The rich soils in Oregon’s Willamette Valley are a gift from the Missoula Floods at the end of the last Ice Age. Between 15,000 and 13,000 years ago as glacial ice sheets melted and retreated, the valley was flooded about 40 times–essentially becoming a temporary lake hundreds of feet deep, over and over again.
For 13,000 years now, rivers have sculpted this once flat, lake-bottom landscape into well-defined channels that don’t meander frequently like they would in a delta zone. But over the past several thousand years Willamette Valley rivers have jumped out of their main channels hundreds of times and occasionally even found new routes, leaving behind clear signs of their movements in features such as oxbow lakes.
When looking over farm fields in the area, the best soils are adjacent to rivers that jump their banks. River-flooded fields tend to have undulations across them, which signifies the deposition of silt, and possibly sand. By contrast, clay is a sticky substance that doesn’t settle out fast during a flood, but will come to rest in calm waters at the bottom of a lake. A good loam is a balance of silt, sand and clay, conditions typically mediated by active river deposition. This means that if we are going to farm on the best soils, we should expect the sporadic flood.
Farmland LP manages three properties in Willamette Valley south of Corvallis. This particular area, and our farmland, was recently subjected to the highest flood waters in about 100 years. The river that set a record wasn’t the Willamette, but a tributary called Marys River.
What Was Learned and Reinforced
Seeing what happens at high water is very instructive. We now know where the river may jump the bank with force and can design mitigation strategies accordingly.
For example, our new fence is made with flexible posts that can take the weight of a tree or the impact of rushing water and debris and stand back up after the force is removed–something metal T-posts don’t do.
Woody vegetation in the riparian zone and along edge spaces has economic and ecological values, including acting to absorb, deflect, and spread the force of flowing water. Our riparian restoration project at Fern Rd Farm (funded by a state OWEB grant through the Marys River Watershed Council) was too young to protect the farmland this year, but will provide a stronger buffer in the years ahead. A hedge row north of the gravel drive at Fern Rd Farm may have protected it from erosion, for example. A thick riparian forest at Wattenpaugh Farm may prevent an overflow channel from down cutting and forming a gully in the farm field.
Our pasture-sown land greatly reduces the risk of erosion. Organic farmers, even if they are not planting pasture, tend to do a good job getting a cover crop on fields to keep soil from washing away and to build organic matter and nitrogen stock. This is both a discipline and a necessity since the soil IS the fertility and synthetic inputs can’t be used to make-up for poor land cover and soil loss. Whereas our land is becoming more resilient over time, the downsides to the shortcuts taken by chemical-based farming are revealed most clearly in times of extremes, such as floods or droughts.
Record Snow and Rain
A very unusual sequence of events led to the flooding. Snow began falling on the valley floor Jan. 15th. It stuck around and accumulated through Jan. 17th. And although snow depth was shallow in the valley proper, the surrounding foothills and colder, outlying valleys had several inches of heavy, wet snow on the ground.
Then came Jan. 18th and the beginning of record rainfall. The rain gauge at the Hyslop Weather Station just north of Corvallis recorded 2.55 inches on Jan. 19th and a record-breaking 4.05 inches for Jan. 20th. Nearly 3 more inches came down over the following seven days, which kept the water near or above flood stage for almost a week.
The water level gauge for the Marys River is situated near Bellfountain Rd, which is between two of our properties. Observation and forecast hydrographs are updated regularly and this one shows the river near its peak on Jan. 19th.
I visited Fern Rd Farm prior to the flooding and while snow was on the ground. I wanted to check on the status of trees planted this fall in the riparian forest, and remove any equipment that may be carried away with high water. Below is an image showing the river level and snow cover on Jan. 17th.
And this was taken about 24 hours later. The river is at flood stage and all the snow is gone. River levels crested over a foot higher than what is shown here.
It is helpful to see where the rivers are in relation to the farms and how the landscape copes with so much water.
Below is a map of the three Farmland LP properties in the area, which are outlined in dark blue. Fern Road Farm is in the northwest of this image, Wattenpaugh Farm is northeast, and A2R Farm in the south. The Marys River creates the northern border of Fern Road Farm, and a southern and eastern border of Wattenpaugh Farm. Muddy Creek, which joins the Marys River at the southeast corner of Wattenpaugh Farm, cuts through the A2R property. Both rivers flow, in general, towards the north and east, with the Marys River entering the Willamette in downtown Corvallis.
Normal river channels are revealed in dark green, which is tree cover. With light blue lines I have traced the approximate additional paths the rivers took when the flow rates exceeded the main channel capacity. For scale, the N-S blue line representing the Muddy Creek overflow route runs just over one mile through the A2R Farm.
Back to Ground Level
Here are some images of what these overflow channels looked like.
Muddy Creek spills across Airport Road the morning of Jan. 20th. Buildings of A2R Farm are visible about a mile in the distance to the left. Any tree or hedgerow plantings along Airport Road should leave ample room for water passage at this location.
Marys River crossed Fern Rd Farm in a braided swale complex (as opposed to a single, wide channel for Muddy Creek at A2R) and took paths that went different directions, including southward to Evergreen Creek. The above image shows where a large ditch adjacent to a gravel road is insufficient for the record flows. The top layer of gravel washed off and will need to be re-applied. In the background it is clear that the well pump and irrigation pipe are on high ground.
The south field at Fern Rd Farm has over a foot of water on it while flowing slowly towards Evergreen Creek. Litter on the wheel line indicates it had been higher. In the foreground is a tall stand of forage brassica, which shelters a fall sown pasture.
The riparian forest is absent from a portion of the Marys River as it passes along the south-eastern edge of Wattenpaugh Farm. Here is where the river jumped the bank and flowed vigorously northward across the field. Planting trees here would slow this flow.
The properties held up well to the record flood with very minimal impact.
Some of the gravel roads need to be topped off and graded. We lost a few of the trees planted in the riparian zone this fall. Our infrastructure and management plans in the works will make these farms even more resilient in the future.
How Are the Sheep?
This is the first question from many concerned friends and colleagues. During the floods the entire flock was at A2R Farm. This was an ideal place as the flooding was restricted to an impressively wide and deep, but single, channel with plenty of high ground on both sides.
So, as you can see below from a picture taken a week ago, the ewes and their babies took the weird weather in stride and are as happy as, well, lambs.