Join Eric Chappell for an in-depth discussion in this video Understanding storm design for sites, part of AutoCAD Civil 3D: Site Design.
- [Instructor] Before we dig into storm design for sites, let's take a look at the finished design so that we can gain an understanding of what we're about to do. If we take a look at the plan view, we see that a lot has happened since we left off with the last chapter, which was focused on grading. We see that we've got some storm structures here. We've got some inlets, some pipes, and everything kind of flows out to a pond over here to the west of the parking lot, which as you might have noticed, is another major feature that's been added to the design since we graded the parking lot.
Now if you're not familiar with how these types of storm systems work, the idea is this. Where we're placing grass or forest, or some very pervious surface, with pavement which is very impervious so that increases the amount of runoff and the speed of the runoff. So one of the ways that that is mitigated is to create a pond, and this pond is actually quite large for this small parking lot, so we would have to assume that the pond is also handling the runoff from this road as well, although we don't see storm pipes leading into it, we can make that assumption.
So what happens is, you take all of the additional runoff and you take it to the pond, and kind of let it sit there for a while, and release it in a controlled manner, so that ultimately the amount of flow, the rate of flow, and the amount, is controlled, and usually the target is to something that is equal to or lesser than the existing condition. So before we ever even built this development, we want to match or be less than the amount of flow that was being released from this area prior to development.
So that's what's going on here. We've got water coming into the pond. We've got an outlet structure that controls the outflow of water, and we're emptying it out into this area, which you can see we've got some sort of stream channel here probably going under the road with a culvert, which we can't really see, but we're just assuming that's what's going on in the back here. So we've got the pond, and the pond has a certain size and depth, and that has to be designed in as well. You may be wondering what these kind of strange contours are over here.
Ponds typically have an emergency spillway, so if I go into 3D view over here, and zoom in a little more closely to that area, you'll see a spillway has been carved out of the pond. Let me just spin that around a bit, and get just the right angle. There you can see the spillway that's been carved out. So in very high rain events, we want to have a designated place for the water to exit, so that it doesn't dump out into the parking lot, or breach the dam, breach the pond wall or something along those lines.
So we've got the storm system, we've got the pond, they're tied together. You can see this outfall is somehow tied into the corner of the pond, and it's not just in its plan view, X and Y location, but also its elevation. We've also got labels on the storm system, so a lot of things are involved with figuring out where the inlets need to go, capturing the water, conveying it to the pond, designing the pond itself, carving out the spillway, and a final thing I'll point out is that this is all one surface.
If I click on one of these contours, all of them light up, even the road contours. So somewhere along the way, we had to combine all of this grading, the pond, the spillway, and we had to make it part of the overall finished ground surface. One more thing that's out of the view that I'll pan over and show you is that we also have a profile of our storm system, and this is typically a requirement to show reviewers and also as a design aid, so we can see that everything is sloping in the correct direction, and that it's interacting with the finished and existing ground elevations properly.
It's pretty common to see a profile as part of your storm design. So now you have an idea what we'll be working on in this chapter.
- What is site design?
- Creating feature lines
- Breaking, joining, trimming, and extending feature lines
- Adding and removing elevation points
- Raising and lowering feature lines
- Creating grading objects
- Building a grading scheme
- Creating curbs and parking lot surfaces
- Labeling a grading design
- Creating a storm design
- Adding inlets and pipes to a storm design