Hi Renata,
I contacted Andy Scott (the Kelpie designer) to ask the same question as yourself and had the reply shown below..
"The kelpie idea originated from the very earliest notion of a large counter-weight lever structure which would act as a boat lift. The earliest images of that idea looked very loosely like a horse's head. One of the senior engineers of BW, George Balinger, hit upon the idea of The kelpie as a theme for the structure, linking with the Scottish mythology. At this point he and the engineers at BW approached me due to my established portfolio of equine sculpture works, as well as many other large scale commissions and asked me to develop the idea.
I duly did so and several interpretations evolved, some literal, some very mythical and "fanciful". However as I researched and developed the idea I was struck more by the historical relationships of horses to the canal and the role they played in society in the past. Not only would they have been used in the construction of the canal and obviously pulled barges, they would have worked the fields around the canals, and worked in the factories and towns along the length of the waterway. So for me the Kelpies theme was really a catalyst for deeper inspiration to celebrate the role of horses in Scottish life. Story has it the biggest horse in Britain "Carnera" used to work in Falkirk... a lovely piece of historical synergy."
I hope this satisfies some of your inquiry and hopefully we can have Andy Scott on the forum at some point to answer in more detail other questions such as time scale etc for the project.
regards..