Recent Sedimentation

Sedimentation on the Chesapeake Bay in 2011

 Discussion to Share with the Classroom

At the water quality station, we have been stirring up a lot of discussion on recent flooding events and how they affect the turbidity of the Chesapeake Bay and the Rhode River. Thanks to NASA Earth Observatory, we have satellite images of the Bay before and right after the heavy rain and flooding events following Tropical Storm Lee and Hurricane Irene. The three images below are from MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA’s Terra satellite taken on August 13th (before the storm), August 30th (right after Hurricane Irene) and September 13th (after Tropical Storm Lee).

August 23, 2011

ChesapeakeBay_tmo_2011235

Chesapeake Bay 8/23/11 NASA images courtesy the MODIS Rapid Response Team at NASA GSFC

August 30, 2011

ChesapeakeBay_tmo_2011242 2.2

Chesapeake Bay 8/30/11 NASA images courtesy the MODIS Rapid Response Team at NASA GSFC

September 13, 2011

Chesapeake Bay NASA images courtesy the MODIS Rapid Response Team at NASA GSFC

Chesapeake Bay 9/13/11 NASA images courtesy the MODIS Rapid Response Team at NASA GSFC

The first image shows relatively normal conditions for this time of year. In the middle picture, taken after Irene, there is a noticeable change in the color of the water in the image.  What normally shows up as black has a brown and green tint due to sediment in the water.  However, after Tropical Storm Lee, the third image shows muddy tan water, which NASA calls an indicator of thick sediment clouding the water after the major runoff event. This shows that the events of and after Tropical Storm Lee could have actually had a greater effect on the watershed than Irene.

How does this tie in to what you learned about at SERC? Well, the excess of sediment and debris causes high levels of turbidity, which you learned about at water testing. And those high levels of turbidity due to mud, debris and excess sediment can prevent light from penetrating through the water column,  choke out filter feeders like the oysters we learned about at the oyster bar community station, and lower the salinity by replacing the brackish water with a massive influx of freshwater into the system.  NASA compares this event to Tropical Storm Agnes of 1972, noting that Irene and Lee were not as severe, and so, in turn, the effects of the recent rain and floods should not be as severe.

Check out the original article posted September 16, 2011 here.

To go along with this Estuary Chesapeake news update, try this activity about sedimentation. This activity and more can be found in the packet of supplementary activities given to teachers at our Estuary Chesapeake Teacher/Parent training workshops.

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