Water Storages (not in soil)
Types of Dams:
• Saddle dams: on skylines, in saddles
• Barrier dams: across valleys (only useful where silt is not a problem or if effective silt-traps installed)
• Contour dams: wall of dam follows contour
• Pediment dams: dam site on a flat at the foot of hill slope
• Ridge dams: dam is on a flat ridge area
Essentials of Dam Building:
• Back slope: 3:1 ratio, especially in sandy soils.
• Front slope: 2-2.5:1 ratio
• Crest: 3m wide
• Freeboard: 1m
• Compaction: every 0.3m of soil rolled down by bulldozer
• Key: a clean cut at base for first layers
• Spillway: made along the contour and end well away from the dam wall. May lead to another dam.
• Surface, fibrous rooting plants grown on front slope (avoid tap-rooted trees)
• Silt traps may be needed in diversion drains leading to dams
• Plant windbreak surrounding dam to reduce wind evaporation loss
• Make dams deep. Try for shade. Taper sides to “V” or cone if practical
Strategies to Reduce Evaporation:
• Cover water surface with rounded, hexagonal “light concrete” blocks using polystyrene beads in
aggregate. Paint upper surface white. Try for 0.8 specific gravity and make 1-2m across.
• Make a sequence of 3 dams, and empty from top dam to the lower dams as soon as these will hold the water. Each time you do this surface reduces by 30%. Several series of 3 is better than a chain of 6 or more dams long.
Water in Landscape
Water as a rare mineral; it is the world’s most critical resource. Fresh water is only 3% of all water (the
rest is in oceans). Of the fresh water, 75% is ice and glaciers, 11% is available ground water* (less than
2500’ deep), and 14% is deep groundwater and aquifers (2500’ to 12,500’)
*These are storages we can influence locally:
Lakes & ponds, surface* 0.3%
Soil Moisture, forests* 0.06%
Rivers 0.03%
Atmosphere 0.035%
Duties of Water: the idea is to use water as many times as possible before it passes through the system.
Duty #1: to procreate life (in growing organisms)
Duty #2: to develop productive water-sytems (aquaculture). Yield of system increases as life increases.
Duty #3: to develop hydraulic uses for energy production (pumping water, generating electricity and mechanical take-off).
Small-scale Water Storages
• Tanks at home for freshwater supplies
• Stock ponds
• Small ponds in gardens (frogs)
• Use of larger catchment area to supply tanks; catchment can be of bituminous material, sealed clay, concrete, sheets of butyl rubber & polyethylene
• Roads, airstrips, firebreaks- all potential catchments if designed to concentrate water in storage structures such as roadside tanks.
Irrigation
• Drip or trickle, especially in drylands
• Flood irrigation (surface & sub-surface wasteful and difficult to control)
• Sprinklers (not efficient, can build up salt in soil
• Under canopy
Components of Irrigation System:
• Water source: dams, bores, soaks, run-off, swales, pipelines, creeks, tanks, lake
• Energy source: water at head, pressure with pump (electric, fuel, wind, hand, or animal)
• Distribution network: net and pan, pipes, channels, buckets
• Emitter: dripline, sprinkler, bucket
Methods & Advantages of Drip Irrigation
• Hole in a pipe
• Flagon or clay pots in ground with nail in cork
• Rocks in deep hole to lead roots down
• Relatively cheap
• Water the root zone directly
• Can use reasonably saline water
• Waters only the plant, not the weeds around it
Subsurface Irrigation
• Pitcher irrigation: 12” wide porous pitchers buried in ground 3’ diameter, 2’ deep, filled with manured
soil.
• Tops of pitchers just above ground level, covered and kept topped up. Gourds, pumpkins, and melons cultivated. Can also be used for planting trees (narrow necked jars).
Irrigation Rules
• Irrigate under mulch (reduces salt problems & increases irrigation efficiency)
• Irrigate at dusk or night if possible (put on a timer)
• Give long watering every 3-5 days rather than a little bit every day (increases leaching effect, particularly for salt, and takes water down)
• Allow for leaching. Put enough water on to leach salt
• Use sealed pipes to convey water; leaky drains may raise the saltwater table.
• Only use sprinklers under tree canopy, never in the open by day.
• Do not over-water; use timers and pits to check on this; turn off drip in winter if enough winter rain.
Minor Water Landscapes
A) Volcanic Islands
• Rich soil- range of crops almost unlimited
• Types of Lava: 1) pahoehoe: rock lava- good only for run-off; 2) u’u: pumice-like with lots of holes: can be planted in.
B) High Islands
• Are either granite or basalt
• Humid to arid aspects
• Keyline, ridge dams, terraces
• Rockwall and cave shelters
• Rich flora and fauna
• Importance of winds and rainfall
• Lagoon catchments and shorelines
• Special problems: cyclone and tsunami; earthquakes, mud flow, lava flow, cinder flow, volcanisms.
C) Low Islands
• Are usually arid islands
• Need essential foreshore plantings
• Need essential windbreaks
• Bi-modal and bi-directional winds
• Caliche or platin-removal techniques necessary (mulch pits)
• Gley (wet, sappy plant material) for tanks
• Atoll structures in lagoons
D) Coasts
• Need frontline vegetation so that beach is not undermined
• Salt-resistant frontline species. Eg. (casuarina, coprosma) have waxy or needle leaves
• Establishing plants in sand- sawdust and paper lowers ph and holds moisture. Chinese plant in woven basket to retain moisture.
• Sand blast resistant plants: thick bark or very fibrous barked trees (pines and palms; casuarinas)
• Alkaline sand needs humus. Soluble sulphates and oxides offset alkalinity.
• Deficiencies in zinc, copper, iron (non-soluble in alkaline)