Hydraflow shed area and tc data

[Anonymous]

First time use of Hydraflow Extension for Civil 3d and have noticed the limitations of entering shed area data at each inlet.The program only seams to allow for three (3) drainage areas and does not allow to change the C Value in each area. Also, the time of concentration only gives three (3) shallow concentrated flow patterns under the TR55 tab. Any way to get more flexibility with this?

[Anonymous]

Why would you want more than three drainage areas per runoff
coefficient?  I find it easier to chart /excel that data and enter only
the total area and composite runoff.

What kind of situation do you have that necessitates four or more
shallow concentrated flow patterns?

Matthew Anderson, PE

Joseph A Schudt & Associates

Frankfort, IL

Civil 3d 2009 / Raster / Design Review

jstrahorn wrote:

First time use of Hydraflow Extension for Civil 3d and have noticed the
limitations of entering shed area data at each inlet.The program only
seams to allow for three (3) drainage areas and does not allow to
change the C Value in each area. Also, the time of concentration only
gives three (3) shallow concentrated flow patterns under the TR55 tab.
Any way to get more flexibility with this?

[Anonymous]

That's one of the main reasons I still use HydroCad. I allows for multiple CN areas that autofill form a TR55 dialogue list, and any combination of TC that even allows for the inclusion of pipes within the flow path. Autodesk should reallly look at others (the competition Carlson).

[Anonymous]

Which Hydraflow program are you using? Hydrographs and Express will allow you to enter up to six drainage areas with independent runoff coefficents and will calculate a composite runoff value. Storm Sewers will allow you to enter up to three drainage areas per node with independent runoff coefficents. Click on the runoff box (C or CN) and it will bring up a dialog box that will allow you to enter multiple drainage areas and runoff coefficents.


You are correct that the Hydrographs and Express extensions will only allow for three of each type of TR-55 Tc (sheet, shallow concentrated and channel), however, the Storm Sewers extension will allow you to specify an independent Tc for each inlet and then design the system by considering both the inlet time and the pipe travel time. Although less convenient, note that you can enter a user Tc value so should you need to utilize more than three shallow concentrated flow paths for example, you could calculate by hand and enter the value manually.


Be careful when using more than a couple shallow concentrated flow patterns. In my experience, the flow tends to transition to channelized flow before I have used all three shallow concentrated flow pattern options. Also note that you can use this TR-55 interface to enter pipe travel time, simply put in pipe cross sectional area and wetted perimeter of your pipe and it will calculate Tc as a function of full flow (gravity) pipe capacity.

Jason Slocum