WASHINGTON -- In what amounts to the largest estuary restoration project in the Western United States, leaders of the U.S. Army Corps of Engineers’ San Francisco District have proposed a nearly $175 million plan to help protect the heart of Silicon Valley from catastrophic flooding. It’s a region that is home not only to the giants of the technology industry but some of the nation’s most expensive residential real estate now at significant risk of flooding because of climate change and predicted sea level rise.