Floods Follow Fires
Catastrophic forest fires impact more than the vegetation. Fires destroy habitat, pollute streams, foul the air, and inflict public health and safety problems. Sometimes, as was the case in the Biscuit Fire (2002), forest fires burn so intensely that the soil is stripped away [here].
After intense fires the soils, baked and/or blown away, cannot absorb water as they did previously. Rain does does not infiltrate the damaged soils due to collapse of soil structure, increased bulk density, removal of organic matter, reduction in soil porosity, clogged soil pores, and increased reaction to rainfall droplet kinetics. Soils can become “waterproof” through decreased soil wettability (hydrophobia), concretion, and increased water repellence. That can lead to increases in surface flow, increased soil particle transport, rilling, gullying, and increased erosion.
And floods. Fire-damaged soils across a watershed can cause increases in discharge rates, seasonal streamflows, and especially peak flows, including flash flooding.
Before the fire the soil acts like a giant sponge; after the fire the soil becomes water repellent. As a result, floods happen more frequently.
Take the case of the Chetco River. It drains 271 square miles, much of which was intensely burned in the Biscuit Fire. Six years later the Chetco River is still prone to flash flooding.
Today (right now) the Chetco River is surging, with a discharge rate of 48,400 cubic feet per second (data from the USGS National Water Information System: Real-Time Data for Oregon Streamflow [here]). That discharge amounts to an acre-foot per second and is more than ten times the median flow.
The little Chetco is running more than the Willamette River at Albany. The Chetco flow is roughly half that of the Columbia River at the Dalles Dam.
The North Umpqua River below the spillway at Slide Creek Dam near Toketee Falls is running at 2,210 cubic feet per second. The North Umpqua below Boulder Creek (incinerated in the Rattle Fire last summer) is running at 4,600 cfs. Boulder Creek alone is outputting 1,640 cfs.
Massive winter runoff also means that minimum summer flows will be truly minimal. There is little deep percolation of precipitation into aquifers and so little water storage. Next August the springs will dry up. The floods and the subsequent diminished flows wreak havoc on aquatic habitat, aquatic biota, spawning gravels, and fish populations.
Thus the ecological effects of intense fires linger for decades.
The Salmon River watershed in central Idaho was subjected to an 800,000 acre burn in 2007. Mudslides tore out roads and filled streams the following winter. This winter more of the same is expected.
Flash floods followed the Zaca Fire (2007), which burned 240,000 acres over a two month period, cost more than $120 million in direct fire suppression expenses, and was the most expensive fire in California history.
That is, until one year later when the Indians/Basin Complex Fires burned 244,000 acres and cost $124 million.
Flash floods are expected and may have occurred in the last few weeks (we haven’t heard — no flood info has been posted on the Los Padres NF site). The trail system has been largely destroyed and the flash floods will finish that job.
Chances are the Los Padres NF will not be forthcoming with that information, either. They are the worst managed, most destruction-prone national forest in the System, and that’s a dubious honor given the horrific management of so many other national forests.
Forest fires are treated by the Media as a one-time, short-term events. When the firefighters leave, so do the reporters. Out of sight, out of mind is the rule. The attention span of the Media is tragically abbreviated. They cannot remember what happened an hour ago, let alone a month or a year ago.
But watersheds have long-term memories. Soil is not repaired over night; it takes decades and sometimes even centuries. Until the water absorption capacity of watersheds is restored, repetitious floods continue.
by YPmule
You are right about how the media likes to ignore a place after the fire is out. We have been trying to set the record straight about the lies told by the media during the 2007 fires. They are not interested. (Unless its a story of more destruction from floods they can sensationalize.) We will have to wait and see what happens when the salmon return, will they find a place that is not full of ash and silt to spawn?
The Lebanon schools elementary school math says that at the flow rate, it only takes two days to drain a foot of water off the entirety of the Chetco watershed.
12″ divided by 48 hours… that’s a quarter inch of water from the entire watershed every hour.
But my thoughts are with the whole of the PNW watersheds and salmon. I added up the high water flows of the Oregon coast major streams: Chetco, Rogue, Coquille, Umpqua, Siuslaw, Alsea, Siletz, Nestucca, Wilson, and Nehalem, and those streams cumulatively were running more than the whole of the Columbia-Snake River drainage which includes Eastern Oregon, Washington, all of Idaho, the western (wet) quarter of Montana, a piece of Nevada, and a goodly part of the southern quarter of British Columbia. Which all begs the question of why these coastal streams, most without significant dams, do not produce more salmon?
If the Feds are addressing culverts, bridges, road locations, sediment inputs, as they claim, and tens of millions a year are going into stream rehab projects, road demobilization, vestigial logging levels on public lands, there should be a whole lot more salmon than current and available habitat is producing. Which then begs the question of what is happening in the ocean? If crabs are way down, and shrimp hard to find, bottom fish off limits, and few salmon predicted to return this coming year, is the problem terrestrial riverine habitat or is the problem some sort of ocean anomaly that is cyclical and will again produce robust aquatic life?
A recent net survey off Oregon and Washington reports record numbers of young salmon in the ocean. And bait fish were back this last summer. So it appears the upwelling along the continental shelf is producing the nutrient and sunlight into cool waters along with elevated oxygen levels, and things are alright in the ocean. Which begs the question will the regulators and managers manage to protect fish stocks, or are they going to once again manage for economic gain for government (income and landing taxes, license and tag fees, increased BreauxWallop funds from fishing gear, the list is long) and economic gain for fishers because without them, the government aspect is meaningless and not funded? I sometimes wonder who in government is going to issue the permit to kill the last salmon. No matter the status of the fish, they always find a way to let people kill them while regulating habitat use and users. Mind boggling.
And, the media is reporting that the spokespersons for the commercial fishers and the charter boats is again making their case for another year on public dole to preserve their ability to kill the last fish once they are allowed. We shut down logging on the commons, and now the accumulated growth is being managed to burn by intent and management direction. You can’t use it, and we will lose it, but at least YOU, you frigging loggers and lumbermen, YOU can’t use it. Not unlike the kid in kindergarten who couldn’t play with your Legos, so he stomped them to their elemental pieces. Our envrio buddies. But on the ocean commons, “sport” fish killing is allowed. Not fishing for food for the market, but sport fishing to kill for the pure thrill of it. From the same people who want you not to be able to own a gun. Meanwhile, the very watersheds that are being protected for salmon habitat are being burned in the WFU and AMR management direction from the Auditor General, head bean counter and resource policy expert. Nothing makes sense. But I guess it is not supposed to.