1. Help Center
  2. Structural BMPs

How do I determine drainage area?

You can delineate drainage areas by either clicking on individual parcels during the inventory, or use the selection tools in the window.

1. Click polygons (consists of parcels and road grids) that drain to the sBMP, OR 


2. Use the selection tools in the drainage selection window

Helpful Tips:

  • As polygons are selected, a table in the top left generates a list with the selected parcel’s APN #, acreage and % of that parcel that is treated. The user can manually adjust the % treated when runoff from an entire parcel is not routed to the BMP.
  • To deselect polygons, either click directly on the highlighted parcel in the map, or uncheck the “Select” box from the table.
  • To add polygons from another catchment, click the desired area on the map to trigger the “Add catchment area” popup.
  • To select all polygons displayed, click “Select All.”
  • Road polygons are based on 30m grid, and do not have an associated APN. The area of these polygons are aggregated in one line in the table ‘No APN’ and it is assumed that 100% of those polygons are routed to the APN.
  • The total drainage area is summed and auto populated in the bottom menu. User must manually enter the impervious area that is routed to the BMP.
  • Parcels shaded white are designated as Trash PLU areas and grey parcels are non-PLU areas.