Free Online Irrigation Flow Measurement Calculators

>> Drop your fears at the door; love is spoken here. You are not ruining everything. Enjoy the free libre HawsEDC AutoCAD tools too. <<

Irrigation Flow Measurement — Weirs and Orifices

Do you have a great vision for a calculator to add here? Can you help me improve translations, program, or host these calculators? [Hide this line]


Weirs and orifices are the standard field tools for measuring water flow in irrigation systems. Select the calculator that matches your structure:

Weir — Broad-Crested (Uniform Width)

Measure flow over a diversion dam crest, check structure, or weir board. Enter weir length and headwater depth above the crest.

Weir Flow Simple
Weir — Irregular Profile

Use when the weir crest is not a single uniform elevation — natural spillways, drop structures with varying width, or multi-section control structures.

Weir Flow Irregular
Orifice — Headgate or Pipe Turnout

Measure flow through a sluice gate, pipe turnout, or culvert opening. Handles both free outfall and submerged (tailwater) conditions automatically.

Orifice Flow
Canal Design & Analysis

Design or check an irrigation canal using Manning's formula. Use the Trapezoidal calculator for new channels; the Irregular calculator for existing natural or constructed sections.

Manning Trapezoidal Channel Manning Irregular Channel
Drip & Sprinkler Design

Calculate application rate, distribution uniformity, lateral flow, zone flow, and runtime for a drip or sprinkler irrigation system. Enter emitter flow, emitter spacing, and target depth.

Drip/Sprinkler Application Rate

Quick Reference

Diversion dam or check structure
Measure headwater depth above the weir crest. Use Weir Flow Simple for a uniform crest, or Weir Flow Irregular for a profiled or stepped crest.
Headgate or pipe turnout
Measure headwater elevation and tailwater elevation (or invert if freely discharging). Use Orifice Flow. For a circular pipe, D = pipe diameter; for a rectangular gate, enter width W and height D.
Reservoir or pond drain time
Use Orifice Drain Time to estimate how long it takes to lower a pond or reservoir through a bottom orifice — useful for irrigation storage planning.
Field standards
Weir and orifice flow equations used here match USBR Water Measurement Manual (3rd ed.) procedures commonly required by water masters and irrigation districts.

Please give us your valued words of suggestion or praise. Did this free calculator exceed your expectations in every way? [Hide this line]

Home | AutoCAD Tools | FreeSoftware | Engineering Services | Engineering Calculators | Technical Documents | Blog (new in 2009) | Personal essays | Collaborative Family Trees | Contact