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.