Spread / Street Capacity

[alberto_go]

Hi all,

I have a few questions regarding spread/street capacity:

When calculating the spread at the catch basin locations, how does it determine the curb height?? Does it always assume 6"?? what if it is a roll curb??? is it olnly determined by the "throat height" of the inlet?? How can I calculate my spread on random spots throughout the street??

TIA

-Alberto

[Matt.Anderson]

According to the calculation methods shown in the help file and User Guide, the spread and depth is calculated using basic geometry.



It uses a modified Mannings equation to calculated the depth of flow in the gutter, thereby determining the gutter spread.



Typically, your worst spread will occur at your inlets, and the narrowest spread at the top of the watershed or just after an inlet. I don't think you can arbitrarily calcuate the spread between two inlets unless you use the Hydraflow Express tools and manually calculate your expected spread with an estimated flow.



Matthew Anderson, PE CFM

[alberto_go]

Hi Matt,

I understand that the spread is being calculated by the geometry/slope of the street/gutter. However, how does it know the maximum depth that it can go?? (before overtopping the curb) ... where are we (the users) controlling this parameter?

For this particular project (and it is very typical), for the 10-yr event I need to contain the water within the curb and gutter, with a max spread of 16'; and for the 100-yr event it needs to be within the ROW... by running Flowmaster I can see that my water depth is going to overtop my curb and gutter at the 100-yr event (based on geometry and existing conditions)... however, when I run the same scenario on Hydroflow Storm Sewer, it only gives me a larger spread, and it does not show (or take into account) the heigth of the curb, disregarding the water that is going behind the curb and gutter.

Can we control this parameter at all?? Or do I need to go back to Flowmaster, check my street capacities over there and then comeback to Hydroflow to finish my design??

Any input will be greatly appreciated?

Thanks!!

-Alberto

(see attachment)

The only reason I'd like to know this, is because I need to identify the areas where my spread is greater than our restrictions...

[Matt.Anderson]

Alberto -

No, I don't think you can modify this - it assumes a basic vertical curb and a basic Sx slope. (ie, yes, it will likely assume incorrectly if you calculate the flow depth over the curb and or crown.

The Channel -> User Defined calculator in the Hydraflow Express might be able to give you a little more flexibility. Edited by: Matt.Anderson on Mar 17, 2009 3:23 PM

[alberto_go]

Matt,

yeah... that's what I was affraid of... and trying to avoid... same process as FlowMaster... I see one advantage though, we don't have to buy a license for FlowMaster anymore, since these Hydroflow packages come with C3D 2009... a little bit of savings...

BTW, I like how the reports look in HydroFlow...

Thanks!!

Alberto González, PE

[Anonymous]

When calculating the spread and depth of flow at a sump inlet, does hydraflow assume that the flow is coming from a single direction (like with an inlet on grade)?  Or does it assume that the flow is coming in from both sides of the inlet?