AdH calculates system hydraulics and can also calculate the transport of constituents within the system. These constituents might represent a certain size of sand grain, a dye, or perhaps dissolved oxygen (using the associated water quality libraries for any reactions). Often these constituents are passively transported. That is, they move along with the water. However, if these constituents form a solution that is of a different density than the surrounding water, constituents can actually change the flow field. This is often true in estuaries or in reservoirs. Within a reservoir, temperature can cause stratification. Cold water may be covered by warm water, for example. The flow field is quite different from a uniform density case. Transport that is affected by density is termed "baroclinic transport".
AdH presently has special variable designations for "salinity" and "temperature" that modify the density of the solution with one or both constituents. Because density differences can impact the flow field, the baroclinic feature in AdH is critical for simulating reservoirs and estuaries.