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This dataset is a combination of 2 data projects:
1- Data were updated within NYC watershed portions using 1m resolution LiDAR and 1ft orthoimagery collected in 2009 as part of the NYS Digital Ortho Program under contract with NYCDEP under CAT-371.
For NYC reservoirs only: NYCDEP BWS GIS Staff (T. Spies) edited all polygons representing NYC reservoirs to show the true inundation area of water impoundment when the reservoir is full, including all areas separated from the main pool by a road or bridge. Therefore, any streams or rivers wider than 5m and represented in this NHDArea feature class were also edited as needed to match any edges where they transitioned from a NYC reservoir polygon. All edges and vertices were snapped to eliminate any gaps or slivers between reservoirs/lakes/ponds (NHDWaterbody) and stream/rivers (NHDArea).
QA edits to NHD hydrography, including this feature class, were also made where needed based on field verification and correction of the NYCbasin1m boundary.
As an additional departure from standard NHD to meet DEP’s needs, DEP GIS staff attributed all flowlines by their respective NYC reservoir basin and NYC water supply “region” as defined in the feature class “NYCbasin1m”. This was done using the “select by location” tool rather than “identity” tool, so as not to split any flowlines across boundaries. Any flowlines crossing basin boundaries in error were corrected by splitting the lines and snapping their endpoints to the appropriate spillway or basin edge instead.
2- Data was updated within portions of Ulster County outside the NYC watershed using NYS 1ft orthoimagery collected in 2013 and multiple Elevation datasets (2013 NYS DEC 1m Lidar Hudson River, 2005 NYS DEC 3m Lidar Ulster Stream Corridors, 1992 USGS 10m Digital Elevation Model (DEM)).
Primary quality control was performed visually using enhanced symbology and supporting reference data. A detailed QC checklist is provided in the QC report. Specific emphasis was placed on the areas bordering the NYC Watershed and the areas encompassed by the Town of Woodstock’s local hydrography data. To the extent connections occurred, the data captured on this project was “snapped” to the corresponding locations in the NYC Watershed so that the data could be seamlessly integrated. The hydrography data from the Town of Woodstock, however, was inconsistent when applied to the data capture protocol. Many locally derived features did not appear to be supported by the source data (i.e., they did not exist) and were not included. All visual inspections were made at 1:1000 scale or better.
During data capture, the Data Capture Analyst used a separate point feature class named “Flags” to identify locations where there may have been some interpretation or confusion. Later, the QC Analyst also used additional bookmarks in ArcGIS to track locations where additional investigation or interpretation was required. Finally, after an initial pass through the data, the QC Analyst evaluated and resolved all such flags and bookmarks, collaborating with the Data Capture Analyst as necessary to discuss findings and resolve questions.
As data was completed, naming convention and separate storage locations were used for data management to ensure that source and modified datasets were clearly separated. In addition, a detailed QC tracking spreadsheet was used to track and manage effort on completing QC and resolving any issues.
Finally, after the initial data delivery, several rounds of QC review were performed by Ulster County to include: additional visual inspection of flow line connectivity, geometric network tracking, and utility network analysis
Most of the issues that were not readily apparent in the manual QC process were attributed to minor errors in data capture and discovered here. Examples include digitizing lines in the wrong direction (not downstream), existence of multi-part features, and topology errors. In all cases, issues were evaluated and resolved