HydraFlow warning: Outflow greater than inflow

[jab1776]

When I try to run my hydrographs through a pond I get an error stating something to the effect of: Outflow greater than Inflow on Hydrograph 6 for the 50-yr storm.

How can this be? How can the outflow be greater than what is flowing into it? Has anyone else recieved this before? This is not much of a hold up for me, but I was just wondering how the program can calculate this.

[TerryStringer]

This can happen when routing hydrographs with extremely small flows. Basically rounding errors. Try changing the Time Interval of the inflow hydrograph(s) to something either larger or smaller.

[Anonymous]

Hi jab1776,

The whole idea of a detention basin is that the outflow is delayed and
ALWAYS eventually the outflow will exceed the inflow. If you don't
reach the stage where outflow exceeds inflow, then you must be designing
something else.

Regards


Laurie Comerford

jab1776 wrote:
> When I try to run my hydrographs through a pond I get an error stating
> something to the effect of: Outflow greater than Inflow on Hydrograph 6
> for the 50-yr storm. How can this be? How can the outflow be greater
> than what is flowing into it? Has anyone else recieved this before? This
> is not much of a hold up for me, but I was just wondering how the
> program can calculate this.

[tspoon005]

True, but I think the number in question was the peak flow, not the flow at any one point.  I have been receiving the same message and I believe it has something to do with Hydraflow screwing up whether or not things should be controlled by inflow or outflow.

Although I believe I have diagnosed the problem, I have yet to find a solution and am curious if anybody else has found one.

Thanks.

[Matt.Anderson]

A bit of an old post, but Terrys answer is correct.

[annw2]

Usually this happens with a small flow & large weir.  A weir is usually the highest , ie. 100 year discharge.  With the flow dependant on H^1.5 you can go from 1 cfs discharge to 10 cfs discharge with a 0.01 ft increase in head.

Set your weir length for 100 year storm down to something very small, such as 0.5 or 1 ft weir length and see if you still get the error.

[wyattbone]

I am attempting to model an underground detention system and am getting this error. I have tried adjusting the interval as other posts have suggested however the error persist. The problem is with the error, the model shows more flow coming out of the system than was ever generated by the post development drainage area draining to it. I have tried all sorts of different configurations on the outlet to remedy this, but nothing fixes it. What I am most concerned about is the stage the system gets up to. It is quite high. However when I go to pond tools and trial route the system, the stages are at much lower (expected) levels. Why are the results in the pond tool tab different than the hydrograph tab? Thank you for the help!

I have can send the file, right now and have the outlets set based on some trials to fix the error. What I am ultimately going for is a box with small draw down orifice through a wier. Top of weir at 105 culvert A invert 100.