Drainage area is an alternate term for drainage basin. Roof Catchment Area: The roof catchment area (watch video on how to calculate from a PDF plan) is the plan area as shown on the drawings. The command defines the surface region with a depression low point (catchment point), delineates the region with a boundary, and calculates the area of the catchment region. (iv) The coefficient of runoff is same for all storms of varying frequencies on a given drainage basin. Before publishing your articles on this site, please read the following pages: 1. img.wp-smiley, Plagiarism Prevention 4. Hence, for large catchment areas the utility of rational formula is questionable. To this amount base flow may also be added to get total peak flow. Some important empirical formulae are mentioned below. In general, and all else being equal, the drainage area required to form a channel increases with decreasing slope and decreasing runoff potential. Video on how to calculate catchment area from a PDF file. The catchment area is the area from which rainfall is collected. Step 4: As the flow accumulation grid was outputted we can determine the drainage network of the area and where the most of the water will be accumulated. /*