Before urbanization, storm drainage was simply a natural process of precipitation, infiltration and, occasionally, surface runoff. Most streams were fed by groundwater seepage, not runoff. But in the past century, as our increasingly industrial and urban society began to manage stormwater, the solutions turned toward containment and conveyance of runoff - an inevitably doomed practice.

During the early 1900s, the "get out of the mud" movement brought cobbles and paving to most city streets, and the 1950s federal highway programs upped the ante, with sealed asphalt surfaces becoming the predominant paving technique. These new highway designs used a "dry bed" construction technique, which required stormwater to be captured in storm drains, and piped to streams to protect the road's structural base. Grass lanes and gravel roads and parking lots came to be viewed as dirty and old fashioned, and were largely replaced with asphalt and concrete.

When rains fall on these pervious surface, it washes the accumulated road oil, grease, and rubber dust into storm drains, and from there directly into streams and rivers, untreated. Runoff from these surfaces is also accelerated, creating large flushes of stormwater that dramatically alter the natural hydrologic cycle of small streams, and ruining fish habitats.

Though well-intentioned developers and municipalities planted trees in asphalt parking lots and along asphalt streets, these trees often fail to thrive, and eventually starve and die because their roots to not have enough air and water. Wherever asphalt was placed against mature trees, a new struggle began: roots easily break through asphalt in search of air and water, and the owner or municipality routinely patched over the breaks, only to have repaired surfaces further damaged by a tree determined to survive. In most cases, the tree eventually lost the struggle - either through the stresses of surviving in an asphalt environment, or by being physically removed as a "nuisance."

This relationship continued until the late 1980s, when environmental engineers began to look for more sustainable ways to manage stormwater in urban environments. One key to the new way of thinking is to view the street system as part of a larger watershed - a simple fact overlooked for decades. The design elements of the new movement were simple: maximize the effective infiltration rate for stormwater. This can be achieved with a broad range of "best management practices", including widespread use of large urban trees, and using pervious paving materials that allow trees to thrive by infiltrating stormwater directly into the soil.

A variety of commercial paving solutions are now widely available. They include:

• pervious concrete that can be used for low volume streets, parking lots and sidewalks
• brick pavers designed to allow a high degree of infiltration (compared to traditional cobbles, which are relatively impervious)
• plastic "geo-tech" fabrics that allow for gravel and grass surfaces to have structural qualities

These products should always be considered when making improvements to existing streets, or building new roads. They are easy to install and maintain, and are an essential part of the solution for restoring stream and water quality, given that 20 to 30% of urban land is covered by streets and parking surfaces. The links section of Bricks & Mortar contains a number of vendors who can provide or install these materials.