enforce min depth of retention compartment for infiltration BMPs

[austinorr]

fix is to set min depth of retention compartment to 0.1 ft if the BMP has a soft bottom.

[austinorr]

• Engine issue: when retention compartment is very small, like when we want to simulate incidental infiltration, the % treatment and % retained are ill proportioned comparted to SWMM examples.
• Partial retention facilities (aka 2-compartment facilities, aka facilities where the user selects HSG for the underlying infiltration rate) should likely perform incidental retention. Options for facilitating this include implementing one or more of the following:
  • Set a default value in OCST website for ‘depth below underdrain’ to be something like ~0.1 feet and/or make it so the user cannot enter zero for this field.
  • Expose another option for HSG which is none/lined/rock which sets the infiltration rate to 0.
  • Change the engine so that for these BMPs the min allowed depth is ~0.1 feet. With this option this value would no longer be user or client configurable.