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 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?

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

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

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

Source of sediments Increased soil erosion by deforestation From CBP CBP

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!

Hart-Miller Island (State Park, today) Poplar Island The next area Corps of Engineers 1999 view NOAANOAA1985 view MGS Dredge Spoil Disposal

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

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

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

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

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

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!

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