Implicit (Sewergems Dynamic Wave) design for storm pipes

Question

We are designing a system with storm water pipes, ponds and storage structures. The rainfall data is in time intensity format. The system needs to be checked for three different return periods-5, 10, 20 years. As the storm event is time-depth or time-intensity type, i have adopted Unit Hydrograph as the runoff method with implicit solver. T he implicit system is doing an analysis of the system. It is not designing the pipe system. The velocity and flow for the system is also coming out as zero. We need to design a dynamic system with ponds. Please suggest the best possible solver for this case which will design the pipe system and will do routing for the pond as well.

Larry Abla · Accepted Answer

Jyoti Maan, 
 Here is a Wiki article to help explain the differences in solvers - Differences between solvers: GVF-Convex vs. GVF-Rational vs. Implicit vs. Explicit (SWMM) 
 The article explains that the StormCAD product (and the GVF Rational Solver in SewerGEMS and CivilStorm) uses the rational method to analyze or design a system under peak flow conditions based on peak rainfall intensity, while the other solvers in CivilStorm and SewerGEMS such as the Implicit or Explicit, takes rainfall hyetographs (rain vs. time) and develops hydrographs (flow vs. time) for each pipe and routes the flows dynamically. If you are studying a small area where only peak flow is of interest, or if you need to design a system based on the standard rational method, then StormCAD or the StormCAD solver (GVF Rational) should be adequate. If you are working on a large area where hydrograph routing and storage are significant, where you need to use a dynamic solver, or if you need to otherwise analyze more complex effects such as flooding and controls structures, then the Implicit and Explicit solvers in CivilStorm (or SewerGEMS) is what you need. 
 Please let me know if this does not answer your questions. 
 Thank-you, 
 Larry

Sushma Choure · Answer

Hello Jyoti, 
 In case of dynamic solver, pipe velocities and flows might be zero based on hydrogrographs for few time-steps, but not throughtout time period of day 24 hours. You can color code the pipes for flow or velocity, or color code for velocity and annotate for flow and then scroll through the time-steps to see how the flow and velocity changes over times in model. 
 Or you can also create graphs to observe closely the variation with time. 
 However, implicit dynamic solver will analyze the network based on inputs it will not do the automated design like GVF rational solver which calculated peak flow. 
 If you want software to design the sizes for you then initially you can use GVF-Rational solver, IDF event, design the pipes which will give estimate about the pipe sizes required. And then change solver to implicit and do the modifications as required and as per changes in the runoff method to unit hydrograph, and storm event.

Jesse Dringoli · Answer

Comparing GVF-Rational results to Implicit dynamic results is like comparing apples to oranges - refer back to the Wiki article regarding the differences. 
 The Rational solver uses the Rational method for a steady state peak flow and needs to use IDF curves for rainfall information. It also calculates profiles using a Backwater method. The Implicit solver in contrast computes an unsteady (flow over time) simulation, with dynamic routing and profile calculations. Additionally, the unit hydrograph method is an entirely different method that the Rational Method, and would produce a different peak flow that would not be comparable to the Rational Method flow. You can also look at journal papers and textbooks for differences between Rational Method and Unit Hydrograph Method. 
 If you are looking for a solver that will perform automated design as well as hydrograph routing for pond sizing, you could use the GVF-Convex solver as it has been automated design (steady state) as well as extended period simulation (hydrograph routing), and supports the use of the unit hydrograph method for catchments. Another option to consider would be to use the Rational Method for pipe sizing (this is common for sizing pipes), and then when you want to size the pond or route hydrographs, switch to the Implicit or Explicit (SWMM) solver for the most comprehensive flow routing methodology.

Larry Abla · Answer

Jyoti Maan, 
 This isn't relevant, since Implicit doesn't do design runs. However, it is possible that peak conditions may be higher than the results in the Implicit solver. 
 HTH, 
 Larry

Implicit (Sewergems Dynamic Wave) design for storm pipes

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