I still don't necessarily agree, just because the dam makes building the canal much easier.
So basically what I said... Also, it depends on if you think we're actually going to be trading large amounts of cargo at this stage of dev or not. Trading food would be dumb because any place that's big enough to be worth trading w/ probably already produces enough. Smaller luxuries like dye are better, and smaller.
Dams need to be vertical and withstand pressure, canals need decent stonework to not need as many repairs. Both need good organization. Great... So since they're different types of difficulty, building a canal won't contribute to preparing for building a dam, since they require such different things. So we might as well build the dam first, once we're ready to, since it will speed up the canal. Yay.
How a dam speeds up canal construction remains an inexplicable leap of logic. Your dams must be built where the water
already flows, to trap it and gather it.
A dam is a challenge of engineering knowledge and expertise. The danger is orders of magnitude higher than a canal because if you screw up a canal, you need to do more work. If you screw up a dam, it means in the next generations to come, everything downstream gets Harzivan'ed.
A canal requires extensive earthworks, but not special skill.
So look at the logical elements here:
Canal:
-Aided by:
--Roads and the ability to ferry workers and construction materials.
--Step Farms and the ability to both feed more specialists and experience in learning how well large structures deal with water.
--Walls and the improvements in brickwork, masonry and construction techniques in general
--Expanded fishing and the ability to both feed more specialists and the improved boatworks to use a partial canal to transport materials
--Expanded pastures and the ability to make more use of animal labor for digging and moving materials
--New settlement and the ability to improve organization of resources, as well as the ability of the settlement to provide a supply midpoint for the canal.
--Megastructure experience
--Development of engineers to plan out the depths and sidings, as well as how to handle erosion.
-Aids:
--Development of specialist artisan caste for constructions. Given the scale of the construction, you'd have actual architects and engineers arise.
--Development of megastructure experience.
--Development of logistics and centralization resistance.
--Development of hidden hydrology experience, particularly the things you learn when you have tons of water on a structure.
-Consequences:
--Trade routes will change. The heavy traffic such a structure would require during it's construction will reshape trade routes, and settlements along it will recieve disproportionate trade as you can travel faster along a canal even without boats, due to cleared land.
--Rerouted water can affect the lowlands, depending on whether the canal finds an alternative route to the sea(favors us if we link it to the fishing village), or relink to it. Some of them might be a bit salty about that.
--Disease will spread much faster along the route.
-Risks: Low. Failed canals costs time and manpower.
Dam:
-Aided by:
--Step Farms and the ability to both feed more specialists and experience in learning how well large structures deal with water.
--Walls and the improvements in brickwork, masonry and construction techniques in general
--Expanded pastures and the ability to make more use of animal labor for digging and moving materials
--Megastructure experience
--Hydrology experience to understand what large amounts of water does to seemingly solid earth.
--Geographical experience with the building area to understand it's stability.
--Development of engineers to assess loads and necessary stresses.
-Aids:
--Development of specialist artisan caste for constructions. Given the scale of the construction, you'd have actual architects and engineers arise.
--Development of megastructure experience.
--Development of logistics and centralization resistance.
--Development of hidden hydrology experience, particularly the things you learn when you have tons of water on a structure.
-Consequences:
--Ruination of flooding based agriculture downstream. Dams trap silt even if they let the water through. The floods can still happen, but the soil will not be replenished. On the other hand if we figure this out our farms will be ludicrously rich if we seasonally dredge the dam to prevent buildup(and we will want to, because the silt piling up will gradually choke the water outflows and stress the dam)
--Significant reduction of water availability downstream until it reaches capacity, but stabilizes flow. Depending on management it can absorb small floods and droughts.
--Potentially induce earthquakes, depending on construction and geography. This will be transient, but terrifying, especially for anything built on hills.
--Ecological changes. Expect more large animals to move into the area to take advantage of a reliable watering hole.
--Disease increase. Until the ecology balances out again, the newly flooded area would result in increases in insects, algae and other microorganisms.
-Risks: High. Failed dams can destroy dozens of villages downstream, with little to no warning
Anyway, while we could probably start the canals safely even without the prereqs, we cannot say the same for dams. Expertise carries over for stonework and earthworks, techniques to build wide also translates to institutional skills needed to build tall...and I'd probably prefer to learn that you need older tree roots to reinforce waterbearing walls without massive use of stone on canals than on dams.
As for trading food, it's much more common than you think. Hell, it's our main trade good, we sell shittons of food, especially non-perishable grains for crafts and luxuries.
