Re:Water City (Score 1)

The mainland is eroding by wind and water but that really isn't the problem with the 'sinking' of New Orleans. Silt erodes from the mountains and the plains all over the country and washes into streams and rivers. The streams and rivers combine and carry the silt a long way. When silt is deposited on land by the river as the flood water recede, the layer of silt is very loose (unconsolidated). Over time, the silt will compress or densify mostly due its self-weight as well as due to the weight any other structures like buildings. In silt, this is a VERY slow process and is slowed down by shallow groundwater. New Orleans is 'sinking' because the silt is slowly densifying and the levees are blocking the Mississippi River from depositing additional material. The levees are also speeding up the flow of the river, allowing the silt suspended in the water to travel farther out into the Gulf before the water slows and drops it in a delta. In a sense, the levees which protect New Orleans are also causing its demise as it forces the silt delta to move further out into the Gulf.