Permaculture Designers Manual
CHAPTER 6 – WATER IN PERMACULTURE
Section 7.2 –
Regional Intervention in the Water Cycle in Permaculture
Silver iodide and no doubt other ice nuclei such as tea dust can be “seeded” into cumulus, cumulonimbus or nimbostratus clouds (by plane, ground burners or rocket) in order to initiate local precipitation.
Until recently these attempts to make rain were assessed as ineffective because no one had, at the time, realized how far and for how long the seeding effects spread and persisted.
More recent analysis shows that rain in fact increases over a very wide area and those secondary effects last for months, so that varying wind directions and speeds carry the induced rain effects for hundreds or thousands of square kilometers (Ecos, 45, Spring 1985).
It also seems probable that ground burners or ground release of ice nuclei could have a similar effect.
On the ground, silver iodide is absorbed into coal dust and this is then burned when clouds form on hill crests. Strategic downwind hills can generate clouds and rain over large areas of land.
Once initiated, however, such effects cannot quickly be stopped and even in places like India or Ethiopia may create a little too much rain if ground storage systems are not previously developed to cope with the extra water.
In arid or semi-arid areas, flood retardation basins, oversized swales, large sand dams, water spreading systems, pelleted seed of fast-growing plants, and in fact any sensible civil strategy to preserve soil and people from any effect of increased precipitation is a necessary prelude to cloud-seeding.
Initial precipitation (due to increased bacterial or ice nuclei stimulus) increases can be as much as 30% and subsequently averaged in Australia at 19% (17% in Israel) over weeks, falling to 8% in months.
The cloud seeding system promises to help increase monsoon or frontal rains in areas where suitable clouds occur without sufficient precipitation.
This system can be very cheap for large land areas.
As similar effects (thunderstorms, rain) have been noted for tea leaf dust downwind of Kenya plantations, more homely strategies may also be developed if the underlying nucleation causes can be established.
It may even be that the fires and dances of the old “rain makers” on a high hill were, in truth, effective.
Certainly, fires of specific vegetation and dances with the “right” dust plume could help seed ice nuclei in clouds; quite local rain falls near some factory smoke emissions.
Windward slope forests, cross-wind tree lines and even slight earth rises of a modest 4-6m have been observed to induce air humidity, cloud formation and even rain, by orographic (uplift) effects on “windstreams”.
Thus, we are not powerless in the matter of increasing local moisture by a series of sensible ground strategies based on providing trees, mounds and cloud ice nuclei and perhaps a serious attempt to induce these changes will in the near future bring relief to areas such as the Indian Deccan, the Sahel, and large areas of Australia and the USA subject to rainless cloud masses.
OROGRAPHIC AND FOREST EFFECTS
Strategically selected crosswind ridges of even modest height (3-20m (10-65 feet)) are ideal sites for the planting of known tree “condensers” and crosswind tree lines.
These ridges are most useful when lying in the path of the summer afternoon sea breezes that now inland or located where the air drifts in at night, such as on the Californian and sub-tropical trade-wind coasts.
The clearing of trees from such sites may well induce long-term drought and create a drying effect for hundreds of kilometers inland.
It is long past time that we also assessed vegetation for some of the following effects:
Ability to provide rain nuclei, as bacteria and natural sulfur particles and also to effectively condense water from air at night.
The rainfall effects from forested ridges, where forests exceed 6-10m (19-32 feet) in height, on rainfall induced by streamline compression effects.
This effect is credited with up to 40% of rainfall where now assessed in Sweden and Australia (Tasmania and Victoria).
The total effect of forested catchment area. Historical and recent evidence suggests that rainfall, stream flow and cloud may all be seriously depleted by upland deforestation.
Such effects are never assessed or cost evaluated against deforestation or wood-chipping.
The soil erosion and salted land effects are, however, well known in deforested areas.
Any conservationist policies of future effective and informed regional governments would first research such effects and then quickly establish national forest and watershed management or restoration policies based on such research.
For ourselves, as designers, the proper approach to land planning infers that we recommend permanent forests and the preservation of older forests on crosswind ridges and on steep (18° slope or more) sea-facing slopes.
The preservation of alpine or upland absorption areas is also essential.
Soil conditioning or “ripping” (see Module 8 Soils), providing it is followed by tree plantation, trace element additions, and a non-destructive agriculture of well-managed natural yields, sparse grazing and conservation farming certainly increases (by factors of up to 70-85%) the ability of soils to hold and infiltrate water.
Areas of up to 85% run-off can be converted to zero overland flow by a combination of soil conditioning, swales and water spreading to forests.
As soils can contain many times the water of open storages or streams, then both the through flow, base flow and water available for plants also increases.
It follows that the CYCLING of water via evapo-transpiration and rainfall also increases.
Soil treatments now need to precede tree planting over almost every area that has been used by contemporary agriculture.
In particular the barren areas used for constant cropping in dry land areas need soil treatment to initiate water absorption. Trees are essential to prevent water-logging of soils and soil salting in the long term.
INFILTRATION VIA EARTHWORKS
Cheap broad scale earthwork systems and many minor forms of earthworks an aid the infiltration of overland water flow.
PITTING, SWALES and WATERSPREADING are the main aids to getting fresh water to deeper storages for long-term use and also to increase base flow.
Diversion of surface flow to sand basins, dune fields, swamps and soakage beds in earth bermed fields all ensure resident water reserves for crops and trees and longer-term storages for use in dry seasons.
Diversion drains and their associated valves, slides, cross walls; intanks and irrigation systems enable effective water harvesting, dependable storage and fast emergency use in normal rolling lowlands, hill country and dry lands.
They can also recharge sand basins and swales from otherwise wasted overland flow and damp our wildfires.
POND AND FARM DAM STORAGES
Wherever precipitation exceeds the demands of transpiration and evaporation, small dams, wetlands and swamps can proliferate.
These all act as long term water and wildlife reserves in the total landscape and many Australian farms are now “drought-proof” due to sensible investment in Keyline or similar water conservation systems by the owners.
Excellent technical manuals exist (see references at the end of this chapter).
Dams and ponds are potential aquaculture sites and the production of a diverse plant and fish or waterfowl protein products should also be considered during their construction. In humid areas, therefore, these water storages can occupy up to 20% of the landscape with great benefit in providing fish and a great variety of aquatic product, while at the same time moderating the effects of drought and flood. (Figure 7.2)
The great forests and the biological water storages in the form of fruits and nuts (such as the coconut) are the basis for the proliferation of life forms where no “free” water otherwise exists.
In particular, browsers, insects and fungi draw on these biological tree reserves year-round and perform a host of useful functions in any ecosystem.
On atolls and arid islands or free draining sands, the biological reserves are the main water reserves. This is often overlooked, except by those inhabitants dependent on the waters contained in fruits or nuts.
Many plants such as cactus, palms and agaves have specific tissues or organs to store water.
In the local microclimate, the water in vegetation greatly moderates heat and cold excesses, and both releases to and absorbs water from passing air streams.
Essential crops such as cassava will produce crop as a result of the humidity provided by surrounding vegetation, so that even this side effect of vegetation is of productive use (New Scientist 29 May ’86).
Water can be captured off roof areas, roads and other paved areas and used for both drinking water and shower or garden water, providing it can be stored.
Roof water is least polluted or most easily treated for drinking and cooking in houses, while absorption beds are sufficient for the muddy or polluted run-off from roads and parking areas.