A weekly blog for all things conservation
By: Joe Quatrini; Technical Team Leader; BCCD
Have you ever seen something that was different than what you’re used to and thought “Hmm, that’s different it must be BAD!” Maybe you’re not even sure what you’re looking at but you decide you should hate it, just because it’s a change or you don’t understand it. Unfortunately, it’s almost what our brains are trained to do these days, especially in today’s society. We see something and judge it before we even try to figure out what it is. We often see this when it comes to projects we’re part of.
Take for example one initiative we are working on to help our municipalities and private landowners reduce flooding and prevent costly damage when storms hit. This initiative has to do with making stream crossings bigger. “What’s a stream crossing?” you ask. Great question and thanks for asking! A stream crossing is where a road (or a driveway) and a stream (creek, brook, run, river, etc.) intersect or cross one another. If you drive on a road and look out the window and see a stream coming right at the road and you don’t get wet, that probably means that stream is flowing through some type of pipe or bridge under the road. Obvious, right?
Well, not to everyone and sometimes these pipes are so small that you can’t even see them if you try to find them. Historically, these pipes or bridges may have very small openings and that’s what we’re used to seeing. This isn’t unique to Bradford County or even PA. Many ‘pipes’ we see under our roads to carry stream flow are just whatever the road or driveway owner had laying around or given to them for free to pass water through. Old tanker cars with the ends cut off, a round plastic pipe shoved into a concrete pipe connected to a metal pipe, two (or 3 or 4…) little pipes side by side because a bigger pipe wasn’t available are all things we see in Bradford County. All are examples of poorly constructed stream crossings, but they’re everywhere and that’s what we’re ‘used to’ seeing.
What we are trying to do to help landowners and our municipalities is size these structures to fit the stream that is running through them. We’ve assessed over 900 stream crossings in Bradford County – and by the way, that’s not even half of what’s out there – and we’ve found that greater than 90% of them are undersized or failing. Aside from most of the crossings that are bridges, if it’s a round pipe that the stream is going through, it’s probably too small.
So, let’s think generally about streams. Streams are free flowing, governed by gravitational forces and characterized by the soils, geology, and landscapes they flow through and over as they flow downhill. Streams never flow through a round opening constricted on all sides (ok, there may be some bedrock formations that have been eroded that water flows through or karst topography in other parts of the state that may challenge this, but you get the idea). We’ve (people) decided to put a stream through a pipe and use engineering, or not, to determine if it will work. Any good engineer will be able to tell you how much water can flow through any given diameter pipe and at what rate, however, the stream characteristics itself are often overlooked. For example, say you’re driving and you come to a stream crossing. Safely take note of how wide that stream channel is and consider what the flowing water might look like if we get a storm. How deep will the water get, how wide will the stream be as it gets deeper, etc. Now take a look at the crossing (pipe, bridge) that is under the road. Is it smaller than the stream width, the same size, or even bigger to maybe pass flood flow through it during a storm event? These are the considerations we need to take into account when properly sizing these new structures as we replace the old failing pipes. It’s not good enough anymore to just throw in what was there before. We need to assist communities in being more flood resilient and reduce the cost of damage during storm events and prevent road closures where we can.
So, here’s where we get to “it’s different, it’s BAD”. Naturally, if you are used to seeing a six-foot round old rusty pipe that usually backs up water during a storm and maybe the water comes across the road or washes it out completely every once in a while, and a new structure (bridge, etc.) goes in its place that may be two to three times wider, you might feel some apprehension. There is a common misconception by people with many of these projects that we’ve created more water. This would be related to the hydrology (or the amount of water) of the project. In reality, we are not creating more water, the storm itself dictates how much water falls to the ground and flows in the stream. We do, however, affect the hydraulics (flow of water) in a positive way. The larger the opening in the structure, the less force that water flows with through and downstream from the pipe. For the inlet of the structure, this means the water will not slow down and cause debris and gravel to deposit and block the channel, backwater swirling will not cause bank erosion and loss of property or the road edge, and flooding will be reduced. At the outlet of the structure, the velocity of the water will remain consistent and therefore excessive erosion will be reduced for both the stream bed and stream banks. Basically, you want the stream to look the same through the pipe as it does upstream and downstream from the pipe. This is known as Stream Continuity. This means there should be some gravel in the bottom of the structure at all times as well. Once again, this seems counterintuitive, and we often hear “why did you put a new pipe in and fill it with gravel again?”. If the structure has a bottom, it should be set lower than the streambed elevation and the bottom should be covered with gravel to match the upstream and downstream elevations of the streambed. The pipe shouldn’t be ‘filled’ with gravel, but some gavel actually protects the pipe from wear and tear from gravel and debris that flow through it during storm events and create friction so the water doesn’t speed up as it flows through the pipe. If the structure has no bottom (ex. bridge, bottomless arch culvert), then the natural stream bottom remains the same.
In addition to sizing the structures better, we also try to align them better with the existing channel. Instead of the stream coming to the road and making a 90 degree turn to go through a pipe under a road, we try to shift the new crossing to line up with the stream. Of course, all permits are secured to make any and all changes at each site.
If you ever have any questions concerning any environmental projects happening in the County, give us a call. If it’s a project we’re involved with, we’ll get you all the details and if we’re not involved, we may still be able to answer some questions. Or, if your first call is to the Eyewitness News I-Team, tell them I said hi and I can’t wait to talk to them😊!
Various staff at the Bradford County Conservation District