Lowdown on the high water…and room for rivers explained

So high the water was risin’ our men sinkin’ down
Man, the water was risin’ at places all around,
boy, they’s all around
It was fifty men and children come to sink and drown

—High Water Everywhere (Part 2), Charlie Patton

A great many blues musicians sang about high water and an old professor of mine once told me there are three things you can do with it:

1- store it    2-convey it to the sea     3- let it flood

Olifants River in Flood. Source: Flickr. Author “Albrigi”

Simple enough.  For years, we’ve mostly managed high waters through options 1 and 2, ignoring 3, with concrete and earthen dams and levees to keep the water away. Championed by engineers like Humphreys on the Mississippi in the mid 1850s, advanced engineering and technologies have “tamed the river,” reducing the frequency of smaller floods (as well as our memories of them) and allowed for more economically productive uses of floodplains. As a result, communities have thrived for centuries on low-lands thanks to deepened channels which allowed for navigation and trade, flat fertile soil for agriculture, residential and commercial development, and beautiful waterways as a scenic place to recreate.

FISK Map 1944, Historical Courses of the Mississippi River.

Over time, this way of management restricted the ability of a river to maintain it’s preference–option 3 above: to spread out on to a floodplain every once in a while when waters are greater than the channel capacity.

The Delta Blues remind us that such is the desired course of rivers where floodwaters use the floodplain– irrespective of  human settlement on it.  Consider  also the numerous historical courses of the Mississippi River.

Mark Twain also understood this well.

“The Mississippi River will always have its own way; no engineering skill can persuade it to do otherwise…”

As did William Hammond Hall,

“It should be fully understood then, that floods will occasionally come which must be allowed to spread.”

Giving room in the past

Humans know that we have repurposed floodplains and placed valuable assets in a rivers’ path.  We are no stranger to the fact that rivers need room in order to protect our cities, farms, industry, and way of life. We remember the Great Floods of 1927 and the multiple breaches on the Missouri and Mississippi systems during 2011.

1927 Mississippi Flood, Hamburg Louisiana. Source: American Environmental Photographs Collection, Department of Special Collections, University of Chicago Library/File

As early as 1918 in the Sacramento Valley,  and in 1928 on the Mississippi River (after 700,000 were displaced), Americans sought to make space for the river. Evacuating of 250,000 Netherlanders in the Rhine basin in 1995 inspired the Dutch to create a national program to let water back into a landscape they had spent centuries keeping dry. Most recently in the San Joaquin Valley after 1997, farmers, engineers, hydrologists, and politicians acknowledged that traditional storage and conveyance alternatives were not alone enough and started discussing a plan. (See: Yolo Bypass, Mississippi River & Trib, Room for the River, and Lower San Joaquin Bypass referenced in 1998 Preface to Kelley’s Battling the Inland Sea.)

Giving room today

Making room for rivers was just the subject of a recent Scientific American article, as well as one in the Economist. Expanding floodways made a grand entrance to the first draft of California’s Central Valley Flood Protection Plan (table 3-2) as a viable way to meet multiple objective, and  to a lesser extent, “Room for Rivers” is also considered in the 5th draft of the Delta Plan. Lastly, in 2008, California Legislation from SB 5 (California Water Code Sec 9163 (c) ) required the state consider the feasibility of a bypass on the Lower San Joaquin.

While the concept and buzz word of “Room for Rivers” might be understood by some, what follows is a brief explanation for those who aren’t quite so hydraulically inclined (great blog by the way), and some detail for those who want to know the practicalities.

  1. What does “room for rivers” mean?
  2. How do you give a river room? (and where is it appropriate to do so?)
  3. What are the benefits? 
  4. Example Projects 
  5. Challenges?
  6. Areas of further research

The explanations and project examples below demonstrate that giving room to rivers actually incorporates all three options above–storing high water, conveying high water, and allowing high water to overflow the banks from time to time.

Presented factually, this post does not advocate for or argue against certain projects– the attempt is to provide information and opportunity for a discussion. There are some additional resources provided at the bottom and please comment if you have questions.

  Continue reading

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Public Involvement in a Better Plan: Letter to the Central Valley Flood Protection Board

For better or worse, in the United States and in Calfornia especially, we have a strong element of public involvement in most planning processes.  Better because it forces transparency, allows voices to be heard, and as Americans we really can have some influence in shaping our future.  Worse because… all of those voices have different perspectives and priorities (often conflicting)– and as a result, the process can take ages.

No where has this been more prevalent over the last 30 years than in California, amidst the struggle to balance competing needs with constrained budgets in the Central Valley, the Delta, and with respect to any topic related to water.  Todays’ post briefly discusses the most recent plan in the headlines and how one group has united behind common goals and interests to improve a policy that will eventually affect multiple parties including all California taxpayers.

The Central Valley Flood Protection Plan.

California has embarked upon large scale system-wide flood risk reduction projects and policies with California Department of Water Resources‘s recently released Draft of the Central Valley Flood Protection Plan. The Central Valley Flood Protection Board must adopt (or reject) the Central Valley Flood Protection Plan (CVFPP) by June of this year  and the public has again an opportunity to play a large role. The Flood Protection Board will both receive recommendations on the plan and will make suggestions to the Department of Water Resources to amend the plan.


The original flood management system in the Central Valley was built over a hundred years ago, much of it created property by property, when at that time it protected mostly agriculture. (For a good history, read Battling the Inland Sea, Kelley 1998). Over the years however, much of the infrastructure has been degraded, levees have failed, and consequences of failure have changed. Today, the Central Valley’s flood management system protects dense urban areas including those of political importance like the capitol city of Sacramento–also critical infrastructure, unique ecosystems, and a valuable fresh water supply.  The state of California recognized the need to improve the system in 2008 and passed legislation (SB 5) to create a system-wide plan (the CVFPP) to address deficiencies in the Central Valley Flood Management system where failure could mean billions in damages for all Californian taxpayers.

To learn more about the plan and process, click here.

The overarching goal of the CVFPP is to “Improve Flood Risk Management.”

Supporting goals are to improve operations and maintenance, promote ecosystem function, improve institutional support, promote multi-benefit projects (ecosystem, water supply, etc).  The billion (5 billion in fact) dollar question lies in how?

How to manage competing interests?

Public Safety and Ecosystem Function (and agriculture and water supply) are not necessarily in conflict, despite that it has appeared that way in the past. A robust flood management approach can reduce flood risk and enhance ecosystems by incorporating both technical and non-technical measures.  Examples of successful projects can be seen in California where the Yolo Bypass has protected Sacramento from flooding since 1933, and in the Netherlands where the burgeoning Ruimte voor de Rivier programme promises to reduce water surface elevations and improve “spatial quality” on a system wide basis.  Other areas in Europe are following suit (Adaptive Land use for Flood Alleviation project).

Weir gates at Hondsbroeksche Pleij flood bypass, January 2012: the first completed Room or River project in the NL . Image credit: Almar Joling

The Department of Water Resources has made a good start in this direction as the first draft of the Plan is not limited to a levees-only approach, and it tries to appease the sum rather than the parts. But I suspect that as public comments begin to arrive to the Flood Board, we will likely see requests  to protect individual interests–requests that miss out on the sense of collective good– something that is really needed if California wants to reduce risk on a system-wide basis as opposed to piecemeal.

I came across this  letter (below)  and I’ve pasted it as an example of how 16 conservation local and national conservation  groups collaborated to provide the Flood Protection Board with clear, implementable recommendations for the Plan to reduce risk and achieve the plan’s stated goals. For full text of the letter, click here:  Conservation Community Letter on Flood Plan 2-15-12  The Board will have a public hearing on February 24 in Sacramento.

The conservation groups identify six areas for improving the plan that integrate instead of separate multiple interests:

  1. Maximize the use of cost-effective and multi-benefit flood management tools such as flood bypasses, setback levees, and transitory storage on floodplains.Fremont Weir (image credit: Katie Jagt)
  2. Specify an overarching strategy with measurable objectives for incorporating ecosystem function.
  3. Clearly state how the flood plan will be integrated with related state and federal restoration efforts within the state flood control planning area.
  1. Develop a more explicit climate change adaptation strategy to minimize projected impacts on flood risk, ecosystems, and water supply reliability.
  2. Explicitly integrate and balance flood management and water supply objectives.
  3. Provide specific guidance to enable local planning.

Signed by: American RiversCalifornia Trout,  National Wildlife Federation California Waterfowl Association,  River Partners,  Environmental Defense FundNatural Resources Defense Council,  Sacramento River Preservation Trust , TheNatureConservancy FriendsoftheRiver ,  PlanningandConservationLeague,  The Bay Institute,  Trout Unlimited,  Tuolumne River Trust PRBO ConservationScience DefendersofWildlife 

What do you think?

(See below for no-explanation-needed-image of “Why floodplains are good for fish”). This  is a fun photo and one that tends to resurface time and again)

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On communicating that other kind of risk…

On the Souris River in 2011, higher mountain snowpack than anticipated combined with increased precipitation and full reservoirs meant that dam operators were forced to release more water than normal downstream. Communities below the dam were not prepared for the extra water and some 4000 houses in Minot, North Dakota flooded to the second floor.  Outside of the regulatory “floodplain”, most of these houses were not elevated, were caught unawares and most were without flood insurance. They will likely be rebuilding their houses and lives for quite sometime. This situation is unfortunately all too common given that a large portion of flood  damages actually come from events greater than a “100-year flood”, or outside of the regulatory floodplain (Burby 2001).

There is an expression known to many experts that describes this type of risk—

Residual Risk.” 

The Inquiry.

Last week, a journalist from a Midwestern newspaper (in the United States) interviewed me to discuss the issue of floods. Beginning with the National Flood Insurance Program, we quickly moved on to the publics’ awareness of flood risk. It surfaced that the perception of safety in the United States and around the world, which can come from dams, levees, and other flood “control” structures, could lure residents (and local governments) into settling flood-prone land with a false sense of security—when in reality, those lands are subject to significant risk from storms larger than the dam or levee was designed to handle. As a result, losses grow.

Had the reporter interviewed William Hammond Hall (1880) instead of me, California’s first state engineer might have rambled a bit less and instead summed it up concisely:

(Image courtesy DWR)

“There are two types of levees, those that have been overtopped by floodwaters, and those that were going to be…”

(As paraphrased in Kelley 1998).

The Issue:

The main topic of discussion for this interview was flood risk perception and Residual Risk. The journalist expressed concern that the general public is not familiar with this term, when perhaps they should be. That inspired me to spend a bit of time thinking about residual risk and how we can communicate it to those who need to know.

Who does need to know actually?


The first step involves simplifying a message which I attempt below.  The second step would be more difficult, however, and involves finding ways to get the message out and motivating behavior both of decision/policy makers and individuals. I welcome your own input, comments, and suggestions on the topic.

Let’s start with Risk. There are a number of definitions of risk, but one of the most common in this field (and one that I will use) is the following:

Flood RiskProbability of a flood occurring X  the Consequences when that flood occurs.

Residual Flood Risk then means the risk that remains (the residual) after some sort of intervention occurred to reduce the risk.  Experts understand residual flood risk to be a function of the probability that lands behind a levee or dam will be inundated from a flood that is larger than the levee or dam was designed to handle. Therefore…

Residual Flood RiskProbability of flood after levee construction X Consequences after levee construction

You could substitute any intervention: Residual risk could also be the probability of flooding after elevating a house and the consequences of flooding after elevating a house; or, the probability after diverting water in a bypass and the consequences after diverting floodwaters in a bypass.

Flood Control Structures, Residual Risk, and the Public

I drew a schematic below to illustrate this concept. In the United States where levees built to protect urban developments must be certified to safely pass a “100-year flood” (light blue), or a flood that has a 1% chance in occurring in any given year, residual probability from larger floods (dark blue) is 26% over 30 years (the average length of a mortgage).

In parts of California where urban areas are required to have “200 year flood” protection, the residual probability from larger floods is 14% over 30 years, and 22% over 50 years. S

Residual risk behind FEMA-Certified Levees (100-year levees) would be quantified most likely as 26% multiplied by the value (in $$) of the damages (and sometimes also of the replacement costs) to all structures and human life behind that levee. The discussion of how much a human life is worth is commonly debated in many countries, and I will not address it here.

So what to do with this information
It’s a lot to expect non-experts to understand complex terminology, especially when the messages from the media might communicate otherwise, for example, that a 100-year flood only happens once in 100 years. The general public, educated decision makers, local governments likely don’t have time to understand probabilities and statistics when they have many other concerns in daily life. Perhaps the most important aspect of it to communicate is:

There is still a risk. Period.

In my opinion, what most of the public thinks about when they hear “Risk” is actually only the probability. While this may seem like semantics, it is important because considering only probability likely biases (and limits) the types of measures people can take reduce their own risk. People tend to think that a levee removes risk because it reduces probability, and they forget that if the levee fails, the consequences part of the equation has not changed.

A survey in north Stockton, California reported some residents firmly believed that their property would not flood if a levee near their house failed.

Some argue that levees increase risk because they allow land behind levees to be developed densely which significantly increases the consequences (see schematic below). This is also because while rivers rise slowly, levees tend to fail catastrophically with minimal warning time, and deep, fast moving water, which does not allow for safe evacuation.

Do levees increase risk? (Graphic Credit: J. Ludy, 2009 “Before the Flood”)


What would you communicate?   Trying not to be alarmist, here is what I would say:

Risk involves both Probability that you could flood and Consequences to you when a flood occurs.  You are never at Zero Risk.  Sometimes larger floods come and they can overwhelm the flood defense measures that are in place like dams or levees.  Land “protected” by 100-year levees and dams can still be flooded by a 200-year flood, a 500-year flood, and even a 101-year flood. If consequences haven’t been reduced, risk is still high and damages could be devastating.

1-    Probability: If you are living behind a levee or a dam, there is still a 26% chance over 30 years that you could flood.  Greater than 1 in 4.

2-    Consequences: If you flood, your damages are going to be the same or maybe even worse because you won’t be expecting it, you wont have time to move your valuables to higher ground, or worse when levees fail, water often comes quickly and destructively. You may not be able to safely evacuate which is dangerous if you are on low lying ground.

What you can do to reduce your Residual Risk

A sobering, simple, and real message should be presented and perhaps Gilbert White is the man to introduce it:

 “Floods are acts of God, but flood losses are large acts of Man”

Probability: You are not in charge of managing the probability of a flood. You cannot control the precipitation, wind, or the path of the watercourse. Likely you yourself can not manipulate your flood management system by helping store more water upstream or building a higher levee.

Consequences:  You can reduce your consequences however (damages) for when a flood occurs. (This list is not exhaustive).

Before you buy a house, find out if it is protected by a levee or a dam.  If yes, try to live in an area that is on higher ground and not protected by a levee.

If you already live in a house protected by a levee:Elevate your house.  This means that when a levee fails or is overtopped, higher water levels won’t reach your house and you will suffer less damage.

-Raise your valuables to a second floor.

-Keep all living quarters on the second floor.

-Be prepared: Have an evacuation plan (with preferably a vertical evacuation route-keep a hatchet in the roof). Emergency responders  told me that during the flood they could tell the difference between those people who were prepared and those that weren’t.  Those who were prepared had a greater chance at staying alive.

-Purchase a boat.

-Purchase a flood insurance policy. Yes, even if you are not officially in a “special flood hazard area.”  When the property floods, this will help you deal with the economic loss of both your building and contents.

A few other organizations have attempted to address this issue before with suggested behavior for those who live behind levees:

So you live behind a levee   American Society of Civil Engineers

Living with Levees: know your risk, California Department of Water Resources

Living behind levee systems: Information for Property Owners, FEMA

The Outlook

That people don’t understand the concept of residual risk is not limited to the United States. Further, it is not guaranteed that if people understood residual risk that they would necessarily change their behavior. However, exposing people to involuntary risk means that they do not have the option to take actions to reduce it.

As a species, we have always settled on floodplains, and for better or worse, we probably always will.  Communities in the Mississippi and Missouri Basins experienced significant flooding last year, and they also had major floods in 2010 (Nashville), 2008 (Iowa), 1997 (North Dakota), and of course, the Great Floods of 1993. While there are surely others on this list that I missed, and there are likely that will be added as the land is flat, our memories are short, and rivers will continue to do what rivers were meant to do. The important question is whether the losses from floods will continue to grow, or whether we can intervene to reduce them. Just as great rivers cultivated rich floodplain soil, so hopefully will they cultivate a culture of risk, adaptation, and appreciation for the power of water in the region.

Your thoughts?

(apologies for the formatting, having wordpress struggles this day)


Burby RJ (2001) Flood insurance and floodplain management: The US experience. Global Environ Change Part B Environ Hazards 3(3–4):111–122

Kelley R (1998) Battling the Inland sea. University of California Press, Berkeley

Ludy J and GM Kondolf (2012). Flood Risk Perception on Lands Protected by 100-year Levees. Natural Hazards Volume 61, Number 2, 829-842, DOI: 10.1007/s11069-011-0072-6


Ludy J (2009) Before the Flood: Misperception of Flood Risk in the Sacramento-San Joaquin Delta

Posted in Flood Risk Management, Flood Risk Perception, Uncategorized | Tagged , , | 9 Comments