Striper Talk Striped Bass Fishing, Surfcasting, Boating - View Single Post - Dredging b-ways

RIROCKHOUND · 12-06-2004, 08:33 PM

A geologists perspective..
I'm not an expert in this type of coastal geology; I'm more of a beach and glacial geologist, but here goes...
Seawolf is right; the dredging project in C-town is designed to "restore" (read change) the Flood tidal delta (FTD) from an inter-tidal habitat (wading birds etc) back to a subtidal eelgrass habitat. In the channel they will be digging a sedimentation basin to capture sediment coming into the inlet before it can reach the FTD, and bury the newly planted eelgrass, then the basins can be dredge as needed to keep the project going, but this is RI, who knows if the maintenance dredging will happen. A FTD is defined simply as the accumulation of sand landward of the inlet throat, shaped chiefly by flood-tidal currents... Basically there is a reason there is sand there in the first place, and it will likely go back there again...

That was all eelgrass habitats at one point, and they want to restore it. Habitat restoration is a hot button issue lately, even though it is really change, since one habitat is there already.
My opinion is twofold 1; the sedimentation basins will/could fill up with one good storm (read Hurricane passing west, onshore surge etc.. or a very powerful Extra-tropical storm (SE’er that persists for an extended period (a few days)) Get another sizable storm before the next round of dredging and there willbe alot of sand back in the inlet headed for the FTD
. 2. Eelgrass has not done well in recent years in the salt ponds (coastal lagoons technically, salt ponds is a local name) because of Nitrogen coming in from the septic systems of the houses on the ponds... Those houses on the barrier are built on sand, the houses on the back of the pond are built on sandy glacial delta deposits that generally dip seaward (to the south) the sewage doesn’t have a very long residence time in the leach field,, and Nitrogen goes into the ponds... Remember, these are my opinions, but check back in a few years......

30ft and 60ft are VERY deep, especially when you consider the width, the channel would never be stable at that width/depth, for some reason the number 18ft for the basins is sticking in my head, but that may not be true.. That is being plucked from way back in my head...,

As far as changes in current, the tidal range in the lagoon probably wont change appreciably, the width of the inlet relative to any depth change is very large, and water is still fairly restricted into and out of the pond by the shallowest and narrowest points of the inlet. Since that isn’t going to change, the current probably wont change much. Current flow will likely slow a bit at the basin (which is why the sediment is supposed to deposit in the basin, through a process known as flow separation) but overall I suspect it wont change much.

For the health of the pond, I hope the project succeeds, the eelgrass would be beneficial habitat for winter flatties, schoolies, etc.. But my gut feeling says in a few years there wont be much eelgrass left where they dredged...

Bryan

12-06-2004, 08:33 PM	#8
RIROCKHOUND Also known as OAK iTrader: (0) Join Date: Apr 2003 Location: Westlery, RI Posts: 10,408	A geologists perspective.. I'm not an expert in this type of coastal geology; I'm more of a beach and glacial geologist, but here goes... Seawolf is right; the dredging project in C-town is designed to "restore" (read change) the Flood tidal delta (FTD) from an inter-tidal habitat (wading birds etc) back to a subtidal eelgrass habitat. In the channel they will be digging a sedimentation basin to capture sediment coming into the inlet before it can reach the FTD, and bury the newly planted eelgrass, then the basins can be dredge as needed to keep the project going, but this is RI, who knows if the maintenance dredging will happen. A FTD is defined simply as the accumulation of sand landward of the inlet throat, shaped chiefly by flood-tidal currents... Basically there is a reason there is sand there in the first place, and it will likely go back there again... That was all eelgrass habitats at one point, and they want to restore it. Habitat restoration is a hot button issue lately, even though it is really change, since one habitat is there already. My opinion is twofold 1; the sedimentation basins will/could fill up with one good storm (read Hurricane passing west, onshore surge etc.. or a very powerful Extra-tropical storm (SE’er that persists for an extended period (a few days)) Get another sizable storm before the next round of dredging and there willbe alot of sand back in the inlet headed for the FTD . 2. Eelgrass has not done well in recent years in the salt ponds (coastal lagoons technically, salt ponds is a local name) because of Nitrogen coming in from the septic systems of the houses on the ponds... Those houses on the barrier are built on sand, the houses on the back of the pond are built on sandy glacial delta deposits that generally dip seaward (to the south) the sewage doesn’t have a very long residence time in the leach field,, and Nitrogen goes into the ponds... Remember, these are my opinions, but check back in a few years...... 30ft and 60ft are VERY deep, especially when you consider the width, the channel would never be stable at that width/depth, for some reason the number 18ft for the basins is sticking in my head, but that may not be true.. That is being plucked from way back in my head..., As far as changes in current, the tidal range in the lagoon probably wont change appreciably, the width of the inlet relative to any depth change is very large, and water is still fairly restricted into and out of the pond by the shallowest and narrowest points of the inlet. Since that isn’t going to change, the current probably wont change much. Current flow will likely slow a bit at the basin (which is why the sediment is supposed to deposit in the basin, through a process known as flow separation) but overall I suspect it wont change much. For the health of the pond, I hope the project succeeds, the eelgrass would be beneficial habitat for winter flatties, schoolies, etc.. But my gut feeling says in a few years there wont be much eelgrass left where they dredged... Bryan
	Bryan Originally Posted by #^&#^&#^&#^&#^&#^&#^&#^&#^&#^&#^& "For once I agree with Spence. UGH. I just hope I don't get the urge to go start buying armani suits to wear in my shop"