Road Drainage Calculators
From rainfall on the pavement to the outfall: the H&H Tools calculators for a road drainage check, in the order you would use them.
- Time of concentration — Sheet, shallow and channel flow to the inlet.
- Peak flow — Q = CiA with NOAA Atlas 14 intensity for a Texas location. For larger or undeveloped watersheds, NRCS Runoff or the Regional Regression Peak Flow.
- Gutter and inlets — Spread and the flow each inlet takes, down a run with the bypass carried on, to a sag inlet at the end (FHWA HEC-22).
- Storm drain — Energy and hydraulic grade lines from the outfall upstream, with access hole losses. Single pipes in Pipe Flow.
- Crossing — Culvert headwater and flow over the road (FHWA HDS-5).
- Outlet protection — Riprap apron or basin at the outlet (FHWA HEC-14).
- Roadside channel — Lining by shear stress (FHWA HEC-15), and Channel Flow for depth.
Each is a calculation aid and each step takes its inputs from you: values do not pass automatically from one to the next. Your reviewing agency’s criteria decide the design frequency, the allowable spread and the methods; the Texas Drainage Criteria Directory links to the published documents.
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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.