Overview: The Runoff Analysis functionality allows you to calculate runoff depth and velocity maps during a storm event (e.g. 1 in 5yr storm). The outputs allow the designer to assess the risk of erosion (high velocity) and overtopping of furrow (depth greater than furrow) for a particular landform design or the existing topography.

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Menu:  Tools> Runoff Analysis...   

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Topography

Surface: The surface that you want to carry the analysis out on.

Calculation Grid: The cell spacing of the grid that the drainage analysis is calculated on. 10m is a typical useful value.

Hydrology

Watch this video for a description: Runoff Analysis Part 2

Hydraulic Roughness (n): This is the same as Mannings ‘n’ used commonly in engineering calculations. Here are some values as measured by Chow (1959): 

Furrows or Beds

Furrow or Beds Restrict Water Flow Direction: If furrows or beds exist tick this on.  

Furrow/Beds Direction (deg): The direction of the furrows relative to north. Use the ‘Pick’ button to click two points to define the direction or type a number in. 

Furrow/Beds Spacing, w (m): The spacing between the furrows/bed. i.e from one crest to the other as shown in the diagram on the dialog box.

Furrow/Beds Height, h (m): The height of the intended furrows in the field. The water will build up in the furrow and only spill across the furrow when it exceeds this depth. 

Furrow/Beds Side Slope, s (?h:1v): The side slope of the furrow as shown in the diagram on the dialog box. This is the horizontal distance per 1 vertical. eg 1 mean 45% gradient and 3 would mean 33% gradient.

Furrow/Beds Bottom Width, b (m): The width of the bottow of the furrow as shown in the diagram on the dialog box.