HydroCAD alternative for site detention
For an engineer who sizes ponds in HydroCAD: the method basis PondSheet shares with it, where each runs and what each costs, and what PondSheet leaves out. Each HydroCAD fact links HydroCAD’s own page.
What is the same
Both rest on the NRCS method: HydroCAD describes itself as combining the capabilities of TR-20 and TR-55 (HydroCAD: TR-20 and TR-55 comparison). Each HydroCAD term maps to PondSheet’s on the term map.
| Method | HydroCAD | PondSheet | Basis |
|---|---|---|---|
| Runoff | The SCS/NRCS unit hydrograph procedure (TR-20), one of its runoff optionsHydroCAD: runoff | TR-55 runoff with the NRCS dimensionless unit hydrograph | TR-55; NEH 630.16 |
| Rational method | The Rational method, another of its runoff optionsHydroCAD: runoff | Rational method, as a drainage area’s method | FHWA HEC-22 |
| Curve numbers | Curve number lookup and weightingHydroCAD: TR-20 and TR-55 comparison | CN looked up from the TR-55 tables, area-weighted or runoff-weighted | TR-55 Tables 2-2a to 2-2d; NEH 630.10 |
| Tc | The TR-55 Tc methods, among othersHydroCAD: TR-20 and TR-55 comparison | Sheet, shallow concentrated and channel segments, or Tc entered | TR-55 Chapter 3 |
| Pond routing | Storage-indication, one of its pond routing methodsHydroCAD: TR-20 and TR-55 comparison | Storage-indication routing | NEH 630.17 |
| Outlets | Orifice, weir and culvert calculations, alone or combinedHydroCAD: TR-20 and TR-55 comparison | Orifices, weirs, a riser, a barrel and an emergency spillway | FHWA HEC-22, Chapter 10; FHWA HDS-5 |
What differs
| Topic | HydroCAD | PondSheet |
|---|---|---|
| Where it runs | A native Windows applicationHydroCAD: comparison | In the browser, on every edit; the server runs the same engine for the stored run and the report |
| Price | $375 a year for its popular annual license, as quoted in October 2026HydroCAD’s own pricing page | $99 per firm per month, unlimited engineers and projects |
What a PondSheet project carries
- Reviewer link
- A read-only link for the plan reviewer, with the report, the SWMM .inp and the model file. The reviewer needs no account.
- SWMM 5 input
- Every report comes with a SWMM 5 .inp per storm: the pond’s stage-storage, its outlets and the inflow hydrographs, to open and re-run in EPA SWMM.
- Frozen site data
- NOAA Atlas 14 depths and the USDA soil survey are fetched by the server for the site and frozen with the project. An update is the engineer’s choice, and it is logged.
- Check sets
- The criteria are the engineer’s: peak control, WQv, drawdown, freeboard, the emergency spillway, the smallest orifice, each with the source the engineer cites. The NYSDEC manual ships as a built-in template.
What PondSheet does not do
HydroCAD’s own feature table lists reach routing, pump simulations and dynamic tailwater (HydroCAD: TR-20 and TR-55 comparison). PondSheet models none of these in this version.
- Reach
- No reach routing. A channel appears only as a Tc segment.
- A pond draining to a pond
- Ponds drain to a design point; a pond-to-pond link is a note, not a run.
- Pump
- Not modeled.
- Exfiltration, discarded outflow
- Not modeled; every outlet discharges freely.
- Tailwater
- Not modeled; every outlet discharges freely.
The equations, with their pages, are on the methods table; how the engine is checked against published examples and EPA SWMM is on the validation page. The free calculators run the same engine with no account.
14-day trial, every feature, no card.
HydroCAD is a trademark of HydroCAD Software Solutions LLC. PondSheet is not affiliated with it.