California is moving forward with its biggest water project in decades, a single tunnel beneath the Sacramento-San Joaquin River Delta that will help move Northern California water south to cities and farms, state water officials said Wednesday. The proposal piggybacks on plans by former Gov. Jerry Brown, who wanted to build a pair of 30-mile-long tunnels through the delta but was stymied by funding shortfalls and controversy. The project shares the same vision as Brown’s: to halt deterioration of the delta’s fragile ecosystem — the pinch point of the state’s water delivery network — while ensuring adequate water shipments to the rest of the state.