Modeling for Hydraulic Capacity: Fid-Bau Portal

Modeling for Hydraulic Capacity

Boxall, J.B. / Saul, A.J. / Skipworth, P.J.

Pipes in distribution systems often become tuberculated because of internal corrosion, sliming, and scaling. This condition frequently leads to an increase in the roughness of the pipe wall and in a reduction of the pipe diameter. Such changes lead to reduced hydraulic capacity of the pipes within distribution systems. Most model calibration is undertaken by adjusting roughness coefficients alone; the reduction in pipe diameter is often neglected. This may have a significant effect on the prediction of the correct flow velocity. The calibrated models often correctly predict the pressure distribution and the flow balance at each node in the system; however, the representation of the flow paths and velocity distribution may not be well predicted. As a consequence, the prediction of the travel time may be inaccurate. Water age is a function of the travel time, and water age is known to have a significant effect on water quality and on the way in which water quality changes within distribution systems. This article describes the relationship between pipe roughness and effective pipe diameter based on a series of fieldwork measurements and a modeling study. On the basis of the system studied, it is shown that to accurately model measured pressure response, flow, and velocity, an increase in effective roughness height of 1 mm (0.04 in.) is equivalent to a 2‐mm (0.08 in.) reduction in effective diameter. Therefore, the change in diameter caused by turberculation of the pipe wall is an important parameter, and such changes, together with changes in roughness, should be taken into account in any mathematical model, particularly those in which consideration is given to water quality.