Chesapeake Bay Sediment All time Record


Last March 2011 sediment intrusion into Chesapeake Bay reached an all time high as shown on the attached (click to see the aerial photograph and accompanying dialog). The dialog supplied by The Chesapeake Bay Foundation implies that urban storm runoff is relatively equal to farm fields as the cause and that the latter can be alleviated with buffer strips.  A little common sense coupled with our experience with sediment runoff alleviation success at the headwaters of LaTrappe Creek causes us to disagree with the alleged source and buffers as a proposed fix.

USGS calculates the area of farming in the Susquehanna watershed as 2% of land use versus 29% of land use for farming. Urban development has been required to retain impervious surface runoff on site for  60 to 100 year storms for decades. The same picture shows the Delaware Bay, a primary urban watershed, with very little sediment runoff. So it is likely that unprotected farm fields are the primary source of  sediment. We have found that winter cover crops (roots in the ground) are the only effective solution to farm field sediment runoff. We have also found that buffer strips of any width do not drop out significant amounts of sediment in stream flow. Grassed field trenches are effective in eliminating trench erosion but will not do much to remove sediment already in suspension. An adjacent farmer simply stopped retrenching field trenches. He lost some yield but slowed sediment runoff considerably. We have also found that installing a small retention pond at the end of every field trench is somewhat effective for small rain events but is no match for the amount of water we had last Spring. An aerial survey of unprotected tilled farm field trenches in the Susquehanna watershed would confirm the true source.


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