Aquatic Organism Passage


Hello. My name is Jim Schall, and I am an instructor for Federal Highway
Administration training delivered under the
National Highway Institute. The National Highway Institute,
or NHI, is the training branch of the Federal Highway Administration. The videos you are about to watch are based on some of the training courses developed by the National
Highway Institute. In particular… the Introduction to
Highway Hydraulics course NHI Course 135065 and the Culvert Design course NHI Course 135056. I’ve been an instructor for National Highway
Institute training courses for 25 years. I completed my undergraduate
engineering degree at Purdue University and
did my Masters and PhD at Colorado State. The videos are based on
demonstrations and experiments that we do primarily in
these two training courses built around a portable flume. The flume is six inches wide and approximately five feet long and recirculates water
from a thirty gallon sump. The videos-there are six of them to watch. The recommended order in
which to watch those videos, first, open-channel flow concepts, then, gate inlets, culvert hydraulic concepts, hydraulic effects of culvert liners, aquatic organism passage design concepts, and energy dissipators for culverts. Thank you for your interest in Federal Highway
Administration Training. I hope you find this video series helpful in completing highway
drainage design projects. This video will demonstrate
the hydraulic performance of a culvert traditionally
designed to one designed more with the AOP, aquatic organism passage design criteria. We’ll be looking at changes in the velocity through the
barrel using a floating ball, and we’ll also be looking at changes in the head water elevation. Initially, I’ll run the
water through a culvert that is designed the way we
have traditionally done it which is to maximize
the available ponding, the head water depth at the upstream side allowing us to downsize the barrel, minimizing the construction cost of that particular crossing. Then we’ll look at a culvert designed with AOP considerations in mind. An AOP culvert is oversized. It’s typically embedded
into the stream channel to simulate what I have here- a natural invert twenty
to forty percent embedded, or it could be a pipe arch type culvert with a natural invert or a arch culvert. The idea with that is that the natural material
slows the velocities down. One of the fish passage barriers, AOP, aquatic organism passage
barriers is high velocity and another one is shallow flow depths. And so, additional
roughness reduces velocity, increases flow depth. We’ll be comparing the hydraulic
performance of these two at a couple different flow conditions. The first flow condition
is what I would call the design Q. As engineers, we still have to be sure that whatever culvert we design passes the required design discharge, typically a twenty-five
year return period or maybe a fifty year return period flood. That’s a pretty good size flood, and in aquatic organism passage design, we don’t typically design for fish passage at those flood flow conditions. There’s design standards
that have been developed by the Federal Highway Administration that are presented in Hydraulic Engineering Circular Number 26 based around a stream
simulation design concept. And part of that is defining
a range of discharge at which fish movement and aquatic organism movement will occur. If we think a minute, what that really means,
certainly at a flood flow at this twenty-five or
fifty year design condition, we don’t normally see fish moving around. It’s like us going out during a storm. We quite often will wait
until the storm passes, and then go about our business- go the grocery, do our shopping, whatever. Fish do the same thing. They’re not going to be out
moving around, foraging, looking for food at the time of a storm. They’re probably going
to be down in a pool waiting for this flood
flow condition to pass. So, A.O.P. design following
a stream simulation concept defines the bandwidth between
which fish are thought to be moving-the Q high flow condition and the Q low flow. The QH as I call it-the
Q high flow condition- is the condition at which the fish might still be moving around, but anything above that gets
into the flood flow conditions that they’re not going to
be spending too much time in the stream channel. They’re
going to be hanging out in a pool somewhere. In contrast, the Q low is
such a low flow condition that, and it might be say during a drought where the stream is particularly dry, the flow depths are really shallow, maybe the temperature of
the water is really hot. And at that time, the
fish as well aren’t going to be moving around. They’re going to be hanging
out in a pool waiting for better times right? Better conditions. So, the QH and the QL define a bandwidth between which the fish movement-the aquatic
organism passage movement is expected to occur. So, we’ll look at a flood
flow condition first where we have an HW over D of
one-and-a-half approximately. Meaning we’ve ponded
upstream of the barrel like we might have done in
a traditional culvert design on my two-inch culvert, which in my one to twelve scale model is a two foot culvert in the prototype, and we’ll compare that then to a more AOP-friendly culvert design. In this case, it’s a four-inch
Barrel, or a four-foot pipe, embedded twenty to forty percent. So, let’s start with the
traditional culvert design. We’ll mark the head water at
this flood flow condition. We’ll look at the velocity with the ball, and then I’ll switch over
to the AOP structure and we’ll look at the
same flow conditions, and then, we’ll lower the discharge down to something more in the realm of this QH to QL range. So, marking the headwater
with my stilling well. I’m trying to get to maybe
one-and-a-half HW over D, headwater depth to diameter. And again, this is how we might have traditionally
designed a culvert. We create some ponding upstream to minimize the size of the
barrel we’re going to need, but by so doing, we end-up with a culvert that’s really not very
fish-friendly, right? Because we have pretty high velocities. If I run this ball through, I’ll do that a couple
times, so you can see it, it’s moving quite fast. That’s a fish passage barrier. Fish would have trouble swimming upstream against that current. And even if they could swim
upstream against that current, they might get to the
upstream side so exhausted that they don’t survive, or they’re subject to
predation at that point. So, with a good headwater let’s go ahead and switch
over to the AOP design. Which again would be a larger barrel that’s embedded twenty to forty percent. And part of the reason to
show it at this flow is to demonstrate that we can still pass the design Q. And again, as engineers, that’s one of our first responsibilities is the safety of the traveling public, and to make sure this culvert is, from an engineering point of view, safe. You can see that the ball,
even at the design flow, is traveling at a slower
rate down this barrel. This is still not a fish passage flow, because again, the fish aren’t
going to be swimming around at the flood flow condition. Notice we’re passing this flow at a lower headwater which also means these AOP designs, even with
the increased roughness, we’ve got a larger barrel, we’re able to pass our
design Q, our Q25 or our Q50, with less headwater giving us
more capability to surcharge. More ability to take a larger
flood, if that comes along, is one possible advantage
of this AOP design approach. But let’s go ahead and slow this down now to something more in that QH to QL range. And I do have to slow it down quite a bit, because one way of calculating the QH is it’s approximately twenty-five percent of the two-year flow. Well, the two-year flow
is already fairly small. You take twenty-five percent of that, you can see that we’re really
not defining a bandwidth with large flow conditions
when we’re talking about fish passage. So, now let’s look at the velocity of the ball
under this condition. As you can see, we hardly
have enough velocity to even make it move. Let me increase the
flow just a little bit. I may have gone below the QL. Okay, so there we go. And that’s the idea- the rocks and the roughness increase the flow depth
to allow fish swimming and also reduce the velocity
down to a level at which they can easily traverse the culvert. When you have larger
roughness elements like this, if that’s part of your
natural bed material, it also provides resting
areas when the rocks get particularly large. So, I’ll go ahead and mark this headwater, and we’ll compare this flow condition with, again, my more
traditional culvert design and see how the velocity
and headwater compares at flow in the range of the QH to QL. So, the headwater
doesn’t change very much. The velocity is clearly faster
than it was with the rocks. Remember, we had trouble even
getting the ball to move in the AOP structure, and that’s the benefit of an AOP design- slowing the velocities down, increasing the flow depths. We’re getting flow depths here because of our smooth boundary
that might not be deep enough for a fish to even swim
through the barrel. One of the early design
concepts in AOP design was the thought of using baffles to create the roughness we
need to increase the flow depth and slow the velocity down. Let me put the AOP structure back in using the baffles to illustrate
what that would look like. So, the idea of the baffles, particularly this alternating design, was to create a more sinuous path, as well to create some resting areas. And it may be that I’ve
got too much flow there. There we go. But you can see and this
is kind of what happens, in fact problematically
with even organic material and trash that’s coming down the channel. That was one reason baffles
were less than desirable, because baffles often
cause a culvert to plug. So, in the newer design concepts, the idea of using baffles is typically limited to a retrofit. If you’re designing a new
structure or replacement culvert and providing an AOP design, the preferred option is to design the culvert with either an embedded structure or use a pipe arch that’s embedded or an arch culvert allowing
that natural invert to develop, over-sizing the barrel. And one of the common
complaints and concerns about this is, yes,
this is a larger barrel and it will cost more money initially. But perhaps, it’s not as
much in the long run as you might think when you start comparing the capital cost to the maintenance cost. Certainly, a larger culvert
like this is going to have less trouble with debris
blockage at the upstream end which is a common maintenance headache for our traditionally designed culverts. The natural invert will
protect the channel, the culvert invert,
from the channel material that’s moving through, the bed material, so that you may not perforate
the invert quite as quickly. And, in total over the
life of the culvert you may actually have a
lower life cycle cost, or at least comparable. So, the idea of an AOP structure is to create a design
that allows fish passage and aquatic organism passage to occur with some of the common
fish passage barriers being shallow depths that inhibit
swimming, high velocities, perched outlets-that’s a
big problem that we have with traditional culvert
designs where we have a scour hole forming at
the outlet of the barrel, because of the high velocities
coming out of that barrel, creating a situation where a
fish has trouble getting up into the barrel and moving
to the upstream side. All of this information and the design procedures
are summarized in Federal Highway Administration
Hydraulic Engineering Circular Number 26, Culvert Design for
Aquatic Organism Passage. And if you need more information, that’s a good resource to turn to. Thank you for your interest in Federal Highway Administration training. I hope you found this demonstration of the comparisons between a
traditionally designed culvert and a culvert designed
with AOP in mind useful.

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