Suggest looking at the Swiss PLANAT program for guidance on this topic as they have over 15 years of implementation experience we can learn from. A few key points of their program:
1. They do risk based cost benefit analysis and assign funding requirements based on the level of risk reduction that is received. A town, railroad, highway department, and even private entity can be asked to contribute a share of the mitigation costs following a defensible cost-benefit analysis. They have also developed the cost-benefit software to reduce the chance for inconsistency.
2. They have a 4 year rotating oversight council that consists of various government officials from different impacted agencies, engineering and science experts, and insurance companies. Need both public and private sector representation for success.
You can see more at :http://www.planat.ch/en/planat/.