We have just brought a secondhand JCB Hydrainer (Hydralic) 2" pump. By f**k does it shift water.
Sykes Self priming, or any similar pump though is the boy for emergency pumping as James has said. There about the only type of pump that will happily deal with varying volumes of water over a long period... that's the issue with rotary pumps that end up cavitating and killing themselves, and electric ones wind up stopping and starting too much

The self primers come up in the 4" size quite often for under a couple grand. Something worth having in the yard if your at risk...