They're not meant to reduce sea levels.
But they could be.
The dam around the eastern end would have to be more than a half mile high
.
Not quite 800m tall.
As I noted above there would have to be some north south dams. The number of north south dams would depend relative cost of length verses height.
The tallest earth fill dam in the world is 300m high and was started in 1961 in the former USSR. If the USA is not capable of building dams 400 or 500m high I would be surprised.
From Wiki
The Nurek Dam (Tajik: Нерӯгоҳи обии Норак, Nerūgohi obii Norak, Tajiki for Nurek Hydro-electric Station) is an earth fill embankment dam on the Vakhsh River in the central Asian nation of Tajikistan. Construction of the dam began in 1961 and was completed in 1980, when Tajikistan was still a republic within the Soviet Union. At 300 m (984 ft) it is currently the second tallest man-made dam in the world. The Rogun Dam, also along the Vakhsh in Tajikistan, may exceed it in size when completed.
http://en.wikipedia.org/wiki/Nurek_Dam
How about an internet tax to help people displaced by rising seas?
The US could impose a tax on its population to pay for the displaced people in Bangladesh, Maldives etc. Obviously it would be cheaper to use the tax that you propose to stop the seas rising in the first place.
The rift is not a small area, and the Dead Sea is already holding water for that region - and its shrinking.
The rift is very long and narrow hence the name. Almost all of it is above sea level so storing water there would also involve massive dam construction just like a US storage site. Obviously there would be problems building dams across the rift. The GDP growth in Africa is higher than the US and Europe so it is likely that the countries along the rift valley would want to use it for there own water storage site if the construction problems could be overcome..
How can the Dead Sea be holding water for the region when it is shrinking. Where do you think the water is coming from that is greening the desert. Where do you think that water goes when it evaporates.
Not as renewable, we're already over fishing seas.
We are also over farming the land. Lake Kansas would take pressure off the US coastal fisheries.
Tourism would also benefit with beaches, sailing, water skiing and diving to see flooded cities such as Topeka.
Thats why doing this in deserts is smarter than flooding arable lands, but you cant turn Kansas into a lake or a poorly thought out troll into a gem of wisdom.
So which US state do you propose to flood rather than Kansas.
Link? I didn't suggest we flood quality farmland, why do you? How much good farmland in the Danakil and Afar Depressions? E Kansas has the most valuable farmland in the state and thats where the water would be if you surrounded the state with a dam tall enough to hold all the water.
A link for you.
http://www.nass.usda.gov/Charts_and_Maps/Land_Values/crop_value_map.asp
Whilst Kansas does not have the cheapest farm land it is far from the most expensive.
Obviously if inaction has produced the need to store water on land the lake would have to be filled as fast as possible. Kansas has the Missouri River which could be dammed and the water diverted into Lake Kansas. A hydro electric power station on the dam could be used to pump the water into Lake Kansas. This power station along with others on outlets from lake Kansas would form a major source of power to Nebraska and Missouri when lake Kansas was full.
Is there another US state that could so easily have a major rivers water diverted into it to quickly form a lake but is also relatively flat.
Danakil and Afar Depressions are volcanically active so are not the best place for dam construction.
If flooded to sea level the Danaki it would only be around 100m deep. It is also smaller in area than Lake Kansas would be. So would hold far less water than Kansas flooded to an average depth of 297m
http://www.nelsonelson.com/ethio-eritrean-danakil-canal-and-harbor/
The lake Kansas dam would most likely be build a few miles west of the Missouri. This land could become part of the state of Missouri.