I was watching the Super Bowl a couple weeks ago and was struck by how the referees spot the football after each play and how it’s really an approximation or “best guess” of where the football actually progressed to. This approximation suddenly becomes an exact science when the chains are brought onto the field to measure weather a team moved the ball far enough to get the first down. The approximation is now measured in mere inches, but the reality is that the placement of the football was probably plus or minus 6 inches to 1 foot depending on the referees view of the play; viewing angle, number of players in the way, and whether the referee saw when the players body made contact with the ground.
As I watched and thought about this, I realized the similarity to what we do in floodplain management. The spotting of the football is very similar to hydrology. Hydrology is not an exact science. Rainfall and runoff response is a complex interaction between water, the ground, the topography of a drainage basin, and the infrastructure already constructed. Not only that, the chances of nature actually replicating the design storm used to analyze peak stream flows is highly unlikely. It doesn’t mean that the hydrologic analysis engineers perform isn’t a good starting point for evaluating floodplain boundaries or sizing infrastructure, but it remains an approximation.
The irony of all of this is how closely we evaluate hydraulics (the measuring chain) when the hydrology is really only an approximation. When we evaluate floodplain hydraulics we often measure impacts not only to the tenth of a foot, but all the way down to one hundredth of a foot. Although it’s never discussed, this measurement is absurd in light of the accuracy of the hydrologic analysis. As engineers we often have this conversation with one another, but regulations remain that measure impacts to mere fractions of a foot.
While I don’t anticipate floodplain regulations changing in light of this truth, I think it at least reminds us as floodplain managers to have perspective on the analysis we’re reviewing, evaluating, or explaining to the public. Our end goal is to protect the life and safety of the public. Conservative hydrologic analysis is a tool we have in our toolkit to achieve this goal. Tedious hydraulics that evaluate impacts to one hundredth of a foot is probably less of a tool in achieving that goal and really the result of how precise the modeling software we use measures the results of our hydraulic backwater analysis. However, in the end both the hydrology (spotting of the football) and the hydraulics (the measuring chain) work together to preserve life and safety as well as the natural and beneficial functions of our stream.