The bar charts on the left side of the Gowdy Output window show all the individual inputs to the river reach and the diversions from it. The source allocations are activated for flow and all chemical constituents, but not temperature or hydrologic properties like velocity. The inputs shown in green include river inflows from the upstream end of the reach and from tributaries, inflows from local land catchments, point source discharges, and unused diversion flows returned to the river. Shown in red are diversions. If the option to ignore in-stream processes is selected, the values shown represent what was simulated actually entering or leaving the river reach at the location of each input source or diversion. For a conservative substance adding up all the inputs and subtracting the diversions is approximately equal to the in-stream load at the downstream end of the river reach. There is some error introduced into the calculations as travel time is discretized into whole days, but this is error generally just a few percent. Flow is assumed to be conservative, ignoring the small amount which is lost to evaporation.
If the option to account for in-stream processes is selected, the inputs and outputs are scaled up or down from their actual values to reflect their contributions toward what remains in the river. This is solved from upstream to downstream. For each segment, all the inputs are summed and compared against the sum of outputs and change in storage. A ratio of outputs to inputs is developed. Then the loads for all inputs to and diversions from the river segment and all segments upstream are multiplied by the ratio.