( ( A confluence ) ( ( is ( where ( ( ( ( two or ) more ) ( ( tributaries or ) rivers ) ) ( flow together ) ) ) ) . ) )
(ROOT (S (NP (DT A) (NN confluence)) (VP (VBZ is) (SBAR (WHADVP (WRB where)) (S (NP (QP (CD two) (CC or) (JJR more)) (NNS tributaries) (CC or) (NNS rivers)) (VP (VBP flow) (ADVP (RB together)))))) (. .)))
A confluence is where two or more tributaries or rivers flow together.
(ROOT (S (NP (CD Two) (NNS tributaries)) (VP (VBP come) (ADVP (RB together)) (PP (IN at) (NP (DT a) (-LRB- -LRB-) (NNP n) (-RRB- -RRB-) (NN confluence)))) (. .)))
Two tributaries come together at a(n) confluence.