California and Atmospheric Rivers 

By Luke Carothers

For Californians, discussions about water are frequent.  And, when it comes to water, California’s vastness gives a depth and complexity to the challenges that come with not only providing water to its citizens, but also protecting them from it.  Recent events have made the latter a pressing issue for AEC professionals.  Earlier this year, California saw unprecedented storms, culminating in a three-week succession of severe storms known as atmospheric rivers.  Atmospheric rivers are flowing columns of condensed water vapor that flow from tropic waters and release massive amounts of rain and snow as they flow over land.  These events have spurred a renewed conversation about the way various agencies monitor the effects of such weather events and mitigate damages from flooding.  

To protect from the damages brought on by excessive precipitation in California, different areas require specific solutions.  For example, there is a substantial amount of building on hillside slopes in the San Francisco Bay Area, and substantial rain can threaten communities and vital infrastructure. ENGEO’s Mark Gilbert points out that these rains have a tendency to cause shallow earth movements as the ground becomes more saturated.  Once the soil breaks free and starts flowing, it can accelerate rapidly, causing damage to property and threatening life.  Other places in the state face a substantial threat of flooding as rainwaters feed rivers flowing down from mountains.  To protect lives and property, the state of California has invested heavily in measures to manage the flow of water and prevent/monitor landslide activity.

ENGEO has a number of projects throughout the state, and has helped build the infrastructure that protects it from this unprecedented weather.  In this, ENGEO has worked with over two dozen entities to provide flood mitigation.  ENGEO also currently manages 14 geological hazard abatement zones within the state, which has made them very busy recently according to Gilbert.  In managing these zones, ENGEO is responsible for observing and managing any landslide activity.  The recent amount of precipitation has resulted in significant hazards to places like the San Francisco Bay area, in which many communities and infrastructure points are built on steep hillside slopes.  This includes public requests to address emergency slope stability caused by recent rain events from: the Oakland Zoo, the City of Oakland, San Carlos County, San Mateo County, the City of Danville, and the City of Hercules.  

In the Central Valley, ENGEO has worked with state and local agencies to build state-of-the-art levees for the last 20 years.  During this time, ENGEO has been involved with a number of significant projects including a 2.6-mile long levee for the Three Rivers Levee Improvement Authority.  ENGEO is also currently working with a team of engineers on the Natomas Interior Levees.  ENGEO’s work is part of a larger effort throughout several agencies at the state and local levels to prepare and create systems that can handle intense precipitation and weather events.

Recent storms have tested the capacities of these systems.  Atmospheric rivers are not an uncommon phenomenon in California, but the recent frequency has led to widespread flooding and challenged the state’s infrastructure. Gilbert says that these sort of storms result in a lot of careful monitoring for levee maintaining agencies, reclamation districts, and flood control agencies.  The result of this careful monitoring, according to Gilbert, is a series of proactive steps.  Local agencies have set up on-call agreements with local pump and generator rental companies should the water level rise threaten current systems.  If, for example, a critical pump station loses power, these sort of agreements allow agencies to rapidly respond to developing challenges.   By monitoring water levels and deploying these assets, levee and flood control agencies have been able to mitigate damage from recent flooding. 

While monitoring and preemptive planning helped mitigate serious damages from recent flooding, Gilbert believes that there is more work to be done when it comes to preparing for the future.  Many flood control projects that are under construction or have recently been announced focus on expensive permanent infrastructure.  While this is a good solution when it comes to planning for bigger, more rare events, Gilbert believes that the focus needs to be shifted towards developing flexible and rapidly deployed protective measures.  By developing these measures, agencies can reduce project costs while also responding to flood events in a more dynamic way.

Luke Carothers is the Editor for Civil + Structural Engineer Media. If you want us to cover your project or want to feature your own article, he can be reached at lcarothers@zweiggroup.com.