FEMA flood plain maps = zero reliability.
Corps flood plain maps = very good, but not perfect.
Flood plain developers = scum of the earth cuz they buy it knowing they will develop it, flip it, run off with the profit, and leave the problems to the buyers and taxpayers.
It's hard to blame the Corps for simply trying to do the will of the people, even if the people's will is unreal. When asked why the Corps builit the huge and high maintenance Mississippi levey system, the Corps said it was too expensive to move Vicksburg. Asked the same question 100 years later, the Corps admits it would have been far cheaper to move Vicksburg, but now there are 100 other cities built smack dab in the flood plain.
Flood plains are for agriculture. Hillsides are for towns' residential and commercial areas. That model functions all over the planet. Deviations from it result in wet feet or worse.
If the US government wanted to join the smart set and stop rewarding stupidity, it would not issue any new flood insurance policies, except for agriculture (= low risk & high benefit).
As for the Green River, the risk is being over played. They are doing that for a reason. The reason is because too many people are too stupid, and the Corps is trying to compensate for their stupidity. Howard Hanson Dam still functions, but it is able to contain less than its full flood storage capacity. This means that GR flood plain risk is increased only if a large flood occurs. This is a calculated risk, but a real one. Howard Hanson Dam is designed to allow no more than 12,000 cfs at Auburn during a 100 year flood. With less than full storage available, GR flow at Auburn will only exceed 12,000 cfs if this winter's flood is closer to a 100 year event than if it is a less than 10 or 12 year event. It's all about probabilities. But because too many people are too stupid to take action to reduce their risks, the Corps is over playing the risk to reduce the impacts to idiots. What a society we live in.
Sg