Where does all that water go?
When rain falls more quickly than it can infiltrate the soil, overland flows result. These flows are referred to as stormwater. The more impervious a surface is, the more likely stormwater is to be a factor. Impervious surfaces may be natural (eg. compacted clay soil or rock) but in many cases they are part of the built environment (eg. roofs and pavement). Traditional patterns of development, especially urban development, have resulted in the proliferation of impervious surfaces. In cities and other densely populated areas, this has vastly reduced the capacity of the earth's surface to hold water or allow it to seep into the groundwater to recharge streams, lakes and aquifers.
traditional stormwater management
In addition to disrupting the normal water cycle, all those impervious surfaces have created a management problem because the water has to go somewhere. To prevent flooding, complex systems of drainage have been created. Whereas natural systems generally work to slow the flow of water, discharging it gradually through the watershed, stormwater services have generally been designed to channel water as quickly as possible to a lake, river or the ocean. These services may take the form of an urban network of drains, pipes, catch basins and outlets or rural drainage ditches.
problems, problems, problems
Facilitating runoff through traditional stormwater management practices has created significant problems:
- By preventing the infiltration of water, the opportunity to recharge aquifers, streams and rivers is lost and we effectively create deserts beneath our feet.
- Whereas natural biological and filtering processes relieve groundwater of many of the contaminants it accumulates along the way, stormwater tends to pick up pollutants and concentrate them in sensitive, high value aquatic areas such as rivers, lakes and beaches.
- Water is conveyed as quickly as possible, resulting in significant erosion in many areas.
- Even in times of drought, traditional systems actively prevent water from being retained. Much of this water is high quality and has the potential to be made available for a host of beneficial uses.
Ironically, our approach to water management has been to treat the water that naturally falls on a site as a waste substance to be disposed of. At the same time, we have created energy-intensive systems to deliver water from long distances to our homes and businesses. The majority of this high-quality, potable water is used for activities like flushing toilets or irrigation. We can do better!
Slow the Flow!
The best way to deal with water in the spaces we manage is to try to mimic what happens naturally in areas that are undisturbed. In nature, water's journey through its never-ending cycle is slowed along the way as it is utilized over and over again for many different purposes. By viewing your land and building holistically and planning carefully to ensure we make the most of the rain that falls on the site, we can build resiliency, support natural processes, and reduce the negative impacts associated with our traditional ways of managing water.
The tools we have to accomplish this are detention, retention and infiltration.