How do YOU design storm sewer?

[hydroponder]

I am wondering how some of the users here design storm sewer. I have always used a spreadsheet I put together that uses the rational method along with Manning's formula to design storm sewer. I have heard of some folks using HydroCAD to design storm sewer, and I have used it on some smaller sites, but never on a site with more than a half dozen catch basins. If you do use HydroCAD, how do you compare it to using the rational method in regards to design time and pipe sizing? As always, I try to walk the line between undersized and oversized, trying to keep the costs to a minimum. I am just about to design a site with about 50 catch basins, and am thinking of trying HydroCAD, but am a bit worried about design time and pipe sizing. Thoughts?

 

[WL123]

I always do it in a spreadsheet also. It is easier for me to follow that way and also for the reviewer.

 

[Ryb01]

Before you consider using HYDROCAD, understand how it works, try a few examples and ask some questions. You as designer need to comfortable with the method of design you are using wehether it's using the rational method or HYDROCAD or any other design method.

Speak with your reviewing agency to see if HYDROCAD is an acceptable modelling software.

Generally speaking there's no perfect/ideal or preferred method to design storm sewer other than to design to your specicific site criteria. The rational method works well for storm sewer design as it prodces conservative results, which is never a bad thing when designing an underground piping system.

I typically use a spreadsheet for small projects and/or minor system design, major system conveyance I'd use something a little more poweful than a spreadsheet.

Hope this helps.

 

[froude]

I typically use StormCAD to model storm drain systems. I like StormCAD because it makes visualizing the system alot easier. Also you can set boundary conditions and change them easily (as I'm sure you can with any of the modeling software available). After the initial time to get it set up and running (which really is pretty intuitive), it's trivial to go change parameters (pipe sizes, inverts, etc.)

However, formatting the output from StormCAD can be cumbersome. I still tabulate a spreadsheet so that I can track my HGL elevations (my local municipality requires a spreadsheet in a particular format anyway).

Just my two cents.

Thanks.

 

[cvg]

rational method does not always produce conservative results, only when conservative assumptions are made on Tc and C and drainage areas and routing. Depending on the size of the site and drainage area, rational method may be inappropriate for estimating runoff. If so, a spreadsheet method would be difficult for designing a storm drain using a unit hydrograph method.

 

[Rye1]

I like using HydroCadd. The learning curve is relatively small it does the things it does very well.

The plan reviewer guys got me hooked on Hydrocadd. Whenever they had a plan come in with a complicated HEC-1 model, they would put together a simple Hydrocadd model to check - if the results were in the ball park they moved on.

Robert

http://www.newrivereng.com

 

[Trackfiend]

In the past I've used spreadsheets, then used SWMM for a couple of years, and now I use StormNET (which is SWMM with a nicer GUI). I can use the StormNET software faster than I could with the spreadsheet, although I still tend to back check the model with the older spreadsheets (at certain points in the system).

The spreadsheets do come in handy for the reviewing party though, since most don't have access to some of the larger modeling software.

 

[HEHurst]

The question possibly could be broken down into a couple other questions:

1. What hydrology method is used to compute design flows (Rational, SCS, SWMM Runoff, etc.)?
2. What hydraulic method is used to calculate depths/water elevations? (uniform flow computation for each pipe segment, steady-state backwater analysis using energy equation, dynamic routing using SWMM or similar)
3. What computer software or manual method is used to do the above?

In my opinion, the most uncertainty surrounds question 1, the design flows. I agree with cvg that the Rational Method is not necessarily conservative - most side-by-side comparisons of flows calculated using the Rational and SCS methods that I've seen have higher flows from the SCS method. Rational Method seems to more closely match gage flows / actual catchment data without much conservatism, which is a good or bad thing depending on your situation and how you account for variability/factors of safety. Granted it all depends on your procedures for calculating input parameters.

Item 2, hydraulic method, sometimes is quite important and sometimes makes little difference. When you're designing a new system without a significant downstream backwater and can design in adequate freeboard, probably all methods will work well if used properly. But when you've got backwater effects, hydraulic restrictions, intentional or unintentional storage in the system, you need a more detailed analysis.

With regards to item 3 Computer Software, something that has puzzled me is that in a field where so many of the industry-standard water resources software is government-developed freeware (TR-20, TR-55, HEC-HMS for hydrology; HEC-2 and HEC-RAS for river hyraulics, HY8 for culverts, SWMM for dynamic hydraulics), steady state sewer modeling is the one big application where no government agency has stepped in with a widely-used, Windows-based software, something along the lines of StormCAD (I consider SWMM to be in a separate category). I guess the government has never felt the need for a public-domain application of this nature (though let me know if you know about one). Good thing for Haestad and the other software vendors. Maybe it's because it's possible to do the core analysis in a spreadsheet?

 

[cvg]

... no government agency has stepped in with a widely-used, Windows-based software, something along the lines of StormCAD

not entirely true, LA County Flood developed WSPG software for storm drain design a long time ago, it is widely used at least in California, although to my knowledge it does not have a GUI interface yet...

http://www.ladpw.org/wrd/Publication/index.cfm

 

[HEHurst]

Thank you cvg, I will check out that LA County software. I also believe there is some sort of steady-state sewer analysis software included in the Federal Highway Admin's HYDRAIN package of programs, but from what I understand it is still DOS-based, not that intuitive or friendly to use, and I've not run across anyone that actually uses it regularily; therefore I haven't explored it and it doesn't seem to have made a major impact.

 

[gbam]

For us Microstation/Inroads users Storm & Sanitary does a nice job that includes time functions for the rational method. It also ties in with the roadway surfaces and existing dtms. However, I typically start with a spreadsheet to estimate the location and inlet sizes then code into S&S or StormCad to compute the inlets and pipe system hydraulics. The spreadsheet, I use, computes the drainage area, discharge and spread based on station, which makes it easy to locate each inlet and tweak.

 

[rday]

The Urban Drainage and Flood Control District along Colorado's Front Range has developed an extensive set of spread sheets.

http://www.udfcd.org/downloads/down_software.htm

 

[Crystalct1]

I recommend InRoads Storm & Sanitary also - but it has the best advantages when your roadway guys are modeling using InRoads. It is very easy to see conflicts, check cover, etc visually. When I first used it, I checked it against my spreadsheet and the answers are identical - not just close. It uses HEC-22 for system losses and the HGL/EGL calculations. I'm not impressed with the reports it produces - mere text files with not any formating options. And it may be expensive and time-consuming to get up-and-running.

Spreadsheet is a problem for me because of composite slopes. In order to get the spread and efficiency of an inlet on a composite slope, a trial-and-error procedure is needed - or Excel's goal seek. This is a manual calculation that must be done one by one whenever anything changes upstream. This is a pain to keep track of. There is no simple equation on composite slopes. Without using goal seek or the nomograph, you would have to use a conservative revision to the cross-slope.

I do not like this because we water-people are already using conservative estimates for all the parameters that we are not sure about. For this reason, many of our designs are little more than "guesses" that any intelligent person could come up with and defend. We need to do better than we have been and "pin down" some more of our numbers and stop using "engineering judgement" when we don't know the answers.

Use the software so we can at least get the numbers right for the stuff we DO know.

 

[brandoncdg]

WSPG, the manual written in 1979 and software based on punch cards. Why was that software never updated to anything current??

CDG, Civil Engineering specializing in Hillside Grading in the Los Angeles area

http://www.CivilDevelopmentGroup.com

 

[cvg]

WSPG was converted from punch cards to PC a long time ago and is available free. Like I said, I don't believe it has been converted to windows format, there are too many other commercial programs out there such as stormcad to compete with.

 

[brandoncdg]

cvg: Except do cities where WSPG originated accept other methods for calcs? Just throwing that out there, since not every city allows you to use any software for reports and calcs.

CDG, Los Angeles Civil Engineering specializing in Hillside Grading

http://www.CivilDevelopmentGroup.com

 

[cvg]

I have used WSPG for projects in California and Arizona and not just in Los Angeles. Los Angeles County Flood Control District is one of the largest agencies in the states with thousands of miles of storm drains and channels many of which have been designed using WSPG. It is perhaps more widely used than some of the other software that has been mentioned.