Chapter 03 / BUILDING YOUR POND
Draw the water level before drawing the bottom.
At a glance
A pond drawing becomes useful when it explains height as well as shape. Start with a fixed reference mark outside the excavation. Use it to show the intended water surface, the overflow and the retaining edge. The bottom, shelves and planting positions can then be measured from that common reference.
A plan shows the pond from above. A section cuts through it from the side. You need both. A smooth outline on a plan can hide a shelf that is too narrow, an edge that is too low or a plant crown that will sit at the wrong depth. A couple of carefully chosen sections reveal these problems early.
Depth is not the same as excavation depth. Underlay, protective layers, substrate, baskets and construction tolerances all take up space. Allow for them in the drawing. When a plant label gives a planting depth, check whether it means water above the crown, above the soil or above the container.
The main idea: Calculate with the depth of water that will actually be present, then verify the first fill.
In practice
- Mark a fixed datum and record the intended water level. Do not rely on the existing lawn being level.
- Break the pond into simple zones: shallow margin, intermediate shelf and deeper open water. Write an approximate area and average water depth for each. Add the zone volumes together.
- Place the overflow and all pipe crossings on the plan. Check the entire retaining perimeter against the same datum before completing the edge.
Going deeper · the science behind this chapter
For a zone with approximately uniform average depth, volume V = area A × mean depth d. Suppose an illustrative pond has 8 m² at 0.25 m, 6 m² at 0.60 m and 4 m² at 1.20 m. The corresponding volumes are 2.0, 3.6 and 4.8 m³, giving 10.4 m³ before accounting for displaced water and details of sloping sides. The averages, not the deepest point in each zone, determine the estimate.
A liner take-off begins with the maximum basin length and width, the profile over the sides and an allowance for the chosen edge detail. A quick rectangular approximation is length + twice maximum depth + edge allowances, repeated for width. Complex shelves and irregular profiles are better measured along their actual route with a flexible tape after excavation. Manufacturer joining and anchoring requirements still apply.
The first fill provides an opportunity to measure actual capacity using a suitable water meter or a known supply flow over a recorded time. Compare the result with the drawing, noting water held in filters and streams. This measured volume becomes the basis for later concentration and inventory calculations.
Avoid false precision: an estimated 10.4 m³ is not the same as a surveyed 10,400 litres. Record how the estimate was obtained and revise it when better information becomes available.
Plan view + side sections + one datum → a buildable description of the pond.
Watercolour scenes are AI-generated illustrations. Diagrams and teaching models are identified in their captions.