In practice, it has been seen that in alluvial deposits characterized by sands of moderate permeability, the error in estimating the pumping rate – on the basis of the acquired practical experience alone – remains within acceptable limits for at least 70% of the drainage interventions. This correspondence has contributed to spreading the belief, denied every day by the inconveniences found on construction sites, that drainage with the wellpoint system is an easy technique, and therefore that does not require particular attention to the design. The problems caused by an insufficiency of the wellpoint system are often solved mechanically by means of the additional use of filters and pumps without the foresight of experimentally tracing the causes of the detected insufficiency.
The experimental investigation in the specific field of drainage with the wellpoint system is extremely limited but the same can be said for all the other drainage systems and the lack of specific research is also partly due to the lack of interest shown by specialized companies that tend to provide only data relating to positive experiences.