You can have a huge one, or lots of small ones. Using what is...

You can have a huge one, or lots of small ones.  Using what is already there, saves construction costs.  In some places, such as the NSW South Coast, such storages already exist, (Cordeaux Dam, Cataract Dam and Woronora Dam are all conveniently located on the plateaux above the coastline).

http://www.nccarf.edu.au/settlement...astructure/files/Discussion Paper Z Final.pdf

"In NSW, coastline cliff tops and large headlands offer potential sites. The stretch of coastline just north of Wollongong shown in Figure 14, from Austinmer to Stanwell Park, is bound by the steep adjacent Illawarra Escarpment with flat elevations up to 400 m near Maddens Plains; this is approximately 2 km horizontally from the coastline. 0.010PJ of stored energy generation could be provided potentially by a 3000ML pondage in the upper escarpment."

"Because here are three things you don’t need for pumped hydro: a lot of land, a lot of water, or even a river valley."

"useful pumped hydro reservoirs might be only 50 hectares, or even as small as five."

http://reneweconomy.com.au/2014/pumped-hydro-the-forgotten-storage-solution-47248