Extent and Channel Morphology of Unmapped Headwater Stream Segments of the Quabbin Watershed, Massachusetts1

Effective regulatory protection and management of headwater resources depend on consistent and accurate identification and delineation of stream occurrence. Published maps and digital resources fail to represent the true occurrence and extent of headwater streams. This study assessed the accuracy of mapped origins of blue-line streams depicted on U.S. Geological Survey topographic maps, and, if present, the morphological characteristics of unmapped stream segments. We identified 170 mapped stream origins on the Quabbin Reservoir watershed, Massachusetts. Of 30 mapped stream origins, we identified and examined 26 unmapped stream segments above 25, with an average length of 502 m. Twenty unmapped tributaries occurred on 10 of the 26 unmapped segments, with an average length of 127 m. Wetland reaches occurred more frequently and were larger on unmapped than on mapped stream segments. A significant and complex stream network occurs above most mapped stream origins. For the Quabbin watershed, we estimate that there are 85.8 km of unmapped stream upgradient of 314.5 km of mapped streams. Reliance on mapped stream networks for regulatory standards allows for the potential disturbance or even destruction of the unmapped stream resources. Jurisdictional regulations and guidelines should be revised so that the occurrence of streams should require field validation.