The United States Geological Survey’s (USGS) Streamer app allows users to trace a body of water either upstream or down stream, connecting it to its broader watershed. Cross referencing this information with the elevations provided in Google My Maps creates a fairly accurate depiction of a watershed. The Blackwater River has a few challenges when delineating its tributaries. Fed by low swampy headwaters, there are often swamps that occur between the Blackwater River and other watersheds such as tributaries of the James River or the Nottoway River. Whether or not to include these swamps as part of the Blackwater River watershed may depend on conditions specific to individual weather events.
Hey Robert. The difficulty in delineating your watershed due to the low elevation, swampy nature of its headwaters was an interesting point. I had the same issue with the Elizabeth River watershed immediately to the east in the Hampton Roads region of southeastern Virginia. Specifically, I struggled to determine if certain tributaries in southern Chesapeake, Norfolk and Virginia Beach ultimately flowed into the Elizabeth or North Land River. I suppose mapping watersheds in more elevated regions may be slightly more intuitive, with streams following down a more obvious gradient (mountains and valleys, etc.).
Great work on the blog!
Certainly an interesting condition! Considering the nearby Great Dismal Swamp may have been up to 1,000,000 acres at one point, its not hard to imagine much of SE Virginia and NE North Carolina as a giant swampy ecosystem that shared outflowing water between both the Chesapeake Bay and the Albemarle-Pamlico Sounds.