HYDRAFLOW-STORM SEWERS HGL NOT UPDATING

[Anonymous]

Greetings,

Just set up my first model in Hydraflow. 

I've created the catchments and pipe network in Civil3D and exported that to Storm Sewers.

I've defined my IDF curves based upon the NOAA atlas.

Problem I'm having is that the HGL is not updating when I change the return period, say from the 100-yr to the 2-yr flow. Not sure what in my model would affect this, nor if there are any bugs that are causing this issue, and what sort of workarounds there may be.

Any suggestions?

.stm and .idf files attached.

[Anonymous]

Here's the IDF:

[Anonymous]

Never mind. Wont let me attach it for some reason.

[wpagl452 · Accepted solution]

Hi @Anonymous, thanks for your post! 

Thanks for posting that file. What type of calculation are you running? I ask because it sounds like you might be running a Capacity calculation if your HGL is not changing with return period. Rational method and known flows are ignored in this type of calculation. Essentially, enough flow is run through the system to fill the pipes to capacity and no more or less. 

On another note, I'd also like to point out that it appears you are modeling catch basins and cleanouts (CB and CO for your junction names) as manholes. This is an acceptable workflow, just be sure to keep Inlet Captured Flows unselected in your design codes and be aware of the implications of this decision. For example, inlets and junctions usually have different junction loss coefficients.  

Below is a link to the Hydraflow Storm Sewers User's Guide which may be helpful as you get started with this program.

http://images.autodesk.com/adsk/files/storm_sewers.pdf

[Anonymous]

Winston,

That definitely solved the issue! When I ran Analysis w/ Design calculations the HGL does indeed update.

I wanted to experiment with grate inlets on sag vs. manholes to see how the HGL is affected. One parameter needed is the Grate Area (sq ft) which is defined as the "Clear opening area of the grate" when hovering over the respective column header on the Inlets tab of Storm Sewers. There's nothing about this parameter in the User's Guide, so I referred to HEC-22. Section 4-57 states that:

"Use of Equation 4-27 requires the clear area of opening of the grate. Tests of three grates for the Federal Highway Administration(27) showed that for flat bar grates, such as the P-50x100 and P-30 grates, the clear opening is equal to the total area of the grate less the area occupied by longitudinal and lateral bars. The curved vane grate performed about 10% better than a grate with a net opening equal to the total area less the area of the bars projected on a horizontal plane. That is, the projected area of the bars in a curved vane grate is 68% of the total area of the grate leaving a net opening of 32%, however the grate performed as a grate with a net opening of 35%. Tilt-bar grates were not tested, but exploration of the above results would indicate a net opening area of 34% for the 30-degree tilt-bar and zero for the 45-degree tilt-bar grate. Obviously, the 45-degree tilt-bar grate would have greater than zero capacity. Tilt-bar and curved vane grates are not recommended for sump locations where there is a chance that operation would be as an orifice. Opening ratios for the grates are given on Chart 9."

The grate we are specifying for sag's could qualify as a 45 degree, 2'x2' tilt bar grate, so according to this figure, the opening ratio is ~0.34, and thus the Clear Opening Area (A) would be A=2'x2'x0.34=1.36'. Is this correct? 

As for the junction loss coefficients, I see fromt the User's Guide that inlets are K=1.5 and Manholes are K=1.0

What is the physical reasoning for these differences and why would I use one option over another?

[wpagl452 · Accepted solution]

Storm sewers automatically calculates junction losses for you, based on the angle between incoming/outgoing pipes. You can manually type in these coefficients by setting the Junction Loss Coefficient to Manual Entry under Design Codes if you wish.

These coefficients are based on testing of loss that is induced as water passes through structures, bends, valves, etc. 

Most municipalities require that you conduct a gutter spread analysis for road safety during storms. In this case, you would use inlets where appropriate. If you are doing a preliminary layout/sizing design, you may want to skip inputting the inlet information and leave them as manholes.