Civil 3D is a complex program. It has many tools to accommodate the various aspects of Civil engineering and surveying. Sometimes these tools appear to overlap – you can use different Civil 3D features to solve the same problem. A case in point is pond creation.
Pond design is a serious business. If ponds aren’t properly designed to accommodate the proper volumes and discharge rates, a project can fail (and the environment can suffer). There are many types of ponds, including retention ponds (where there is no outlet), detention ponds (with a controlled outlet to regulate the flow), lagoons with multiple bays, etc.
ASCENT covers two different ways of creating a pond in its Autodesk Civil 3D: Fundamentals for Land Developers (Grading) guide, and another way in its Autodesk Civil 3D: Fundamentals for Grading Optimization guide. Below I have summarized the different tools that can be employed to create a pond using Civil 3D.
Civil 3D Grading Tools for Designing a Basic Pond
There are four basic grading criteria one can employ in Civil 3D:
1. Grade to a distance
2. Grade to an elevation
3. Grade to a relative elevation
4. Grade to a surface
One can use any of these to create custom criteria. It is with these basic criteria that a “simple” pond is created in Chapter 6 of the Autodesk Civil 3D: Fundamentals for Land Developers guide. This chapter covers how to add feature lines, upon which grading objects of different criteria are based. The chapter cumulates with calculating the volume of the pond at various levels (or stages), which is known as stage storage.
The resulting pond is dynamic in that modifying any of the grading criteria or the feature lines’ shapes or elevations will modify the entire pond. With each such modification, a new stage storage analysis needs to be run.
Civil 3D Corridors for Lagoon Design
The appendix in the Autodesk Civil 3D: Fundamentals for Land Developers guide deals with grading a pond using the corridor creation tools within Civil 3D. It demonstrates creating a corridor with alignments and profiles, as well as with feature lines. Then assemblies are created which emulate the three of the four basic grading criteria within Civil 3D:
1. Link Width and Slope = Grade to Distance
2. Link Slope to Surface = Grade to Surface
3. Link Slopes to Elevations = Grade to Elevation or Grade to Relative Elevation
The pond created has different bays and contains a weir. The corridor contains different regions for different grading criteria and different baselines for the separate bays. Corridors are dynamic, and modifying and adjusting any part of the alignment, profile, feature line, or assembly will reshape and adjust the overall pond.
Grading Optimization
Grading Optimization for Civil 3D is an alternative approach to designing grading solutions to those mentioned above. It works in tandem with Civil 3D but is a separate application that processes many iterations of the grading parameters assigned in Civil 3D to create a grading solution.
Designing a pond using Grading Optimization is covered in Chapter 3 of ASCENT’s Autodesk Civil 3D: Fundamentals for Grading Optimization guide. The approach is to define the pond perimeter with a simple polyline and then assign the pond grading object to the polyline before entering specific parameters for the requirements of the pond, such as storage volume and slopes for various parts of the pond.
The Grading Optimization program then processes these parameters and the geometry within the given base surface to establish a preliminary pond design. Within the Grading Optimization program, adjustments can be made to any of the given parameters, but not to the geometry of the polyline or the base surface.
Once an acceptable preliminary solution is found, the result is exported back as a surface, feature lines, and points into Civil 3D, where refinements can be made.
Pond Design with Feature Lines
The option for creating ponds with only feature lines is not covered per se in our guides; however, the topic of grading with feature lines (for parcels and parking lots) is covered extensively in the Autodesk Civil 3D: Fundamentals for Land Developers guide.
The advantage of using feature lines is simplicity. One can lay out the pond control lines in three dimensions and add them to a pond surface. The feature lines remain connected to the surface, so editing the feature lines will affect the surface.
The disadvantage is that this method does not take advantage of Civil 3D’s problem-solving abilities. For example, one cannot prescribe the slopes of the grading or the storage volume the pond should contain.
Conclusion
Civil 3D users have many tools at their disposal. Just like in any craft, one tool won’t do it all. The experienced user understands which tools are best used for which situation, and that any complex problem will require many different tools.
A proper pond design may use any or all of the tools described above. With proper usage of such tools, the pond can be a dynamic object that can easily be modified and adapted as design parameters change.
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