On a cool, foggy, February morning I walked out into our native grass planting at Willow Bend, a 175-acre habitat preserve owned by River Partners. I’ve been to this site a bazillion times, but this time was different, I was wearing waders. Forty acres of the site was under three feet of water after the Sacramento River had jumped its banks in January. The heads of last year’s grasses were just breaking the surface of the still water.
I was surveying the native bunch grasses – which are perennial and long lived – to see how they were surviving after being submerged for weeks. The north field the Willow Bend is bowl-shaped, and after the river crests, the site becomes a lake until the water that spilled into the bowl percolates or evaporates, which can take up to two months.
As I waded across the field I kept noticing minnows darting away from me. Later, I saw three fish, each about a foot long, swimming together. I wondered what species they were.
After my grass survey was done, I waded back toward shore, and when I was in just inches of water I noticed a dead minnow at the water’s edge. It was still brightly colored, so it couldn’t have been dead for long. On a hunch, I carried it to the car and placed it in my water bottle.
Back in Chico, I swung by the office of one of our fish expert partners, FishBIO and showed the minnow to two fisheries ecologists. One of them dipped a plastic spoon into my water bottle and grabbed the fish. The moment it broke the surface both of the biologists yelled one word at the same time: “Salmon!”
This 2-inch long fish was a fall-run Chinook salmon. They pulled up dozens of photos and taught me how to identify young salmon in case I saw any more in the field.
I’d seen dozens of minnows in the water, all about the same size and shape. Could they all have been salmon? And if I saw dozens while I was just walking around, how many did the 40-acre pond hold? And what about the three bigger fish that I saw?
Back at the office we placed calls to the California Department of Fish and Wildlife. They visited the site but determined that the grassy vegetation and size of the pond made a fish rescue logistically problematic. Besides, the Department lacks the resources to perform fish rescues on the thousands of acres of disconnected floodplains that line the Sacramento River, so the rescue did not happen.
Over the next couple of weeks, as the pond water level went down, I found 18 more dead “minnows”. All 18 were salmon.
Then another storm came. The site flooded again.
We wanted to know exactly when the property flooded. So when we heard about the storm coming we mounted time-lapse cameras in two trees at Willow Bend to photograph the water coming on to the site. Using time stamps from the photographs, we next gathered data for the same time from the nearest river gages. From this we were able to calculate the exact height the Sacramento River needs to be in order for the site to flood. Checking historical gauge data it turned out that the site had flooded in fourteen of the past fifteen winters.
These juvenile salmon trapped in the lake at Willow Bend were acting exactly the way the salmon experts would expect them to. When rivers rise, the salmon which are too small to swim in the floodwaters get pushed around and end up on the river edges, and disproportionately close to the surface of the rushing floodwaters. Then, when the river jumps its banks, the fish get washed onto the floodplain.
Years ago, this was a great thing. The food web on floodplains – if you’re a salmon – is an all-you-can-eat buffet. As the water warms, it becomes thick with tiny plants and animals on which the young salmon gorge. Many studies (including one led by River Partners) have shown that salmon grow far faster on the floodplain than they do in the river.
The reason this is important is that the single biggest factor that predicts a salmon’s fate once it reaches the ocean is how big that salmon is. If they get fat on the floodplain on their trip to the sea, then they are more likely to survive. Which means more make it back to their home streams in order to spawn.
At least that is how it used to work.
Now, because of dams, diversions, and revetment, they have become hazardous to salmon. At Willow Bend, for example, those cameras we mounted to capture the flooding were right along the river’s edge. But we knew they were safe, that the bank wouldn’t erode in the flood because that bank is armored with rock revetment. Like many miles of the Sacramento River, this bank was armored decades ago to keep the river from meandering onto the farm. As the water – and the salmon – spill over that revetment it erodes the ground behind the armor, creating the lake that is disconnected from the river once the river stage drops.
The salmon were out on the floodplain getting fat, just as their genetics programmed them to do. That’s the good news. The bad news is that they were trapped. And because of the way our rivers are managed, there are other “Willow Bends” everywhere you look. Luckily, there is a fairly straight-forward fix for this. The temporary lakes just need a drain back to the river.
The way it would work at Willow Bend is that a channel would be bulldozed from the low point in the field to the river. It would need to be armored where it met the river to keep it from filling in or eroding. And the problem would be solved.
But we want more than just to solve the problem. We also want the salmon to be able to get fat on the floodplain. This means that it needs to stay flooded for at least four weeks at a time in order to give those little salmon time to gorge and grow. There are two ways to do this. 1) Release way more water from the dams, or 2) capture the water on the floodplain when the river is naturally flooding.
Releasing a ton of water from reservoirs isn’t a viable option, especially considering our current drought, but capturing the water when rivers flood is easy. That channel we bulldoze at Willow Bend? Just install a rice box or some other water control structure at the end, and we can hold back the water. If we can implement this relatively minor fix, those “minnow” salmon can continue to use Willow Bend to get fat, only now they’ll be able to get back to the river. In the coming months, we hope to implement this fix at Willow Bend and at the other properties we own and manage. Hopefully we’ll learn as much through those projects as we learned in the first two months of 2016!