I often title my blogs with a question that I’m very happy to try to answer. “What’s the Capacity of That Pipe?” is not one of those questions. Unless you make some simplifying assumptions such as “The pipe is flowing at normal depth” or “The full pipe velocity is 5 ft/s,” the real answer is elusive. I usually respond with a litany of questions, including “Why are you calculating this?” and “What assumptions are you willing to make?” The most important distinction is whether the pipe is designed to flow full, like a water distribution pipe, or a sewer force main, as opposed to a gravity sanitary, combined, or storm sewer. Therefore, there is a two-part answer to the question in this blog but they both go back to this simple equation: Q = A V Where Q = flow (and in this case capacity), A is the cross-sectional area occupied by the flow, and V is the velocity. Such a little equation for such a big concept. Regulatory/administrative people like to treat the capacity as a fixed number. If someone says the capacity is 500 gpm, and you want approval to use the pipe to move 499 gpm, you

Work on the upcoming AWWA Manual on Energy (M83) is wrapping up, and I’ve been working with Eric Dole, National Water and Energy Practice Lead for Garver, on the pumping chapter. It’s shaping up nicely. One topic that has come up is: What’s the best metric for judging if a pump or a pump station is working well vs. one that is wasting energy and money? There are quite a few potential metrics, and they all have their strengths. The definitions vary, but the most common are: Efficiency Energy intensity Or, in some cases: Where e = efficiency, Q = flow, h = pump head, P = power, i1 and i2 are two different formulations for energy intensity, and the k values are unit conversion factors that depend on the units used. Efficiency can either be pump efficiency or wire-to-water efficiency. For pump comparison, it is best to use wire-to-water efficiency because it accounts for motor and drive efficiency. We can solve these equations simultaneously to give: Or Essentially, energy intensity is just the inverse of efficiency. Efficient pumps have a low energy intensity. The difference between i1 and i2 is that i1 has a worse intensity for pumps discharging

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?