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Sediment Happens! It’s cleaning it up that’s difficult

Sediment Happens! It’s cleaning it up that’s difficult. ESI. What if we piled up the estimated 5 million tons of sediment/year carried into the Bay and its tidal tributaries ?. Bay Journal July/August 2002. Colonial ports.

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Sediment Happens! It’s cleaning it up that’s difficult

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  1. Sediment Happens!It’s cleaning it upthat’s difficult ESI

  2. What if we piled up the estimated 5 million tons of sediment/year carried into the Bay and its tidal tributaries ? Bay Journal July/August 2002

  3. Colonial ports • Joppatown at the mouth of the Gunpowder River (today 2 miles inland from mouth!) • Bladensburg on the Anacostia River • Port Tobacco on the Potomac River • Charles Town at Jug Bay on the Patuxent River What was the purpose of the ports?

  4. Siltation Massive sedimentation in river channels What is the source of all the sediment? New channel is cut as marsh develops in shallow waters Present channel Ancient channel

  5. Youngest Oldest How does sediment pile up? particles settle from water column Where is the oldest sediment?

  6. Does particle size make a difference? sand (0.063 – 2 mm) silt (0.0039 - 0.063 mm) clay (<0.0039 mm) The larger the particle, the faster it settles. Which particle will get transported the greatest distance? Fine grain material is the cause of siltation.

  7. Source of sediments Increased soil erosion by deforestation From CBP

  8. Baltimore Harbor • Very large commercial port today • Dredged to maintain channel for ships • Larger ships need deeper channel • What do you do with the contaminated dredged material (dredge spoil)? Overboard disposal is banned!

  9. Dredge Spoil Disposal • Hart-Miller Island (State Park, today) • Poplar Island • The next area 1985 view MGS 1999 view NOAA Corps of Engineers

  10. Stream Flow How does the velocity vary in the channel? c Faster on the outside of a meander Slower on the inside of a meander a e d b f Same velocity in straight sections of channel

  11. c d Meander bend inside outside Channel cross-sections a b Straight erosion deposition How does the water velocity vary from c to d? Draw the cross-section for e-f.

  12. The geology at a meander in a stream Outside of bend EROSION undercutting of stream bank Inside of bend DEPOSITION young or no vegetation How does the channel migrate with time?

  13. …another source of sediment to the Chesapeake Bay Wave erosion This will worsen as sea level rises! From NOAA

  14. Here is a lake/reservoir formed by damming a stream valley. stream lake Former stream channels before flooding What do you notice about the shape of the man-made lake? dam What is the fate of the lake? As the fast flowing streams flow into the quieter lake water, what happens to sediment?

  15. Natural vs. Man-Made Lakes • How do you tell the difference? • Natural lakes are bowl, rounded in shape- formed by subsidence or glacial carving. • Man-make lakes are irregular, typically following topography of stream drainage. Plus look for the dam!

  16. N DEEP CREEK LAKE, MARYLAND Not part of Bay watershed, goes to Miss. River Maryland’s largest man-made lake. dam

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