In this video we show a work process to develop a design for a water storage / fish hatchery pond.
The process starts with a site survey model that provides existing ground information and the desired limits of the pond based on existing site boundaries and tree lines etc. that the pond has to live within.
The process steps include
Defining the Design Criteria
What are the design criteria for the pond - in this case they wanted a 12’ berm top with either a 0% or -2% cross slope and a side slope on the inside and outside of 4:1 in cut or fill (mostly fill). They wanted the berm top to be high enough to be able to a) store water and b) to balance Cut / Fill for the pond. They wanted a fish hatchery area in one part of the pond covering ~40x40 feet and that hatchery area should be 1’ below the water level at its highest level (in this case we chose a water level of 72’ and a berm top of 73.5’). To try to generate a balance of earthworks we excavated 2’ of material out of the existing in the pond base area to generate the material for the berm and to provide sufficient depth of water for the hatchery area. They also wanted a 10’ water safety bench around the pond where the water was >2’ deep.
A key factor here then is if we are to design a horizontal alignment around the outside edge of the berm top, on the inside of the pond we need 12’ for the top of berm, we need 14’ at 4:1 to get to the 70’ elevation for the bench, we then need 10’ for the bench and then we need whatever distance for the remaining 4:1 slopes down to the pond base. As a minimum this is 36’ but with the deeper water areas, this may be as high as 56’ to 60’ for the widest areas of the berm / levee. This means that ideally arcs in the alignment for the top of levee design should not be less than 60’ radius if we want the modeling to go smoothly. if you need 60’ and your arc radius is 35’ then the projected slopes will cross over each other before hitting the target surface - in corridor models and sideslope models this will mean that the slopes are cropped out to stop them from overlapping and crossing over each other (examples of this are shown in the video and how to manually address them.
Finding The Location of The Design Alignment
Come off the boundary of the surveyed surface at a 4:1 slope to the berm top elevation (73.5) to identify roughly where the design line needs to be. Then you can design the alignment so that it roughly follows the computed line, but now you can design in true tangential curves and straight sections to define your pond shape based on the terrain you are working with.
Design Your Berm Using Sideslope or Corridor or Slope Designer commands
You can use the Corridor command or the Sideslope Command or the Slope Designer command to design your berm. The Sideslope and corridor model provide a more dynamic design tool than slope designer - slope designer provides some other options that are beneficial especially when the source lines are not curvilinear in nature.
Add in you pond base model
Clip the 2’ adjusted existing surface to the base of the tie slope on the inside of the pond berm. Use the Offset Surface command to achieve that. You can then add that clipped pond base into your pond design surface model.
Design your Hatchery Pad Shape and Place it Where You Want It
Design the pad for the hatchery area at 71’ elevation and using a rectangle 40x40’. Fillet the corners of the rectangle to round them.
Move the hatchery pad into position using the Move command and the Rotate command to align it as needed.
Then use the Slope Designer Tool to compute the sideslope at 4:1 from the hatchery pad down to the base of the pond model.
Add the sideslope and Hatchery Pad lines to a new surface - Hatchery
Now use the Merge Surface command to merge the Pond Design with the Hatchery model. Let the Hatchery Model replace the pond model in the area of the Hatchery pad.
You now have your finished model.
Adding a Water Level Surface
Use the Contour at Elevation command to create a contour on the final pond model at elevation 72.
Explode the contours created
Use the contour around the inner sideslope of the pond to create a Water Level Surface Model. Turn off the display of wireframe and change the display to Surface Color Method and set the surface color to Blue - you can now see the Water Level, The Pond Model and the Existing Terrain in the Surface Slicer view.
Adjust and tweak the model as needed.
Run Your Volume Calculations
Use the Surface Earthwork Report to compute the Cut and Fill between your Existing Ground (Original Survey) and Final Pond Model Design). Remember the Cut Material will shrink when placed and compacted in fill. Shrinkage can be anything from 5 to 15% depending on the nature of the existing ground materials. Also remember that you likely need to strip topsoil and use it to respread on the pond slopes after construction. So Your Cut quantity likely needs to be 8-10% more than your fill quantity required.
Because this is a pond - you can likely dig out more material or backfill deeper pond areas with excess material to get your balance - so the Cut / Fill balance needs to be close but not perfect - you could also narrow or widen the bench or increase / decrease the size of the Hatchery Pad or add a second hatchery pad as needed to help balance the materials.