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Pond Design

By Conrad Kleinholz


Sizing

            Pond size is both a personal and practical decision. You are limited by either available space or finances to some maximum size. Attractive water gardens can be made from various water-tight containers, such as wooden half barrels. Several factors determine the size of an ornamental pond (see Site Location for Ornamental Ponds for initial considerations). The surface area is determined by available space. Pond size will also increase as you add accessories or plants. Waterfalls will use at least twice as much horizontal space as height and width, and will use at least three times as much room if you want to plant the side slopes. Decorative edging along the top edge of the pond will occupy at least 12” around the pond perimeter. You will also want room for chairs, benches, bridges, decks or other observation areas. The choice between a water garden or fish pond determines pond depth.

A water garden or bog that will contain only plants should have a water depth between eight and eighteen inches. Floating leaved lilies need shallow water no more than 12 inches, while lotus can grow in deeper water up to 30 inches. Emergent plants like water iris, taro and cattails will grow in water no more than six inches deep. If the pond bottom will be covered by stones, increase the depth by the average diameter of the stones to be used. Plants also need horizontal space. Erect plants such as papyrus, iris and cattails can be contained within the confines of a pot. Lilies, however, use much more space than their container. Native lilies or lotus will spread up to 10 feet in diameter, and tropical lilies can occupy twice as much space.

Ponds designed for fish also have some guidelines. The fish should be able to swim for at least several body lengths without turning, and the water depth should be at least 1.5 times greater than the length of the longest fish in the pond. So, goldfish ponds should be at least 36-48” long and 24” deep. Koi ponds should be at least 72-96” long and 45” deep. To minimize predation from raccoons and wading birds, the pond should be at least three feet deep.

Pond shape will depend on your choice of liner material. Fiberglass liners are available in lots of shapes, but they can’t be customized. Concrete and gunite can be cast in any form. Fiberglass, formed concrete and gunite are best installed by professionals. They have the tools and expertise that easily justify the labor expense.

Flexible liners are the material of choice for owner installation. Among flexible liners, PVC is the least flexible and most difficult to use in free-form or ponds with steps or shelves in the walls. PVC wrinkles because it doesn’t stretch. The wrinkles become hard and brittle within a few months and leaks are common. Poly liner material is intermediate in flexibility and EPDM is the easiest to work with. Wrinkles in the liner can be minimized by careful folding. The folds can then be hidden with cover tape.

Once you decide on a pond size and shape, you can calculate the liner dimensions. Determine the size needed by measuring the total length in feet plus twice the greatest depth x total width plus twice the greatest depth. Then add four feet to each dimension to allow two feet in each direction for overhang. If there will be plant shelves, add the vertical and horizontal dimensions to the overall liner size. You may also want to add a small shelf at or slightly below the water level. Rocks placed on this shelf will hide the liner from view when the water level recedes from evaporation.  As with a plant shelf, add the horizontal and vertical dimensions of the shelf to the overall liner dimensions.

If you want a waterfall, there are two options. You can add the dimensions to the pond liner to make a one piece liner. No seams are required, but often there is a considerable amount of wasted liner with this option. Another option is to make the waterfall from a separate piece of liner material. Make the calculations as for the pond, but add six to twelve inches to overlap the pond liner where they join. After installation, simply glue the two pieces together. For added insurance, cover the seam with cover tape. Liner length for a waterfall equals the total linear distance of pools and vertical drops, plus at least 4 ft. Liner width for the waterfall equals the greatest width of the waterfall plus at least 6 ft. in order to have adequate liner material to bury the edges.

Filtration

            Ornamental ponds need recirculation to avoid stagnation. Water circulation components that remove solid materials from the water, or that biologically degrade and detoxify dissolved materials are classified as filters. Solids collection boxes, referred to as skimmers, and open drains are used to remove most solids from ponds. Surface skimmers are used to remove floating debris such as tree leaves or yard waste. Surface skimmers contain either netting or mats to trap the solids before they can plug water pumps or filter systems. Bottom drains remove solids from the pond, but the solids are transported through the piping to a small mesh ‘leaf basket’ attached to the inlet side of the water pump to trap and eliminate the solid materials. Systems that transform dissolved contaminants are referred to as biofilters.

Filtration requirements for water gardens are much less rigorous than for fish ponds. Water gardens without fish can be maintained simply by moving the water to avoid stagnation and unpleasant odors. Water movement can be provided by a water pump capable of circulating the contents of the pond on a daily basis, or with an air pump attached to porous stones. Air rising to the pond surface then circulates and oxygenates the water.

Ponds with fish, regardless of water garden or fish ponds, have more rigorous requirements for filtration systems if the fish are to receive prepared diets. The minimum requirement for a filter is to remove toxic metabolites from the water. In ornamental ponds with fish, we also want clear water, which increases the complexity and cost of filtration systems. Planning and designing a filtration system requires that you have a final fish number and weight in mind before you build your pond. The demand on the filter arises from the amount of feed placed in the pond, NOT the pond volume. If you are undecided about the final sizes and numbers of fish for the pond, you can begin by adding plumbing sufficient to circulate the pond volume within one hour. You can then add filter components after construction without modification of the pond. Be aware that filtration systems using static media, such as matting, can occupy an area nearly half the size of the pond if adult koi are in the pond. For a complete discussion, see Filter Design and Operation and Table 1, which compares the surface area vs. volume for a number of common media types.

Table 1. Comparison of surface area (ft2) per volume (ft3), and cost per ft2 of various types of commercially available filtration media for use in ornamental ponds. Prices are in US dollars during 2007. The data indicate the amount of media needed to transform nutrients to non toxic components. Up to 10 times the indicated amount of media may be needed to achieve acceptable water clarity.

Media

Surface area

Ft3/Lb Diet

Cost per ft3

Cost per ft2

Bio-glass®

20,000

0.01

$13.00

$0.00065

Blocksom®

200

1.25

$15.92

$0.08

Reticulated foam

300

0.9

$37.25

$0.12

Biofill®

250

1.0

$37.32

$0.15

K-1®

259

1.0

$43.24

$0.17

Lava rock

16

15.6

$2.89

$0.18

Polyethylene beads

400

0.6

$100.00

$0.25

Bio Ball®

98

2.6

$34.66

$0.35

Bio Ball®

160

1.6

$64.66

$0.40

Matala disk®

124

2.0

$52.23

$0.42

Matala®

85

2.9

$42.00

$0.49

Bio Barrel®

64

3.9

$33.00

$0.52

Matala disk®

96

2.6

$50.96

$0.53

Bio Strata®

68

3.7

$38.00

$0.56

Matala®

62

4.0

$37.00

$0.60

Matala®

48

5.2

$36.00

$0.75

Matala®

31

8.1

$34.00

$1.10

Plumbing

            Many water gardens have plumbing connected to a submersible electric pump. The pump is placed directly on the pond bottom or inside a skimmer box at the water surface. For such applications, use the pipe size indicated for the output from the pump.

            Fish ponds usually have all pumps and piping outside the pond to avoid injury to the fish. Drains and return line openings can be molded into the liner in ponds with rigid liners. For additional perforations in rigid liners, and with all flexible liners, the holes are sealed with bulkhead or flanged fittings. Bulkhead fittings are polypropylene plumbing fittings that fill and seal perforations in the liner. They are available as two-piece threaded fittings that compress flexible washers or gaskets against the liner as the fitting is screwed together from opposing sides of the liner. Threaded fittings are available in sizes to 4”, which is adequate for most fish ponds. Flanged fittings are bolted rather than screwed together so the bolt heads will be exposed and visible. Flanged fittings are used for large diameter pipes (4” or greater). If you use flanged fittings, make sure the bolts are high grade stainless steel. Corrosion may still be a  problem if you add salt or other charged chemicals (potassium permanganate, hydrogen peroxide, calcium chloride, sodium bicarbonate) to the pond.

The pipe of choice for plumbing is polyvinyl chloride (PVC). Even rigid PVC is somewhat flexible and doesn’t rust. Use schedule 40 to obtain acceptable crush strength. You can choose between solid and cell core rigid pipe, or flexible PVC pipe. Cell core pipe has the same crush strength as solid schedule 40 pipe, but is roughly fifty percent the cost of solid core pipe. Cell core pipe is also more flexible than solid pipe. Cell core is not recommended for pressure applications, such as municipal water lines, but the pumps used in fish ponds do not provide pressures that would cause internal pressure failure of cell core pipe. Flexible pipe is about twice the price of rigid pipe, but is a good choice for areas where the pipe must bend but you don’t want to increase head pressure with multiple fittings. Flexible PVC has a tendency to become oval because of storage in a roll. Use plenty of glue and make sure to allow the full cure time listed on the glue can before you bend the pipe, or the joint will leak because of the flexibility and ovoid shape.

Another pipe option is polyethylene (poly). Poly pipe is joined with insert fittings that push inside the pipe and are secured with clamps on the outside of the pipe. If the insert fittings are difficult to install, heat the pipe with a hair dryer or heat gun, which softens the pipe to stretch enough to insert a barbed fitting into the end of the pipe. Clamp the pipe to the fitting while still warm for the most secure fit. The advantage of poly pipe is that it is available in 100’ or longer rolls, so fewer joints are needed. The disadvantages include insert fittings and clamps. Insert fittings decrease the pipe diameter, and cause increases in head pressure that reduces water flow rates. Pipe clamps should be totally stainless steel (both clamp and screw). Another disadvantage of poly pipe is that it will kink and collapse if a bend radius is too short. The kinks must be repaired by cutting the pipe and inserting a connector, with additional clamps on either side of the joint. Finally, poly pipe should always be bedded in sand to avoid kinks or punctures from rock edges, and to minimize the chance of kinking from encroaching tree roots once the pipe is installed.

Pumps

Pumps are used to circulate water within the pond and transport water and solids to filtration plumbing. They are also used to operate waterfalls. The pump size needed varies with plans for the pond. The pond water should be circulated through a filtration system every 1-2 hours to ensure adequate removal of waste materials. Waterfalls require a flow rate of approximately 100 gph for each inch of horizontal surface to obtain a ˝” deep flow. Buy a pump or pumps that have at least 25% more capacity than you need. You can then fine tune actual water flow using inexpensive ball valves.

Electrical water pumps for ornamental ponds can be placed in or outside the pond. Submersible pumps are placed in the pond or in an adjacent skimmer or filter box. They are available as magnetic or direct drive centrifugal pumps. The pumps have a slotted rotor (impeller) that rotates within a closed housing. The rotation employs centrifugal force to move water from the center to the outside edge of the rotor and out of the housing. Such pumps are capable of moving large volumes of water with relatively little energy cost.  Magnetic drive pumps are more energy efficient than direct drive pumps. The impeller in magnetic pumps is activated by electromagnetic energy, rather than being attached to a motor shaft. Because of their configuration, magnetic drive pumps do not require seals or lubricants. The greatest advantage of magnetic drive pumps is that if foreign materials stop the impeller, they do not cause the pump to fail from overheating. Hybrid magnetic/direct drive pumps are available. They use less electricity than direct drive pumps, and produce more water pressure than magnetic drive pumps.

Direct drive pumps have an impeller shaft either as an extension of, or attached to, the motor shaft. They do require shaft lubrication and seals to prevent water from entering and damaging the pump motor. Direct drive pumps often deliver water with more pressure than magnetic drive pumps, which make them the pump of choice for high pressure applications, such as large fountains or tall waterfalls. Direct drive pumps are available for either submersible or external use. External pumps have two designs. Flooded suction pumps require the input line to be full of water before operation. Flooded suction pumps are usually used in gravity fed systems where the pump is lower than the pond surface. Self priming pumps have less space between the pump impeller and the pump housing than flooded suction pumps. They create enough suction to draw water above the pond surface to begin operation. Self priming pumps usually develop greater water pressure than flooded suction pumps, and can move water to higher elevations. However, self priming pumps are easily damaged by foreign materials in the water, so they must be used with intake screens. Self priming pumps also use more energy than flooded suction pumps.

Electrical Requirements

            Electrical design for ornamental ponds is dependent on the distance from the electrical supply (the circuit box) and the amount of electricity to be used. We pay for electrical use based on wattage as kilowatt hours (kWh), but for design purposes consider also amperage, or the electrical resistance of all the appliances. Think of amperage as electrical friction. As the work load of a motor increases so does the amperage. Electrical appliances with no moving parts, such as a UV system, usually use a fixed amount of energy. Others, specifically electrical motors with moving shafts, frequently use a variable amount of energy based on the amount of work done. These motors display a dual energy rating, one for ‘starting’ and another for ‘running’ or ‘operating’. The ‘starting’ rating shows the maximum energy consumption of the motor and should be used for designing the pond electrical system. To determine electrical system requirements, follow the steps below:

  1. List all the expected components: air supply, water pumping, UV system, heater, and accessories (lights, ornamental fountains or spitters, outdoor fans, etc.). If possible, separate important components into individual circuits. For example, put the pump/filter system on a different circuit than the aeration components. If one system fails, the other can usually keep the fish alive until the failed system can be repaired or replaced.
  2. Determine the energy use of the components. Most of the circuits can be operated through 20-ampere circuit breakers, but large pumps, water heaters, and air systems with capacitor-start motors may require 30-amp breakers. Fixed draw components such as UV systems are usually 110v. Transfer to amperes with the formula amps = volts/watts. So, for a 40 w UV bulb, the electrical draw is 110/40 = 2.75 amps. Do the calculations for the fixed draw components. Then read the motor plates for the variable draw motors (or look at the specifications in catalog or web pages). Be sure to use the highest stated draw for design purposes. You may decide to use a 230-volt motor for the water pump in the filtration system. 230 volt motors cost more to purchase, but typically last longer than 110 volt motors, and may be less expensive to operate. 230 volt motors usually draw half the amperage of 110 volt motors, but will require an additional load or hot wire for operation.
  3. Sum all of the amperages from both motors and fixed draw components for each planned circuit, and make sure the estimated electrical demand does not exceed the circuit breaker capacity.
  4.  Decide where the electrical components will be located, and measure the distance in feet to the main circuit box that will feed the pond.
  5.  Use Table 2 to find the size (gauge) electrical wire to be used. The wire gauge needed is determined by the total amperage and the length of wire used. Wire size increases with distance from the original service, either at the power pole, or the electrical breaker panel you use to service the pond. Stranded wire is easier to install in conduit than solid wire, and has less electrical resistance. Make sure to plan for copper wire. Aluminum wire is larger diameter, and doesn’t do well in buried applications.
  6. Use the wire diameter to find the size conduit needed. You can buy three-conductor wire in a single insulating sheath, but it is easier to install single conductor wires in conduit because they are more flexible. Make sure to use different colored wires to avoid mistakes in connection. White is used for the load (hot) wire, black for neutral, and green for ground. If you decided to use a 230 volt motor for the water pump, you will need four wires, rather than three. The fourth wire is also a load wire, commonly red. The conduit guide is also in Table 2.
  7.  All electrical receptacles for ornamental pond power supplies should be ground fault circuit interrupters (GFCI). GFCI receptacles are more sensitive to changes in electrical conductivity than normal grounded plugs and provide additional safety when electrical connections must be used near water. Determine the number of GFCI receptacles needed. Use separate circuits and receptacles for the filter and air systems. The separate circuits serve two functions. First is that GFCI receptacles disconnect when the amperage draw exceeds about 60% of the displayed capacity. Separate circuits help avoid outages caused when either the water or air pumps have a variable amperage rating. Second, dual circuits can serve as a ‘fail-safe’ system so that one of the systems can remain in operation if the other fails. Use additional circuits for accessories such as lighting (outdoor or underwater) or small external fountains or spitters, keeping in mind that a 20-amp receptacle will only safely maintain about 12 amperes of draw.
  8. Plan for on/off switches between the feed line and the GFCI receptacles. The switches allow you to turn off the circuit without tripping the receptacle or unplugging the motor.

Plan to place all wiring in PVC conduit, and bury below any future excavation depth. Electrical codes usually require at least 24” of soil above the conduit. Even if you plan to use direct-bury cable, use the conduit. Gophers love to chew on insulation.

Table 2. Electrical wiring sizes (American Wiring Guide, AWG) necessary for operating equipment in ornamental ponds, in relation to the distance from the main circuit box. Information is for 115-volt AC systems, with a maximum allowable voltage drop of 5%.

Maximum  or total amps

< 50 ft.

50 – 100 ft.

100 – 150 ft.

150 – 200 ft.

15

14

12

10

8

20         

12

10

8

8

30

8

8

8

6

 

 

 

 

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