Calculation time (Water Overlay)
When making use of the Water Overlay, the calculation time may depend on a number of factors. Some configurations will be obvious in their impact, while other impacts may be a bit more subtle. To properly calibrate the Water Overlay not just for the correct results but to also be as performant as possible, these factors need to be properly taken into account.
Aspects which impact calculation time
The following aspects can negatively impact the calculation time of the Water Overlay.
Simulation time
The simulation of the Water Overlay requires that the movement of water is computed in small enough steps that the natural flow of water can be accurately simulated. This means that for any given simulation time, the total simulation time is divided into calculation timesteps of less than a second. For each timestep, all grid cells must undergo a calculation. The longer the simulation time, the more individual timesteps must be computed, and therefor the longer it takes to fully calculate the entire duration of the intended simulation.
Ensure the duration of the simulation is set to a timespan suitable for the intended use-case, but not longer than necessary.
Grid cell size
The more cells requiring calculation, the more time is requires to perform the neccesary calculations for every cell in the project area. The Tygron Platform can run many calculations as such in parallel, but with large enough quantities more cells means it may take multiple passes to compute them all. A smaller grid cell size means a quadratic increase in the amount of cells. Halving a cell's size means 4 times as many cells to compute.
In addition, smaller grid cells means that to properly calculate the flow of water, the amount of time per computational timestep is reduced. This is because water with the same impulse can travel just as quickly, but must not be allowed to overshoot any cells in between.
Ensure the grid cell size is set small enough that any significant waterways in the Project area are at least 4 grid cells in width, and water is allowed to flow through any other significant routes. But do not reduce the grid cell size significantly beyond that size.
Geographical spread of water
The Tygron Platform relies on an parallelized but also algorithmically optimized system. This means that although calculations of cells happen at the same time as much as possible, the Tygron Platform will also take note of where there is water to perform calculations with, and ignore regions where there is nothing to calculate. This means the calculations will only be performed for relevant areas where water is present, meaning fewer calculations are required overall, and the calculation may therefor complete quicker.
Ensure that the Project area and the modeled water system are large enough to account for all effects relevant for the case, but avoid introducing water in locations where not is required. Use Limit Areas, and/or Rain Areas to restrict the calculations or the introduction of water into the system.
Applicable models
The Tygron Platform uses a number of different formulas to compute the movement of water across different parts of the water system. Depending on the fidelity and complexity of the models used, it may take time to compute small enough steps for water to move, or to synchronize different models so water can move across them. The most important impactors are the formulas used for the above-ground water flow, and whether the groundwater model is active.
When simulating surface effects, be sure to take into account whether complete groundwater simulation will significantly impact the results for your use-case, and refrain from using full groundwater simulation where possible. If groundwater is the main interest, the extended simulation time required to properly propagate groundwater effects will mean the surface simulation can be simplified instead.
Aspects which do not impact calculation time
There are also a number of configurable elements to the Water Overlay which may appear to take additional time during the simulation, but in practice have a non-existent or negligible impact.
Timeframes
During the simulation, a number of "snapshots" are made of the current state of the simulation. A common misconception is that more timeframes leads to a longer calculation time, stemming from the idea that the amount of timeframes affects the length of timesteps in which the calculation is performed. However, the amount of timeframes does not have a significant effect on the required timesteps, and therefor also not on the calculation time.
Result Types
Similar to timeframes, additional result types do not significantly impact the amount of time required to complete the simulation.
Notes
- If the calculation time cannot be reduced to below 30 minutes, it is possible to schedule longer calculations in such a way that they may exceed the 30 minute cut-off.
- Although timeframes do not affect how long it takes for the calculation to complete, a larger amount of timeframes does mean the results consist of more data, and as such may take longer to download.
