set model and wl.opt problem

Hi,I want to set a model for a river ,but I am facing some problems
1.The river I want to use W2 have two split streams ,but these two split stream converge again in the downstream,and then ,split again.I am wondering how to set the branchs and waterbody accurately.So I ask for help.
2.When I run the model , it produce a wl.opt about the water level ,but the water level increase quickly as the date goes by ,it may increase from 10m to 200m!!I don't know what happen ,so I just want some help.
Thank you for your helping