Sierra Garcia | KneeDeep Times
For years, sea level rise planning in the Bay Area has carried a dark asterisk: Protect your own city with caution, or your seawalls and levees might contribute to flooding your neighbors.
Fears of cross-bay flooding — or inadvertently foisting extra water onto parts of the San Francisco bayshore by defending other areas of shoreline from rising seas with flood walls — have taken on a life of their own in public discourse from San Rafael to the South Bay. But the magnitude of these redirected effects may be far smaller than the public imagines.
“The myth comes from the perspective of flood management along a river, when the narrow channel has little storage,” explains Matt Brennan, a senior engineering hydrologist with Environmental Science Associates, a firm involved in many local sea level rise adaptation projects.
But the San Francisco Bay is not a river or a coastline pounded day in and day out by surf. The ancient riverbeds and valleys that determine the topography of the Bay shoreline allow water more room to spread out in some places than others. Around the edges, boundaries also vary, ranging from absorbent and gradual, like wetlands, to impervious and steep, like concrete seawalls.
