What Is Permeable Landscaping?

Permeable Landscaping is that which allows water and air to penetrate the soil. It may be populated with trees, plants, rocks or other natural or manmade materials. It is the natural state of land that permits the earth to "breathe". When permeable landscape is covered with impermeable surfaces (paving, sidewalks, buildings, etc), water is diverted by way of treatment plants to major waterways (ocean and bay), air cannot reach the soil, excess heat is generated and plants cannot grow. Re-introducing permeable landscape where it has been removed is extremely valuable to the health of cities, and is easily and immediately achievable. It simply requires the removal of impermeable materials and replacement with soil, plant material, rock or porous manmade materials.

It should be noted that permeable landscape does not necessarily mean "trees". In San Francisco and other municipalities, trees very frequently are not allowed in desired locations because of proximity to underground and/or overhead utilities. By contrast, many plants (other than trees) have shallower and less invasive roots, and do not reach the heights of overhead wires. They are permitted directly next to and above underground utilities. For those who are intimidated by maintaining plants, permeable rock gardens are a viable alternative which likewise do not present the problems that trees often do.

Permeable Landscaping:

  • Reduces storm sewer loads, reducing potential for backups and flooding;
  • Creates habitat for birds, butterflies and other wildlife;
  • Makes a place to garden;
  • Provides potential for urban farming (foodscape);
  • Beautifies the neighborhood;
  • Creates opportunities for community interaction;
  • Deters crime;
  • Increases property values;
  • Reduces global warming (by absorbing heat rather than reflecting it);
  • Increases oxygen production; and
  • Recharges ground water.

Don't just take our word for it - see the benefits outlined in this Resolution composed by the Board of Supervisors: Click HERE.

For more information on how permeable landscaping interfaces with the sewer system, see this report (.pdf 822kb).


How Does It Work?

It's SIMPLE! ... water that falls on impermeable surfaces runs downhill until it is absorbed by exposed soil or meets a catchbasin, the entry point to the sewer system.

It's FAST ACTING! ... water is absorbed as soon as soil is exposed, regardless of plantings or other amenities.

See Permeable Landscaping in action in the photograph below: Water falling on the left is absorbed by the soil and nourishes the plants. Water falling on the right enters the city sewer system through a catchbasin.

If there is no exposed ground between the point where water falls and the catchbasin, 100% of that rainwater enters the sewer system. In San Francisco, which has a combined sewer system, rain mixes in the sewer lines with wastewater from buildings and is sent to treatment plants. During large storms it is not uncommon for untreated sewage and storm water to be released as overflow into public waterways including San Francisco Bay and the Pacific Ocean, resulting in contamination, unsanitary conditions and beach closures. The more storm water that can be kept out of this system, the more these occurrences can be reduced.

Permeable landscaping is part of the sewer system for storm water ... the most beautiful, sustainable and efficient part! .



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