The Russian River flooded parts of five California counties in late February after more than 20 inches of rain fell on the hilly area over a two-day period [1]. The river crested at 45.4 feet – more than 14 feet above flood stage – on February 27 near the Guerneville Bridge, downstream from most of the areas affected [2]. Flooding hit more than twenty towns, with officials issuing mandatory evacuation orders and estimating that over 4,000 structures were flooded [1]
AER’s automated FloodScan system mapped the extent of the flooding from satellite observations made on February 27 and 28 and March 1 [3]. The image below shows flood water stretching from Sebastopol in the south up through Healdsburg and into the vineyard region of the Alexander Valley to the north. FloodScan uses data from passive microwave satellite sensors to penetrate clouds and vegetation and measure large-area flooded fraction in close to real time. A relative floodability database transforms flooded fraction into a depiction of flood extent at 90-meter resolution, accounting for topography, streamlines, and land cover.
(Click image to enlarge)
Flooding isn’t a rare occurrence in the valleys of the Russian River. The river has overflowed its banks at the Guerneville Bridge gauge 38 times since 1940 [2]. The previous high-water mark was 41.8 feet on January 1, 2006 – lower than the latest crest but still high enough to flood many of the same areas affected now. FloodScan data reach back to 2002 in the US, so we took a look at the 2006 flood extent to compare it with the current situation. The January 1, 2006 FloodScan map below shows less flooding overall, with most flooding concentrated in and around the wetlands areas between Sebastopol, Windsor, and the Russian River.
(Click image to enlarge)
For more information and access to a web-based interface to FloodScan’s automatic flood maps, visit floodscan.aer.com.
Footnotes
[1] https://www.mercurynews.com/2019/02/27/this-sonoma-county-town-got-20-inches-of-rain-in-48-hours-san-jose-averages-about-15-a-year/
[2] https://www.mercurynews.com/2019/03/04/why-does-guerneville-flood-so-much-and-why-cant-it-be-fixed/
[3] http://floodscan.aer.com