Island Water & Watersheds

Photo: High Island [photo credit: http://tropicalparadise.net].

Photo: Low Island (Ifira Island).

When we understand the importance of water and the watersheds which catch, store, filter & deliver our fresh water to us, we gain a deeper understanding of where we fit in to the ecology of a place.

Permaculture Publications managed to record, transcribe, and publish to the public domain a series of lectures from a PDC given by Bill Mollison in 1981 (New Hapshire, USA).  The treatise he gives on High Islands & Low Islands are excellent (and highly entertaining, if you can manage to read them in a lazy aussie drawl to fully capture the dry ironic undertone in his delivery).

There are both High & Low Islands on Vanuatu, so it is important to understand the way each is formed if we are to understand the differences in managing & protecting their watersheds.

Permaculture_on_Islands.pdf Download this file

Download: 'Permaculture on Islands', by Bill Mollison (1981)

For a detailed description of these differences, download the above Mollison transcript (well worth the read), for the cliff notes, see below:

High Islands:

    •    Air is funneled up the mountains of the windward side.
    •    Clouds form as condensation occurs at upper levels.
    •    Most rain is dropped on windward side.
    •    Rain shadow is created on leeward side.
    •    Upland forests seeds clouds with transpiration, which increases precipitation.
    •    Over time, forests can descend from the upper slopes of the leeward side.
    •    Clouds follow the forest into rain shadow.
    •    Watersheds filter water through sedimentation, solarization, oxygenation & filtration.
    •    Trees protect the watershed.

Low Islands:

    •    Bird droppings (phosphates) & sand (calcium) form basis of soil.
    •    Pioneer plan species must break through 'platen' layer of phosphate + calcareous sands.
    •    Once platen layer is penetrated by pioneers, groundwater table can form.
    •    Organic matter from vegetation creates humus for succession species.
    •    Groundwater table only 3-5 feet deep.
    •    If groundwater is overdrawn, salt water can get in.
    •    This groundwater is shallow & must be protected!
    •    Surface water catchment strategies help protect groundwater.
    •    Low islands must be protected w/ trees or wind & waves will quickly erode.
    •    Trees protect the island & watershed.