Fish ladders usually consist of a series of pools connected by weirs or narrow slots which enable migrating fish to climb upstream over large dams. Depending on the type of ladder, there are two overall approaches to modeling the flow through the fish ladders using SewerGEMS or CivilStorm.
If the ladder is a series of pools with weirs, they can be modeled using the pond element, with an Composite Outlet Structure corresponding to the weir or orifice with a short conduit discharging into the next downstream pond. The upstream inflow can best be modeled by a fixed inflow element (e.g. manhole, transition) or an inflow directly in the properties of the upstream-most pond. Layout details can be seen here.
If the pools in the ladder are connected by slots, each pool can be modeled as a rectangular shape conduit connected to the downstream conduit by a manhole or transition element. For calculation simplicity, the head loss through the slot can be modeled as Absolute (structure loss method field in the node). For more precise calculations, the user would need to develop an approach using one of the other head loss methods.
Using conduit control structures is also an option, but may introduce too much complication in the calculations, potentially leading to numerical instability (it is suggested to use the Explicit (SWMM) solver with a small Routing Step in this case). On the other hand, reduced complexity (such as using only a single conduit with roughness set to model the total headloss through all the weirs/slots) may not present an accurate representation of the fish ladder. See more in the below forum discussion on this topic.
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