The rivers of a terrain often form in places that have a large upstream area draining through them. By dragging the slider you set the minimum upstream area required for a river, and in this way you choose the level of detail of your flow network. The thickness of the blue line indicates the size of the upstream area. Use the point query tool to determine the exact size of the upstream area for individual points.
Using the watershed tool you can click anywhere on the terrain and see the upstream area of that point (marked in green) and the downstream path (marked in red). Activate the tool by hitting the watershed button in the layer selection dialog.
Depressions in the terrain will impede flow leading to a disconnected river network unless depressions have been removed before the analysis has been run. Using the Flash Flood Map, you can investigate flow accumulation after the terrain has been exposed to several different rain-amount scenarios. The rain water will pool into depression which get filled – resulting in a more connected stream network.
Here we demonstrate the flow accumulation data and show how the minimum upstream area (set using the slider) affects the set of rivers displayed. We also demonstrate watersheds, as well as the powerful watershed tool that enables you to click on any point in the terrain and see its downstream path (in red) as well as its watershed (in green).