water evaporation on a pond or dam

In warmer regions of the world, pond evaporation is a year-round battle. In any part of the U.S., the summers are warm enough to speed up water evaporation in ponds to where it must be tackled. Because it’s a natural occurrence, you can’t prevent evaporation completely, but reducing evaporation by 80% or more makes a noticeable difference.

You can drastically reduce how much water you lose in the warmer months by keeping your water shaded and at cooler temperatures. Many methods are available. And while not everyone can afford to purchase a floating cover, other natural options may help. Use a combination of techniques to protect your pond from evaporation.

1. By Keeping Free Water Surface Area Minimum:

Reservoirs and lakes are the water bodies with large surface area.

It is possible to reduce the surface area by adopting following measures:

(a) The reservoir site may be selected in such a way that area to storage ratio is minimum.
(b) To avoid water loss water could be stored below ground.
(c) When there are number of reservoirs on one river the water may be stored in one large reservoir when possible rather than in several small reservoirs.

2. Add aquatic plants that will partially cover the water surface to your pond. Aquatic plants will not only shade the water below, they will also absorb some of the sun’s energy, keeping the water cooler. Buy plants that will grow easily in your U.S. Department of Agriculture zone. In the warmer USDA zones of 7 to 10, where pond evaporation is more of a challenge, you can use plants such as yellow floating hearts (Nymphoides peltata), water lilies and green taro plants (Colocasia esculenta).

Add free-floating water plants, such as water lilies and duckweed, in quantities that block approximately 40 to 60 percent of the pond’s water surface. At this rate, the floating plants’ flowers and foliage help to shade the pond effectively to keep it cool and reduce sun exposure, and in turn minimize the risk of algae blooms and weed invasions.

3. By Spreading Surface Films on the Reservoirs and Lakes:

Though still under experiment stage this method when used will prove to be most economical and of practical utility. The method is based on the principle that a thin layer of oil film when spread on the water surface is capable of reducing evaporation to significant extent.

Experiments have shown that a compound called hexadeconal or cetyl alcohol derived from tallow, sperm oil or coconut oil is capable of forming monomolecular film on the water surface. This material is white, waxy, crystalline, solid and is generally available in flakes or powder form.
It is relatively tasteless and odorless. It is pervious to oxygen and carbon dioxide. It is also nontoxic to living being. It is a polar compound in which one end of the molecule is hydrophilic and therefore, shows great affinity for water whereas the other end is hydrophobic and repels water.

Because of this property it forms a monomolecular film on the water surface. The film so formed is only about 15 x 10-4 mm thick but it is tight enough to prevent water molecule from escaping the water body. It is flexible and moves with the motion of water surface without breaking. The film is penetrable by rain drops but the film again closes after allowing rain drops to enter.

It is estimated that such a film may reduce evaporation by one-third. Theoretically only 25 gm of hexadeconal is sufficient to spread a mono-molecular film on one hectare of water surface. In practice, however, due to working problems as much as 100 times of theoretically required quantity may be necessary. Even then it is quite economical and promising. Combination of hexadeconal and octadeconal was also used for better results.

4. Plant tall bushes or trees around the outside of your pond to shade the water. Choose hardy, marginal pond plants around the edges of your pond, such as sweet flag, pickerel weed and soft rushes. Such low-maintenance vegetation serves several beneficial purposes, including keeping debris from falling into the pond (soil runoff and organic debris increase water nutrient levels and encourages algae growth) and also casting shade along the edges of the water. Try to choose evergreen bushes and trees that drop few leaves or seed pods to keep the water clear. If you choose a tree or bush that can get messy, plant it farther away from the pond where it will still provide shade but will not drop leaves or seeds into the water. The leaves or seeds can change the chemistry of the pond and may even be toxic to pond fish.

5. Install a trellis on the edge of the pond in a position where it will block the afternoon sunlight. Afternoon sunlight during the hottest part of the day causes the most evaporation. The trellis will shade the pond during this time. To provide extra shade, plant a vine to grow up the trellis.

6. Reduce the amount of agitation caused by any water features in the pond. Waterfalls and filters that splash and agitate the water cause the water to evaporate more quickly.
Things You Will Need
Aquatic plants

7. Add nontoxic pond water dye to the water while you’re waiting for your free-floating pond plants and marginal plants to become established. Such over-the-counter dye products, available in most pond stores and many nurseries, add pigment to the water, which reduces ultraviolet penetration into the water.