Mechanical design of a side hung tide gate for a levee

I'm looking for a freelancer to design a side hung tide gate for a levee.

The main purpose of the gate is flood control, fish passage and environmental enhancement.
I would like to have some sort of delayed closing mechanism it needs to be adjustable and simple with no electricity. Either a SS spring or tension arm that is adjustable.
When the tide is low the gate needs to be fully open, perpendicular to the culverts and then close at a given height.
The specific dimensions are 5m head from the bottom of the gate to the hydraulic top to levee and open dimensions of the gate 2m wide and 1.5m high. As far as materials go, the gate should be constructed out of 316 Stainless.
With gates of this size the forces exerted when closing will be great and consideration should be given to a damper to absorb the energy from closing and preventing hammer.
The successful freelancer will need experience and knowledge in this specific engineering field, expertise in hydraulic design, excellent communication skills, and outstanding attention to detail.