Engineering issues raised by Dan Krocker - Poor Farm Ditch

Edloe Street bridge looking south from the West U side. Photo, Jim Shields.

It is not surprising that two different engineering firms came up with different answers. The models that are used to predict the extent of flooding under different scenarios have a lot of uncertainty and are hardly objective. Typically, the hydraulic models that are used to simulate floods rely on several variables

• the drainage area (the total area contributing to runoff during a storm event),
• the permeability of the land surface (porous surfaces such as grass and green-scape will produce less runoff in a storm that pavement)
• the topography of the landscape (which determines the direction and velocity of runoff),
• the intensity of the rainfall event (e.g., inches of rainfall per hour over a particular duration).

Modifying any of these variables will give you a different prediction for potential flooding effects. In general, hydraulic engineers don't fully report the uncertainty in predictions and study results are often presented as hard facts. So that's probably part of the problem here.

Source - Dr. Theodore Grantham - University of Barcelona, the good looking man in my family photo