The Army Corps website is shockingly bad. I'll get you a link for the Draft Guidance tomorrow.

In April, the federal Army Crps of Engineers issued new Draft Guidance for Treatment of Vgetation within Local Flood-Damage-Reduction Systems. I’m sure you remember the uproar. The new Draft Guidance says that all l*vees in the country must remove all vgetation besides grass. In California, this turns out to be a spectacularly bad idea. In California¹, rivers are confined to fairly narrow channels (compared to their flood flows), so the river usually comes up to the toe or banks of the l*vees. There’s farmland or city on the other side of the l*vee. Removing trees and shrubs from l*vees would remove almost all lowland riparian habitat in the state².

Why does the Army Corps of Engineers want all vgetation removed from all l*vees in the country? For three reasons. First, they say that if there are shrubs and thickets on the l*vee banks, inspectors can’t see holes (mostly burrows) in the l*vee. Second, they worry that vgetation being ripped out of the ground in high flows will rip chunks of l*vee away and weaken l*vee integrity. The third concern is that vgetation on your l*vee bank takes up flood capacity³.

All of those sound very plausible, and may well be true on the far side of the Sierras. Maybe those river systems are different. But here in California, they aren’t incontrovertibly true, or even straightforward. Here in California, the native vgetation evolved for annual floods. UC Davis researchers just released a study showing that in large floods, willows lie flat. They aren’t taking room or causing turbulence (and may be reducing it, by acting as straightening vanes). They protect the ground from erosion. They do not rip out of the l*vee under high flows, leaving holes in the l*vee for the floodwaters to gouge out. Removing all willows and other native vgetation from California l*vees, in addition to the environmental costs of losing nearly all our lowland riparian habitat, would counter the goals the Army Corps is trying to further⁴.

So the Army Crps of Engineers has issued the national Draft Guidance and they are a bad plan for California. The Dprtmnt of Wter Rsourcs has opposed them; local l*vee districts don’t know where they would get the money to take out all l*vee vgetation; state and local politicians are lobbying the Army Corps to change them or make an exception for us. Opposition here is pretty stiff; everyone wants the Draft Guidance to be overturned, or at least not finalized into regulations. Since no one here is rushing out to mow their l*vees and rip out trees, what can the Army Corps do to enforce their new guidelines? Well, what the Army Corps can do is refuse to certify your l*vee.

The Army Corps is the agency that sets standards to certify l*vees to draw 100 Year Floodplain Maps. Those maps are what insurers use to set the price of flood insurance. The Army Corps has two settings in its fancy-dancy flood models to make maps. In the fancy flood model, you can say that there is a certified l*vee in place or you can say that there is no certified l*vee. Then the model draws the floodplain boundary that determines whether you pay $600 per year for flood insurance for your house (inside the 100 Year Floodplain) or $150 per year for flood insurance for your house (outside the 100 Year Floodplain). There is no model setting for “perfectly good l*vee that would have passed under the old guidelines but now fails under the new guidelines and in any case is the exact same physical structure in the exact same place as last time when it was certified.” If Californians do not remove all vgetation from our l*vees, the Army Corp will say those are not certified l*vees. Their model will now ignore most of the l*vees in California, meaning that it will draw 100 Year Floodplains extending over most of the San Joaquin and Central Valleys. That will mean a huge increase in flood insurance costs for all the interior cities and farms, although the physical conditions will not have changed.

What is likely to actually happen? Well, it doesn’t look like we will actually remove the l*vee vgetation. I wish that were because of our dedication to the environment and not because the cost is prohibitive, but you take your victories where you find them. It would also require an ESA permit that could never be issued because you can’t remove all riparian habitat without damaging endangered species. If the Army Corps looked serious about finalizing the Draft Guidance, California’s national level politicians would oppose them from Washington. If the Army Corps wants a way to adjust the Draft Guidelines for local conditions, studies like the one at UC Davis gives them a way to say they are taking new scientific findings into consideration. If they don’t want to change the Draft Guidelines, but face too much political opposition to make them regulations, they can postpone for another year and a half and then let them fade away in the confusion of a new administration. That’s my prediction.





UPDATE: Sac Bee columnist Dan Walters' take. Much like mine, but mine was first.








¹This is not the case for big Eastern rivers, where the l*vees are set back quite a ways from normal river flow. The part between normal river flow and the toe of the l*vee (if there is one) is called a terrace. Hmmm. I would call regions 3 and 5 in this diagram terraces. I also note that the upside-down triangle that this diagram uses to mark the water surface is not the same one I was taught, although I understood what it meant. Margie, Tracy and I discovered one day that the three of us, water engineers all, had been taught three different versions of that triangle to mark the water surface. You can count on nothing in this world.

At any rate, big Eastern rivers have considerable terrace space between the low water channel and the slope of the l*vee. You could clear vgetation off your l*vees and still maintain riparian habitat in the East. Not so in California.

² It will also be incredibly expensive, in the hundreds of millions of dollars. We’re talking about hundreds of miles of l*vees. There are lots of other good reasons not to denude the l*vees, but the part that will end up winning big politicians over to the side of the angels is that doing the wrong thing in this case will be very, very expensive.

³I misunderstood the part about flood capacity at first. First time through, I thought they meant that trees and bushes inside the l*vees would take up room, that it is the volume displaced by the actual trees that diminishes capacity. Nope. When vgetation is a problem, it isn’t the space it takes up that eats up your flood capacity. Turns out, the turbulence it causes (making the water all swirly and reducing how fast your flood flows can move through the system) is most of the capacity loss. Who knew?

⁴The other Army Corps reason, that vgetation hinders a visual inspection, still holds. Although, it isn’t clear that thickets obscure a burrow more than a foot of grass would. And usually reliable sources in the hallways here say that visual inspections only catch the stuff above the waterline (naturally) and that don’t catch most structural failings, like underseep. The change in ability to do visual inspections probably doesn’t outweigh the damage caused by the loss of the vgetation.