Above: A rain garden under construction
Link:
http://www.public.coe.edu/McLoud/RainGarden/Articles/NewsUWMadison.pdf
Rain gardens provide one way to counter the unintended negative effects of water conservation on the groundwater table and local ecology. A rain garden captures rainwater from roofs and diverts the water from a gutter downspout into a two-layered bed of soil with a sublayer of sand and gravel and a top layer of plants or vegetables. Rain gardens are designed to be esthetically pleasing and enhancing to urban property values and are relatively inexpensive.
Rain gardens only have to be about 10% of the hard surface area of a property to be effective according to civil engineers Kenneth Potter and Alejandro Dussaillant of the University of Wisconsin. What is counterintuitive is that smaller rain gardens are more effective than larger rain gardens. Borrowing from nature, watering a large surface such as your lawn results in rapid evaporation and absorption by plants and less net recharge to the water table. Urban rain gardens function much as do dry streambeds and prairie potholes in recharging the groundwater.
City negligence?
Has the City of Pasadena been environmentally negligent in not encouraging the creation of rain gardens along with all the drought gardens now emerging in Pasadena so as to lessen any negative impacts on the Raymond Basin on which Pasadena has been 40% dependent for its drinking water?
Where are the environmentalists?
With all the so-called environmentalists and preservationists in Pasadena one would think that the matter of rain gardens as mitigation for water conservation would have been raised by them. Neither the Pasadena Environmental Advisory Commission, the Sierra Club, the Arroyo Seco Foundation, nor Pasadena Heritage or other groups have raised this issue. Which raises a question: who in Pasadena is really concerned about protecting Pasadena's natural environment and source of cheap groundwater from the Raymond Basin?
Latin: Quis custodiet ipsos custodes? Who will guard the guardians? Who shall watch the watchers? Who polices the (water) police? Environmentalists have no monopoly on what is best for the environment.
See abstract of technical article on rain gardens by civil engineers Potter and Dussaillant below:
Title: Stormwater infiltration and focused groundwater recharge in a rain garden: simulations for different world climates.
Personal Authors: Dussaillant, A. R., Cuevas, A., Potter, K. W.
Author Affiliation: Department of Hydraulic and Environmental Engineering, P. Universidad Católica, Correo 22, Casilla 306, Santiago, Chile.
Editors: Savic, D. A., Bertoni, J. C., Mariño, M. A., Savenije, H. H. G.
Document Title: Sustainable water management solutions for large cities
Abstract:
Traditional stormwater management does not mitigate groundwater depletion resulting from pumping and loss of recharge. There has been an increasing interest in the use of alternative practices, such as rain gardens, that enhance infiltration of stormwater. We developed a simple numerical model for their design and evaluation. Water flow through the soil is modelled over three layers: a root zone, a middle storage layer, and the site subsoil. To continuously simulate recharge, runoff and evapotranspiration, a Green-Ampt equation coupled with a surface water balance is used. For the humid climate of Madison, Wisconsin, USA, results show very high recharge rates in the rainy season, where a rain garden with an area of 10-20% of the contributing impervious area maximizes recharge. For the semiarid climate of Santiago, Chile, the optimum ratio was 10-20%, and for the arid climate of Reno, Nevada, USA, it was closer to 5%.
Comments