Dear all,
we have a project site situated in the rural mountains where infiltration is not even possible due to geological conditions. The site consists of very low permeable soil, with high groundwater level (only 2 m below grade). The site is currently drained off into existing water surface streams situated 1) on site and 2) at the boarder of the site. One of the streams is drained into underground pipe also situated on site that releases water outside the LEED Site. This pipeline was constructed in the past to prevent the whole area from flooding. Both of the streams are then leading to a local dam (situated roughly 100 m from the LEED Site).
We would like to approach the credit SSc4 LEED NCv4 ideally through option 2: to manage all the incremental runoff volume on site compared the project status after the construction to full natural undeveloped land cover.
But the project team is suggesting not to design on site bioretention ponds but rather to use the already built dam to catchup the incremental runoff from the LEED Site. This sounds very logical to utilize the already built dam nearby that was designed specifically for the flooding prevention purpose.
Is it possible to include retention dam outside the LEED Site to fulfill the requirements of the credit nevertheless what option is used? This approach was possible in LEED v3 by assuming all the credit requirements to be applied for the whole water collection areas including the LEED Site. What approach should be used within LEEDv4 for option 1 vs. option 2?
Is it possible to consider the proposed solution as a low-impact development strategy? The dam is natural based structure – regional soil and stone based bearing structure (layers of stones and soil with different granularity) but of course made by hard mechanization. Dam is equipped with 16 kW output hydro plant. The top of the surface is surrounded by paved concrete road. Also the overflow bypass is concrete based structure. The rest of the embankments is pedestrian based with natural slope into the water.
Thanks in advance for any kind of help
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Michael DeVuono
Regional Stormwater LeaderArcadis North America
LEEDuser Expert
187 thumbs up
November 24, 2015 - 10:23 am
You are increasing both volume and rate to the receiving streams, and piping. You are not restoring your site to the natural hydrologic state. I don't agree with your approach, and your ability to meet the intent of this credit.
Petr Vogel
Specialist ConsultantEkoWATT CZ
4 thumbs up
November 25, 2015 - 3:58 am
Michael, thanks for your answer. The investor is pushing us not to invest to bioretention onsite since it will only retent water, there is nearly no infiltration possibility + it is really hard to argue if the already built dam is nearby. Besides the described above we have designed green roofs + permeable hardscapes. Can you suggest some other ideas please because this is not enough to restore the natural conditions?
Thanks, Petr
Michael DeVuono
Regional Stormwater LeaderArcadis North America
LEEDuser Expert
187 thumbs up
November 25, 2015 - 7:19 am
Do you have any ability to do capture and reuse? That is really what you need to be looking into when infiltration isn't possible.
If you are in an area with no infiltration, a mountanous area, your pre-development runoff is already going to be pretty high. Looking at Option 2, pre vs post, your post development runoff that needs to be managed proobably isn't all that much, especially if you are doing green roofs and porous paving.
Add some ammended soils to lawn areas as well, and model with a 17% void ratio. Constructed wetlands are always great, and look great, if you have the room.
Petr Vogel
Specialist ConsultantEkoWATT CZ
4 thumbs up
November 25, 2015 - 11:20 am
Yes we are considering to capture and reuse rainwater. This is not yet certain due to high potential of greywater to be reused + to recover heat (hotel with welness and swimming pool center).
If I can I do have 2 more questions since LEEDv4 is really fresh for us...
If we take the capture and reuse approach does it have to be also in the logic of LID? Having in mind solution of underground accumulation tank vs. surface accumulation pond to be naturally landscaped.
I would also say that if we add imported soil with higher infiltration parameters it would be in conflict with the SSc2 topsoil compliance " imported topsoils may not include the following: soils from other greenfield sites, unless those soils are a byproduct of a construction process." Am I right?
Petr Vogel
Specialist ConsultantEkoWATT CZ
4 thumbs up
November 30, 2015 - 2:55 pm
Michael or other experts,
some new thoughts?
Thanks for clarifications,
Petr