Flooding or the thought of potential flooding can make people do irrational things.
Why do you want to move? Do you want a bigger house, or have you got your worries about possible flooding? If it's the latter and you rent it out, you'll still worry about it when the river gets high, even though there are none of your things in it.
Personally I'd stick it out and hold out for a sale and move on. Even if it means selling and moving into rented in the short term before you find a new house. You may need to take a little less for your house, but with nothing to sell, you will potentially get any shortfall back by being in a stronger negotiating position for the new house.
Whilst £80k might seem like a fair amount of equity, it's not that much if you share it over two properties. "Buying" a second house may stack up on paper providing that things go well, but it will mean that you will owe a considerable amount of extra money. If you struggle getting tenants due to their concerns about flooding, you make struggle to fund the debt.
You can make your house more saleable by putting flood defenses in place. Flood doors and covers for air bricks needed cost that much, but it could ease potential buyers minds.