Southern California’s powerful water agency committed more than $4 billion to the Delta tunnels Tuesday, giving the troubled plan a desperately needed vote of confidence. The Metropolitan Water District of Southern California’s board voted to pay for about a quarter of the tunnels project, Gov. Jerry Brown’s $17.1 billion effort to re-engineer the Sacramento-San Joaquin Delta and improve water deliveries to south state cities and farms. The vote was 69 percent to 22 percent under Metropolitan’s voting system, which gives more weight to the largest cities, with the rest abstaining.