H&H Tools
Free hydraulics and hydrology calculators for engineers. Pick a tool, enter your values and print a calculation sheet: quick, verifiable calculations in the browser — the single-element checks engineers usually open a desktop program for.
Calculators
Hydraulics
Channels, pipes, culverts, weirs and orifices, lining and roughness.
- Channel Flow Water depth, flow, slope or width of an open channel or partly full pipe (Manning). Checked against 11 reference cases, 11 within tolerance
- Pipe Flow Depth, flow, slope or size of a pipe partly full, or head loss in a pipe flowing full. Checked against 13 reference cases, 13 within tolerance
- Weir & Orifice Flow over weirs and through orifices, risers and gates, or the water level for a flow. Checked against 14 reference cases, 14 within tolerance
- Channel Lining Whether grass, riprap or another lining can take the flow, and the stone size it needs. Checked against 7 reference cases, 7 within tolerance
- Manning’s n Roughness values by source, Cowan’s method for natural channels, and a composite n for mixed perimeters. Checked against 11 reference cases, 11 within tolerance
- Culvert Headwater for a flow, or flow for a headwater: inlet and outlet control, identical barrels, roadway overtopping. Checked against 14 reference cases, 14 within tolerance
- GVF Profile Water surface profile in a prismatic channel by the standard step method, from a control depth. Checked against 6 reference cases, 6 within tolerance
- Hydraulic Jump Sequent depth, energy loss and jump length in a rectangle, trapezoid or triangle. Checked against 4 reference cases, 4 within tolerance
- Riprap Apron & Basin Riprap apron rock size, class and dimensions at a culvert outlet, or a riprap basin for a trial rock. Checked against 5 reference cases, 5 within tolerance
Hydrology
Rainfall, time of concentration and runoff for a Texas location.
- Atlas 14 IDF NOAA Atlas 14 rainfall depth and intensity for a Texas location: the full table, IDF curves and any duration. Checked against 13 reference cases, 13 within tolerance
- Time of Concentration Tc by TR-55 sheet, shallow and channel flow, Kirpich, Kerby-Kirpich (TxDOT) or the NRCS lag equation. Checked against 13 reference cases, 13 within tolerance
- Rational Method Peak flow Q = CiA with Atlas 14 intensity for a Texas location, weighted C and every return period. Checked against 9 reference cases, 9 within tolerance
- NRCS Runoff Curve number runoff depth and volume, weighted CN, and the TR-55 graphical peak discharge. Checked against 7 reference cases, 7 within tolerance
- Regional Regression Peak Flow Peak flow of an undeveloped Texas watershed from area, slope, rainfall and OmegaEM, with the TxDOT conditions of use. Checked against 5 reference cases, 5 within tolerance
- Detention Routing Route inflow hydrographs through a pond: stage-storage, orifices, weirs, riser, barrel and spillway, peak outflow, highest water and drain time. Checked against 32 reference cases, 32 within tolerance
- Pre/Post Development Comparison Pre- and post-development peaks and volumes side by side, a TR-55 storage estimate, or numbers from a report lined up by outlet and event. Checked against 14 reference cases, 14 within tolerance
Road drainage
Gutter spread, inlet capacity and storm drain grade lines by FHWA HEC-22, after the Rational Method peak and before the culvert.
- Gutter & Inlet Gutter spread, and the flow a curb opening, grate or slotted inlet takes on grade or in a sag. Checked against 20 reference cases, 20 within tolerance
- Storm Sewer HGL Energy and hydraulic grade lines of a branching storm drain, from the outfall upstream, with access hole losses. Checked against 1 reference case, 1 within tolerance
Site & water quality
Construction sediment basins and water quality volumes under Texas permits and guidance.
- Water Quality Volume & TSS Load Required TSS removal, load removed by a BMP, and the capture volume on the Edwards Aquifer, in the order of the TCEQ worksheet. Checked against 8 reference cases, 8 within tolerance
- Sediment Basin Volume Storage for a construction sediment basin under the Texas Construction General Permit. Checked against 2 reference cases, 2 within tolerance
How these tools work
- Published methods
- Each calculator applies a method published by FHWA, USACE, USGS, USBR, NRCS, NOAA or TxDOT and names it on the page and on the calculation sheet, with the equations and the limits of the method.
- Checked against reference cases
- Every calculator is tested against published worked examples and reference programs or data services every time its code changes. The cases and the largest differences are listed on each page.
- In your browser
- Calculations run on your device. Your inputs are not sent to or stored by HERO E&C; a link to your inputs carries them after the # in the address.
- A calculation aid
- Results are not a sealed engineering document. Your reviewing agency’s criteria decide which methods and values apply; the engineer of record is responsible for the design.
Built by HERO E&C, a Texas water-resources firm led by Seoyoung Kim, Ph.D., P.E., CFM (20+ years of personal experience).
Where to start
The Texas Drainage Criteria Directory links to the manuals Texas cities, counties and agencies publish, with the edition each one shows. Road Drainage Calculators puts the road tools in the order you would use them.
Coming later
- Retention ponds — Water budget, infiltration and drawdown for ponds that hold water.
- Dam design — Embankment geometry, spillway capacity, freeboard and TCEQ dam safety checks (30 TAC Ch. 299).
Need an engineer’s review?
HERO E&C prepares drainage and floodplain studies, channel and culvert design, HEC-HMS / HEC-RAS models, and development permit applications across Texas.
Free calculation aids using published methods. Not sealed engineering documents; the engineer of record is responsible for design. HERO E&C · TBPELS Firm F-27793.