California and US federal officials have commenced on improvements to the Prado dam, aimed at protecting Orange County cities while limiting development in southern Riverside and San Bernardino counties.

Planned for more than 30 years, improvements include raising the dam by nearly 9.1m, building new dikes in the Prado Basin to protect property and increasing the height of a nearby spillway by 6.1m.

The work will ultimately result in greater flood protection for cities south of the dam, it will also increase the amount of land in Riverside and San Bernardino counties that is designated as a flood plain, thus limiting development. The project, expected to cost more than US$400M, is to be completed in five to 10 years.