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Any flood modeler is well aware of the challenges that this particular peril presents, for several reasons.  Ivan Maddox lays this out quite well in his Risks of Hazard blog where he discusses “The Ingredients of a Good Flood Model.”  The National Research Council raised similar concerns about the need for high quality elevation data in their 2009 Mapping the Zone report which is available at a free pdf download here.

In addition to the challenges of obtaining high quality elevation data, there is also the question of which discharge to model.  To the extent a flood model is based on an historic analysis of annual peaks, and the methods put forth in either Bulletin 17B (four pieces of software are currently available from four different agencies that incorporate this method) or 17C, eventually some significant uncertainty arises as one moves further along the curve towards higher magnitude, lower frequency events. Another approach to flood modeling is a Monte Carlo analysis with thousands of modeled events, but given how common an annual peak analysis is, I am going to stick to this type of analysis.

The graph below is taken directly from the macro enabled Excel spreadsheet that the Natural Resources Conservation Service provides on this page. Upon downloading the file and opening the ‘freq curve’ tab, a user will see this graph for the Yellowstone River near Sydney, MT. With over 100 years of annual peak discharge, it’s a pretty robust empirical set of observations.  The orange rectangle is what I refer to as the ‘box of uncertainty’, and in this case, it is the box for the 1% annual chance flood.

It has been pointed out that communicating about floods and especially flood frequency to the general public is challenging for agencies, disaster planning teams and hydrologists.  The NRCS recognizes this, and to their credit, they put exceedance probabilities on the x-axis at the bottom of the graph and they also include some flood frequency recurrence intervals (RI) in years on the top of the graph, which I clipped out.

The key point here is to look at the uncertainty that surrounds a given exceedance probability which is what the orange rectangle highlights for the 1% exceedance probability event.  For starters, if one holds to the 1% event, in my experience, the typical application is to read the value off the blue line and say that the value is 158,000 cfs.  In other words, a colloquial interpretation would be to say, “the 100 year flood is 158,000 cfs.”  A more nuanced and admittedly more challenging way to communicate the analysis would be to acknowledge the uncertainty and state that staying within the 5% and 95% percentile estimates, the 1% exceedance flood could be as low as 140,000 cfs and as high as 184,000 cfs.

In addition, if we hold to the 158,000 cfs estimate, one should also recognize that within the 5% and 95% estimate, this discharge could have an exceedance probability of as much as 3% (e..g ~33 yr RI) to as low as  0.3% (e.g. ~333 yr RI).

The air photo below is a screenshot from FEMA’s National Flood Hazard Layer (NFHL) Viewer. The USGS Sidney, MT gage is just to the northeast of the bridge crossing; flow is from the bottom to top. The blue-green shading represents the “1% Annual Chance Flood Hazard.” If I happened to own the property with the red roof near the bottom of the image, given all the modeling uncertainty and assuming the road just to the west of the property doesn’t provide any flood protection, it seems like purchasing flood insurance would certainly be in my best interest.

Communicating flood risk is and will continue to be a challenge.  I certainly prefer exceedance probability to recurrence intervals with years as the unit (e.g. the 50 or 100 year flood). In closing and keeping Ivan’s excellent piece in mind, another ingredient of a good flood model would be a well written flood model report explaining some of the uncertainty in the model results.

 

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I’ve recently come across some papers that Jeffrey Opperman has published by himself or as lead author. It appears as though he attended UC Davis and if nothing else, he really knows how to write some wonderful opening sentences. Here are two that not only caught my eye, but also resonated immediately with me:

“Flooding is the most damaging natural disaster worldwide, and the flood-vulnernable population is expected to grow in the coming decades. Flood risks will likely increase because of both climate change and shifting land uses, such as filling of wetlands and expansion of impervious surfaces, that lead to more rapid precipitation runoff into rivers.”(1)

“Floodplains are among the most biologically productive and diverse ecosystems on Earth and they provide significant benefits to society such as attenuation of of floodwaters, groundwater recharge filtration of nutrients and sediments, carbon sequestration, fisheries productivity and recreation. However, floodplains are also among the most converted and threatened ecosystems.”(2)

This is short, concise and compelling writing in my opinion. These papers, along with many others, make the case for restoring floodplains so that rivers have lateral connectivity to these vital and important habitats.  Kiedrzyńska et. al. (2015) mentions several benefits of  functional floodplains including, but not limited to:

  • increased water retention
  • reduced flood pulses & reduced outflow velocity
  • improved water quality
  • groundwater recharge
  • side habitat for fish
  • fine grain sediment deposition
  • biodiversity maintenance

Functional floodplains should be considered part and parcel with an overall resilience strategy.  Floodplains, by definition, are supposed to be flooded.  Direct beneficiaries of restored floodplains include insurance agencies that sell flood policies to policy owners downstream of the  floodplain restoration project.  Other beneficiaries could include water suppliers due to increased baseflows and preservation of water quality.  Groundwater recharge and slow release back to the main channel, in some cases, could increase baseflows which in turn could provide some additional revenue to a hydropower project downstream of the restored floodplain.

  1. Kiedrzyńska, Edyta, Kiedrzyński, Marcin, Zalewski, Maciej. 2015. Sustainable floodplain management for flood prevention and water quality improvement.  Natural Hazards, 76, pp 955-977.
    https://link.springer.com/article/10.1007/s11069-014-1529-1
  2. Opperman, Jeffrey, Gerald Galloway, Joseph Fargione, Jeffrey Mount, Brian Richter, Siliva Secchi. 2009. Sustainable Floodplains Through Large-Scale Reconnection to Rivers. Science Vol 326, pp 1487-1488.
    http://science.sciencemag.org/content/326/5959/1487
  3. Opperman, Jeffrey. 2012. A Conceptual Model for Floodplains in the Sacramento-San Juaquin Delta. San Francisco Estuary & Watershed Science. Vol 10:3 pp 1-28
    https://escholarship.org/uc/item/2kj52593

 

Author’s note: I just wrapped up a course on Coursera titled “Innovative Finance: Hacking finance to change the world.” Aunnie Patton Power and Tsakane Ngoepe from the University of Cape Town taught the course. They taught me a great deal. I very much enjoyed the content that they developed as well as solicited. Over the 5-week course, I completed weekly assignments. The text below is my submission for the final assignment in Week 5. In addition to this course, I’ve also found Blue Forest Conservation’s work very inspiring. While there are some differences in the forest resilience bond and the flood resilience bond, they are minor. (I’ve heard that imitation is the sincerest form of flattery.) In short, I’m very grateful for the work of others in helping me shape some ideas about finding alternative financing mechanisms to fund floodplain restoration work.

 

ISSUE AREA AND THE OUTCOMES IDENTIFIED

Inland flooding is a massive problem around the world. In the US, the Federal Emergency Management Agency (FEMA) has developed the National Flood Insurance Program (NFIP). Several large storms have put this agency severely in debt to an amount that exceeds $30 billion. This bankrupt program would benefit greatly from private capital working to reduce flood risk. In addition, many rivers have been cut off from their floodplains due to development, river incision due to poor upstream land management and levees. In these cases, several ecosystem services are degraded. Runoff tends to be flashier which leads to worsened flood conditions downstream and summer low flows tend to be lower. Other degraded ecosystem services can also include lower water quality, higher water temperatures, and degraded fish habitat.

A flood resilience bond seeks a win-win-win outcome. The first win is for the investor that gains a market rate return on their investment. The second winner are the multi-stakeholders who finance the bond with monthly cashflow payments. These entities are insurance agencies, water suppliers and hydropower operators who have been able to price out the benefit of the floodplain restoration project through various modeling exercises. Finally, the ecosystem benefits because a restored and intact river floodplain has been created.

CHALLENGES IDENTIFIED THAT THIS DESIGN ADDRESSES

Determining the value of the floodplain restoration will be extremely challenging. Stakeholders will be presented with a brand-new idea. The value of the restoration will need to exceed the cost of the monthly cash flow payments. The forest resilience bond that Blue Forest Conservation has developed is an innovative financing tool that really is a ground-breaking idea. The flood resilience bond is designed in many ways to mimic this bond.

This idea will only work if a significantly large enough area of floodplain can be restored. In other words, if the project only connects an extra acre or two of floodplain, then very little measurable benefits for the Phase 2 cash flow providing stakeholders will accrue. The GIS screening tool really is a cherry-picking exercise where sizable chunks of land can be set aside to flood when a flood does occur.

Landowners that are in the floodplain likely won’t be thrilled about hearing that their land will be flooded more often. They might need to be compensated.

Any investor that might invest in the bond will be doing due diligence. The bond must have rock solid numbers, risk assessment and contracted cash flow that make the deal even worth the time of the investor taking the time to look at the deal.

Ultimately, this design starts to address the disastrous debt that FEMA has accrued in its NFIP by lowering flood risk at no cost to FEMA and it provides private capital to fund river restoration.

RESOURCES I’VE IDENTIFIED THAT THIS DESIGN USESS

As an individual with an idea, I need foundation money to back this initial idea. A partner such as the Rockefeller Foundation would be ideal as they have backed Blue Forest Conservation and they have excellent contacts with banks and modelling firms. Given their understanding of the challenges and structure of the forest resilience bond, they would have valuable insight.

Phase 1 funding would also go to catastrophe modeling firms such as AIR Worldwide or RMS. They could look at flood scenarios before and after the floodplain restoration project and determine the savings in claims payment for insurance companies that have policy holders downstream of the project.

Phase 1 funding would also go to either a firm such as ESRI, or it could go to a university geography department. The purpose would be to develop a screening tool to identify potential floodplain restoration sites that are large enough for benefits to be accrued.

Phase 1 funding would also go to a bank capable of structuring the bond. The bank would provide the legal and financial expertise to vet the idea and identify potential funders.

Phase 1 could also involve a land trust or environmental NGO that might be interested in obtaining or managing the restored floodplain land.

Phase 2 would be to develop a flood resilience bond. Outside investors would put real money into the bond with expectation of a return on their investment. The stakeholders that are benefiting from the restoration project would be providing contracted cash flow into the special purpose vehicle. These stakeholders would include insurance companies selling flood insurance policies, hydropower operators benefiting from higher summer baseflows and water suppliers also benefiting from higher summer baseflows.

THE OPPORTUNITIES AROUND BUSINESS MODEL INNOVATION, MULTI-STAKEHOLDER PARTNERSHIPS AND FINANCING STRUCTURES THAT I’VE IDENTIFIED

The project would be outcome based. Measurable improvements in flood claim reduction and increased baseflow must be demonstrated.

The flood resilience bond involves multi-stakeholders in Phase 1 and Phase 2.

Floodplain restoration has typically been publicly funded. Private financing of restoration is a new and exciting idea. Private capital could change FEMA policy through the value creation in floodplain restoration.

NEXT STEPS TO PILOT MY DESIGN

I’m an individual with an idea and a love of rivers. I could approach the Rockefeller Foundation or the Hewlett Foundation and pitch them the idea. I could have conversations with ESRI or geography departments to develop a screening tool. Foundation backing with money in hand will allow me to approach modeling firms to spend time on their analysis.

 




If you are a member of LinkedIn and you are interested in stream and river restoration, I recommend joining the ASCE River Restoration TC group.  Over the years, there have been some great discussions swirling around restoration. Doug Shields recently posted this question:

“How do you design a stream channel for a project that includes channel reconstruction/reconfiguration?” The responses so far have been quite good and I look forward to reading more. Jim MacBroom was my former boss and his opening sentence is perfect: “The most important step is to have a clear understanding of the channel’s physical processes and how they relate to the project’s goals and objectives.” Clear, articulate and difficult to argue otherwise.

 

I don’t use this blog too much for advocacy, but on March 1, 2016 the EPA and USGS released a draft report whereby public input is being solicited. Have a read and let your scientific expertise on ecology, hydrology and anthropomorphic alterations to flow be heard:

http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OW-2015-0335

REFORM stands for REstoring river FOR effective catchment Management. It’s a pretty cool effort and I’d recommend spending some time noodling around the site. www.reformrivers.eu

The publication ‘Final report on methods, models, tools to assess the hydromorphology of rivers’ can be viewed as a pdf here. It’s a little over 100 pages, but it’s worth the read as it focuses on monitoring standards and assessment procedures to characterize the consequences of river degradation and restoration.  The report contains the following chapters:

  1. Introduction
  2. Overall Methodological Framework
  3. Stage I: Catchment-wide delineation and spatial characterization of the fluvial system
  4. Stage II: Assessment of temporal changes and current conditions
  5. Stage III: Assessment of scenario-based future trends
  6. Stage IV: River management

The report is chock full of good information, useful graphics, and literature. I particularly enjoyed this summary table in chapter 6.

hydromorphological_restoration

ESRI has created it’s own social network for user’s of its software called GeoNet. Back in March, ESRI created a webinar titled “Community Maps for Hydrology” and can be viewed here. The entire video is 53 minutes. Viewers might want to fast forward to about the 22 minute mark where the speaker starts to talk about and demonstrate the watershed delineation and downstream trace tools.  If you have points on a stream in a watershed, it is a fairly straightforward affair to delineate a watershed in either ArcMap or ArcGIS Online.  The appeal to doing this workflow in ArcMap is that if the delineated watershed is in a geodatabase, it is easy to get an area straight from the attribute table.   The video also discusses maps that provide real-time stream gage data and how it is possible to get a hydrograph plotted just below the map.

ESRI has also updated Maps for Office to version 3.  The interface is a bit more modern. As for new functionality, I think one of the biggest additions is that users can have more than one map displayed for a given tab.  ESRI’s blog post on the update is available here.

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