Dams have been useful structures to man for the longest time. They have become a primary agent for civilization and the growth of economies that’s why methods of mitigating evaporation in dams stand out for a long time now. Even as technology progresses, individuals are finding it worthwhile to own personalized dams.
However, dams are susceptible to several tragedies and mishaps . Apart from seepage issues, dams are also likely to suffer loss from soil erosion, overtopping, and piping leading to massive failures of earthen embankments.
As if that’s not enough, occurrences such as earthquakes may cause catastrophic results when dams are impounded.
One more challenge dams and other water storage structures such as ponds face is evaporation and water loss. Unfortunately, this is often neglected or considered insignificant but may have dire results especially in drier areas.
The current intense weather patterns have proven this to be a sad reality. Cases of lower rainfalls, longer sunshine periods, coupled with flat landscapes filled with sandy soil may cause major water runoff and loss.
When evaluating evaporation concerns, the following issues stand out conspicuously:
- Capturing rainwater effectively to ensure there is enough storage during dry seasons and minimum loss.
- Preventing water loss, once you have harvested enough, through cases of evaporation.
- Albeit a minor concern, the growth of algae should also be considered in water management techniques.
Why Prevent Water Loss Through Evaporation?
The National Centre for Engineering in Agriculture (NCEA) in Australia has developed a monthly evaporation calculator. It’s used to determine the average extent of water loss every month in dams. They claim that individuals lose as much as up to 2 meters of water storage annually through evaporation alone. This is close to 20% of an average dam’s water content.
If these numbers don’t scare you, then nothing can scare you. Evaporation occurs even more rapidly during the summer and dry seasons and previous patterns have demonstrated unreliable rainfalls that’s why we need to seek effective methods of mitigating evaporation. With industry heads realizing the immense loss this could mean for a majority of people, they went ahead to find ways to counter this.
Methods of Mitigating Evaporation to Prevent and Control Water Loss
1. An Appropriate Dam Design
How a dam is constructed greatly influences the extent of evaporation. The most effective dam designs have a reduced surface area ratio to the dam’s volume. Being one of methods of mitigating evaporation, it minimizes the surface on which the water is exposed to the sun. This can be achieved by constructing narrower but deeper dams. For existing dams, this may be fairly hard and even costly or impossible.
This can also be achieved by subdividing the dam into cells. The water content in one cell can then be transferred into another. To attain maximum benefits, a cover is placed over the dam. More about this as we progress.
2. Using Management Strategies
This is another one of methods of mitigating evaporation Since it may be costly to change the design of the dam, one may consider planting trees around the dam system. This is not meant to beautify the surroundings even though it achieves this. It acts as a windbreak and offer a degree of protection from evaporation. Factors to consider when planting trees include the number of years it will take for trees to mature. Future expansion of the dam should also be factored in.
Whatever the case, planting the trees closer to dams also has its potential risks. The roots may reach the dam walls if close and cause failure or worse, source water from the dam and cause more loss. They also aren’t very effective when used to control water loss.
3. Evaporation Control Covers as Management Strategies
There various options for dam covers which are considered as effective methods of mitigating evaporation in the market . Some of these may be expensive but offer the highest degree of protection against evaporation. They can be as effective enough to control 96% of water loss through evaporation. They are all discussed below.
i. Floating Covers
Floating Covers
These can be made from different materials that hugely affects the price. These include polyethylene plastic which offers the most satisfactory results, polystyrene, foam, and wax. The material needs to be tough and multi-layered to prevent degradation and offer some heat reflection respectively. The top layer usually has a white and underneath black hence eliminating light transmission to the water.
Modular Covers
These are individual units akin to the continuous plastics but aren’t restrained. They are hence allowed to freely move on the water surface and are usually cheaper to install. They may be attached or come as freely individual units. However, it may offer slightly lower evaporation levels due to non-tightly packed modules.
They are usually small in size and a large storage unit may contain thousands of these. They can be made from recycled material. However, it may have traces of pollution with zinc found in water systems. It reduces evaporation rates up to 70-80% while allowing rainwater to flow in as it partially covers the dam. It is usually transported to the downwind margins where most evaporation occurs. When the water is about to try, the covers ought to be removed, or else they will get stuck to the mud.
Examples are Aquacaps which act as a web of interlinked domes joined and supported by a ring and E-Vapcap that acts like a denser version of bubble wrap.
ii. Suspended Shade Structures
Cables are used to suspend these above the water. They not only trap humid air between the water and the structure but also reduce wind speed and solar radiation. This enables the storage to be emptied without hassle since there’s no contact with water. Evaporation is reduced to about 75% and also allows rainwater to flow freely into the system.
The structure dries out quickly after raining thus reducing soil collection on top. The growth of algae is highly unlikely with this method. They come in a wide range of UV-reduction ratings which may be the most expensive part of using this method. When the shade cloth is wide, it minimizes cost by using fewer cables.
iii. Bladders
This method makes use of the wine cask bladder principal. It offers an impermeable lining through its polyethylene structure which prevents rainwater from entering in. It works as a floating cover but also stops seepage from occurring. Changes in water volumes on the bladder cause the top cover to rise and fall. Factors influencing the bladder’s performance are generally size and shape.
iv. Bubble Plum
The water surface of reservoirs aka epilimnion gets heated during the summer. It thus becomes less dense while the deeper surface – hypolimnion – becomes cooler and denser. The thermocline is inserted in the middle acting as separators. This prevents normal water convection from occurring through a process called stratification. To prevent disruption of bed sediments, one places diffusers that are injected at a specific height into the bubble plumes.
4. Chemical Control
Physical barriers give more protection against evaporation than chemical covers. At the start, nevertheless, the chemical covers tend to be cheaper but increase with costs due to regular reapplication. A good case is Polyacrylamide (PAM) which is broken down by UV rays. It works by binding the water body together.
They are also effective in the sense that they do not have to be in use all-year-round. They can be used when most needed and have little restrictions on animal life (fish and birds). That notwithstanding, they are usually affected by windy conditions. That said, they are useful in controlling seepage.
5. Biological Trends
Say you are sensitive to using chemicals and can’t afford the physical structures, is all hope lost for you? Heavens no! Most biological methods of mitigating evaporation still need more research to evaluate their viability and efficiency.
For instance, using floating aquatics such as duckweed may lower evaporation levels up to 10%. Nonetheless, some of the plants may have a reverse effect. Hyacinth, for instance, raises the transportation surface area, therefore, increasing evaporation levels.
Arid areas have palm fronds that are normally used to cover water surfaces. When a pool is fully covered with palm leaves, evaporation levels may lower up to 55% according to various researches. Moreover, using single-layered covers may offer less efficiency than double-layered covers. The best thing about using palm leaves is that it endures harsh arid conditions and also has no adverse effects on the quality of water.
Conclusion and Recommendation
It is important to maintain water storage levels by maximizing on inflow and reducing evaporation loss and other means. There are factors you cannot control such as the soil type. Focus on the ones you can control and maximize on them.
Chemical coverings are seen to have a low initial cost during set-up and relatively lower maintenance costs. If frequently used, though, these costs may overburden the users.
Biological methods of mitigating evaporation, on the other hand, may not be fully effective but do have their effectiveness. They are also not hard to acquire and one may opt to use them in the long haul.
Using physical covering – both modular and floating – offers the highest prevention against evaporation. Costs to set up are the major hindrance for most people. Furthermore, they also tend to suffer from tears due to the sun thus need frequent maintenance. That said, the ball is in your court to decide which method best works for you.
