# Hydrology & Open-Channel Calc — Weir Flow

> Hydrology & Open-Channel Calc — Weir Flow is a paid API for AI agents from hydrology-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-11-02).

Calculates discharge (flow rate) over a sharp-crested rectangular (Francis), V-notch, or Cipolletti weir from head measurement, in SI or US customary units.

## Facts

- Endpoint: GET https://hydrology-calc.x402tookit.com/weir-flow?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-11-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/hydrology-open-channel-calc-weir-flow-93d87ee9
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_wx1OZUCbkI0UwrqSTNs9D

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability hydrology-open-channel-calc-weir-flow-93d87ee9
```

Example prompt: Calculate the discharge over a 90-degree V-notch weir with a head of 0.35 metres using SI units.

## When to prefer this

Use this endpoint when you need a fast, authoritative hydraulic calculation for standard sharp-crested weir types (rectangular/Francis, V-notch, Cipolletti) given a known upstream head, and you want SI or US unit output with optional custom discharge coefficients or Francis end-contraction corrections. Prefer this over general engineering calculators when you need weir-specific formulas with proper physical constraints and structured JSON output.

## Known failure modes

- Missing required 'type' or 'head' parameters returns an error
- Head value of zero or negative causes invalid computation
- crestLength omitted for rectangular or Cipolletti weir returns error or null flow
- notchAngleDeg outside 10–120 degree range may trigger a warning or rejection
- Invalid weir type string returns an unrecognised-type error
- Extremely large head values may produce physically unrealistic results with a warning

## How this service works

Discharge over a sharp-crested rectangular (Francis), V-notch or Cipolletti weir from head, SI or US units.

## Output

Returns the computed flow rate (Q) in m³/s or ft³/s, along with the weir type, head, flow unit, effective discharge coefficient, crest length, notch angle, contraction count, a plain-language summary, and any applicable warnings or disclaimers.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "type",
      "head"
     ],
     "properties": {
      "cd": {
       "type": "number",
       "description": "Discharge coefficient Cd: rectangular then uses the (2/3) Cd sqrt(2g) form instead of Francis; V-notch default 0.585"
      },
      "head": {
       "type": "number",
       "description": "Head over the crest H in metres (si) or feet (us), measured upstream of the drawdown"
      },
      "type": {
       "type": "string",
       "description": "rectangular, v-notch or cipolletti"
      },
      "units": {
       "type": "string",
       "description": "si (metres, m3/s; default) or us (feet, ft3/s)"
      },
      "crestLength": {
       "type": "number",
       "description": "Crest length L in metres or feet (rectangular, cipolletti)"
      },
      "contractions": {
       "type": "integer",
       "description": "Rectangular end contractions 0, 1 or 2 for the Francis correction (default 2)"
      },
      "notchAngleDeg": {
       "type": "number",
       "description": "V-notch included angle in degrees, 10 to 120 (default 90)"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "flow": {
       "type": [
        "null",
        "number"
       ]
      },
      "head": {
       "type": [
        "null",
        "number"
       ]
      },
      "type": {
       "type": [
        "null",
        "string"
       ]
      },
      "units": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/hydrology-open-channel-calc-weir-flow-93d87ee9/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
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