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 JournalJuly/August2002

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

(0.0039 - 0.063 mm) clay

(<0.0039 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

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 IslandThe next area

Corps of Engineers

1999 view NOAA1985 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 meandera

b

c

de

f

a b

Straight

c d

Meander bend

outside inside

Channel cross-sections

Draw the cross-section for e-f.

erosiondeposition

How does the water velocity vary from c to d?

The geology at a meander in a stream

Inside of bendDEPOSITION

young or no vegetation

Outside of bendEROSION

undercutting of stream bank

How does the channel migrate with time?

From NOAA

…another source of sediment to the Chesapeake Bay

Wave erosio

n

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