Level 2 Project Plan

Complex (Active) Rainwater Harvesting Systems:
Collection – roof
Conveyance – direct water from catchment area to storage
Storage – aboveground or underground tank
Filter – gutter debris screen, downspout debris screen and filter, diverter, first flush, roof washer

View example of Level 2 Project Plan.

Step #1.  Site Analysis:

  • Assess site conditions to determine rainwater harvesting goals.
  • Draw site to scale and include dimensions.
  • Show direction of water flow off roof tops with arrows.
  • Where are the high points/ridge lines? (Indicate with a + sign.)
  • Where are the low points/outlets? (Indicate with a - sign.)
  • Determine catchments.
  • Identify areas that require irrigation.
  • Label surface areas of hardscapes and landscapes, identified rainwater practice(s), and associated potential storage volume.

Step #2.  Calculations:

  • Calculate the total amount of water which could be collected from roof each year and calculate the total amount of water currently needed to meet landscaping needs each year.
  • Calculate site's water budget and determine whether current site conditions will meet rainwater harvesting goals.
    º Calculate monthly supply (rainfall harvest potential).
    º Calculate monthly demand (plant water requirement).
    º Calculate monthly storage/supplemental water.
  • Calculate minimum requirement for storage (retain one-inch rainfall).
    º Formula: Catchment area * 0.6 = required storage.

Step #3.  Final Design:

  • Use supply and demand calculations to size and locate tanks.
  • Use gutters and downspouts to convey the water to the storage.
  • Locate storage close to plants needing water and higher than the planted area to take advantage of gravity flow.
  • Provide for distribution to all planted areas.
  • Provide retention area(s) for overflow.
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