CA SB1390

Expands conditions for diverting floodflows for groundwater recharge without requiring an appropriative water right, including flows projected to inundate ordinarily dry areas in terminal lake beds or threaten residential, commercial, or industrial structures.

Requires local or regional flood management agencies to declare that diversions align with adopted flood control plans, general plans, or federal hazard mitigation plans, and give public notice that areas face imminent risk of flooding (high confidence within 72 hours).

Mandates diversions cease no later than 30 days after public notice unless renewed, and requires agencies to issue declarations at least 48 hours before projected end of flood conditions informing when diversions must stop.

Requires diverters to file notice and preliminary and final reports with the State Water Resources Control Board, the issuing agency, and applicable groundwater sustainability agencies, with reports posted publicly on the next business day.

Specifies that temporary floodflow diversions from Delta tributaries are only authorized when Delta is in excess water conditions, with additional restrictions on San Joaquin River diversions upstream of Vernalis, and applies only to diversions commenced before January 1, 2029.