I do mean the Holtan Infiltration Method. I was looking specifically for an explanation of the various parameters in the equation and where it is still used. A discussion of the method in a textbook or handbook. Thanks, I'll keep looking.
Sorry water2004, I completely forgot about Holtan. I had a look in my copy of the "Handbook of Hydrology" (Editor- David R. Maitland) and it has a one page explanation of the equation parameters and a couple of tables with typical parameter values.