modeling storm chambers and upstream diversion structure

[murdock]

I am working on a model of some underground storage chambers with a catch basin upstream acting as a diversion structure. The catch basin has two outlets, one 2' higher than the other to bypass larger storm events.

The chamber system is designed to infiltrate/detain the 1-year storm. This part works OK, it's the larger storm events where the model goes off. During the 10-year storm, the storage range for the chambers peaks 8' above storage level (elev. 230.39), while the upstream diversion structure peaks at 224.03, well within its limits (overflow culvert inlet at 224).

I have my model setup with the dyn-stor-ind routing method, so the two structures should be dependent on each other, correct? What is triggering the chambers' high peak elevation? In real life, will the water simply peak at 224.03 in both the chambers and overflow structure?

Let me know if you need some more detail.

TIA

 

[psmart]

I would need to see the model to provide specific advice. But I assume there are warning messages, such as "overfilled storage"? For details please click the message or see

http://www.hydrocad.net/overfilled.htm

As a general recommendation, it's easier to model this type of "off-line" storage as if it were in-line. That is, route the inflow directly to the pond/storage node, which will include an appropriate overflow device. This avoids the complexity of modeling any reversing flows between the diversion structure and the storage.

For details see

http://www.hydrocad.net/pondstore.htm

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[murdock]

Thanks for the reply. I took out the diversion structure and it helped a bit, though I still have overflow issues. The inflow out is bigger than the inflow in; and while the inflow is able to be handled by my overflow culvert, the bigger outflow is not. Here's the HCAD file that spells it out:

[HydroCAD]
FileUnits=English
CalcUnits=English
InputUnits=English
ReportUnits=English
Source=HydroCAD® 8.50 s/n 001547 © 2007 HydroCAD Software Solutions LLC
Name=storage overflow example
Path=C:\Documents and Settings
View=3.99779888879831 -0.64174397726739 17.3909417736784 11.4073687237427
GridShow=True
GridSnap=True
TimeSpan=18000 259200
TimeInc=36
SubIntervals=3
RunoffMethod=SCS TR-20
ReachMethod=Dyn-Stor-Ind
PondMethod=Dyn-Stor-Ind
UH=SCS
InitialTW=True
RainEvent=100-year
P2=0.191666666666667

[EVENT]
RainEvent=1-year
StormType=Type II 24-hr
StormDurat=86400
StormDepth=0.175

[EVENT]
RainEvent=2-year
StormType=Type II 24-hr
StormDurat=86400
StormDepth=0.191666666666667

[EVENT]
RainEvent=5-year
StormType=Type II 24-hr
StormDurat=86400
StormDepth=0.235

[EVENT]
RainEvent=10-year
StormType=Type II 24-hr
StormDurat=86400
StormDepth=0.266666666666667

[EVENT]
RainEvent=25-year
StormType=Type II 24-hr
StormDurat=86400
StormDepth=0.325

[EVENT]
RainEvent=100-year
StormType=Type II 24-hr
StormDurat=86400
StormDepth=0.433333333333333

[EVENT]
RainEvent=WQv
StormType=Type II 24-hr
StormDurat=86400
StormDepth=0.075

[NODE]
Number=2S
Type=Subcat
Name=
XYPos=9 7
Outflow=3P
LargeAreas=True
[AREA]
Area=51052.32
CN=98
CNindex=7D
Desc=Paved parking & roofs
[AREA]
Area=18469.44
CN=39
CNindex=5A
Desc=>75% Grass cover, Good, HSG A
[AREA]
Area=566.28
CN=74
CNindex=5C
Desc=>75% Grass cover, Good, HSG C
[TC]
Method=Sheet
Desc=watershed bdry to EOP
Length=32
Slope=0.17
Surface=Grass: Short
n=0.15
[TC]
Method=Sheet
Desc=EOP to 100'
Length=68
Slope=0.05
Surface=Smooth surfaces
n=0.011
[TC]
Method=Shallow
Desc=100' to CB
Length=41
Slope=0.05
Surface=Paved
Kv=20.3
[TC]
Method=Pipe
Desc=CB network
Length=695
Slope=0.025
n=0.013
Diam=1

[NODE]
Number=3P
Type=Pond
Name=UGS
XYPos=9 3
Outflow=
Note=new underground retention system
Message=[93] Warning: Storage range exceeded by 4.45'
Message=[58] Hint: Peaked 4.45' above defined flood level
Message=[90] Warning: Qout>Qin may require Finer Routing or smaller dt
Message=[87] Warning: Oscillations may require Finer Routing or smaller dt
LargeAreas=True
FloodElev=225
[STORAGE]
Type=Prism
Desc=gravel backfill
Invert=213
OpenSpace=0.4
Height=4
BotWidth=20.5
BotLength=100
[STORAGE]
Type=Prefab
Desc=StormTech SC-740
Invert=214.5
StoreMult=4
Imbed=0
Length=98
Model=StormTech SC-740
[STORAGE]
Type=Hcyl
Desc=culvert connecting diversion to UGS
Invert=214.5
Diam=1
Length=75
Slope=0.012
[STORAGE]
Type=Cone
Desc=observation ports
Invert=217
StoreMult=4
Height=7
BotDiam=0.33
[STORAGE]
Type=Cone
Desc=STMH2
Invert=220.52
Height=4.48
BotDiam=4
[DEVICE]
Type=Culvert
Desc=discharge culvert
Routing=Primary
Invert=213
Diam=0.5
n=0.013
Length=10
OutletInvert=212.5
Entrance=CPP, square edge headwall
Ke=0.5
CC=0.9
[DEVICE]
Type=Orifice
Desc=control orifice
Routing=Device 1
Invert=213
Diam=0.1
C=0.6
Plane=Vert
[DEVICE]
Type=Culvert
Desc=Overflow culvert of diversion MH
Routing=Secondary
Invert=221
Diam=1
n=0.013
Length=93
OutletInvert=212
Entrance=CPP, square edge headwall
Ke=0.5
CC=0.9

 

[psmart]

I assume there are warning messages related to the Qout>Qin condition? Please click the message for details and follow the instructions to resolve the problem.

As a guess, this is the overfilled storage condition I noted above. Please see the link for details.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[queque]

A sketch of the propblem would be great. Does this forum allow sketches?