Think Out Loud

Tide gates come with ecological costs

By Rolando Hernandez (OPB)
Oct. 26, 2021 6:54 p.m. Updated: Nov. 3, 2022 4:11 p.m.

Broadcast: Tuesday, Oct. 26

In one of the most surprising relationships, salmon and other fish also benefit from regular fire on the land.

Tide gates affect migratory fish such as salmon.

Will Harling/Mid Klamath Watershed Council


Tide gates control water movement in rivers, which allows for more dry land and agriculture. But, these gates also obstruct the natural flow of water. Guillermo Giannico is a professor at Oregon State University and joins us with details on how these gates affect the wildlife around them.

This transcript was created by a computer and edited by a volunteer.

Dave Miller: We start today with Oregon’s coastal tide gates. These gates are put in to allow fresh water to flow downstream into estuaries while preventing salty or brackish water from going upstream. In other words, they can help create farmland where there used to be flooded land. But many of Oregon’s tide gates are getting old, which can lead to all kinds of problems, challenges for fish passage, backed up fresh water or inundations with ocean water. Guillermo Giannico is a professor at Oregon State University. He has been studying tide gates for more than 20 years and he joins us with more. Let’s start with the basics because my one sentence description, I don’t think that does this justice. What exactly is a tide gate?

Guillermo Giannico: Imagine a door or a flap door, like a pet door in your garage that opens when the water from the extreme side, which tends to be the river or stream is high enough to push the door open and drain into the estuary or the side where the bay and the ocean are. And then when the tide goes up, the pressure from the downstream, or bayside, is high enough to shut the door and basically keep higher tide water from flooding low fields.

Miller: This is a very, very old human technology, right?

It’s been used for hundreds of years in Europe, in Asia and here probably in the Pacific Northwest. We can date them to the late 18 hundreds or early part of the 20th Century, about 100 years to 120 years.

Miller: What would the areas in the Oregon coast that have tide gates be like without them?

Giannico: If you saw them from the air, they would look almost like a christmas tree pattern and then a 3-tree pattern with branches that are the little marsh channels, inundated periodically by the high tide and then drain away when the tide recedes. And you will see all these branches connected into a sandy silty area in the day. And then eventually as you keep going up and away from the title influence, it becomes almost a single or a simple channel that would be the freshwater portion of the system.

Miller: But for that lower part, that would be maybe a place to grow oysters as opposed to grazing cattle?

Giannico: Yes. To a large extent and you would have a lot of plants that wouldn’t be necessarily cattle friendly because they would have a lot of salt in their tissues and they would be seasonally and periodically inundated with saltwater.

Miller: So these flood gates have enabled farming and have created valuable farmland by keeping saltwater out?

Giannico: Yes, they basically have transformed the ecosystem from a saltwater dominated system into a freshwater dominated system which is more compatible with cattle raising or other types of human activities. You can also have vegetables or other crops that cope with the fresh water but would die under salt water conditions.

Miller: How many tide gates are there in Oregon right now?

Giannico: We don’t have an exact count, but I would estimate probably a couple thousand. That’s a conservative estimate because they are not only [at the] mouth of river, larger structures, but these things in the small tributaries and also draining fields and those are even smaller. So for every large tide gate there are maybe a dozen or more smaller ones that are further away, into the, what’s almost entirely, freshwater environment.

Miller: And so many that there is no full count of them because you are aware of the bigger ones but, as you’re saying, the further upstream you go, the more there are. Do you have a sense then for how old the bigger ones are on average?


Giannico: Well, the ones that started being considered a problem and paid attention to and in some cases replaced or upgraded aware in the 80-100 year old age.

Miller: What happens when those tide gates get to be 80 or 100 years old?

Giannico: Well, they basically stopped functioning even for their original purpose. So in some cases actually they may have less of an environmental impact, in the sense of allowing the system to have more of a connection between the salt waterside on the freshwater side.

Miller: [So is] the problem with them that the door is always open, for example?

Giannico: Yeah. So it’s a matter of luck. The door may fail and remain always open. So for fish and the associated creatures in the estuary environment, that’s not bad news. But by the same token, the door may fail almost in a short position or open enough to let water through, but at the speed that the fish cannot negotiate. So it becomes an almost constant barrier.

Miller: There are so many competing needs here as in so many conversations we have about hydro infrastructure. This is not a dam, but it seems like we’re talking here about some of the same questions about fish passage. What have these tide gates meant, for example, for native salmon in the Northwest?

Giannico: Well, there has obviously been an addition to the number of barriers and problems and changes in the environment that they have undergone and experienced. So the plight of salmon is not just one associated with a particular type of infrastructure or management plan or land change. It’s the type of death-by-a-thousand-cuts that we can find or describe when we’re looking at the change in the entire landscape of the Pacific Northwest for the past 150 years. And tide gates are one more element. And a critical part of their route to the ocean and back to fresh water. So there’s almost like a barrier. That is quite important because a lot of the work you do upstream to improve fish habitat, may be [negatively affected] by a faulty tide gate at the mouth of the river.

Miller: How important is the meeting place of freshwater and saltwater for the lifecycle of salmon?

Giannico: Well, it is critical because they obviously transition from one environment to the other. They reproduce in freshwater and then they migrate to the ocean to grow and mature. That’s the majority of salmon at least along the coast. There are some species of trout that may remain in freshwater, but for the most part we’re dealing with what we call an anadromous species. That means they go into the ocean but they spawn in freshwater. If you have this transition zone that is critically important and altered by infrastructure and particularly failing infrastructure, then we have a problem. That transition zone needs to be negotiated over time. Changing from one environment to the other has a very costly price, if you want to express it that way, on their metabolism. They need several days or weeks actually to transition.

And in an ungated system, we see that the juvenile fish that are ready to move into the bay are negotiating the transition between the brackish lands of water and the fresh water, over an extended period of time, maybe two weeks in some cases. When you have a tide gate, the transition from freshwater to the estuary site is within hours. And for the most part, the few that we have monitored indicate that there is no way back. They have a problem negotiated the tide gate in the upstream directions. So once they’re in the estuary, they’re stuck there. If they can cope with it fine, if they cannot cope, there might be some negative effects that we don’t immediately find out. The fish may not necessarily die right on the spot at that moment. But they may be taxed metabolically in such a way that they are going to be weaker, they may be more prone to being predated by other fish or birds. So there are mortalities that we don’t account for, but I’m sure occur, as a result of stress.

Miller: We’re talking right now about the aging tide gate infrastructure along the Oregon coast and what they mean for fish and for farms. Is there an engineering solution that lets fish get that transition they need to be able to go to the ocean to begin with and lets grazing or farmland thrive close to the coast?

Giannico:Yes, there have been many attempts and we refer to them as fish friendly and the fish friendly models. Fish friendly tide gates come associated with levers, float hinges or regulators, that basically extend the period during which the tide gate is open. There are a variety of models and the latest ones have even incorporated electronics that basically allow the user to set certain levels for the incoming tide to be allowed before the tide shuts. So there are solutions.

The best tide gate is a tide gate that is absent from a fish perspective. But we recognize that that’s not a possibility, especially if we’re looking at future forecasts of ocean levels. Tide gates may be here to stay and that’s not good news for the fish. But operating them in a way that allows for a maximum level of exchange between the estuary and freshwater environments before they shut down, rather than letting them shut down at whatever level the original door was designed for, will certainly improve the situation dramatically while allowing for the use of the estuary land.

Miller: How much might that cost a private landowner (a farmer) to replace an aging maybe faulty tide gate stuck open or stuck closed with one that meets the kind of fish friendly standards you’re talking about?

Giannico: Well, these are very expensive infrastructure projects and to my knowledge, normally, individuals don’t undertake these. They are funded by county, state and other types of sources of funding - agencies such as the Department of Transportation as well as OWEB, Oregon Watershed Enhancement Board, are heavily involved in these processes because many of these tide gates are on dikes over which we have roads crossing. So ODOT gets involved whether you like it or not. And we’re talking about a price tag that, at least 15 years ago, was in the $1.5 to $2.0 million dollar [range] for several gates under a bridge and embedded in a dyke. So an individual landowner normally doesn’t do this. It is part of a cooperative process involving watershed councils or even worse, an enhancement board and different state agencies.

Miller: You’re talking about different jurisdictions there. A recent Capitol Press article about tide gates noted that the barriers to tide gate replacement are not only technological but regulatory. They noted that projects typically require approval from nine levels of federal, state and county governments. What does that mean for actually getting them off the ground?

Giannico: Well, my research doesn’t deal with that part of the equation. But I can understand, and I’ve seen, how these things take a lot of time, years, before all the approvals in the process you just mentioned are dealt with. And it really represents delay and probably increased costs as well. So yeah, it is a problem. And it has to do with the fact that they are associated with public infrastructure and also affecting areas, in many cases, [which are] protected or of interest.

So, whether it is a good idea to have that many layers of bureaucracy involved in the process or not, I cannot speak to that. But certainly it is a problem. And someone and different organizations sitting at the table discussing the need to really streamline the process should probably work to find the solution to that. But I’m not surprised at what you’re describing that came out in the newspaper.

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