Summary #
A weir is a low dam or barrier placed across a stream channel to measure flow rate. This page explains how weirs work, the types commonly used in watershed monitoring, and basic measurement procedures.
A weir is an overflow structure that is built in-stream, perpendicular to the direction of flow, and measures the water’s flow rate. A weir will impound water behind it, acting like a small dam, so site locations must be evaluated before construction. Many weirs are situated on smaller streams in areas where current meter measurements are not applicable. This type of structure is frequently utilized to establish stream flow over long periods of time. Flow measured over an extended period of time helps to establish a rating curve, which will allow flow to be predicted at that location. A weir can be constructed of any type of sturdy material, such as wood, metal or concrete.
The type and size of weir chosen for your site will depend on the flow characteristics of the stream. There are two commonly used types of weirs, V-notch and rectangular. A notch weir is designed to measure small flows and a rectangular weir to measure larger flows.
Sources/Links (as provided in the source text):
Related Pages #
- Developing a Monitoring Plan
- Field Assessment Tools — Equipment for physical monitoring
- Field Assessment Procedures — General field procedures
Source and Last Reviewed #
Source: AMR Clearinghouse (amrclearinghouse.org). Migrated to AML-Connect. Last Reviewed: 2026-03-13.
[Admin note: Some external links in this article may be outdated. Verify before relying on them. Flag dead links for removal or replacement.]
Tags: monitoring, sampling, practitioner
