backflow anaylsis

[tsli001]

I had come across some project is looking for backflow calculation on some drainage flow. I have never done it before , but done a lot of drainage analysis by using ratioanl method to see the capacity of the drain pipe. For back flow analysis what am I looking for? I'm sure people here can answer me for that.

 

[RWF7437]

Do you mean " step backwater analysis", perhaps ?

 

[tsli001]

Yes

 

[PELS]

I have seen the term, "Backwater Analysis" used in the context of computing the Hydraulic Grade Line (HGL) back through the pipe system to compare the profile of the HGL with the profile of the pipe system and the profile of proposed finished grade along the pipeline.

 

[cvg]

step backwater analysis takes into account flow restrictions and other energy losses caused by junctions, manholes, bends, transitions, structures, changes in slope etc. These can cause a rise in the flow depth which is not predicted by a normal depth calculation alone. For subcritical flow you will start at the outfall and work your way up by calculating the headlosses including expansion, contraction, momentum, friction and elevation changes to estimate the water surface elevation. This is usually easier to do by computer program.

 

[RWF7437]

Some useful software and documentation for computing the HGL:

SWMM 5
HEC-RAS
Hydraflow Storm Drains


all free or low cost.

Read the documentation; especially the hydraulic basis for the calculations.

good luck

 

[tsli001]

So in a lame term, it basely two way. 1, grahic-compare HGL with the profile fo the pipe system. 2.Rim elevation-make sure that the water wont blow up the manhole. May I correct.