Did not see this post, just now saw.
thanks for the Orville dam picture.
None, no extra flooded land for this example.
This is an example that breaks the two parts of the dam into 3/5 & 2/5
The yellow line in the picture crosses the narrow section of the two parts of the lake
It allows for:
Water to be pumped between dams for cleaning out the other without wasting water or wating for a drought year every decade to clean.
This allows cleaning each year in the late summer one of the two sides.
The extra dam can have its own turbines or use the existing ones at the main dams turbine house and just add the piping connections.
On your question about more land used, couple of points that need understanding for context.
Pumped hydro takes a samll fraction of alnd compared to a one way dam.
Pumped hydro land use is a fraction of one way dams.
1/100th to 1/10,000th the volume of a one way dam such as Orville dam. But every location is unique and must use what the topology allows. The surface area is smaller than the volume and can be approximated by triangular troughs, roughly 1/3 of it being the surface area of water to air that covers any new land use. So ~ roughly 1/10th to 1/100th surface area of water. Just the top would be 1/30th to 1/300th the surface area used for pumped hydro to one way hydro.
Depends where the sediment capture dam goes.
If it goes up stream of river it needs to add some land use.
If it is built with the dam surface area, so that water is on both sides f the dam when both are full then no land is used.
By having a way to pay for sediment removal with the pumped hydro synergistic income stream designated to sediment removal less land area is needed for water storage, because each dam with the system holds significantly more water than if no system to clean is present.
This easily swamps out any land use by hydro, just by itself.
Even more significant is the land use avoidance of building more one way dams instead of sediment + pumped hydro.
Pumed Hydro allows less land use not more land use, because more one way dams must be built for the equivalent storage of present, sediment filled one way dams.
If we add pumped Hydro to most foothill dams like Orville, we can drain Hetch Hetchy and return it to its natural prestine wilderness, without loss of water storage.
In the Orville 2nd dam, that was my idea during the near catastrophic collapse of the dam because the spillway was eroding the dam base.
sediment dams at mouth rivers can be built, but may not be needed in this example. Since water can be stored in either section the other can be cleaned out with normal earth moving equipment, without the capitol cost of adding catchments dams at river mouths.