help with spur dike
 

i want to model a spur dike
but i faced some problem
1) scour happened at first of channel when the material change from solid to sediment, how can i define my problem to avoid these scours???
2) scour happened at the place where mesh boxes joins!!! how can i avoid this problem??
3) my flow depth should be 15 cm ,but after a long time running the model
flow depth became 10cm :| and i don't know what to do

i attached my model to the post
and the result after 160s
and flow depth
if anyone have any idea or suggestion i would be very thankful

Regards,
Hanif