I’ve read a lot of papers about water loss reduction. Two concepts that show up frequently are Minimum Nighttime Flow (MNF) and District Metered Areas (DMA). DMAs are areas in the distribution system that can be isolated such that all system inflows and outflows (not including customer use) are metered. They are helpful in identifying areas where leakage is prevalent. Most of the time, leakage is a small fraction flow, and it is difficult to identify a small/medium leak in a DMA. For example, recognizing a 10 gpm leak in a DMA with a 200 gpm average flow is easier than finding one when the demand is 20,0000 gpm. However, in the middle of the night, water use in DMAs decreases and leakage becomes a more easily identifiable portion of the flow. The flow at this time is referred to as the MNF and it is usually measured at an hour somewhere between 1 a.m. and 5 a.m. If the MNF is less than or about 50% of the average daily flow, that DMA is not considered a likely source of major leakage. If it is higher and if it changes fairly suddenly, that’s a good place to look for

First of all, we need to forget about the word “exactly” in the title. When dealing with turbulent flow in water and wastewater systems, there is no theoretically perfect equation for head loss. All turbulent flow head loss equations for water are empirical to a certain extent. If you ask university faculty who teach hydraulics, they will tell you that the Darcy-Weisbach equation is the correct equation, and they will denigrate the Hazen-Williams equation. My fluid mechanics textbook from my school days, Streeter, Fluid Mechanics, did not even mention the Hazen-Williams equation. However, if you walk down the street to the local water utility or engineering consultant office, they will be using the Hazen-Williams equation. Why the discrepancy? There are some good reasons why the Darcy-Weisbach equation is theoretically better. It is based on a force balance between pressure and gravity forces driving the flow and the friction/turbulence restraining the flow. This equation applies to any Newtonian fluid, not just water at room temperature. It can accommodate not only a range of roughness but also a range of boundary layer types. Why don’t practicing engineers use Darcy-Weisbach? Looking at the Darcy-Weisbach equation below, everyone understands the independent variables: head loss

The ability to integrate your sanitary and combined sewer models with some of the leading engineering software is essential to delivering accurate and optimal designs.

Hydraulic modeling is not new to the water industry; however, recent industry influences have resulted in utilities expanding the use of modeling software. COVID has changed the game for many industries and their workforce, and this has had an impact on water utilities and the experts who serve them. Water utilities are able to use software to operate smarter, in terms of both saving operational time and expense as well as preparing for anomalies and emergencies. The “brain drain” of the retiring workforce can result in lost expertise about how the water system responds to operational stresses and where vulnerabilities exist. You do not have to be an expert in hydraulic modeling to gain value from a hydraulic model. In this podcast, Todd Danielson, the editorial director for Informed Infrastructure, interviews Joel Johnson, Manager of Engineering for Water, Wastewater, and Stormwater for Bentley Systems; and Angela Suarez, Product Consultant for the OpenFlows product line at Bentley Systems. Podcast Transcript

The title of this blog comes from a question asked by one of our Bentley OpenFlows users. If the temperature of water in a pipe changes, does head loss and flow change? 

The correct answer is “Never.” A variable frequency drive (VFD) is generally described as a “motor control device that controls the speed of AC induction motors.” A VFD has never pumped a drop of water. Despite this, I hear many people in our industry state that their VFD “pumps 800 gpm”. A VFD is an electrical device that, when connected correctly with a pump, can make that pump behave like a variable speed pump. A pump with a VFD is not a VFD. It is a variable speed pump (VSP). I realize this is a minor point, and most people understand that a VFD is not a pump, but it can be misleading (or at least confusing). Imagine what will happen if somebody tries to hook a VFD to a 12-inch water main. As a matter of clarity, we should not refer to a pump with a VFD as a VFD. I can’t help but get mildly annoyed when someone says, “We have two constant speed pumps and a VFD,” when they should say, “We have two constant speed pumps and a VSP.” We tend to use a lot of incorrect terminology in the water industry, such as saying we

We regularly seek feedback from our users on how we’re doing. In a recent survey, we received excellent scores across the board on our OpenFlows products like OpenFlows WaterGEMS and OpenFlows SewerGEMS. One individual noted it would be great if Bentley were to “Provide additional training, demos, and webinars.”