Channelization: a solution or a problem?

Smooth symmetrical stream channel and high artificial banks of a poorly channelized stream. (Photos by Robert Titus)

In the immediate post-flood times you may well have seen a lot of stream engineering going on. Across our devastated Catskills, stream banks had been badly damaged. Creeks and rivers had cut into roads. People were anxious to repair the damage and prepare the rivers for the next potential flood event. It’s just our nature as a species to want “to do something.” That gets us to one of those thorny issues in environmental science: something called channelization.

Channelization refers to a host of different strategies of stream bank engineering. If you create a new berm alongside a river, that’s a form of channelization. If you pile up boulders along the edge of a river to protect it from future erosion, then that too is channelization. Sometimes it goes as far as bulldozing a whole new river channel: that really is channelization.

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Well, if you traveled around in September and October, you may have seen a lot of this going on. There was such a strong desire to see to it that the damage was fixed and not repeated. The Department of Environmental Conservation (DEC) felt that communities needed to respond to their immediate needs without waiting for prolonged permit processes to be completed. So the permit requirements were relaxed for two months. That is what led to all the activity; it was well-intentioned, but it may have been a mistake.

Suppose a stream eroded into its banks and then cut into a nearby road. We have seen many such cases since Irene. What highway engineers are likely to do is pile up a load of very sizable boulders to stabilize the banks, before filling in the earth that was lost and replacing the highway pavement. Watch for boulders of a gray rock. These are probably the Helderberg Limestone, and they are well-suited for this sort of thing and readily available in our area. They are the boulders of choice for such repairs. They are big, heavy and very resistant to weathering; they make for good repairs.

There is nothing very controversial about such engineering; roads need repairing and this strategy does work. But will it last? That’s not certain. Giant boulders of the Helderberg look like they will stay in place forever, but just wait until the next big powerful storm; it’s not for certain. Still, it’s probably as good a strategy as we can devise and there are usually few complaints. Let’s call this “good channelization.”

 

“Good channelization” along Rt. 23, near Stamford. (Photos by Robert Titus)

Another strategy is far more controversial; that is the re-engineering of whole stretches of a stream channel. That’s what went on in a number of locations, including Palenville. Local residents, who had made it through Hurricane Irene, woke up a few days afterwards to hear and see bulldozing in Kaaterskill Creek. Over the course of a very short time, the local creek bed was completely rebuilt. Sizable berms of large cobbles were bulldozed up on the banks. The channel bottom was scooped out for quite a long stretch. The result was a nice, neat, symmetrical looking stretch of the creek — so what’s the controversy? Well all the complexities of a natural stream ecology have come to be homogenized. That will likely disrupt all the fish, amphibians, reptiles, birds, mammals and plants that live there. The aesthetics, too, come to be degraded. The result is just not a natural looking stream. Nature’s sublime beauty is replaced by something that looks like it should be in a highly manicured park, picturesque but not natural.

The biggest irony of all is that a channelized stream is likely to encourage a faster flow of water the next time it floods. Instead of mitigating flood damage it quite very possibly will increase the threat. All the natural irregularities of the stream provided a needed friction and they are now gone. The word ironic gets a tough workout here. It describes that fact that these stretches may have been made more susceptible to future damage, not less. Floods of fast flowing waters are powerful agents of erosion. They can sweep up very large cobbles and even large boulders and carry them long distances. This is bound to happen, sooner or later. So, what’s the point?

 

If you visit the Palenville site you may well form the impression that these changes will last forever. You would likely be wrong. The sad fact is that these new banks will be just as susceptible to erosion the next time there is a bad flood, as the old banks were during Irene. And the threat seems to be increasing. We have talked to stream flow geologists, people who study just this sort of thing. They are nervous about what has been happening in our region. Over the course of the last half century, rainfall rates have increased by at least 16%; we now annually receive one sixth more rain than we did during the 1960’s. That’s a lot, but the story gets worse. This year we are running at 36% above the old averages (Albany records). We think that is downright frightening. And then it gets still worse. There is something called the “recurrence interval.” That is the average length of time between storms of some specified magnitude. Bad storms, not necessarily as ferocious as Irene, but just bad ones, are occurring far more frequently than any time in the past.

We recently attended a US Geological Survey presentation about Hurricane Irene. They have determined that, throughout much of Greene County, Hurricane Irene produced a 500 year flood. That is a real horror, but most of you saw it for yourself. We can imagine that you believe the experts. As you may know we have experienced several 100 year floods over the past several decades. Our point is that the numbers are getting out of date. 100 year floods are coming more frequently, because the climate has become rainier. We all need to understand this. Efforts at channelization such as we see in Palenville, are likely to be expensive and, quite possibly, futile. ++

 

Contact the authors at titusr@hartwick.edu

 

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