# Hydrology & Open-Channel Calc

Manning flow, normal and critical depth, Froude number, weir flow, rational method, time of concentration and orifice flow.

## How to pay

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No accounts. No API keys. No signup. The paying wallet is the account.

## Machine-readable

- OpenAPI: https://hydrology-calc.x402tookit.com/openapi.json
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## Endpoints (8)

### GET /critical-depth — $0.02
Critical depth where Froude number is 1 (Q^2/g = A^3/T) for rectangular, trapezoidal, triangular or circular channels.
Params: shape: string, flow: number, bottomWidth?: number, sideSlope?: number, diameter?: number, units?: string, gravity?: number
Example: https://hydrology-calc.x402tookit.com/critical-depth?shape=rectangular&bottomWidth=5&flow=10&units=si

### GET /froude-number — $0.02
Froude number V / sqrt(g A/T) and flow regime (subcritical, critical, supercritical) for an open-channel section.
Params: shape: string, depth: number, flow?: number, velocity?: number, bottomWidth?: number, sideSlope?: number, diameter?: number, units?: string
Example: https://hydrology-calc.x402tookit.com/froude-number?shape=rectangular&bottomWidth=2&depth=0.5&flow=5&units=si

### GET /manning-flow — $0.02
Manning flow, velocity and hydraulic radius for rectangular, trapezoidal, triangular or part-full circular channels, SI or US.
Params: shape: string, depth: number, n: number, slope: number, bottomWidth?: number, sideSlope?: number, diameter?: number, units?: string
Example: https://hydrology-calc.x402tookit.com/manning-flow?shape=rectangular&bottomWidth=3&depth=1&n=0.015&slope=0.0004&units=si

### GET /normal-depth — $0.03
Normal (uniform-flow) depth for a given discharge in a rectangular, trapezoidal, triangular or circular channel by bisection.
Params: shape: string, flow: number, n: number, slope: number, bottomWidth?: number, sideSlope?: number, diameter?: number, units?: string
Example: https://hydrology-calc.x402tookit.com/normal-depth?shape=trapezoidal&bottomWidth=2&sideSlope=1.5&flow=8&n=0.03&slope=0.001&units=si

### GET /orifice-flow — $0.02
Orifice discharge Q = Cd A sqrt(2 g h) for a round or given-area opening, with typical Cd by edge type, SI or US.
Params: head: number, diameter?: number, area?: number, edge?: string, cd?: number, units?: string
Example: https://hydrology-calc.x402tookit.com/orifice-flow?head=2&diameter=0.1&edge=sharp&units=si

### GET /rational-method — $0.02
Peak runoff Q = C i A by the rational method, from a runoff coefficient, surface type or weighted sub-areas, SI or US.
Params: rainfallIntensity: number, area: number, c?: number, surface?: string, subareas?: string, units?: string
Example: https://hydrology-calc.x402tookit.com/rational-method?rainfallIntensity=50&area=10&c=0.5&units=si

### GET /time-of-concentration — $0.02
Time of concentration by the Kirpich formula and the NRCS lag equation, with the limits of each stated.
Params: flowPathLength: number, slope: number, method?: string, curveNumber?: number, units?: string
Example: https://hydrology-calc.x402tookit.com/time-of-concentration?flowPathLength=1000&slope=0.01&curveNumber=75&units=si

### GET /weir-flow — $0.02
Discharge over a sharp-crested rectangular (Francis), V-notch or Cipolletti weir from head, SI or US units.
Params: type: string, head: number, crestLength?: number, contractions?: integer, notchAngleDeg?: number, cd?: number, units?: string
Example: https://hydrology-calc.x402tookit.com/weir-flow?type=v-notch&head=0.2&notchAngleDeg=90&units=si

## Terms

Hydraulic arithmetic computed locally from the numbers given, using standard published formulas, provided as is. Educational estimates only: not for design or code compliance. Roughness, runoff and discharge coefficients are typical values; real channels need site data and a licensed engineer.