And Here We Flood Again

Its been two days now that schools have been closed in Whatcom County, not for snow, but for rain and flooding. This unusual event coincides with record flooding throughout Western Washington, just a year after record flooding closed I5 for three days and Lewis County businesses experienced what they then called an unprecedented 500 year flood. I guess not.

There are many strange things about flood risk notation, and this idea that a 500 year flood often trips people up. They often believe a flood of that size will happen only once in 500 years. On a probabilistic level, this is inaccurate. A 500 year flood simply has a .2% probability of happening each year. A more useful analogy might be to tell people they are rolling a 500 sided die every year and hoping that it doesn’t come up with a 1. Next year they’ll be forced to roll again.

But, this focus on misunderstandings of probability often hides an even larger societal misunderstanding . Flood risk changes when we change the environment in which it occurs. If a flood map tells you that you are not in the flood plain, better check the date of the map. Most maps are utterly out of date and many vastly underestimate present flood risk. There are several reasons this happens. Urban development, especially development with a lot of parking lots and buildings that don’t let water seep into the ground, will cause rainwater to move quickly into rivers rather than seep into the ground and slowly release. Developers might complain that they are required to create runoff catchment wetlands when they do build. They do, but these requirements may very well be based upon outdated data on flood risk. Thus, each new development never fully compensates for its runoff, a small problem for each site but a mammoth problem when compounded downstream.

Deforesting can have the same effect, with the added potential for house-crushing and river-clogging mudslides. Timber harvesting is certainly an important industry in our neck of the woods. Not only is commercial logging an important source of jobs for many rural and small towns, logging on state Department of Natural Resource land is the major source of funding for K-12 education. Yet, commercial logging, like other industries, suffers from a problem of cost externalization. When massive mudslides occurred during last year’s storm, Weyerhaeuser complained that it wasn’t it’s logging practices, but the fact that it was an unprecedented, out of the blue, 500 year storm that caused it. While it is doubtful the slides would have occurred uncut land, that isn’t the only fallacy. When the slide did occur, the costs of repairing roads, treatment plants, and bridges went to the county and often was passed on to the nation’s tax payers through state and federal recovery grants. Thus, what should have been paid by Weyerhaeuser, 500 year probability or not, was paid by someone else.

Finally, there is local government. Various folks within local governments set regulations for zoning, deciding what will be built and where. Here is the real crux of the problem. Local government also gets an increase in revenue in the form of property, sales, and business income taxes. Suppress the updating of flood plain maps, and you get a short term profit and often, a steady supply of happy voters. You might think these local governments will have to pay when the next big flood comes, but often that can be avoided. Certainly, they must comply with federal regulations on flood plain management to be part of the National Flood Insurance program, but that plan has significant leeway and little monitoring. Like the commercial logging, disaster-stricken local governments can often push the recovery costs off to individual homeowners through the FEMA homeowner’s assistance program, and off to state and federal agencies by receiving disaster recovery and community development grants and loans. Certainly, some communities are so regularly devastated, and are so few resources, that disasters simply knock them down before they can given stand up again. But others have found loopholes and can profit by continuing to use old food maps and failing to aggressively control flood plain development.

What is it going to take to really change this system and make it unprofitable to profit from bad land use management?


Here’s a good in-depth article on last year’s landslides in Lewis County. http://seattletimes.nwsource.com/html/localnews/2008048848_logging13m.html

An interesting article on the failure of best management practices in development catchment basins can be found here: Hur, J. et al (2008) Does current management of storm water runoff adequately protect water resources in developing catchments? Journal of Soil and Water Conservation, 63 (2) pp. 77-90.