Open-channel hydraulics — modelling gravity flow in channels, launders and weirs to set the plant hydraulic profile and avoid surcharge.
Hydraulic Modelling — in depth
Much of a treatment plant flows by gravity in open channels. We compute normal and critical depth, weir and flume behaviour and backwater so channels, launders and distribution structures pass peak flow without surcharging — the open-channel half of the plant hydraulic profile that complements the pressurised pipe network.
What matters in practice
Manning flow in channels.
Level-flow relationships.
Profiles upstream of controls.
Gravity flow without surcharge.
| Item | Basis | Note |
|---|---|---|
| Depth | Manning | Normal/critical |
| Weir | Head-flow | Measurement |
| Backwater | Profile | Controls |
| Freeboard | Standard | Safety |
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Read MoreReynolds & Bauhm designs and delivers hydraulic modelling solutions backed by process engineering and performance guarantees.
Fundamentals, design drivers and practical guidance
Open-channel hydraulics — modelling gravity flow in channels, launders and weirs to set the plant hydraulic profile and avoid surcharge.
Open-channel hydraulics is governed instead by Manning's equation and specific-energy concepts, distinguishing sub- and super-critical flow, locating hydraulic jumps, and sizing channels and weirs so they pass design storm flow with adequate freeboard. Across both regimes, the same care over roughness, geometry and boundary conditions separates a model that protects the asset from one that merely decorates a report.
Reynolds & Bauhm builds and calibrates hydraulic models for pressurised and open-channel systems, sizing pumps at their best-efficiency point, checking surge and NPSH, and proving conveyance under design conditions — so plant hydraulics are engineered, not assumed.
Hydraulic modelling underpins reliable water and wastewater conveyance: it predicts how flow, head and pressure behave through pipes, channels, pumps and structures, so a design can be proven on paper before steel and concrete commit it. Whether the question is pump selection, surge, or whether a channel will surcharge, the model turns governing equations into actionable design margins.
What our engineers assess on every scope of this type
| Parameter | Typical basis | Why it matters |
|---|---|---|
| Open channel | Manning's equation | Sizes channel for design flow |
| Regime | Froude number | Locates jumps; sets freeboard |
| Friction | Darcy-Weisbach / Hazen-Williams | Sets head loss along pipes |
| Duty point | System curve x pump curve | Fixes flow and head delivered |
| NPSH | Available > required | Prevents cavitation damage |
| BEP | Operate near best efficiency | Saves energy, extends pump life |
Common questions on hydraulic modelling
It is governed by Manning's equation and specific energy rather than pressurised pipe losses, and must account for sub- and super-critical flow, hydraulic jumps and freeboard so the channel passes design storm flow without surcharging.
Calibration and disciplined inputs — realistic roughness, accurate geometry and correct boundary conditions. A model is only as good as those assumptions, which is why Open-Channel Hydraulics is built and checked against known operating data where available.
Because head, surge and capacity failures are expensive and disruptive to fix in concrete. Open-Channel Hydraulics proves that pumps, pipes and channels deliver design flow at acceptable pressure and margin before construction commits the layout.
The network's system curve — static lift plus friction and minor losses — is intersected with the manufacturer's pump curve. The crossing point gives the delivered flow and head; the design aims to place it near the pump's best-efficiency point.
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