I found this article in Mother Earth News!

[busdriver]

Natural Swimming Pools
   
Whether you like to practice your dolphin dives or lounge away the day on a raft,
swimming is one of summer's perfect pleasures.
With a minimum of materials and without an arsenal of chemicals, you can build
an idyllic water oasis right in your own back yard and thwart summertime's sultry dog days.
Though fairly common in Europe, natural swimming pools (like the one pictured
below in an Austrian family's backyard), are in their infancy in the United
States. Ask most American swimming-pool contractors to build a backyard pool and
chances are they'll roll out a long list of goods, including rebar, gunite,
fiberglass, chlorine and an energy-sapping filtration system. But in recent
years, a few builders and a growing number of homeowners have learned how to
build pools without relying on a mass of manufactured materials and chemical
additives. They've found it's possible to construct pools that are more about
building with nature and blending into the natural landscape. Natural swimming
pools use gravel stone and clay in place of concrete or fiberglass, and aquatic
plants instead of harmful chemicals and complicated mechanical filtering
systems. The plants enrich the pool with oxygen, support beneficial bacteria
that consume debris and potentially harmful organisms, and give habitat to
frogs, dragonflies and other water life. The result is a beautiful, ecologically
diverse system that is relatively inexpensive to construct. (A natural pool can
he constructed for as little as $2,000 if you do it yourself, while conventional
pools can cost tens of thousands of dollars.) Natural swimming pools require no
harmful chemIcals, are fairly low-tech, and once established call for only a
modicum of management. You won't have to drain the pool each autumn. Except for
topping it off now and then, you'll fill the pool only once.
DIG IT
The cheapest and most ecologically sound way to build a swimming pool is simply
to hollow a hole in the ground. You can make your pool as shallow or as deep as
you want, but the key is to make sure the sides slope: Otherwise the soil will
cave in. The ratio should be a 1-foot vertical drop for every 3 horizontal feet.
"It's not a bathtub effect, but more like a soup bowl," says Tom Zingaro,
partner with Denver-based Blue Lotus Designs, a pool-and pond-architecture
company. One of the main reasons traditional swimming pools are constructed with
a steel framework is to ensure the walls stay vertical and perpendicular to the
bottom surface of the pool. Construct a pool with sloping sides and you'll
eliminate the need for any steel reinforcement.
ZONING
Reserving at least 50 percent of your pool's surface area for shallow plants,
either at one end or in a ring around the sides, eliminates the need for
chlorine and expensive filters and pumps. You'll want to separate the swimming
area of your pool and the filtration area, or plant zone (see the illustration).
A rim within an inch of the water's surface keeps plants in their place but
allows water from the swimming area to move to the plant zone for filtering, As
water passes through the fibrous root structure of the plants, bacteria
concentrated on the plants' roots act as a biological filter, removing
contaminants and excess nutrients in the water. Decomposer organisms, also found
in the plants' root zones, consume the bacteria, effectively eliminating
underwater waste buildup.
Inside the plant zone, the water should get steadily deeper, reaching a maximum
depth of 18 inches near the swimming zone. The outermost 6 inches of the plant
zone will be 2 to 3 inches deep, providing a home for taller aquatic plants.
Submergent and floating vegetation occupy the deeper area.
Besides cleaning the water and making your pool beautiful to behold, the shallow
plant zone warms the water quickly and provides habitat for frogs and many
invertebrates. They'll appreciate the shallow water for breeding grounds and
repay the favor by eating mosquito larvae.
NATURAL FILTRATION
The water needs to circulate continuously for the plants' roots to cleanse the
pool. You also may need to aerate the water so the water organisms' oxygen needs
are met. (Without adequate oxygen, your pool could become stagnant, harboring
odoriferous anaerobic bacteria.)
Water can be channeled from your pump into your plant zone through the use of
PVC tubes. (Zingaro recommends using flexible PVC in cold climates.) In any
climate, bury the tubing in the soil about 18 inches deep. Underwater aeration,
which uses less energy than constructed waterfalls and circulates water more
effectively, involves diffusing air at the pool's bottom. You can build your own
aerator, using an air compressor (1/4-horsepower for a pool smaller than an
acre) and high-strength tubing that connects to a diffuser. The diffuser (see
"Equipment Sources"), which bubbles air through the water, rests in the deepest
part of the pool, where swimmers are not likely to damage it. Connect a brass
manifold to the compressor to regulate the air pumped into the pool. Don
Schooner at Inspired By Nature, an Ohio-based, pond-and-lake-restoration
company, suggests aerating the pool four to eight hours a day: in the morning,
when oxygen demand is greatest, and again in the evening. Place your aerator,
pump and skimmer in a plastic container, such as a bucket or large plant
container, and put a steel-mesh filter mat over the top, to keep debris out of
your equipment. Expect to pay $1,000 to $1,200 for a quality underwater aeration
system.
Some folks use skimmers hooked up to an additional small pump, to suck off
floating undesirables. While these devices are not essential, you might want to
consider purchasing one if leaves or seeds from nearby trees and shrubs are
likely to litter your pool. The skimmer removes detritus that would otherwise
sink and contribute to algae growth.
Installing pumps and compressors can be a tricky business because you're running
electrical devices near or in water, You'll want to connect electrical hardware
to your home power supply through a buried conduit. Do not run your power
through an extension cord. Hire a skilled electrician who will ensure the safety
of the system.
SEALING THE POOL
Once you've dug the hole for the swimming pool and the plant zone, you have a
couple of options, depending on your soil conditions, to make sure the pool
holds water: You can apply a layer of bentonite clay to seal the soil or lay a
synthetic liner. Bentonite is usually the cheaper option, averaging 35 cents per
square foot. Liners can cost 25 cents to $1 per square foot, depending on their
composition and weight.
Bentonite works as a glue, bonding with the soil particles and preventing pool
water from seeping into the ground. Some soils may contain enough clay that
simply compacting the pond bottom will enable it to hold water. Talk to local
pond builders to find out for sure. But beware: Bentonite doesn't bond well with
sandy soil. Particularly sandy soil can require up to 12 pounds of bentonite per
square foot, as opposed to 6 pounds in clay-rich soil. Bentonite also can be
troublesome when the surrounding soil is very dry. In arid climates, Zingaro
recommends bentonite be applied beneath a plastic liner that is woven or
textured on the bottom. This liner keeps the bentonite from shifting. In more
humid climates, bentonite can be applied directly to the soil. Before treating
your pool with bentonite or any other clay powder, thoroughly compact the soil.
You can do this with a lawn roller or a plate compactor. Then, while wearing a
mask, spread a 2- to 3-inch layer of bentonite powder along the pool sides and
bottom. Pack it down with a tractor or plate compactor. Then apply another foot
of quality topsoil and compact again.
If you choose a liner, select one made of ethylene propylene diene monomer
rather than PVC. EPDM is a synthetic rubber twice as expensive as PVC, but it's
worth the extra cost. It has protection from ultraviolet rays, and unlike PVC
remains flexible in cold weather. If your soil has a lot of rocks or roots,
select a 45- or 60-millimeter liner. You can use a 30-millimeter liner if your
soil is very sandy and smooth, and if you and your guests aren't likely to tear
holes in a liner while frolicking in the pool. Before laying your liner, compact
the sod and cover it with a layer of sand or an absorbent material such as old
carpeting or newspaper. Newspaper is a good option: When wet, it bonds to the
liner, providing extra protection if the liner develops a small hole.
After the bentonite clay or a liner is installed, cover the bottom of the pool
with 4 to 5 inches of gravel. The gravel provides a habitat for beneficial
bacteria, which help biodegrade leaves or other natural materials that sink to
the bottom of your pool. Make sure you use clean gravel. Fill a 5-gallon bucket
with a spigot with some of the gravel you intend to use. Open the spigot and run
water through the gravel. If the water comes out dirty, you need to clean the
gravel (a taxing, water-wasteful process) or find another source. Expanded shell
aggregates and other manufactured gravels are likely to be clean enough to use
in your natural pool. In addition to lining the pool with gravel, many people
opt to build cobblestone steps for access into and out of the pool. A
cantilevered dock built out over the water also provides an easy way to get in
and out of the pool, and helps protect the pool's sides.
To finish the edges of your pool, run a plate compactor around the perimeter.
This will help with soil erosion, but it's not enough to guarantee dirt won't
fall into your pool. One option is to edge the perimeter with rocks, flagstone
or wood planking. Better still, plant right next to the edge and let the plants
stabilize the perimeter, says Martin Mosko, principal architect with Marpa and
Associates, a Boulder, Colorado-based landscaping company. Plants work not only
to anchor the soil, but create a natural setting for an old-fashioned,
swimining-hole effect. Mosko says if you use plants instead of stone, choose
plants that thrive in wet soil or make sure the water level is at least a foot
below the pool's edge so the perimeter plants don't become waterlogged.
CONCRETE OPTIONS
If you prefer a more conventional pool shape, consider construction with cement
or Rastra block, a material manufactured from cement and recycled foam plastic.
Less ecofriendly than gravel and stone, these systems still can reduce chemical
and energy usage by using plant-based filtration systems rather than mechanical
filters and chlorine to clarify the pool water.
Pouring a concrete pool can be tricky. You have to have the right mix and the
right density to prevent cracking. Because of the intricacies involved in
concrete pouring, Zingaro advises against do-it-yourself concrete pool
construction. If you're experienced in concrete work, he offers the following
tips: Use an 4-1 ratio mix of portland cement and sand, and cover the compacted
soil with fiber mesh, a rubber liner, old carpeting or newspaper, to provide a
stable surface for the concrete to adhere. After the concrete is poured, trowel
on a %inch coat of stucco to waterproof the pool, since concrete is porous.
An alternative to concrete is Rastra block. These blocks are 10 feet long, 15 or
30 inches high, and 10 or 14 inches thick. Made of recycled polystyrene and
cement, they weigh a fraction of concrete: Two people easily can set 10-foot
sections into place. Kenton Knowles of Global Homes in Baldwin City, Kansas,
built a 16x32-foot pool out of Rastra for about $1,600 in materials.
To build a Rastra-block pool, excavate a hole just larger than the pool's
dimensions to allow for ample workspace. Most people choose to construct a pool
5 feet deep. For the bottom, either pour a concrete slab or cover the bottom
with a rubber liner. Then line the bottom with gravel. Make sure to install a
drain and backflow preventer. Lay one section of Rastra block along the edges of
the slab, securing the Rastra to the pad with rebar. Fill the Rastra blocks'
cavities with concrete. As the concrete flows from block to block, the structure
is tied together. An expanding foam sealant is used between courses and at all
joints to hold the blocks in place. Knowles recommends waterproofing the blocks
by troweling on two coats of stucco. Backfill the space between the sides of the
pool and the Rastra block with soil. You can finish the perimeter with stones
laid from the top of the blocks out into the surrounding area, or you can grow
plants to the edge of the blocks.
PREPARE FOR PLANTING
Once your pool is constructed, you'll need to prepare the plant zone with 3 to 6
inches of soil. Choose your soil with care as soil can carry various
contaminants. Avoid harvesting soil from areas where animal excrement is
prevalent, such as in dog runs or from grazing areas. Select soil that's free of
organic matter, which would rot underwater. You can have a lab test soil samples
for potentially pathogenic bacteria. To find a laboratory in your area, contact
your state's health department. once soil, gravel and hardware are in place, you
can fill the pool. Disturb the soil as little as possible and let the pool rest
for a week before installing plants. During this time, you can test your
hardware to make sure it works.
SELECTING PLANTS
Be sure to choose plants suited to your climate. Your best bet is to obtain your
plants from a native-plant supplier. Check the phone book and Internet for local
sources. Home and garden centers also carry more aquatic plants now that
backyard ponds are growing in popularity. End-of-the-season sales can save you
money. Several mail-order nurseries also specialize in water-garden plants. (See
"Pool Construction and Design.")
Sedges (Carex) and rushes (Scirpus), both aquatic plants, make great emergent
vegetation for your pool's perimeter. You can also consider lesser cattails
(Typha angustifolia) and aquatic irises, though be sure to ask which varieties
won't overcrowd other plants. Pickerel weed (Pontederia cordata), arrowhead
(Sagittaria) and water primroses (Ludwigia) are all contenders for the
shallowest areas of your pool. Be sure to include submergent plants such as
common waterweed (Elodea) and hornwort (Ceratophyllum) for their high oxygen
output.
In water 6 to 18 inches deep, plant a mix of floating, submergent and emergent
plants. Water lilies (Nymphaea) adapt to any depth, so use them liberally.
Floaters, such as pondweeds (Potamogeton) and common duckweed (Lemna minor),
drift freely on the surface and quickly cover the surface of the plant zone.
Before you make plans to tromp off to the nearest country pond and gather up a
truckload of greenery, wait! Before collecting a single plant from the wild,
know the laws protecting wetlands and their plants. if you do collect, be
careful to guarantee the health of the wetlancl by selecting only a few samples
from larger populations. Consider rescuing plants from a threatened site.
Perhaps a new corporate headquarter's construction is going to destroy your
favorite frog hollow. Contact the company to see if it will allow you to rescue
the imperiled plants and maybe a few amphibians.
Once you've purchased your plants, you can plant them in the filled pool. Stick
to a plan, grouping plants according to height and type. Place your plants into
the soil, anchoring them, with plenty of gravel.
ALGAE CONTROL
Pond owners have been battling algae the mighty green menace —for eons. Algae
compete with plants for nutrients and light, but spring algae blooms often
decline as soon as water lilies and other plants emerge to shade the water.
Promote plant growth and deter algae by adding plants and eliminating
phosphorous to maintain a lower pH (5.5 to 6.5). The easiest remedy, and the
least risky to your aquatic ecosystem, is to add more plants, which will
outcompete the algae for nutrients. A second option is to monitor the pool for
phosphorus. Fertilizers and urine are the two major sources of this nutrient, so
make sure your pool is free of nutrient-rich runoff and remind everyone to use
the bathroom before swimming. You can also increase your aeration schedule to
stimulate more biological activity.
If algae problems persist, adding small amounts of straw to the pool will help.
For full details, visit the Institute of Arable Crops Research Web site at
www.iacr.bbsrc.ac.uk/pie . Go to the Center for Aquatic Plant
Management link and download "Control of Algae Using Straw." For barley straw
sources, go to www.ianr.unl.edu/pubs/wildlife/nf429.htm or
www.naturalsolutionsetc.com.
Enzymes, bacteria, acids and other strange brews have been offered as magic
bullets for obstinate algae. Introducing additives to your pool may be an
interesting scientific experiment, but it won't necessarily improve the pool
you've invested plenty of time and money in. Beware of salesmen hawking their
grand variety of miracle algae cure—alls. Remember: Your pool is a dynamic,
living ecosystem. Adding synthetic chemicals probably will not bring it back
into balance.
Pool Protection
Do you need to be concerned about cultivating potential pathogens in your pool?
While it's true aquatic plants do not remove all contaminants from the water—
and pools constructed of dirt, concrete or rubber liners don't necessarily keep
bacteria at bay — the probability for contracting a serious disease from your
natural swimming pool is low. Dr. Michael Beach of the Centers for Disease
Control and Prevention says even chlorine-treated swimming pools can fall prey
to fecal coliform contamination, which is responsible for problems such as
cryptosporidiosis, a parasite that can cause diarrhea and stomach cramps. Keep
babies and pets out of the waters to avoid contaminating your pool with fecal
coliform. If you're uncertain about your natural pool's water quality, have it
tested.
MAINTENANCE
Removing plant litter in spring and fall will help maintain the long life of
your natural pool. Keep your water level constant, and be prepared to add water
as needed. inexpensive test kits, available in garden centers, will allow you to
monitor your pool's nutrient levels, alerting you to problems.
In addition to maintaining the pool's biological health, check the mechanical
systems annually. Wipe diffusers with vinegar to remove deposits, check air
hoses for cracks and obstructions, and examine all connections to the pumps.
Given these precautions, your pool should provide you cool pleasure for years to
come.
Environmental writer and educator Douglas Buege is an avid organic gardener and
beekeeper. Freelance writer and editor Vicky Uhland has written about holistic
lifestyles for a variety of publications.



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[kennyman]

Clay lining is really hard to do here. We have three dug ponds on the golfcourse I work at and we used some local clay to try to seal them. It helps but does not work well. But overall an ok article. All they are really saying though is build a pond big enough to swim in.

[The Pond Boy]

Hi,

To make a "man made" with clay is not that though, but it is almost impossible to keep the water clean. to do it well you need a liner. To make a pond that you can use for swimming is easy, but expensive. The most expensive is the liner and the filter system. If there is someone interestedand want more info, please reply or drop a line.
Thanks,

The Pond Boy,
Greg

[Sue]

When we went on the pond tour this summer, one of the people had just made a 'swimming pond' and filled it that day. I think it was with a liner.  It was cloudy because it was brand new. It was the guy from the Pond Clinic's house. Here's picture I took, I wonder how it looked when finished!

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[The Pond Boy]

Sue,

Yes it is at Nicholas house. I was there a month ago, it looked good but as I said it isn't cheap. Also a inground pool is expensive to build. An inground pool is easier to maintain then a pond. Beside that after a couple of years the rocks will become green/black and will become slippery. It is all what do you prefer.
Thanks,

The Pond Boy
Greg