Studying the Effect of Factors Influencing the Change in Hazen-Williams Roughness Coefficient of Cast Iron Pipes during Operation Period

Considering the importance of sufficient pressure in supplying demand in water distribution networks, it is necessary to study the factors affecting pressure variation, that the roughness of pipes directly affects the pressure of nodes. Therefore, the study of factors affecting the change in roughness coefficient (Hasen-Williams) in water distribution networks is important. Pipes diameter, age and corrosion are among factors affecting the change in the roughness coefficient of pipes that are evaluated in this paper. The roughness coefficients were plotted against each of the above mentioned factors, and the approximate relations of the roughness coefficient was obtained by fitting to the obtained graphs. Finally, by combining the relations obtained, a general relation is obtained for the roughness coefficient. Also, in this paper, the cast iron pipes, for which laboratory data is available, were used to obtain a mathematical relationship.Then again, instead of using the roughness coefficient of new pipes in analysis and design, the roughness coefficient for the end of the design period was used, taking into account the effective factors mentioned.To evaluate the results of the proposed method, a two-loop network was investigated in two common and real situations. The results showed that if the roughness coefficient of new pipes at the end of design period is used for designing, there will be a save of about 50% in cost of pipes, but then the network pressure at the end of design period will be reduced by more than 25%. Therefore, in order to ensure that there is sufficient pressure and demand satisfaction throughout the design period, it is necessary to accept an increase in the cost of network implementation at the beginning of the project.