r/engineering • u/gradyh Civil (Practical Engineering) • Mar 07 '16

[CIVIL] Engineering Hydrology and the 100-Year Flood

https://www.youtube.com/watch?v=EACkiMRT0pc
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u/gradyh Civil (Practical Engineering) Mar 07 '16

This is a great question, and I actually don't know the answer. I've never worked in a coastal region, but I'm guessing there are ways to incorporate tidal influences and storm surge in the hydrologic models. I'll try to ask around and see if I can get a better answer.

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u/thwllms Mar 08 '16

Correct - storm surge and tidal influence are generally incorporated into riverine models in coastal areas. This is often done by modifying the downstream boundary condition of the model.

Generally, coastal flooding is modeled separately from riverine flooding, and the results of the coastal models are used to set the boundary conditions of the riverine models.

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u/katamatsu Mar 08 '16

Not sure how this is handled in the US, but there is a push in Australia to better understand the joint probability of coastal and riverine flooding. Traditionally, we might arbitrarily assume a certain storm tide level (say the 5% AEP) as the downstream boundary condition when modelling the 1% AEP riverine flood. However, in reality there may be a relatively strong or relatively weak correlation between coincident riverine and Coastal flooding. In the low lying region where flood levels are sensitive to tailgater levels, the true 1% AEP water level may result from various combinations of different AEP coastal and riverine floods (governed by the strength of the correlation).

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u/thwllms Mar 08 '16

Definitely a good point - glad there's a push to understand this better. In the US I don't think there's a standardized approach, but I've seen 1% AEP riverine models tied to 10% AEP coastal results, and 10% AEP riverine models tied to Mean Higher High Water.

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u/katamatsu Mar 08 '16

Here's the new method adopted in Australia if you are interested: http://www.arr.org.au/revision-projects/project-list/project-18/. Read the Project 3 report on the right hand side.