Sara Brandt Peter Steeves 20090609 vector digital data Reston, VA U.S. Geological Survey http://water.usgs.gov/lookup/getspatial?ds451_hydro_units Sara L. Brandt and Peter A. Steeves 20090609 Data Series 451 (1 of 3) DS451 Reston, VA U.S. Geological Survey http://pubs.usgs.gov/ds/451/ 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 hydrologic units in Massachusetts using a newly available statewide 1-m binary raster dataset of impervious surface for 2005. A hydrologic unit consists of all or part of a drainage basin, or an area of coastal drainage. Hydrologic units subdivide large drainage basins into discrete, non-overlapping areas. This is one of three data layers in this data series publication. This data layer was created in cooperation with the Evironmental Protection Agency (EPA) to assist 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 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. 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. Each hydrologic unit in this data layer has a corresponding subbasin delineated from the same outlet point and which shares the same unique identifier attribute in the data layer Massachusetts Nested Subbasins 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. Hydrologic Units were delineated from a 10-m resolution 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. Hydrologic units were delineated in batch by an automated procedure using ArcHydro Tools in ArcHIS 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, drainage divides from the WBD were used to enforce the DEM to recognize these divides. There were several steps in choosing the delineation points. The high-resolution National Hydrography Dataset (NHD) stream layer (http://nhd.usgs.gov) was preprocessed to remove arcs in braided streams and eliminate divergent stream paths, resulting in a purely dendritic stream network. Strahler stream order was calculated using an existing USGS Arc Macro Language (AML) computer routine on 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 all streams of third or higher order. 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. Delineation points were also placed at the outlets of streams along coastlines and estuaries. The dendritic stream layer includes centerlines through water bodies and wetlands, as well as 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. 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/). Hydrologic unit linework generally conforms to previously published basin boundaries at the 12- and 8- digit HUC levels, however minor discrepancies exist due to the difference in base layers used for these delineations. With the exception of headwater basins, hydrologic units consist of the intervening basin area between any two confluence points. Delineation points which resulted in headwater basins less than 2 mi2 were removed in order to prevent the inclusion of intermittent-stream basins. However, in downstream areas, hydrologic units can become quite small when there are multiple tributary confluences within a short distance. These tiny units were left in the data layer and not altered in order to preserve the consistancy of the delineation method. A 15 mi2 maximum was enforced on hydrologic units, except in the case where a large lake or large culverted area was present in the unit. This maximum was chosen because impervious surface cover can change dramatically in space and small units are needed to accurately capture the variability in local impervious surface cover. In hydrologic unit was greater than 15 mi2, delineation points were added at the junction of the largest 2nd order stream within the hydrologic unit, and the unit was redelineated. For coastal areas, the stream layer was extended past the shoreline and hydrologic units were delineated from an offshore pour point and clipped with a 1:25K shoreline layer. The percent impervious area was calculated as an attribute for each hydrologic unit. Impervious surface for a hydrologic unit represents the percent impervious at a localized area upstream of the outlet point and does not include upstream area outside of the hydrologic unit. 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 layer 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 hydrologic unit polygons. The percentage of impervious area in each hydrologic unit was calculated by using both impervious surface data layers. Although the data from both these 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 hydrologic units entirely within MA, a regression equation was developed relating the percenage of impervious surface calculated with the 1-m MassGIS impervious data layer to that calculation with the 30-m NLCD data layer. 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 was 93.9% and regression coefficients were significantly different from zero at the 0.05 significance level. Ln (Imp_1m) = 1.15 + 0.601 * Ln (Imp_30m) where, Imp_1m is the percentage of impervious area for a hydrologic unit calculated with the 1-m MassGIS impervious grid, Imp_30m is the percentage impervious area for a hydrologic unit calculated with the 30-m NLCD impervious grid For hydrologic units partially outside of Massachusetts, the percent impervious surface was calculated with the NLCD grid and then transformed by using the above relationship. unknown publication date Complete None planned -73.584130 -70.568959 42.910248 41.463959 U.S. Geological Survey inland waters U.S. Geological Survey Massachusetts, excluding Cape Cod, Martha's Vineyard, Nantucket, and the Plymouth Carver region 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_hydro_units 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 http://www.mass.gov/mgis/impervious_surface.htm online unknown publication date MassGIS Impervious Surface See Supplemental Information U. S. Geological Survey http://ned.usgs.gov/ online unknown publication date NED See Supplemental Information U.S. Geological Survey (USGS) Water Resources Division (WRD) U.S. Department of Agricultural (USDA) Natural Resources Conservation Service (NRCS) http://nhd.usgs.gov online unknown publication date NHD See Supplmental Information U. S. Environmental Protection Agency http://www.epa.gov/mrlc/nlcd-2001.html online unknown publication date NLCD See Supplemental Informatiln See Supplemental Information. Unknown Dataset copied.T:\SubHUC12\ds451_hydro_units2009060912074000 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_hydro_units vector attribute table U. S. Geological Survey Shape Feature geometry. ESRI Coordinates defining the features. FID Internal feature number. ESRI Sequential unique whole numbers that are automatically generated. Shape_Area Area of feature in internal units squared. ESRI Positive real numbers that are automatically generated. Shape_Leng Length of feature in internal units. ESRI Positive real numbers that are automatically generated. UniqID Unique Identifier See Overview Description for valid values Positive real numbers that are automatically generated. HUC8 8-digit Hydrologic Unit Code of the major basin that contains the hydrologic unit 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 HUC12 12 -digit Hydrologic Unit Code of the major basin that contains the hydrologic unit 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/ 12-digit Hydrologic Unit Code U. S. Geological Survey AREA2MI Area in square miles ESRI 0 60.5 Square Miles MajBasin Name of the Major Basin that contains the hydrologic unit. 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 Drainage Basin MassGIS, http://www.mass.gov/mgis/maj_bas.htm Impervious Percent Impervious Surface U.S. Geological Survey 0 100 Percent 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 34.988 http://water.usgs.gov/GIS/dsdl/ds451_hydro_units.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_hydro_units FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998