Obviously, there will be a runoff component, but the presence of the tiles means that the soil will not exhibit standard runoff behavior as predicted by the SCS method, so standard CN values will not apply. You will also have some storage and time lag as the water penetrates the soil to the...
Assuming that the equalizer pipe is adequately sized, modeling as a single pond is recommended for simplicity and stability. Modeling as two ponds may become unstable (oscillate) as the ponds equalize, especially if you a modeling a reversing flow. I would start with DSI assuming one-way flow...
Since the media layer is generally the outlet control (using exfiltration), the pond storage storage should include only the volume above the media. In other words, you should ignore the storage in the media and underlying stone. For details see www.hydrocad.net/raingarden.htm
OK, so the "outlet pipe" at the bottom of the control structure is the final discharge, and the bioretention area is basically "offline" storage.
You could try:
Pond 1 = "Dry Pond"
Device#1=Culvert (connecting pipe), routing=Primary (routed to pond 2)
Devcie#2=Rectangular orifice...
The connecting pipe is easy. That's just a culvert outlet from the first (dry) pond. But you seem to be also be feeding water through the perforated underdrain, into the media and presumably into the upper part of the pond as it fills up? So the same media is actually receiving water from...
As swazimatt points out, you also need to consider the available storage. Assuming that you are trying to limit (regulate) the flow to a certain maximum, you will have to detain the excess volume and release it over time. You cannot do this with a flow-limiting device alone. You also need an...
I suspect that the pipe diameter will become the limiting factor before the perforations or flow rate through the gravel. Otherwise you could use an exfiltration outlet and/or orifice array in front of the culvert.
When configuring any outlet setup, start at the final device and work backwards towards the pond storage. For example:
Device#1=Culvert outlet from riser structure, routing=Primary
Device#2=Orifice at top of riser, Routing=Device#1
Device#3=Orifice in side of riser, Routing=Device#1...
Not sure exactly what "issues" you're trying to address.
Normally you would set the starting elevation to the permanent pool. But your underdrain will cause the level to draw down, correct? So it's no longer a permanent pool. If you want to maintain the initial WSE you would need to...
You would probably need to model the space upstream of wall (A) as a separate pond. But then you'll have to deal tailwater issues. I would simplify the model rather than trying to include all the details of the WQ unit. Unless it provides a large storage (detention) volume, the WQ unit isn't...
The weir and orifice can both be primary, routed to the control structure. Just one culvert, leaving the control structure. Don't include anything twice.
If I understand correctly, you would need to model the inside of the outlet control structure as a separate zero-storage pond, so that you can route the inflows accordingly. For example, working from the bottom up:
Pond 3 would be a zero-storage pond representing the inside of the control...
An exfiltration invert of zero with HydroCAD 8 is equivalent to "Allow exfiltration at all elevations" on later versions. Later versions will then report a zero invert. They do NOT set the pond bottom elevation.
Remember that if you restrict the flow, you will have to detain the excess volume. You are essentially creating a detention pond. Do you have the space/volume to accommodate the excess? The required volume could be considerable. At some point it may also overflow (in undesirable directions)...
The minimum Tc is applied only if you enter a Tc value for the subcat. You can even enter zero, but there must be at least one Tc segment in order for the minimum Tc to be applied.
The minimum Tc is normally used to avoid very small values (a few minutes). Since you have a significant Tc of...
At the water/media interface you would use an exfiltration outlet at 2 in/hr. Since the media is acting as an outlet control, the pond storage should include only the open space above the media. Any water below that point is not part of the same level-pool and ignored as far as the pond...
It is assumed that all the pond storage is interconnected so that it will fill from the bottom-up, always maintaining a level pool. The outlet devices, including exfiltration, regulate the flow of water out of the defined storage.
The problem with your setup is that you are attempting to...
