[A high flow event at Glen Canyon Dam in November 2013. Photo by the Bureau of Reclamation via Flickr & CC 2.0 License.]
How an Invasive Species (Almost) Stopped a Flood
“High flow events” or controlled floods are a key tool for managing the Colorado River. But what happens when an invasive fish gets in the way?
Hi! While recently visiting Utah, I came across an interesting story about the Colorado River. Let me know if you’d be interested:
Is the threat of spreading an invasive species enough to justify canceling projects that help maintain the ecosystem? That’s the question facing resource managers at the Glen Canyon Dam on the Colorado River.
Last year, they had to cancel a controlled flood or “high flow event” because there were a large number of green sunfish in backwater sloughs just downstream of Glen Canyon Dam. They were concerned that opening the dam’s floodgates might wash the green sunfish downriver into the territory of an endangered fish species called humpback chub. However, controlled floods are crucial for releasing sediment that builds up near the dam and rebuilding shorelines and sandbars downstream in the Grand Canyon area. “When the Glen Canyon Dam was built, it blocked 90% of the sediment that was coming through the Colorado River,” explains Rob Billerbeck of the National Parks Service. “So it changed what used to be a red river to a clear river.”
Without the floods that carry sediment downstream, shorelines erode. But more water flow also means more risk of invasive fish spreading. This year, the green sunfish may cause the cancellation of a second flood. So far, Parks Services officials have dealt with the situation by killing and removing the invasive fish from the river system. The NPS and the Bureau of Reclamation are optimistic that they’ve “treated” all of the green sunfish and will be able to move forward with a controlled flood, but the issue of balancing the need to prevent invasive species’ spread with the need to rebuild sandbars and shorelines will likely be a recurring one. This year’s controlled flood will go forward on November 7th, but the green sunfish problem seems likely to come up again.
Although it’s primarily an environmental and resource management story, I think the philosophical hook of “dammed if they do, dammed if they don’t” (sorry; couldn’t resist the pun) that raises an interesting philosophical question: What happens when invasive species begin to take wildlife management decisions out of human hands?
Why It Didn’t Quite Land:
There are two main problems with this pitch:
(1) It’s anti-climactic. I described a problem, but by the time I pitched, the wildlife management authorities had found a solution. In fact, they’re going forward with the flood–or “high flow event”–starting today. As one of my science writer friends pointed out to me, most people don’t have a problem with invasive species being killed or removed. And since the fish didn’t actually stop the flood this year, that bit of the drama is resolved.
(2) Water and wildlife management are already full of difficult decisions. The philosophical angle of “How do you weigh the benefits of a controlled flood against the potential damage dealt by invasive fish?” was what hooked me on the story, but I didn’t do enough to distinguish this problem from the other cost-benefit problems that water management teams encounter.
Another factor which may have factored into editors passing on the pitch was that it’s a local problem, the sort that would typically be covered by regional newspapers, but I’m not from the area. I couldn’t even be on site today to see the flood.
But who knows? …Maybe it was just my bad pun.
[Another angle on The Glen Canyon Dam. Photo by Jim Trodel via Flickr & CC 2.0 License.]
Stuff That Didn’t Make the Pitch:
- One female green sunfish can lay as many as 10,000 eggs. So even a single breeding pair of green sunfish can cause a big problem. “We had over 5,000 small green sunfish that we removed from that one little pond,” explained Ken Hyde of the National Parks Service. “So then the big worry is that if we do a high flow event, we might wash 5,000 small green sunfish into the water, and a larger number than normal might make it downstream. We know that there’s always a few green sunfish moving up and down the river, but not in the number [range] of 5,000,” Hyde added.
- High flow events (HFEs) are important for rebuiliding downriver sand bars, which are an essential part of the Colorado River ecosystem. Without the high flow events, dirt and mud would build up behind Glen Canyon Dam, and the water flow would gradually erode the sandbars and river banks where local species make their home. [Correction: One scientist I spoke with Scott Van der Kooi of the US Geological Survey pointed out that although sedment behind the dam plays a key role in the timing of the HFE, the HFE actually moves the sediment from downstream tributaries. He wrote in an email: “Colorado River sediment, primarily sand and silt rather than dirt and mud, settle out in Lake Powell far upstream (100 miles or more) from the dam. Essentially as soon as the river meets the upstream end of the reservoir. HFEs are used to manage the sediment that enters the Colorado River from tributaries downstream of the dam, mostly the Paria River and the Little Colorado River.” ] Loss of river banks and sandbars would also be bad from a recreational perspective, because Glen Canyon Dam is just upstream of Grand Canyon National Park. Visitors to the park like to camp along the shorelines.
- The controlled floods are actually a bit controversial. Some environmentalists argue that the National Parks Service and the U.S. Geological Survey have not done enough to assess the effects of the high flow events on the downstream shorelines. The Sierra Club and other organizations have called for a monthly flood that will send smaller pulses of sediment down the river rather than the twice-a-year high flow events that currently take place.
- The sloughs were the green sunfish were breeding were treated with ammonia, a new fish-removal technique that the National Parks Service wanted to try out. The idea is that ammonia would be easier for the water system to break down than other toxins. So far, the ammonia treatment seems to have been a success, but they are still monitoring the sloughs to assess the longterm effects.
- The determining factor in the timing of the controlled floods is the amount of sediment that has built near the dam. USGS measures how much sediment enters the river and when a trigger level is reached, an experimental flood can occur . Curious citizen scientists can track the buildup via the USGS monitoring website.
Invasive green sunfish nearly derailed a planned flood on the Colorado River. The incident raises the question: What happens if your wildlife management strategy risks spreading invasive species?