Ezigrade (version 2)

Ponded Landscape with Drains

In this tutorial we are presented with a surface that contains a number of natural ponding area's. These area's hold water and don't typically drain by themselves. There are a number of ways to handle this scenario:
  • The "do nothing" option.  You can leave the pond as is, Ducks need somewhere to live. In this case modify the natural surface so that the surface does not include the pond area. The grading will grade around the pond; leaving the pond as is.
  • Let the grading option simply fill in the pond. Whether to drain or not depends on the volume of the pond, and whether it is worthwhile putting in a drain. Australian "Melon Holes" are typically smaller and best option may be to simply fill.
  • Cut a drain into the pond before grading. You may partially drain and fill. The operator needs to decide how much dirt needs to be removed against how much dirt needs to go into the pond.
In this scenario we intend to cut one or more drains into the ponded area's. The procedure we follow is:
  • design drain so that a large portion of the troublesome area would be drained
  • incorporate the drain into the natural surface
  • redo the grading as always ( the grading knows to leave the drain in situ as long as it means the water drains). The smoothing goes around the edges.

Analysing the Natural Surface:

We are presented with the following natural surface:
We have outlined some of the deeper pond area's. We can pick the problem area's in the natural surface by displaying the surface by height. We can then look for area's that are lower than surrounding area's without any exit channels.
To make this easier to pick we have also added in a special surface.

Ponding Surface

A ponding surface shows the water depth across the surface; assuming that all area's are filled with water. Click on the Contour ->Surface Parameters menu item. Click on the "Add" option and select a ponding surface. We suggest that you make this surface4. Ezigrade by default, sets up the surfaces as 1 Natural, 2 Design, 3 Difference (Cut/Fill). Once the surface 4 (ponding) surface is created click the "Reset" button. This sets up the surface.
You can reform the surface at any time. The contour intervals etc are identical in nature to all the other surfaces. Once the surface is formed we suggest that you set up surface colors as this is a good way to represent the ponds. Click on "Contour - Surface Parameters - Surface Colors". We have the following dialog.
In this instance we wish to ignore pond depths less than 1 tenth of a foot. So set the first interval to be between 0 and 0.1 depth and set the color to white. We have split the remaining bands into shallow, moderate and deep bands. In this case more colors can be more confusing.
Close the dialog and display the ponding surface.
This display shows the worst problem area's as dark blue. After rain the cyan area's are filled. The water slowly retreats to the dark blue area's that are probably always boggy, and unusable for agriculture.
In this tutorial we will initially look at the worst ponding area; towards the bottom right of the job.

Grading Design:

Before we start designing drains; it is a good idea to run the grading so that we have a base to compare ongoing designs with. In this case we simply want the water to always flow to the edge of the job. We want a minimum grade of 0.04% and we want some smoothing of the design surface. As per the screen shot above. Set the min and max grades and set the grading type to "AllWay". There is no need to define section links, or define a section. Ezigrade assumes the whole job if nothing is set here.
If we run initial grading on this; ie Grading - Triangle Grading we can generate the following report.

Designing the Drain:

We intend to initially design a drain to partially drain the worst ponding area. We need to run as much of the water out of the drain to another section of the job. Ideally we want to minimize the length and the amount of dirt we need to cut away to make the drain. You as the designer needs to initially decide were to run the drain. We supply the tools to make your job easier. In this example we have gone with a design that drains the water in a westerly direction. Simply click the drain in as per the couple of previous tutorials.
We have designed the following initial design.
Plan View:
Profile View:
The drain runs from West to East. On the right you can see that we have not drained to the bottom of the pond.
Section Design:
You can see that we have a box drain and are setting the batter slopes of the edges to a value of 5%.
The plan view shows the extents of the drain with the top of the bank. If you click on the "Drains - Report Volumes" you will see that we are moving 6360 cubic yards to make the channel. You as the designer need to decide if this is acceptable. In this case we will go with this value. I would note that it is relatively easy to move the drain around in plan view ( change profile design) and recalculate volumes if you need to check other alternatives. (Or put in a whole new drain and then delete worst result).
Once we are satisfied with our drain design we incorporate it into our natural surface. Click on the "Drains - Merge Drain into Natural". This puts in extra points that define the bottom and daylight points of the drain. These points are stringed together as breaklines and any existing points in the drainage corridor are set so that they are not included in the triangulated surface. The drain design is then locked so that it can't be changed. This is necessary if we wish to undo the merge later; we don't want the drain shifting position. If you now run the procedure theabove is done. To see the result you need to turn off the drainage display which overwrites the area. After performing this operation we have:
You can now see how our drain has been cut through and that water is going to flow down the channel in a westerly direction.
We are now in a position to rerun the grading. It is important that the channel grades lie withing our min and max grades for the job. We don't want them changed. Also from the drainage volumes we had a volume of 6360 in the drain. Set this is in the Borrow section of the grading section. This ensures that the volumes balance out at the end.

In Conclusion:

Before drain added we had             Cut   -39830   Fill   33194
After single drain has been added  Cut    -19564   Fill   16319
These values can be further improved upon if we address some of the other smaller ponding area's. However below a certain size it is probably not worth the effort.
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