Sunday, April 17, 2011

Storing Rainwater for Green Roof Irrigation, Florida Green Roofs and Water Conservation

We built a really cool bioswale and rainwater storage system to collect not only rainwater runoff from the green roof, but also to collect any irrigation water seeping from our terra cotta pots and the water we use to wash off shoes and our feet after working in the nursery or with the animals.

MetroVerde Bioswale
We looked at many designs before settling on the final.  There are some nice looking California designed wetlands in a box ( and those designed in northern states ) and we reviewed these products in detail.  Unfortunately, though we get 60 inches average, 154 CM, per year rainfall, most comes only in a few summer months and a nine to ten week drought with little or no rain is not uncommon.

Most 'wetlands in a box' design are for those areas where rainfall occurs every afternoon or every other day where there is a constant water input.   They just won't keep the plants alive during Jacksonville's long, hot droughts.

Florida Bioswale plants, Mentha spicata and Equisetum hyemale
For a modular wetland to work in Florida the design would have to be based around Florida climate and environment.  We are very hot in the summers, cool to cold in the winters, extremely humid in the summers,  subject to 20", 50CM rainfall events during a tropical storm,  prone to weeks without water and have high-speed desiccating winds.

So we thought if we could find an ecological system similar to what we wanted we could study the component parts and duplicate the wetland.  There are many wetlands in Florida to study but the problem is they all possess native hydrology where as the area under our green roofs and the area where we wanted the bioswale to be built was not an original wetland nor did it have any native hydrology.

Stormwater ponds were another resource to consider.  If we could find a small stormwater pond that was originally constructed in an upland area with no native hydrology and no additional irrigation, then we believed we could use the design.

It worked!  We found a system created in an upland now having developed into a nice Florida ecological system we could model our bioswale after.  Our reference wetland is a superb example of a long-term functioning wetland.  The system is located on the University of Florida campus in Gainesville and was designed by Dr. Mark Clark.
Water is stored for reuse within the bioswale system
We began construction in 2008 on our system and are very pleases with the performance.  The system allows for pedestrian access, provides a crisp appearance, allows for collection of rainwater and wash-off water and then reuse of the water through a pump and hose.  Interestingly, the design serves to capture even the smallest amount of rainwater and feeds the adjacent plants through wick action.  The design include multi staging and bay implementation yet the materials are readily available and cost-effective.  If fact, the most expensive component were the rock.  A sharp sand could easily replace the rock for additional value engineering without blinding or otherwise impacting performance of the system.

The functional components are structurally rated for H-20 loadings and one could easily drive a vehicle across the system if appropriate design measures were taken.

The horsetail spreads through rhizomes under the rock (as does the more invasive mint - a must have for iced tea or mojitos) and contributes to the stabilization (horsetail is native in Florida).

Well into it's fourth year of service, the bioswale has become an integral part of extensive green roof design and function.  For a look at another similar bioswale system we've installed here and is functioning well into its second/third year click here.

1 comment:

Alejamuel Sultz said...

That's a good idea to collect rainwater for the purpose of irrigation and watering plant life and flora. This is an environment-friendly project that others should also try to emulate. Congratulations!