In Geopak Drainage, will the software automatically accumulate separate drainage areas and time of concentrations in determining the accumulative flows for a particular system?
For instance at the beginning of the basin you have a sub-basin No. 1 with a pipe as an outlet. This portion of the system has an area A-1 and time of concentration Tc-1 resulting in a calculated flow of Q-1. Now further downstream, you have open channel from the previous pipe discussed to the next pipe that is an outlet to sub-basin No. 2. In this instance with flow being a factor of time and area the following would hold true for its flow calculations in sub-basin 2: Area=(A-1) + (A-2); Time of Concentration=(Tc-1) + (Tc-Pipe) +Tc-Openchannel); yielding a flow of Q-2. And this continues until you have developed all of the flows you want for a given drainage basin. So, moral of the story is flow (Q), is a function of time (Tc) and area (A) accumulated from sub-basins upstream. Of course there are other factors such as land surface coefficients and etc...but that's not important to my question.
Now back to my question....Will Geopak automatically accumulate this information in calculating flows as it moves downstream if the operator inputs separate drainage areas for each inlet node, or will the operator have to "stair-step" through the system including previously developed sub-basins?
To try and be more clear, I have attached a hand drawing of what I'm talking about. I'm no artist, but maybe it will get the point across if my awful attempt of wordsmithing has confused you.
As stated in previous posts this week about Drainage, I'm new to the software and trying to learn as much about it as possible to make sure I fully understand its capabilities, kwirks, and limitations. The software looks to be awesome, but is only as good as the information put into it.
Thanks for any advice given...it will be much appreciated.
Matthew
Hello again Matthew,
You're right - I don't see the calculation method documented for that Tc through the system.
I do recall asking the same question many years back when I first came into contact with the drainage tool, got an answer, followed the calculation myself and being satisfied it made sense.
Of course, now that I no longer use Drainage and don't even have a dataset to look at, working though it to provide an answer isn't possible.
You could zip your dataset up and send it and I'd be happy to take a look.
Or you can contact the experts directly at Bentley through their support.
Michael
I appreciate it. I have already contacted Support and waiting to see what they. If I dont hear from them, I may send you a copy of what I have so that you can give it a look.
Thanks,
Well, I talked to support about my situation. Apparently, Geopak Drainage always assumes that contributing flow from individual drainage areas are applied to the node/pipe completely and does not take into account any bypass flow. In other words, in your network, if you have a drainage area that computed 100cfs, it doesn't matter if your pipe is 2 inches or 20 feet, it will assume that every bit of the flow is being routed through the pipe, resulting in either extremely high or low pipe velocities...then uses this computation to determine the time of concentration. I feel that this is a major downfall in drainage analysis software. The software ought let the designer/engineer have the ability to fine tune the computations of the software. I believe this restricts the uses of the software as well as the users ability to use judgement calculations......which in short is a key factor to doing any hydrologic or hydraulic computations.
Hi Matthew,
Thats interesting - considering the Nodes dialog has an option to allow bypass to another node.
When the node is in sag, the water cannot go anywhere except through the pipe... right? Of course, depending on how deep that sag is and how much volume it can hold, potentially the sag can fill up and the water will run somewhere else. You'd need a Haestad application if modelling that type of scenario is what you need.
But, if the Node is an "on grade" type, then you can set the bypass to go to another node further downstream and the pipe is asked to handle only what it can handle. The remainder is by-pass. Under this scenario, the velocity in the pipe is based on a full pipe + whatever head is there between the pipe and the grate level that is pushing the water through.
HTHs
Well see, we tried that.....or at least thought we did. Where in the software do you setup the criteria to bypass to another node? I saw where you can setup bypass for inlet items such as a grate inlet, slotted drains, etc. but what about just a typical pipe opening? The drainage areas that we are working with have a lot of "free standing" drainage pipes. For example, we have a lot of driveway pipes where there is a roadside ditch, then pipe, then ditch, then pipe, and so on and so on. So, to assume an inlet node would be incorrect. The majority of the pipes don't even have headwalls. How would you model that? Is there a way to create a node feature that would allow bypass on a pipe without it having to be an inlet node?
Hi again,
this just keeps getting more complex :-)
If you wish to go to the trouble of modeling every driveway crossing as a link with "headwalls" (look these up in the Drainage Help>Command Reference>Commponent>Node>Properties Dialog>Headwall) at each end you can.
Between each driveway crossing, you have the opportunity to insert links that are open channels. That should cover your scenario (I think).
But, that would be a lot of effort.
Do you really need to model every driveway crossing OR can you simply run an open channel the whole way through that portion and assume that, at the driveway crossings the water is either going to flow through the pipes OR through the pipes and over the driveway once the pipe is full.
Depends on your goal I guess.
While you are looking in the Help, have a look at the "Other" node type, you may have use for that too.