It just won't work...

Hello everyone, 

My blog probably screams green infrastructure. There has been so much hype and many regulatory agencies now require developers to incorporate it into the design. As much as I am a proponent of it, there are times when it just won't work! You can't just blindly place bioretention areas, rain gardens, porous pavement, bioswales, etc. all over your site because it's cool or it's good marketing. Without strong investigation of the soils and site conditions and even longer term maintenance considerations, it can FAIL! 

The major component is infiltration. If the underlying soils are poor in terms of infiltration (generically speaking - C and especially D soils), how will infiltration work? If you have shallow groundwater, your system may be saturated at all times (hence groundwater separation). Also, on a volume based approach, remember you are not going to be detaining runoff generated from the 100 year storm event. You would be using these techniques to meet WQv requirements (in New York State, 90% rule), especially for bioretention areas, etc. Rule of thumb on volume based approach is the 95% rule (rainfall events < or = to the 95% percentile event). Another important consideration is your surrounding infrastructure. 

It's a bummer though when you have a large site with so much space for green infrastructure implementation, but its all C and D soils and after numerous boring logs, groundwater data and perc tests to confirm, it's just not feasible. Also, keep in mind that subsurface investigation needs to be well prepared. I remember one time when my geotechnical professor said to be very careful when encountering perched water table. It is very true. 

Anyways, a solid site assessment and early planning is key. Also, once it's successfully designed and installed, it's not over! Maintenance.... ooh.... the dreaded word.... I know most people hate the word maintenance like oil changes for a car. But this is a commitment to a more sustainable environment!

There was a good post on LinkedIn related to this matter titled "can green storm water designs aggravate basement flooding" under the Sustainable Stormwater Group. You should check it out. A lot of great points made in the discussion thread.