Runoff from storms is part of the natural hydrologic process: rainwater that does not infiltrate into the ground flows by the force of gravity into water bodies such as lakes, streams, rivers and oceans. As runoff heads for receiving waters, natural vegetation and ground cover slow the water and filter it for pollutants and sediments. In urban settings, however, natural vegetation and topography have been altered or paved and storm water is diverted in storm drain pipes. When the drainage pattern of a watershed is so altered, flows increase in concentration and velocity and pick up sediments and pollutants from land surfaces at an increased rate. Storm water that flows through urbanized areas to receiving waters is called “urban runoff.”

-The California Coastal Commission

The slideshow below details the effects of the construction process on Southern California over the last 50 years.

1. Natural fields once allowed storm water percolation.

2. As construction and building progressed, the natural fields were paved over and the potential for water percolation diminished.

3. The same building in photograph 2 once all construction is completed. Notice the amount of impervious surfaces.

4. As construction progressed more and more percolation fields were covered with parking areas.

5. Now, water collects in gutters and storm drain systems bypassing the natural percolation process.

6. More problems occur as storm drain water collects dirt, silt and nutrients on its way to our oceans.

7. Special applications require special filters to remove toxic chemicals and cleaners before they enter our oceans.

8. Oceansafe allows water to filter and settle back into the ground returning the commonly paved parking areas back to percolation fields.