Subject: Re: [permaculture] Slope- swales vs. terrace
Date: Sat, 7 Mar 2015 20:34:08 -0500
On Fri, Mar 6, 2015 at 7:21 PM, Lawrence London <lfljvenaura@gmail.com>
wrote:
Terraces for water retention, erosion control and gardens/plantings
Swales for waster retention, erosion control and limited plantings before
or after the swales
>From Wikipedia:
The swale concept has also been popularized as a rainwater harvesting and
soil conservation strategy by Bill Mollison, and other advocates of
permaculture. In this context it usually refers to a water harvesting ditch
on contour. Another term used is contour bund[3][4]
Swales as used in permaculture are designed to slow and capture runoff by
spreading it horizontally across the landscape (along an elevation contour
line), facilitating runoff infiltration into the soil. This type of swale
is created by digging a ditch on contour and piling the dirt on the
downhill side of the ditch to create a berm. In arid climates, vegetation
(existing or planted) along the swale can benefit from the concentration of
runoff. Trees and shrubs along the swale can provide shade which decreases
water evaporation.
Berm
>From Wikipedia, the free encyclopedia
A berm is a level space, shelf, or raised barrier separating two areas. It
can serve as a border barrier. The word berm originates in the Middle Dutch
and German berme and came into usage in English via French.[1]
Erosion control
Berms are also used to control erosion and sedimentation by reducing the
rate of surface runoff. The berms either reduce the velocity of the water,
or direct water to areas that are not susceptible to erosion, thereby
reducing the adverse effects of running water on exposed topsoil. Following
the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, the
construction of berms designed to prevent oil from reaching the fragile
Louisiana wetlands (which would result in massive erosion) was proposed
early on, and was officially approved by the federal government in
mid-June, 2010, after numerous failures to stop and contain the oil leak
with more advanced technologies.[2]
Ha-ha
>From Wikipedia, the free encyclopedia
A *ha-ha* (or *ha-ha wall*) is a recessed landscape design element that
creates a vertical barrier while preserving views. The design includes a
turfed <http://en.wikipedia.org/wiki/Sod> incline which slopes downward to
a sharply vertical face, typically a masonry retaining wall. Ha-has are
used in landscape design to prevent access to a garden, for example by
grazing livestock, without obstructing views. In security design, the
element is used to deter vehicular access to a site while minimizing visual
obstruction. The name "ha-ha" derives from the unexpected (i.e., amusing)
moment of discovery when, on approach, the recessed wall suddenly becomes
visible.
The basic design of sunken ditches is of ancient origin, being a feature of
deer parks in England. The deer-leap or *saltatorium* consisted of a ditch
with one steep side surmounted by a pale (fence) or hedge, which allowed
deer to enter the park but not to leave. Since the time of the Norman
conquest of England
<http://en.wikipedia.org/wiki/Norman_conquest_of_England> the right to
construct a deer-leap was granted by the king, with reservations made as to
the depth of the foss or ditch and the height of the pale or hedge.[5]
<http://en.wikipedia.org/wiki/Ha-ha#cite_note-5> On Dartmoor the deer-leap
was known as a "leapyeat".[6]
<http://en.wikipedia.org/wiki/Ha-ha#cite_note-6>
"Grills of iron are very necessary ornaments in the lines of walks, to
extend the view, and to show the country to advantage. At present we
frequently make thoroughviews, called Ah, Ah, which are openings in the
walls, without grills, to the very level of the walks, with a large and
deep ditch at the foot of them, lined on both sides to sustain the earth,
and prevent the getting over; which surprises the eye upon coming near it,
and makes one laugh, Ha! Ha! from where it takes its name. This sort of
opening is haha, on some occasions, to be preferred, for that it does not
at all interrupt the prospect, as the bars of a grill do."
The etymology of the term is generally given as being an expression of
surprise—someone says "ha ha" or "ah! ah!" when they encounter such a
feature. This is the explanation given in French, where it is traditionally
attributed to Louis, Grand Dauphin
<http://en.wikipedia.org/wiki/Louis,_Grand_Dauphin>, on encountering such
features at Meudon, by d'Argenville (trans. James), above, and by Walpole,
who surmised that the name is derived from the response of ordinary folk on
encountering them and that they were "... then deemed so astonishing, that
the common people called them Ha! Has! to express their surprise at finding
a sudden and unperceived check to their walk." Thomas Jefferson
<http://en.wikipedia.org/wiki/Thomas_Jefferson>, describing the garden at
Stowe <http://en.wikipedia.org/wiki/Stowe_House> after his visit in April
1786, also uses the term with exclamation marks
<http://en.wikipedia.org/wiki/Exclamation_marks>: "The inclosure is
entirely by ha! ha!"[7] <http://en.wikipedia.org/wiki/Ha-ha#cite_note-7>
"The contiguous ground of the park without the sunk fence was to be
harmonized with the lawn within; and the garden in its turn was to be set
free from its prim regularity, that it might assort with the wilder country
without."[8] <http://en.wikipedia.org/wiki/Ha-ha#cite_note-8>
You can combine swales with Hugelkultur berms which become large fertile
raised beds. Care must be taken when constructing Hugelkultur mounds in
trenches below grade on slopes in impermeable soils; lack of percolation
and drainage may result in trench infill becoming anaerobic and toxic to
most soil life and plants.
<>
Terrace (agriculture)
>From Wikipedia, the free encyclopedia
Terraced fields are common in islands with steep slopes. The Canary Islands
<http://en.wikipedia.org/wiki/Canary_Islands> present a complex system of
terraces covering the landscape from the coastal irrigated plantations to
the dry fields in the highlands. These terraces, which are named *cadenas*
(chains), are built with stone walls of skillful design, which include
attached stairs and channels.[*citation needed
<http://en.wikipedia.org/wiki/Wikipedia:Citation_needed>*]
The value of the qanat is directly related to the quality, volume, and
regularity of the water flow. Much of the population of Iran and other arid
countries in Asia and North Africa historically depended upon the water
from qanats; the areas of population corresponded closely to the areas
where qanats are possible. Although a qanat was expensive to construct, its
long-term value to the community, and thereby to the group that invested in
building and maintaining it, was substantial.[7]
<http://en.wikipedia.org/wiki/Qanat#cite_note-Kheirabadi-7>
A stone mulch <http://en.wikipedia.org/wiki/Mulch> can significantly
increase crop yields in arid <http://en.wikipedia.org/wiki/Arid> areas.
This is most notably the case in the Canary Islands
<http://en.wikipedia.org/wiki/Canary_Islands>: on the island of Lanzarote
<http://en.wikipedia.org/wiki/Lanzarote> there is about 140 millimetres
(5.5 in) of rain each year and there are no permanent rivers. Despite this,
substantial crops can be grown by using a mulch of volcanic stones, a trick
discovered after volcanic eruptions in 1730. Some credit the stone mulch
with promoting dew; although the idea has inspired some thinkers, it seems
unlikely that the effect is significant. Rather, plants are able to absorb
dew directly from their leaves, and the main benefit of a stone mulch is to
reduce water loss from the soil and to eliminate competition from weeds.[9]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-9>
History
To verify his hypothesis Zibold constructed a stone-pile condenser at an
altitude of 288 metres (945 ft) on mount Tepe-Oba near the ancient site of
Theodosia. Zibold’s condenser was surrounded by a wall 1 metre (3 ft 3 in)
high, 20 metres (66 ft) wide, around a bowl-shaped collection area with
drainage. He used sea stones 10–40 centimetres (3.9–15.7 in) in diameter
piled 6 metres (20 ft) high in a truncated cone that was 8 metres (26 ft)
in diameter across the top. The shape of the stone pile allowed a good air
flow with only minimal thermal contact between the stones.[13]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENelson2003-13>
Inspired by Zibold's work, Chaptal built a small air well near Montpellier
<http://en.wikipedia.org/wiki/Montpellier> in 1929. Chaptal's condenser was
a pyramidal <http://en.wikipedia.org/wiki/Pyramid_%28geometry%29> concrete
structure 3 metres (9.8 ft) square and 2.5 metres (8 ft 2 in) high, it was
filled with 8 cubic metres (280 cu ft) of limestone
<http://en.wikipedia.org/wiki/Limestone> pieces being about 7.5 centimetres
(3.0 in) in diameter. Small vent holes ringed the top and bottom of the
pyramid. These holes could be closed or opened as required to control the
flow of air. The structure was allowed to cool during the night, and then
warm moist air was let in during the day. Dew formed on the limestone
pieces and collected in a reservoir below ground level. The amount of water
obtained varied from 1 litre (0.22 imp gal; 0.26 US gal) to 2.5 litres
(0.55 imp gal; 0.66 US gal) per day depending on the atmospheric conditions.
[14]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEHills1966232-14>
Klaphake experimented with a very simple design: an area of mountain slope
was cleared and smoothed with a watertight surface. It was shaded by a
simple canopy supported by pillars or ridges. The sides of the structure
were closed, but the top and bottom edges were left open. At night the
mountain slope would cool, and in the day moisture would collect on and run
down the smoothed surface. Although the system apparently worked, it was
expensive, and Klaphake finally adopted a more compact design based on a
masonry structure. This design was a sugarloaf
<http://en.wikipedia.org/wiki/Sugarloaf>-shaped building, about 15 metres
(49 ft) high, with walls at least 2 metres (6 ft 7 in) thick, with holes on
the top and at the bottom. The outer wall was made of concrete to give a
high thermal capacity, and the inner surface was made of a porous material
such as sandstone.[16]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan200672-16>
According to Klaphake:
“ The building produces water during the day and cools itself during the
night; when the sun rises, the warm air is drawn through the upper holes
into the building by the out-flowing cooler air, becomes cooled on the cold
surface, deposits its water, which then oozes down and is collected
somewhere underneath. It is wrong to think that this process works only on
days with dew, as the inner surface becomes much cooler than one should
expect. In Dalmatia, that day was a rare exception which failed to produce
water.[15]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEKlaphake1936-15>
”
There are three principal approaches to the design of the heat sinks that
collect the moisture in air wells: high mass, radiative and active. Early
in the twentieth century, there was interest in high-mass air wells, but
despite much experimentation including the construction of massive
structures, this approach proved to be a failure.[38]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEAlton_StewartHowell20031014-38>
>From the late twentieth century onwards, there has been much investigation
of low-mass, radiative <http://en.wikipedia.org/wiki/Thermal_radiation>
collectors; these have proved to be much more successful.
High-mass
The high-mass air well design attempts to cool a large mass of masonry with
cool nighttime air entering the structure due to breezes or natural
convection. In the day, the warmth of the sun results in increased
atmospheric humidity. When moist daytime air enters the air well, it
condenses on the presumably cool masonry. None of the high-mass collectors
performed well, Knapen's aerial well being a particularly conspicuous
example.
The problem with the high-mass collectors was that they could not get rid
of sufficient heat during the night – despite design features intended to
ensure that this would happen.[13]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTENelson2003-13>
While some thinkers have believed that Zibold might have been correct after
all,[39]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-popular_science_1992-39>
[40]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-new_scientist_2005-40>
an article in *Journal of Arid Environments* discusses why high-mass
condenser designs of this type cannot yield useful amounts of water:
“ We would like to stress the following point. To obtain condensation, the
condenser temperature of the stones must be lower than the dew point
temperature. When there is no fog, the dew point temperature is always
lower than the air temperature. Meteorological data shows that the dew
point temperature (an indicator of the water content of the air) does not
change appreciably when the weather is stable. *Thus wind, which ultimately
imposes air temperature to the condenser, cannot cool the condenser to
ensure its functioning.* Another cooling phenomenon — radiative cooling —
must operate. It is therefore at night-time, when the condenser cools by
radiation, that liquid water can be extracted from air. It is very rare
that the dew point temperature would increase significantly so as to exceed
the stone temperature inside the stone heap. Occasionally, when this does
happen, dew can be abundant during a short period of time. This is why
subsequent attempts by L. Chaptal and A. Knapen to build massive dew
condensers only rarely resulted in significant yields. [Emphasis as in
original][3]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimoukNikolayevBerkowicz2006-3>
”
Although ancient air wells are mentioned in some sources, there is scant
evidence for them, and persistent belief in their existence has the
character of a modern myth <http://en.wikipedia.org/wiki/Urban_legend>.[3]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEBeysensMilimoukNikolayevBerkowicz2006-3>
Radiative
<http://en.wikipedia.org/wiki/File:Radiative_condenser_%28section%29.jpg>
Diagram of a radiative collector. (a) radiating/condensing surface, (b)
collecting gutter, (c) backing insulation, (d) stand.
<http://en.wikipedia.org/wiki/File:Dew_water_from_metal_roofs.jpg>
Structures with metal roofing, such as this one, can be used to harvest
dew water simply by adding gutters and, for increased output, a layer of
insulation underside. Without the insulation the output is nearly half of
that from plastic condensers.
<http://en.wikipedia.org/wiki/File:Condenser_on_roof_Sayara.JPG>
An example of a condenser-on-roof installation, condenser made of plastic
film with special properties, with insulation layer between film and
concrete roof surface. This installation is on school buildings at Sayara
(Kutch, India). Unlike metal roofs, concrete roofs do not attract
condensation without any treatment, hence the need for an external
condenser. The output from such condensers is nearly two times higher than
from a bare metal roof, all else remaining constant.
The 600 square metres (6,500 sq ft) radiative condenser illustrated near
the start of this article is built near the ground. In the area of
north-west India where it is installed dew occurs for 8 months a year, and
the installation collects about 15 millimetres (0.59 in) of dew water over
the season with nearly 100 dew-nights. In a year it provides a total of
about 9,000 litres (2,000 imp gal; 2,400 US gal) of potable water
<http://en.wikipedia.org/wiki/Drinking_water> for the school which owns and
operates the site.[1]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTESharan2007-1>
Although flat designs have the benefit of simplicity, other designs such as
inverted pyramids and cones can be significantly more effective. This is
probably because the designs shield the condensing surfaces from unwanted
heat radiated by the lower atmosphere, and, being symmetrical, they are not
sensitive to wind direction.[44]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEClusOuazzaniMuselliNikolayev2006-44>
Because mechanical refrigeration is energy intensive, active collectors are
typically restricted to places where there is no supply of water that can
be desalinated <http://en.wikipedia.org/wiki/Desalination> or purified at a
lower cost and that are sufficiently far from a supply of fresh water to
make transport uneconomical. Such circumstances are uncommon, and even then
large installations such as that tried in the 1930s at Cook in South
Australia failed because of the cost of running the installation – it was
cheaper to transport water over large distances.[21]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-uncommon_lives3-21>
In the case of small installations, convenience may outweigh cost. There is
a wide range of small machines designed to be used in offices that produce
a few litres of drinking water from the atmosphere. However, there are
circumstances where there really is no source of water other than the
atmosphere. For example, in the 1930s, American designers added condenser
systems to airships <http://en.wikipedia.org/wiki/Airships> – in this case
the air was that emitted by the exhaust of the engines, and so it contained
additional water as a product of combustion. The moisture was collected and
used as additional ballast to compensate for the loss of weight as fuel was
consumed. By collecting ballast in this way, the airship's buoyancy could
be kept relatively constant without having to release helium gas, which was
both expensive and in limited supply.[51]
<http://en.wikipedia.org/wiki/Air_well_%28condenser%29#cite_note-FOOTNOTEAllen193137-51>
A method of constructing the base layer using chalk puddle was
described in *The
Field* 14 December 1907. A Sussex farmer born in 1850 tells how he and his
forefathers made dew ponds:
Fog fence
>From Wikipedia, the free encyclopedia