We have several buildings which we are seeking to harvest rainwater to an earth dam for use. Basically we have several gutters and downpipes. The Downpipes will in turn be connected to collection pipes which eventually flow into the earth dam. The water should basically flow into the earth dam through gravity. The objective here is to establish the furthest building we can collect water from and size the collection pipes accordingly.
So far I have done the following:
Am i in the right direction so far? Is WaterGEMS the right modelling solution?
I currently seem to have one problem though. Negative Junction Pressures, with reasonably high velocities, in areas where logically there shouldn't be none. Am i missing something.
Hi Japheth,
When you say that the objective is to determine the furthest building you can collect rain water from, do you mean that you want to determine the capacity of existing pipes, so you can determine how many building can connect to this system without causing an overflow/backup? Or, are you trying to size the pipes and find a balance between the material/excavation cost and the number of buildings that can contribute to this? Or, something else?
The underlying assumption with WaterGEMS is that pipes are flowing full and under pressure. So, if these "downpipes" are flowing partially full, the results will not be accurate and it would be better to use SewerGEMS or CivilStorm. Both of these programs can model unsteady simulations for gravity pipes, and model ponds, pond outlets and pond sizing. See:
You would then be able to model the runoff hydrograph of the contributing buildings (timing of the hydrograph peaks could be of concern, if some buildings are much farther away than others) and view a profile of the pipeline to determine if it has adequate capacity, along with sizing of the pond and pond outlet.
If the "downpipes" are flowing under pressure/full and you want to assume a certain inflow rate, then WaterGEMS can be used with a negative demand as you described. Keep in mind that the negative demand is a flow rate, which is different from a volume (unless perhaps you configured a demand pattern to model the varying inflow to get the desired overall volume after a period of time). In this case you would need to make an assumption on the downstream side, such as using a reservoir or tank to model the hydraulic grade at the pond (earth dam). Whether or not this is an OK approach may come down to what you ultimately need the model to tell you (see further above).
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Answer Verified By: Japheth Osumo
Japheth Osumo said:Now since i already know the flows do i really need to draw the catchment areas accurately or i can simply have random shapes
Yes, you can hold the CTRL key and left click in the drawing to start drawing the default shape. Move your cursor and then click again to place. Select "None" as the runoff method in the catchment properties (or global edit in the catchment Flextable), then enter your fixed flow in the "Inflow (wet collection)" as a fixed flow. You can also use the Inflow Control Center (Components > Loading) to initialize and enter a fixed flow for all catchments, if needed.
Note that the Implicit and Explicit solver perform an unsteady simulation where the element of time is involved. This means that if you enter a constant flow, it will be the same flow value for all timesteps. So, you would want to make sure that the flow values you calculated are acceptable to assume as a constant flow rather than a hydrograph that rises up to a peak for a short period of time and then drops back down. Consider the amount of water volume from a constant flow and the impact it has on the hydraulics of an unsteady simulation.
Japheth Osumo said:Use of Manholes: There's Ground, Rim and Invert Elevations. Assuming my pipe will basically follow the ground surface (Invert= Ground Surface). What is the best way of populating these..
If you are modeling an enclosed junction of pipes (no vertical vault structure) and the pipes are resting on the ground, then the manhole invert and ground elevation would be equal to the ground and the rim elevation would be equal to the pipe top/crown.
To quickly populate the ground, you could use Terrain Extractor, and then copy/paste the ground elevation values to the invert elevation, using the Flextable: Copy and paste (import or export) tabular or Flextable data
If all pipes are the same diameter, you could also paste the ground elevation to the rim elevation field, then perform a global edit to globally add the pipe diameter/rise value. If there are varying conduit diameters, you would need to manually add the diameter of the adjacent conduit to the invert to get the rim elevation. You could perhaps use annotations to help with this.
Am getting somewhere. So basically i need to create like 1,000 catchments and associate them to Transition Elements. Any quick way of doing this, like in one or two clicks. Currently am going into the properties of each catchment and selecting the outflow element. For 1,000 catchments this can take a while. Looking for an option to simply select a catchment and click on a transition element, then the transition element gets tagged as the outflow element..
A workaround i found is in the link below. Though not exactly what i was looking for but it is better than the alternative.
communities.bentley.com/.../assigning-catchment-outflow-node-and-tc-automatically-in-bulk
Jesse Dringoli said: Select "None" as the runoff method in the catchment properties (or global edit in the catchment Flextable), then enter your fixed flow in the "Inflow (wet collection)" as a fixed flow. You can also use the Inflow Control Center (Components > Loading) to initialize and enter a fixed flow for all catchments, if needed.
I get the following Error,
The Selected Runoff Method None is not supported. Only the Rational Method is supported by this Solver.
I wanted to use GVF Rational, as my analysis is more or less Steady State and not Dynamic/ EPS. I have already calculated specific Base Flows at each downpipe.
What i simply need is to size the network to convey these flows.
For the Rational solver you would need to use manholes or catchbasins to directly enter your flows. For a manhole at an upstrea-most point, you can use the Known Flow field or the inflow collection in the manhole properties. For a catchbasin there are a few more options as seen here, though it cannot be modeled with a bolted cover.
Per my previous replies you can configure the manhole with a bolted cover to allow surcharging (if expected) and set the rim elevation equal to the pipe top if it represents an enclosed junction.