Thirty meter DEMS were used to create the 120m resolution river network. An existing thirty meter DEM was obtained from Clark University for the Ipswich R. watershed. A thirty meter DEM for the Parker R. watershed was created in Arc/Info from 1:5000 elevation contours obtained from MASSGIS. In each case pits were filled using arc grid commands. Grids were aggregated to 120m grid cell resolution. Flow directions were determined for the 120m resolution DEM’S using a “burning in” technique that ensures that flowdirections follow known surface channels. The arc aml program AGREE (D.R. Maidment, University of Texas) was used with the 1:25000 Hydrography layer obtained from MASSGIS. Settings in AGREE include: Buffer Distance (map units) = 240, gradual drop = -20, steep drop = -20. The flow directions for both watersheds were merged in arc grid. The combined flow direction grid was exported as ascii and imported into the UNH River GIS (RGIS) software. In RGIS, the flow directions were manually edited to conform with the standard basin boundaries as defined in the Major Drainage Basins data layer obtained from MASSGIS. RGIS commands were used to define river network attributes for each grid cell (Stream Order, SubbasinArea (= Contributing Area), SubbasinLength, BasinCells (Number of Contributing Cells), Travel (number of cells to basin mouth), DistanceToOcean. Some of these attributes are saved as an independent grid layer in this database.

Process_Date: 2001-2003

Information relevant to the GIS data encoding

Direction of flow to next downstream grid cellHorizontal Coordinate System Name:NAD 1983 StatePlane Massachusetts Mainland FIPS 2001

Datum: D North American 1983
Reference Ellipsoid: Name: GRS 1980 Semi Axis: 6378137.0
Meridian: Greenwich
Projection Name : Lambert Conformal Conic
Number of bands : 1
Raster Origin : Lower Left
Rows : 392
Columns : 467
Cell Geometry :pixel