Randy,
Rustic bridges are the way to go – cheap and quick construct but they will need to be maintained on a regular basis and occasionly repaired. A few of my golf courses have rustic bridges, some using round timber as main structural members and rock foundations – I’ve even constructed the good old stone arch bridges. If you want a removable bridge then a pallet bridge can do the job for a short span.
The obvious questions if you want to calculate the bridges are strong enough but not overbuilt are:
– what clear spans are you talking about
– what are the strength of materials involved (quality of the timber)
– how much freeboard will you have (distance between high water and the soffit of the bridge deck)
– what kind of loads are they expected to carry, particularly snow loads in winter.
– Also don’t forget the planning regulations and insurance considerations with respect to safety.
This photo shows a bridge spanning a total of about 35m made up of 2 clears spans of 15m with a central island. The main members are two timber logs from a local forest.
I’ve some pictures of my courses in Switzerland, some of which are close to ski resorts, that may correspond to your Patagonian project. If you are interested you can email me.
John