You should review Page 16-51 of the User’s Manual, in which User Defined Rules for operation of hydraulic structures are discussed. User rules are incredibly powerful and I think one of the most overlooked features in HEC-RAS. If you have any experience with any type of programming language (even Excel Macros and VBA) you should have not problem picking it up. Even if it is all new to you, you should be able to pick it up pretty easily.