Mar 13 2012

Central Valley Flood Protection Plan: DWR Interview (Part 2)

This is Part 2 of our interview with folks at the California Department of Water Resources (DWR) about the draft CVFPP. Check out Part 1 for our questions related to the feasibility studies, real estate and land use, and the ecosystem integration. In this post, we’ll hit the climate change strategy, residual risk, and some discussion on public education. Again, here are the folks that Dusty and I were talking with:

  • Michael Mierzwa (Michael): FloodSAFE Communications Lead / CVFPP Technical Lead, Supervising Engineer
  • Merritt Rice (Merritt): Project Manager, CVFPP
  • Maria Lorenzo-Lee (Maria):  Communications lead for FloodSAFE


Dusty: Question on climate change. Obviously it is difficult to design and plan a system this large and complex and then you throw in variable hydrology and climate adjusting, so how do you guys plan to handle that future change? Is it just by adding in a safety factor to the system? What is the future view and goals and plan around climate change?

Michael: It is kind of yes, yes, and yes. In the plan, there is a set of technical attachments that you can view if you go the CVFPP web page. There is a climate change threshold approach and what we would ask to go through and do is to develop an approach that when you are going through and designing a specific project, which comes down later, how would you go through and access the uncertainty associated with hydrology to design that project? So the first thing we do in this pilot study is the threshold approach, is that we use HEC- ResSim and we have a model sitting for operations of Oroville and New Bullards Bar on the Feather River, which is a state and locally owned reservoir that work together and we talked about for a given flow period, which we were exceeding a downstream flow objective meaning criteria, what would be the current flexibility in the operation of those two reservoirs if we increased the flows to 10 percent, 20 percent, 30 percent, 40 percent, 50 percent, and literally went through, and using the model, we talked about how using those two reservoirs together we could re-operate Oroville to account for increased releases from New Bullard for a 10 percent flow increase. But when we got to the 20 percent flow increase, we began again exceeding the objective releases and downstream flow constraints. Then, in the climate change threshold approach, we said if we are going through and looking at climate change, you would either have to set back levees or raise levees downstream to account for that 20 percent. Is 20 percent real? In California an important mechanism of the climate change is the atmospheric river. These are the storms that are really intense that bring the water right from the Pacific across and then they slam into the Sierra mountain range and these generate our 12 inches of rain in a 24-hour period. Basically, in some instances, the majority of our rainfall for the year can happen in two or three events, which is different than in many other parts of the nation. But with these storms, we would look at, based on climate change, what is the likely intensity of these storms. Based on research coming from the Scripts Institute and B&K, we are seeing that in the next 50 to 100 years, the intensity of these storms is likely to increase upwards (and this is the upper end) of 120 to 130 percent. This means there is a possibility that the 10 percent increase of flow, or the 20 percent, is realistic. But we call this the bottom up approach. Instead of running the climate model and having a watershed model breaking down, you want to build enough resiliency into your system to address that.

So that gets to the next thing, when we talked about the benefits of the bypasses. I can raise the levees on the bypasses and the rivers to accommodate the flow or I can widen the bypasses, and by widening the bypasses, I’m not increasing the water levels. So that means that I am going to take more of the water out of the rivers as I continue to heighten or increase the water level in the bypass so the bypasses literally become that mechanism to keep or reduce the stages and accommodate for likely increases in the stage.

And the third thing that is not covered in the plan but in another effort we are developing here, with DWR in combination with the Corps, is a program called the Central Valley Hydrology Study update. The first phase is going through looking at how the Corps developed the hydrology for the Missouri River. They had a new method that was actually a historically based approach where most of the hydrology is within the call of synthetic hydrology, sort of a statistical hydrology. We took that approach and we are updating the hydrology. Then the second phase is to start doing sensitivity. We are going through and doing some pilot studies where we actually have the watershed models and do the top down approach: climate model rains, rain generates run off, how does the system respond, update your stage frequency curves and your flow frequency curves throughout the system. That’s going to be a couple years out but the intent is to have that product ready for when we start going through and actually getting into the actual design work.

There is a third level of planning when you get to the project design. You would incorporate climate change there. Now at sea level rise, which impacts the downstream boundary in the delta here (the Sacramento/San Joaquin rivers). We have to account for that as well. That’s going to happen in our project design world, where we have other programs in the department that talk about how you do design levees based off of likely sea level lines. For that we have been looking at the National Research Councils’ guidance on what sea level rise estimates are, which in turn are based off of the Intergovernmental Panel on Climate Changes modeling and efforts to show that a 2100 maximum set of sea level rise to the coast is 55 inches. As you move inland into the estuarine and riverine environments, the amplitude of that increase is decreased over time. We have methodologies for going through and doing that. But we really, in a way, put the focus on providing at the high level, you can use something like our capacity approach to find out what you need to resize bypasses, or how far you might want to set back your levees. When you get to the project design is where you are actually going to want to account for the uncertainty in the water surface.

One last thing, as I mentioned earlier, when we go through and design a levee, typically on the project levee we have had three feet of freeboard there. That’s to account for uncertainties in the hydrology and the hydraulic routing, and the bypasses due to actually the wave run up. We have six feet of freeboard that is required. It is actually pretty hard to get more than six feet of wave run up as we extend the bypass out to a larger reach. Six foot is what you commonly see in the coastal marine environments so we probably won’t have to take our three and double it. If we took the three feet and doubled it to get the six to account for the wave run up, we probably won’t have to double it again to twelve or anything crazy like that [to account for the climate change uncertainty].


Dusty: With the improvements of the flood system, there is obviously still a risk with the levees. As far as the public’s education and awareness of what you guys are doing and the residual risk that is still there, do you guys have plans regarding how to educate and communicate all of this to the public that is affected?

Maria: Yes, there was legislation that was passed where we have to provide written comments or written notification to the citizens in the Central Valley, where they are located for the flood risk and to actually help them prepare [for floods]. For example: have evacuation routes ready, or have evacuation “go kits,” and  things like that so just to make sure that the community and the people are aware of their flood risk and where they can contact people. Now this is the first state program to do it and people have taken notice. In fact, in about a couple weeks, we are going to be talking to the National Research Council and they want to know more about our flood risk communication and just that project in general.

Michael: The notices, they are actually are well received here. They actually listed the specific water body that would threaten your house so it wasn’t just that you were threatened, it would say that you could be threatened by this stream or river which made it real to people. Most people liked it, and as you can imagine with any of these programs, we had some people, “how dare you tell me that the water is going to reach my house.” We hit the emotional residents that we were looking for, and, of course, we are the government, so we are taxing the properties, we know where people live, but they were surprised.

Maria: I actually got one and I knew that it was coming but I didn’t realize that it was actually matching my address to my water body.

Michael: That connection made it very real and this program is one that won some awards from a number of floodplain management groups.

That marks the end of Part 2 of our interview! Look for Part 3 to conclude the interview and cover public education, future development, data collection, and use of the census data in the studies.

2 pings

  1. » Central Valley Flood Protection Plan: DWR Interview (Part 3) Hydraulically Inclined

    […] related to the feasibility studies, real estate and land use, and the ecosystem integration and Part 2 for our questions related to the climate change strategy, residual risk, and some discussion on […]

  2. » Central Valley Flood Protection Plan: DWR Interview (Part 1) Hydraulically Inclined

    […] concludes Part 1 of our interview! Look for Part 2 to cover the climate change strategy, residual risk, and public […]

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