H & H: Hydrology and Hydraulics - Why It’s Important to the Design Process
H & H (Hydrology and Hydraulics) is an industry term that is less commonly used in the public eye but is very important to project design. Let's take a closer look!
What is H & H?
H & H stands for Hydrology and Hydraulics. Both terms focus on the study of water.
Hydrology is the study of how water accumulates to predict how much flow there may be.
"This requires an understanding of rainfall data including duration and intensity and determining characteristics of the ground topography along with other variables like infiltration and evaporation," said Schemmer's Alex Roth, PE, and H&H expert.
Hydraulics is the study of how water moves from one place to another.
"Examples of this can range from simple to complex. We use hydraulics to size a spillway on a reservoir, to determine how a river will flow through a series of bridges, or for managing how rainfall will collect as it accumulates through a series of pipes."
When you put both of these studies together, you get H & H.
"Hydrology and Hydraulics is the study of determining where storm water runoff comes from, how much water could accumulate, and predicting how it will move from one place to another," as defined by Roth
How does H & H impact you?
You may be surprised how common H & H is around you. Have you driven anywhere today? An H & H design was nearly everywhere you looked and you didn't even know it!
"We use H & H to size pipes and ditches, locate where drains need to be, design ponds and reservoirs, determine the height and length of bridges over water, and map floodplains," said Roth.
Why is H & H important?
As mentioned above, H & H impacts almost everything you use for transportation and more. Without the understanding H & H brings to a project design, the end product might look good but may not completely function the way it's supposed to.
"H & H is our way of quantifying and managing storm water to ensure what we build can serve its intended purpose," said Roth.
How do we show how H & H will impact a project?
H & H presentations can range from simple to complex. A simple H & H presentation may be in the form of a spreadsheet or a list of calculations. A more complex presentation could be a simulation or model using thousands of data points and mind-blowing amounts of information.
Information that goes into the models ranges from rainfall data to flood data and river flow rates. Our engineers take that data and run it through the model to simulate how water will impact their design and then make changes to correct or prevent those impacts.
"Most infrastructure that can be used by the public has to follow some design regulations or codes related to drainage," Roth said. But, the beauty of H & H comes in when an engineer decides a project might need more than what codes suggest.
Real World Example
Take a look at the picture above. This is what an H & H model looks like. In this case, a flood model for a bridge replacement. The blue-shaded areas show water depth. The darker blue represents the deepest water where a river channel is located. The lines show the direction and how fast the water is moving. The lighter blue shows shallow areas of flooding outside of the river channel. This image shows a flooding event where water is flowing over a road because the existing bridge over the river did not have a large enough opening for all the water to pass under the road.
In this picture, the same scenario is unfolding, but our engineers added a larger bridge opening at the river channel. With this change, you can see that while water still flows into the floodplain, it does not run over the road anymore. That's the type of problem H & H can solve.
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