CHALLENGES USING THE PENNSYLVANIA IMPAIRED AND NON-IMPAIRED STREAMS GIS COVERAGE
1) 14% of Attaining stream kilometers are identical to segments of Non-Attaining streams. This overlap is contrary to what the metadata indicate.
2) There are 30% more apparent Attaining plus Non-Attaining kilometers than National Hydrography Dataset (NHD, from which most Integrated List segments were copied) kilometers.
3) 25% and 15% of Attaining and Non-Attaining stream kilometers, respectively, are listed for more than one use; e.g., a segment can be Attaining (or Non-Attaining) for both aquatic life and recreational uses.
4) A few Attaining (0.5%) and Non-Attaining (0.7%) stream kilometers extend beyond the PA border.
6) A small number of NHD Flowline segments do not match geographically with Attaining and Non-Attaining segments.
7) After “correction” for the problems listed above, there are a 1.4% more NHD stream kilometers than the combined Attaining and Non-Attaining kilometers. This small percentage of stream kilometers is apparently not assessed.
End users need to be aware of these issues with the data and metadata to avoid over-counting of stream lengths and problems in conclusions drawn regarding stream data.