The MWRD's Tunnel and Reservoir Plan, also known as TARP or "The Deep Tunnel," is designed to reduce flooding and pollution caused by combined sewer overflows. The Deep Tunnel system is designed ...

The system is named for the former Hetch Hetchy Valley, which is now underwater in Hetch Hetchy Reservoir, held back by the O’Shaughnessy Dam that impounds the Tuolumne River inside Yosemite ...