[Therion] Two scraps, one river...

Hi all, We´re using Therion to produce maps for many caves in Brazil but I´m having some poor results wen I have to join scraps with intersecting areas…. I know that Therion is only able to join lines so how do I represent a river, for exemple that spreads between two or more scraps? Usualy there is a gap appearing due to the scraps adjustments… Is there any trick to solve that? Thank you, Fabio