Coming from HydroCAD
HydroCAD’s term on the left, PondSheet’s for the same thing in the middle, and the document both rest on at the right.
Terms
| HydroCAD | PondSheet | Basis |
|---|---|---|
| Subcatchment | Drainage area, entered once for pre-development and once for post | TR-55 runoff; NRCS unit hydrograph (NEH 630.16) |
| Area listing: cover, soil group and CN | Subarea sheet: cover, HSG and area; CN looked up, or entered as an override | TR-55 Tables 2-2a to 2-2d |
| Weighted-CN, Weighted-Q | Composite CN: area-weighted, or runoff-weighted | TR-55 Worksheet 2; NEH 630.10 |
| Tc: Sheet Flow, Shallow Concentrated Flow, Channel Flow, Direct Entry | Tc segments: sheet, shallow concentrated and channel; or Tc entered | TR-55 Chapter 3 |
| Rainfall event, such as Type II 24-hr | Storm: the project’s frozen rainfall table and a 24-hr distribution (the NRCS nested site storm, Types I, IA, II, III or a regional table) | NOAA Atlas 14; NEH 630.04 |
| SCS TR-20 method, UH=SCS | NRCS (TR-55) method with the dimensionless unit hydrograph | NEH 630.16 |
| Rational method | Rational method, as a drainage area’s method | FHWA HEC-22 |
| Pond | Pond: a surface pond, or a manufactured chamber system | Storage indication (NEH 630.17) |
| Stor-Ind routing | Storage-indication routing, the one routing method | NEH 630.17 |
| Custom Stage Data, conic or prismatic | Stage-area sheet, conic or average end area, typed or pasted from Excel or a Civil 3D report | FHWA HEC-22, Chapter 10 |
| Orifice/Grate | Orifice, circular or rectangular | FHWA HEC-22, Chapter 10 |
| Sharp-Crested Rectangular Weir | Rectangular weir, with or without end contractions | FHWA HEC-22, Chapter 10 |
| Sharp-Crested Vee/Trap Weir | V-notch weir | FHWA HEC-22, Chapter 10 |
| Broad-Crested Rectangular Weir | Emergency spillway, broad-crested, tagged emergency | FHWA HEC-22, Chapter 10 |
| Culvert | Barrel, with devices routed to it or not | FHWA HDS-5 |
| Primary and Secondary outflow | Outlets that discharge directly, or through the barrel; the emergency spillway is tagged as such for the checks | FHWA HEC-22, Chapter 10; FHWA HDS-5 for the barrel |
| Link to a node | Design point: where pre- and post-development flows are compared | The criteria you select |
| Peak Elev, Storage, Inflow, Outflow | Peak water surface, peak storage, peak inflow and routed outflow, per storm | The run’s results and the report |
What PondSheet does not model
- 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 behind each term, with their pages, are on the methods table; how the engine is checked against published examples is on the validation page.
HydroCAD is a trademark of HydroCAD Software Solutions LLC. PondSheet is not affiliated with it.