One of the main functions of sewers is to move solids. Simply moving the liquid phase while leaving the solids behind would not be satisfactory. The calculations of whether flow in a sewer is adequate to move solids are governed by tractive force design. (Actually, “tractive force” is not a force but a shear stress usually referred to as tractive stress or tractive tension.)

Leaks in water distribution systems depend on the pressure in the pipe. Given a certain size opening, the leakage is roughly a function of the square root of pressure. If you lower the pressure, you’ll get less leakage.

For a model to have credibility, it needs to be calibrated against data from the distribution system. While this sounds simple, there are issues that can steer the calibration in the wrong direction. This paper discusses some common pitfalls and how to avoid them.

We need to develop a method to divide total loss into apparent and real. Hard data on this divide can’t be determined. Some estimation is required. We provide two methods, each with its own strengths and weaknesses. We’d like to get some feedback.

Readers of this blog already know the basics of how to calibrate a water distribution system model. Compare system data with model results and make the necessary adjustments so that the model agrees with the data. But not all data are equal. Some data are valuable; others are of poor quality and must be discarded, while other data looks good but is useless. How to tell the difference? Understand why data is being used It’s important to understand why data is being used. If data is used to evaluate the model when head loss is very low, then that data cannot shed any insights regarding pipe roughness, demands, or closed valves. To make those adjustments in anything that affects head loss, there must be measurable, meaningful head loss. Unfortunately, in most developed countries, especially North America, velocity in pipes under normal conditions are low and head loss is therefore often minimal. It is often on the same order of magnitude as the error in measurements. To make any adjustments to pipe roughness, or similar input (e.g. closed valves), it is necessary to have significant head loss. For example, calculating C-factor essentially boils down to C = k V/h0.54 Where V

This is a problem in any system, but this particular system served some of the most influential and wealthiest people in the city, (I’ll call this area “Mountaintop”—not its real name). When these people complained, the folks at City Hall listened.

Quiz time! Test your hydraulics knowledge. Take Tom Walski’s short hydraulics test.