What do all those lines represent, in the graph seen in steps 4 and 5 of Pondmaker?
The bold blue line represents the rating curve of the outlet structure you computed. The horizontal dashed lines represent the estimated water surface elevations for each of your return events. Each of these has an orange dot, corresponding to the target peak outflow that you’re designing for. The orange line connects these dots, so it is the target rating curve. Basically this is a good way to visualize how close your trial outlet structure is at achieving your design goal for each return event. The goal is to get the blue outlet rating curve as close as possible to the orange target rating curve. When you tweak your outlet structure and click the green compute button, the outlet rating curve will update, to give you a good visual idea of how well the adjustment was.
