Flood

The flood plain at Nine Mile Ranch along the Walla Walla River last month.

Last month was a real doozy with a massive flood in the Walla Walla and Umatilla river systems.

Once again, conditions were met that allowed for a high-velocity, high-volume runoff of rain and some snow melt waters.

I have been asked how will these shorelines and riparian buffers recover after these floods?

What will nature’s response be to the destruction of forest buffers, scouring and deposition of silts, soils and cobble bars?

Nature is amazingly elastic in its ability to recover over time. All the native species of plants that naturally grow along these highly flashy streams and rivers have outstanding abilities to recover with the passage of time.

The many uprooted trees and woody shrubs that were left littered all along the new river and creek channels will create new shaded pools.

Floods create opportunities for new beginnings within native plant communities or riparian buffers.

Keep in mind that all streams and rivers create and maintain flood plains, and these thin-soiled cobble flats allow for extra-capacity flows of water during spring runoff.

Flood plains are a very important part of the physical component of all the streams and rivers in Walla Walla County.

These flat areas along the local water courses are where the native plants that have adapted to sudden and catastrophic change grow — plants like willows, cottonwoods, river birch, alders and red Osier dogwoods, to name a few local species.

These natural plant buffers between the average water flow and the rest of the flood plain are known as the riparian buffer. This strip of trees and shrubs is a clear signal, a natural signal from nature that this area is an important flood plain.

Riparian buffers host a huge diversity of native wildlife with up to 82% of Washington’s wildlife living some part of their life cycle in a riparian buffer.

Floods are devastating to all that live in, and along, flashy systems — by flashy systems, I mean streams and rivers that are prone to flooding.

The aftermath of high-volume, high-velocity flood events changes the course and structures within stream beds, creating new pools, riffles and surfaces for whole new populations/generations of invertebrates, fish and amphibians.

Often fish will survive flooding by holing up inside channels or going up lesser-flooded streams.

Smaller fish, crayfish and some amphibians will burrow into the gravels of these streams and rivers to wait out a flood event.

Some fish go with the flow, and get flushed out into larger bodies of water like lakes or larger rivers only to work their way back up the home stream after the flood has subsided.

One of the other side ramifications of floods is the spread of invasive weeds such as Japanese knotweed.

In 2015, Brian Casey, Dave Maiden and I did a major knotweed extermination campaign with funding from the Snake River Salmon Recovery Funding Board.

We attained a 98% kill rate on knotweed along Mill Creek.

This plant goes dormant in September and re-emerges in mid-April. It only takes a one-ounce piece of viable root or stem and you will have a brand-new plant.

So, floods uproot these shoreline plants, and as these clumps of roots and shoots are tumbled in the raging flood waters, this plant breaks all apart thus spreading new plants all along the streamline.

All kinds of non-native plants will pop up wherever the flood waters washed over.

So, be prepared.

The basic morphology of a stream is so complicated, yet very understandable with a little effort.

Folks that like to build right up against streams and rivers in this basin are at great risk for loss of property.

Remember that you never ignore what a riparian buffer is warning you of.

Never clear a riparian buffer away; if you do it’s like turning your back on the ocean while standing on the beach.

Remember, life is good!