http://arkitrek.com/http:/arkitrek.com/sustainable-design-mantanani-style/ environment • responsive • design Mon, 23 Apr 2012 15:50:15 +0000 hourly 1 http://wordpress.org/?v=3.3.2 http://arkitrek.com/http:/arkitrek.com/sustainable-design-mantanani-style/comment-page-1/#comment-207 Mantanani Driftwood | Arkitrek Thu, 01 Oct 2009 13:18:38 +0000 http://arkitrek.com/?p=306#comment-207 [...] The success in the use of drifwood logs however, is not in their appearance, but in that we have managed to avoid using posts made out of wonderful and scarce belian wood (see my earlier post). [...] [...] The success in the use of drifwood logs however, is not in their appearance, but in that we have managed to avoid using posts made out of wonderful and scarce belian wood (see my earlier post). [...]

]]> http://arkitrek.com/http:/arkitrek.com/sustainable-design-mantanani-style/comment-page-1/#comment-186 Keith Hall Wed, 03 Jun 2009 10:28:38 +0000 http://arkitrek.com/?p=306#comment-186 Many years ago, I did a feasibility study into the use of groundwater for public water supply on Grand Cayman. This is a small coral island which is nowhere more than about 10 m above sea level but it did have some minor groundwater resources. Freshwater “floats” on top of salt water because it is less dense. Theoretically, for every centimetre that the water table is above sea level there will be 40 cm of freshwater (memorably known as the Ghyben Hertzberg relationship) The theoretical thickness of freshwater will be reduced in practice because there is brackish transition zone. On a small island, the natural order is for rainfall to infiltrate and, net of evapotranspiration by plants, flow out imperceptibly along the foreshore. A lens of freshwater is formed but as the water table is likely to be only a few centimetres above sea level, at most the maximum thickness will be a few metres in the centre of the island. You can sustainably abstract a limited amount of water from the lens provided that the amount taken is less than infiltration net of evapotranspiration but this will reduce the thickness of the lens. You must find a way to skim water from the top of the lens as if you pump a lot from one spot, lowering the water table will draw the salt water up at that point. In Grand Cayman we proposed radial trench wells. Rainwater harvesting may be the best way forward for your development but will need storage, which carries an environmental cost, to ensure a continuous supply. The amount collected is unlikely to be a material proportion of total rainfall on the island meaning recycling to groundwater would be of no measurable benefit to the environment. More significantly, to recycle treated effluent to groundwater could put everyone else who currently relies on it as their water supply at serious health risk. Many years ago, I did a feasibility study into the use of groundwater for public water supply on Grand Cayman. This is a small coral island which is nowhere more than about 10 m above sea level but it did have some minor groundwater resources.
Freshwater “floats” on top of salt water because it is less dense. Theoretically, for every centimetre that the water table is above sea level there will be 40 cm of freshwater (memorably known as the Ghyben Hertzberg relationship) The theoretical thickness of freshwater will be reduced in practice because there is brackish transition zone.
On a small island, the natural order is for rainfall to infiltrate and, net of evapotranspiration by plants, flow out imperceptibly along the foreshore. A lens of freshwater is formed but as the water table is likely to be only a few centimetres above sea level, at most the maximum thickness will be a few metres in the centre of the island.
You can sustainably abstract a limited amount of water from the lens provided that the amount taken is less than infiltration net of evapotranspiration but this will reduce the thickness of the lens. You must find a way to skim water from the top of the lens as if you pump a lot from one spot, lowering the water table will draw the salt water up at that point. In Grand Cayman we proposed radial trench wells.
Rainwater harvesting may be the best way forward for your development but will need storage, which carries an environmental cost, to ensure a continuous supply. The amount collected is unlikely to be a material proportion of total rainfall on the island meaning recycling to groundwater would be of no measurable benefit to the environment.
More significantly, to recycle treated effluent to groundwater could put everyone else who currently relies on it as their water supply at serious health risk.

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