Expert Witness Blog

In THE PERFECT STORM: The Science Behind Subrogating Catastrophic Flood Losses, hydrology expert witness Richard Van Bruggen writes:

HYDROLOGY VERSUS HYDRAULICS
While hydrology is the study of the rainfall-runoff process, including the
determination of design frequency storms and floods, hydraulics is the study of
how the water flows. In the case of flood flows, this could be the analysis of pipe
and channel systems, culvert and bridge design, and the determination of river
floodways and floodplains. The hydraulics part is essential to determine how
much water fits in the pipe or channel or how far it spreads out on the floodplain.
As with hydrologic simulations, hydraulic simulations can also be conducted.
Frequently, hydrology and hydraulics are combined in order to connect with a
coherent theory as to why a specific torfeasor caused the flood damage, even
though the rainfall is considered to be an act of God. Sometimes a tortfeasor can
be blamed for the flood damage simply because a channel or culvert system,
while adequate to handle the storm, became inadequate over time because of
sedimentation, overgrowth, or lack of maintenance of the system. Hydraulic
simulations will explain whether or not that lack of maintenance actually caused
the water to overflow the banks of the culvert or channel, or whether it would
have overflown anyway. Examples of Hydraulic Simulation Models are:

• HEC-2 (Corps of Engineers – Hydrologic Engineering Center);
• HEC-RAS (Corps of Engineers – River Analysis System); and
• WSPRO - USGS/FHWA, Water Surface Pro.