Peak Flow during analysis

[jahunt05]

I am modeling an existing storm system that is under capacity. After running the model, some of the flows seem to be incorrect. I have one section that has a known flow of 1.31 cfs. The results for this pipe section shows 28.82 cfs (peak flow during analysis) and 6.06 cfs (design flow capacity). The pipe section is a 15" with constructed slope of 0.0088 ft/ft. The max velocity attained is 23.48 ft/sec. I know that the downstream is undersized. Could this flow rate be caused by the downstream backflows? The model is setup as hydrodynamic and rational method. My inertial terms are set at ignore, time step = 0, junction surface area = 0 and variable time step with safety factor 75%. I have gutter bypass flows and my sag structures have ponded area set at 100.

[annw2]

How do you know the flow is 1.31 cfs?

With the Stormsewer Program, I often have odd results.  Make sure you set the tail water conditions each time you model.

Also make sure you turn the gutter bypass flow indication on in the plan view.  These will start to randomly jump cross country if you renumber runs.

[jahunt05]

I have modeled the underground detention system using a separate program (Hydrocad) for a previous project. The 1.31 cfs is the known flow for the 10-yr storm event. I have checked my flow arrows and everything seems correct. Also, my boundary conditions for each outfall is set to normal.

[annw2]

You aren't double entering the constant flow rate & the area and CN going into the detention basin?

Which software package are you running?

I could try looking at a Storm Sewer file after work tomorrow.

I don't know SSA yet.

[Matt.Anderson]

Can you post your model?  Sounds like an incorrect routing parameter or interval or pressure flow...

[jahunt05]

Matt,

Do you have an email address I can send the file to? Thanks.

[Matt.Anderson]

Either you can open a subscription support request (they will answer this type of question) or post the file to the forum.

[jahunt05]

Attached is the storm model I am having some difficulty with. The link id, STM-Pipe-40 and Inlet CB-41 is the section that has a known flow of 1.31 cfs from an underground detention system.

[fcernst]

You mention just the 1.31 cfs baseflow, but you have the 10yr 24hr storm running also?

Looks like in other catch basin nodes you are doing both base flows and 10yr 24hr also?