In the first part of this blog, I talked about closed pipe flow and the benefits and disadvantages it can have. In part two, I’d like to focus on open channel flow and how this option can be used to measure water and wastewater flow. Measuring flow through an open channel is a popular choice for water/wastewater applications. It’s easy to see why, with ease of installation and maintenance over time. In open channel flow, the use of a primary measurement device, such as a weir or flume, along with a non-contacting level measurement device is used to determine the flow. There are several choices for the primary measurement device as well as the level device. Let’s take a look at just a few of the choices for this type of flow. The Primary Measurement Device (PMD) is a key component of open channel flow measurement. A great deal of thought should be put into the selection of the primary measurement device. The flow rate that you have today may not be the flow rate that you will have tomorrow and must be considered to avoid the purchase of an inadequate system. Other items to consider are the accuracy of the PMD, maintenance and the fluid to be monitored. Installation of the PMD is critical for the proper reading of the open channel flow meter selected to measure the head of the flow. Improper installation or sizing of the PMD will impact the overall performance of the system.