EngiMetric Arena / Engineering Trade-off
Choose a pond depth that fits the land and the approval limit
Competency Constraints and trade-offs primary Design and sizing supporting
What you should take away: Relate storage volume, pond depth and footprint, and choose a depth that satisfies both a land limit and a depth limit.
The situation
What is happening
A detention basin must store 1 757 m3 from the design storm. The available site allows a maximum pond footprint of 900 m2, and the approval limits the pond depth to 2.8 m. Choose a depth from 1.5, 2.0, 2.5 or 3.0 m.
Given
| Quantity | Value | Unit | Note |
|---|---|---|---|
| Required storage | 1 757 | m3 | From the design storm. |
| Maximum footprint | 900 | m2 | Available site area. |
| Maximum depth | 2.8 | m | Approval limit. |
| Candidate depths | 1.5 / 2.0 / 2.5 / 3.0 | m | Discrete design options. |
Assumptions this challenge makes
- The pond has vertical sides, so footprint is storage volume divided by depth.
- The required storage is fixed by the inflow and permitted release.
- Freeboard, side slopes and sediment storage are not included.
Limits this decision must satisfy
| Limit | Requirement | If it is breached |
|---|---|---|
| Pond footprint | not more than 900 m2 | Above the site limit the basin does not fit the available land and needs a different layout or release rate. |
| Pond depth | not more than 2.8 m | Above the approval limit the basin needs a geotechnical, safety and permitting review that this project does not have. |
Choose 1.5, 2.0, 2.5 or 3.0 m. More than one depth may satisfy both limits.
Your call
Your answer
Hints
- For vertical sides, footprint equals storage volume divided by depth.
- A deeper pond reduces the footprint, but the depth itself has a limit.
- Check both limits for each candidate. One candidate may fit the land but exceed the depth.
Your answer Engine result
Where that comes from
Each limit, checked
Why
- The engine derives 1 756.7 m3 of storage from the inflow and permitted release.
- At 1.5 m the footprint is 1 171 m2, above the 900 m2 site limit. At 2.0 m it is 878 m2, which fits.
- At 2.5 m the footprint is 703 m2, also fits. At 3.0 m the footprint is 586 m2, but the depth exceeds the 2.8 m approval limit.
- So 2.0 m and 2.5 m are both defensible. The shallower pond uses more land but is easier to construct and inspect; the deeper pond uses less land but has higher embankment and safety requirements.
- The calculation uses a vertical-sided basin. Real side slopes increase the footprint at the top of the pond.
What this challenge does not establish
- The pond is treated as vertical-sided; actual side slopes, freeboard and sediment storage change the footprint.
- The storage volume is a single-storm screening result, not a routed hydrograph.
- The 900 m2 and 2.8 m limits are project assumptions, not universal criteria.
- Geotechnical stability, groundwater, outlet control and emergency spillway design are not assessed.