Flow regulation increases mean EAD

[rnugent3]

We have a case where mean EAD increases when a regulated-unregulated transform flow function is applied. This phenomenon only occurs when EAD is computed with uncertainty. The preview compute produces the expected result: deterministic EAD is decreased by flow regulation. The study of interest is Sum City, Impact Area 7, DB Base Scenario.

The behavior appears to be related to the internally computed stage-damage functions. The consequences compute with uncertainty results in significant damage at the most frequent stage. This result points to whacky modeling but a result seen in the field and thus a result we need to be able to handle.

I created two more sets of stage-damage functions to test my suspicion. Manual stage-damage functions. The first set looks normal, has stages that have zero damage. I computed EAD with uncertainty, without regulation: I computed EAD with uncertainty, with regulation, EAD goes down, the expected behavior:

The next is a truncated version, there are no stages with zero damage. I computed EAD with uncertainty, without regulation: I computed EAD with uncertainty, with regulation, EAD goes up, the unexpected behavior:

Somewhere, the math goes awry, and I haven't figured out where that math in the full compute with uncertainty is going wrong, but I know that the stage-damage function is the aggressor.

A recommended path forward might be to force a zero-damaging stage on the stage-damage function with uncertainty and see if this behavior persists. The trick would be, at what stage would we force zero damage? I think that we could go really close to the most frequent stage, something like 0.1 feet, because we need to put a boundary around the bad modeling.

[rnugent3]

Original model is here: \\share.hec.usace.army.mil\USACE\HEC-FDA\Version_2.0\TechTransfer\ApplicationsGuide\Sum City Model

[rnugent3]

Manual stage damage functions are attached sumcitymanualstagedamage.xlsx