Tuesday, November 17, 2015

Flood effects

During flood event are pictures on left, 24 hours later on right.  Click on any picture for a bigger view

I left a bunch of crop residue on the fields as part of the seasonal management; some of the farmers in the area plow and cultivate, but I figured there was no rush to do it, and I didn't want to have loose dirt during the flood season.  I think it was the right call.  Had these fields been plowed I think I would have lost a lot of topsoil in this flood.  

But I did notice a grey mud, and I walked the field to where the flood water had entered, and found it on the upstream side.  So this material didn't come from my fields, but came from the river.  When the river floods it is either a light tan or slate grey, and I think it's related to what the river is eroding.  One thing that it is eroding is the site of the Oso landslide, about 10 miles upstream of me on the same river.  So there's hundreds of tons of sand and silt carried downstream, and during a flood, I get some of it.  

The material is deposited in lower areas in my fields - in the background of the picture above you can see a rough line - that's a tractor tire mark left when I planted the field a couple of years ago.  As the water flowed over it filled and leveled that tire track with this sand/silt combination, and effectively made my field smoother and taller.  I found deposits of the same sand and silt all over the field.  I'm going to guess that I received between 1/8 and 1/4" of this material across 40 acres that got covered.  

With a good soil cover I actually gain soil depth in a flood.  Who would have thought?  


EBrown said...

Very roughly 333,000 lbs per inch/acre of soil. 333,000 x 0.2 (roughly between 1/8 nd 1/4) = 66,600 lbs per acre deposited on your land. Semi trucks can haul almost that much and still be legal... Pretty sweet you got that much dirt added. Leaving residue was definitely a good decision.

I hope you did not lose much at the corner where the river cuts.

Anonymous said...

Yes, we have some bottoms that are prone to flash flooding and when they were in continuous corn the erosion was terrible, but since we have had them in grass it seems they collect soil.