Mar 15 2012

Central Valley Flood Protection Plan: DWR Interview (Part 3)

This is Part 3 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 and Part 2 for our questions related to the climate change strategy, residual risk, and some discussion on public education. In this post, we’ll conclude the interview and cover public education, future development, data collection, and use of the census data in the studies. 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: We’ve done some work in Iowa and the University of Iowa has a flood research center website they’ve developed. One of the things they have on there is an interactive website that you can go to. For the Iowa City area and based on a gaging station in town, they will report possible flood peak at 39 feet and you can go on there and adjust the graph to 39 feet and see if your house is going to get wet. Do you guys have plans to make any kind of information accessibly to people through a website that would help them, inform them during an event or before an event?

Michael: Let me handle that one because that one goes back to when I was the head of the state’s river forecasting program. There is a National Weather Service program called AHPS, Advanced Hydrologic Prediction Service. One of the things they are real time maps just like that. I grew up in Houston, Texas and that was one of the pilot project going through out there. Literally, you would take the National Weather Service river forecast products and you could link that to a FEMA inundation map and you could see for a given water level, what that depth dependent map would be for your house. We are not working on that in the Department of Water Resources, the department is actually our flood management group, the facility we are talking with you in today. It is co-located with the National Weather Service of Sacramento weather forecast office, as well as the California-Nevada River Forecast Center, and they are working on developing those products here.

The other area where we have been talking with the Weather Service, because they have been asking us what we have been doing, is the City of Napa. They have had repetitive flooding and repetitive losses over the years, sitting right there on a river berth that we actually forecast to. It is something that, in fact, the Weather Service wants to go through and work on. The State would have programs that we could cost share the City of Napa to meet some of the funds for a new mapping effort that FEMA could conduct and then FEMA could link that into the Weather Services AHPS program.

Maria: I was also going to mention that there are two websites where you can, in the future, type in your address and you can find out if FEMA maps you in high, medium, low flood risk zone but I also wanted to ask about CDEC because that is real time so you can know what the river stages are.

Michael: Right, so we have a real time data program here in the Department of Water Resources that is called the California Data Exchange Center. Are you guys familiar with it? You can get a lot of real time data from that site. When I was doing levee controls back in 2006, we were using the early generations, just cell phones, maybe it was a smart phone, you could at least get some weather renderings to check periodically with CDEC, to see what the forecasted water levels or stages were both astronomical and the real time forecast and when you are a local, you have in your mind, what a stage at this location translates to, what an impact is at your home, and you use that as literally your trigger.

Merritt: But if you look at Chapter 4, you are going to find as part of the SSIA, the State Systemwide Investment Approach, that we do have a special emphasis on a flood emergency response program.


Dusty: As the system gets upgraded, specifically in and around urban areas, will there be places that you would still discourage development, even though you are going to be upgrading urban areas to 200-year protection, or will development tried to be pushed to specific areas that are not at as much risk?

Merritt: The whole 200-year thing, that’s a minimum. In many communities around the United States, they’ve got 500-year or greater [protection]. I think the notion here was to get something significantly greater than 100-year for urban areas and something that’s achievable. That is not to say that’s the end of the day for urban areas.

Michael: When you go through how you achieve the urban level of protection at 200-year, if you are just raising structures in there, other new structures also have to be raised and built for that new design water surface in the interior. If you are going and fixing the levee, you can go through and use the levee to credit and allow development or in-fill in those areas. But the 200-year level protection is on new development which means if you are going in and you have a house that you want to add an addition to the house, that’s now an improvement, that’s a new development. You are adding square footage and structural value. In order to get your permit, you have to go through and do that. We are not going through and discouraging risk management. So when we talk about it, the difference in risk from 100-year to 99 to a 101-year level of protection is the same. The difference is really the thresholds of the 100-year level of protection or the 200-year level of protection, the insurance requirements that really drive communities to design to those levels. So the point was to get people moving to a lower risk environment by setting a higher level of protection but if a local community can say that or justify that they need 300-year level of protection or higher, we are going to support that. You can see this in a community like Marysville which has levees which are well over a 200-year level of protection.


Dusty: In the CVFPP you guys mentioned some of the data that you collected: 9000 square miles of LIDAR data. Was that information used for this report or is that for future studies?

Michael: That’s for CVFPP in the future. They’ve done the first wave of processing but they still have to finish putting some of the break lines in for the levees. They haven’t defined all of the features out there and the second set of data should be finished this year.

Dusty: Is that included with bathymetric data along the rivers as well?

Michael: Yes.

Dusty: And knowing that this is a 20 to 25 year plan, do you guys have plans at some point in the future to update the data set for the whole area?

Michael: Yes. The Central Valley Hydrology Study, the reason we moved to a different type of methodology for calculating out your flow frequency relationships is so that as we would have major events come through, that would actually change the distributions of how the system responds, we can easily go through and do that by appending those additional years. We basically went through a Bulletin 17-B analysis on the calculation of the flow frequencies and we basically have a transform function between a regulated system and unregulated system and you’d want to go back, when you have a new hydrology, and show how both the transform happens, which is how the system, the natural system changes, and how the unregulated transform. It is fairly easy to go through and do. In the Department, we have a document called a Bulletin 69, and any time there is a high water event, we are required to go through it., Half of that Bulletin goes through and talks about the meteorology and hydrology, the meteorological-hydrological response of the system and the second half of the document actually outlines the economic consequences: what were the damages that were felt? We haven’t updated finally the 1997 event out there, it has been in draft form for awhile but we would go through and continue to work on those.

Merritt: And remember that the plan is going to get updated like I said; every five years and it would be unreasonable to think that in 2017 or 2022 that we will not have used the latest and the greatest.


Anthony: One more quick question. Regarding the life loss analysis in the report, the plan says that you used the data from the 2000 census, and the 2010 was not available yet. Did you guys try to account for new development in any way or just straight use the 2000 census data?

Merritt: It is my understanding that what we used was the existing census data and didn’t project future development in the floodplains.

Michael: And the reason why: are you guys familiar with HEC-FDA, like an economic analysis? We took the same depth damage functions and applied fractional people per dwelling and we actually had for each and every structure within the Central Valley, a depth damage function from the previous model, which is also Flow 2D. We just changed it to people based on the 2000 census data because the 2000 census data gets down to dwelling by dwelling. Where as 2010 data, we have the census track data but we don’t have the parcel data yet.

Dusty: Will that be out this year?

Michael: I think it will be finished this year and the intent is on the five year updates of the plan, in years that end in seven, we will go through and update to that most recent parcel data, and then on the years that end in two, we are always going to have to go back to that data from the seven.

Anthony: I think that is all of our questions. I did just want to say for both of us, we definitely think highly of this report. Just working in the area and finally seeing a system wide approach and a plan moving forward is definitely cool and appreciated. It is a solid document and we think it is going to be great moving forward just watching what happens, and hopefully, you can get all of the funding you need.

That marks the end of our interview! We hope this interview was helpful in clarifying some of the driving  issues of the draft CVFPP.  Our thanks to Michael, Merritt, and Maria for their time in answering our questions regarding the document and plans moving forward!

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

    […] Central Valley Flood Protection Plan: DWR Interview (Part 3) » […]

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