by Artie Valencia, Community Organizer & Government Liaison, Restore the Delta
To understand flood risks from the recent Atmospheric River storms, Restore the Delta is analyzing River Stages in Feet and SWE (snow water equivalent) levels recorded from the latest storms. The ongoing monitoring of River stages in the San Joaquin River at Brandt Bridge is being done by the California Department of Water Resources, while surface water elevations are tracked by UCLA Climate Scientist Daniel Swain.
ABOUT THE DATA
On March 4th, 2023, the river stage in the San Joaquin River at Brandt Bridge was 6.75 and increased up to 10.63 feet between the weekend and March 14th. The River Stage that induced localized and river flooding in Stockton was 15.7 feet during the last storm in January. As of now, we still have rain projected to fall through the week coupled with melting snowpack below about 4,000 ft. The recent “warm” atmospheric river storm increased net watershed SWE substantially due in part to snow occurring still at high elevations, while snowpack at lower elevations absorbed rainwater. There SWE in the Southern/Central Sierra watersheds is record-breaking right now. This snow will melt in late March and into April/May. California has never experienced a snowpack melt this large in our warmer climate. It will be new territory for everyone involved.
WHY THIS MATTERS
Our current threat is directly tied to the effects of heavy rainfall, saturated soils and high river levels from very wet antecedent conditions. There could still be additional snowmelt contributing to severe flooding for larger mainstem rivers in the weeks to come.
With that said, the San Joaquin River at Brandt Bridge is currently 5 feet away from reaching levels that lead to localized flooding in Stockton and had ports (Mormon Slough in particular) a few feet from overtopping. But as UCLA climate scientist Daniel Swain explains, we cannot predict how severe flooding on Sacramento, San Joaquin systems, tributaries and eastern Sierra watersheds will be weeks in advance. However, due to the enormous amount of SWE in the snowpack that will melt, flood risk will increase severely by April.
STOCKTON – The Next Katrina?
For Stockton, this flood risk raises concerns for environmental justice communities redlined into housing on floodplain zones. Currently, environmental justice communities like the residents of Conway homes live across the street from the levee at the previously known Van Buskirk Park. At Mormon Slough, the unhoused reside along the edges of the slough. Back in January, the unhoused community was only a couple of feet from being inundated and there was no action to relocate them on the housing authority, office of emergency services, or Sherriff’s end.
Due to decades of disinvestment, the city’s only defense against flood are decades-old, leak-prone levees. Federal studies found that the levees could burst as mountain runoff flows into the San Joaquin River. Flooding of this magnitude would inundate the city with 10 to 24 feet of water. According to the Delta Stewardship Council’s Climate Vulnerability Assessment, 17 thousand homes will be affected by flooding and $28 billion dollars (closer to $48 billion now due to inflation) in damages for critical buildings will ensue for the city of Stockton. This flood risk only increases with climate change and sea level rise due to increased rainfall and runoff in the San Joaquin watershed compared to the Sacramento watershed.
Historically, Stockton has always been disastrously underfunded and leaders along the San Joaquin River have prioritized securing water for irrigation over flood risk management. Besides funding floodplain projects and upgrading our levees to at least 200-year conditions, we also need upgrades to municipal systems to deal with runoff into the street. Data from Daniel Swain reveals that “the coming superstorm is a rapid procession of atmospheric rivers and will be the ultimate test of the current dams, levees and bypasses in place.” It is known that levee failures can also damage key features of the Delta ecosystem existing on the heavily altered landscape, including managed wetlands. Additionally, levee failure could degrade Delta water quality if waters from the ocean rush into a heavily subsided Delta Island, pulling higher-salinity water.
WHAT CAN WE DO?
Stockton faces flood risk from all sides: both the San Joaquin and Calaveras rivers flood during rain events and high tides from the Pacific can exacerbate flooding. Delta levee improvements and wetland restoration can counteract sea level rise.
Floodplain restoration from Merced to Van Buskirk is essential to take pressure off levees. Restoration offers a multi-benefits solution by recharging groundwater, providing recreation and natural areas, and protecting the neighborhoods where we live.