I am not one to impugn/castigate or even accuse of laziness any "civil engineers" for use of the Hazen Williams approach, and certainly not without specific evidence that the work in the application they are performing is not up to snuff. While I don’t know about Australia, I believe this might be considered an affront of at least our local engineering ethics. I think there are many civil engineers involved in piping work for municipalities and utilities, as well as some civil engineering folks working for consulting firms, that are most heavily involved or specialize in water (the forum we are now in) and wastewater work, and for that matter even in this day and time predominantly not extremely large diameter pipe size jobs. I believe on the other hand many chemical etc. engineers work for plants/energy industries or refineries etc. that may well have many different types of fluid/gas process lines and also with hugely variable temperatures. Is it possible that their or their predecessors direct needs, experience and knowledge influences the tools they in general utilize to perform the jobs? While I think good engineers and scientists in general should try to be as precise as practical in their analyses or progress toward an answer, alas is it possible that (similar to variations in construction methods) there is more than one way to do engineering? If experience indicates the method in effect gives virtually the same result in the application (as it appears in the cases indicated by Friend), I’m not sure I could in all good conscience dictate the method to the practitioner. Of course I know also precise application of DW requires input/knowledge of? the temperature of the fluid to be conveyed. In some parts of our country, I believe fluid temperatures for example of some raw water supplies can fluctuate quite widely with seasonal variations – do you do your DW analyses/sizing etc. at near zero degrees C. encountered in the winter or the 30+ degrees C. encountered in the summer? Of course if one knows the actual temperatures, time can be spent analyzing per DW at either temperature or any compromises between same if anyone wants to, though of course this complexity is not present in the HW approach. Not saying this is the case in any specific application, but if the HW approach with the input values per the experience of the practitioner were to give a result equal to DW at a temperature somewhere in between, who has provided most cost effective engineering services to the Owner?
As far as application to very large size pipes, I suspect pipe size in general, and certainly any available laboratory work were generally some smaller in Hazen-Williams day as a result of populations served (we cannot blame them for this!) Arguably few things in any field stay exactly the same forever, and I believe there has in fact even been some evolution in recent decades of the HW approach, it would appear perhaps even anticipated by folks nearly as far back as Friend (see the last part of the quote I provided earlier). In this regard, I also noticed in a new book published by Haestad/Bentley, “Advanced Water Distribution Modeling and Management that there now are some at least slight adjustments advocated e.g. in the values suggested for friction coefficient C as the pipe sizes get very large – see “C-factor” table at
(is it possible that this has probably been done as a result of what has been observed in subsequent/more contemporary research and/or field and/or laboratory results on larger pipelines?) Of course “Advanced…” hardly conjures up visions of the “horse and cart”!
As far as blaming “university professors” for the use of HW, I wouldn’t do that either. While I haven’t been sitting in a university classroom for awhile, I suspect many competent professors are at least exposing students to multiple methods, and I wouldn’t be surprised if they in general are even spending a great deal more time trying to teach inarguably more complex DW than they are HW, because as you’ve noted anyone who can look at readily available tables or correctly type/chain one formula into an Excel program, or who can input a few numbers/punch buttons on a scientific calculator (in the right sequence for the power functions to work, and in the right units etc.), can in effect thus use HW!
