Ever since having found the old mill dams on Flat Creek last winter, and the massive amounts of sediment behind them (see below), one question continued to nag at me: Just how much silt is still trapped up in that stream valley?

You see, recent research coming out of Franklin & Marshall College, and backed up by quite a bit of ground truthing throughout the region suggests that what we now think of as streams bear almost no resemblance to what those systems looked like just 300 or 400 years ago. This is not to state the obvious, that the land uses around many of these systems have changed dramatically since the pre-colonial days, but instead to challenge the entire notion of what a "stream" is. Radiocarbon dating of soil strata at sites throughout the mid-Atlantic has consistently shown a similar pattern: several inches of quartz pebbles and gravel, overlain with a several inch layer of peat (often containing still viable seeds), covered with between 1 to 3 meters (3-10 feet) of legacy agricultural sediments, washed into stream valley over the past several hundred years (see below; Figure from Walter, R., & Merritts, D. (2008). Natural streams and the legacy of water-powered mills. Science, vol. 319).

The quartz bedding and peat layer extend stream valley wide, but the stream "channel" occupies only a fraction of that width, cut down through the legacy sediments, and often down through the peat layer and/or the quartz gravel. When that occurs, the peat, which is indicative of a historic wetland complex, shows up as a black or dark gray band of soil (see below).
At Flat Creek, the eroding stream still hasn't hit that peat/gravel band, so the question remained: how much lower than the existing stream bottom was it? There was only one way to find out. Armed with soil auger in hand, I cored through the stream bottom (see below).
After piercing about 5' of unconsolidated silt and mud, I hit the "bottom", a mix of sand, quartz pebbles, and woody stems and bark (see below).
Which means that the historic stream and wetland complex that once occupied this segment of Flat Creek is now buried under between 15 and 20 feet of fine agricultural sediments, slowly washing their way down towards tidewater. Though, thankfully, we have two beaver complexes between this area and tidewater right now.