geological Survey FID Internal feature number. ESRI Sequential unique whole numbers that are automatically generated. Shape Feature geometry. ESRI Coordinates defining the features. AREA2MI Area in square miles ESRI 0 10000 Square Miles Shape_Area Area of feature in internal units squared. ESRI Positive real numbers that are automatically generated. HUC8 8-digit Hydrologic Unit Code of the major basin in which the outlet point is located. Natural Resources Conservation Service, 2008, Watershed Boundary Dataset (WBD): U.S. Department of Agriculture, accessed November 13, 2008, at http://www.ncgc.nrcs.usda.gov/products/datasets/Watershed/ 8-digit Hydrologic Unit Code U. S. Geological Survey MajBasin Name of the Major Basin that contains the subbasin. This attribute is not directly related to the 'HUC8' attribute, as it is a State designated name MassGIS, http://www.mass.gov/mgis/maj_bas.htm Major Basin Name MassGIS, http://www.mass.gov/mgis/maj_bas.htm Shape_Leng Length of feature in internal units. ESRI Positive real numbers that are automatically generated. Impervious Percent Impervious Surface U.S. Geological Survey 0 100 Percent UniqID Unique Identifier See Overview for valid values 10000 - 29999 See Overview Description U.S. Geological Survey This is a detailed breakdown of the polygon attribute 'uniqueid', which has a many - to - one correspondence with the HUC8 field: HUC8 UniqueID (valid range) 01060003 10000 - 10999 01070004 11000 - 11999 01070005 12000 - 12999 01070006 13000 - 13999 01080201 14000 - 14999 01080202 15000 - 15999 01080203 16000 - 16999 01080204 17000 - 17999 01080205 18000 - 18999 01080206 19000 - 19999 01080207 20000 - 20999 01090001 21000 - 21999 01090002 22000 - 22999 01090003 23000 - 23999 01090004 24000 - 24999 01100001 25000 - 25999 01100002 26000 - 26999 01100005 27000 - 27999 02020003 28000 - 28999 02020006 29000 - 29999 See Supplementary Information U. S. Geological Survey Ask USGS - Water Webserver Team mailing address

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Reston VA 20192 1-888-275-8747 (1-888-ASK-USGS) http://water.usgs.gov/user_feedback_form.html Downloadable Data Although this data set has been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data and related materials. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. ESRI Shapefile 138.091 http://water.usgs.gov/GIS/dsdl/ds451_subbasins.zip None 20090609 U.S. Geological Survey Ask USGS - Water Webserver Team mailing address

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Reston VA 20192 1-888-275-8747 (1-888-ASK-USGS) http://answers.usgs.gov/cgi-bin/gsanswers?pemail=h2oteam&subject=GIS+Dataset+ds451_subbasins FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998