Not Leaking. Evaporating

Importance of proper evaporation management

Many dam owners think their dam is leaking when they see the water levels going down each day

In a lot of cases, the missing water can be accounted for with the natural process of evaporation.

Many dam owners are unaware of the significant water level loses that are caused by  incorrect evaporation management.

Key points:

  • Evaporation occurs every day
  • Evaporation losses from dams are significant
  • The rate of evaporation is proportional to the temperature
  • Solutions include windbreaks, shade balls, covers & vegetation
  • Evaporation losses can be reduced by up to 80%

Evaporation Management in Australia. Overview

Rainfalls in Australia are declining

At the same time evaporation rates are increasing due to the warming climate – so while the quantity of water that is getting into dams is decreasing, the evaporation losses from those dams are increasing.

The result is that water is becoming steadily harder to get.

The simple loss of water is not even the whole problem.

When the water evaporates – any salt (there is always salt in natural water) is left behind; so the salinity of the remaining water increases.

The higher the salinity of water, the less useful it is

What Is Evaporation?

Figure of evaporation

Evaporation is the process whereby water enters a gaseous state, which then enters the atmosphere as water vapour.

The rate of evaporation depends on the temperature difference between the evaporating surface and the air, the relative humidity, and wind.

Water boils at 212 degrees F (100 degrees C), but evaporation actually begins at 32 degrees F (0 degrees C); it just occurs extremely slowly.

As the temperature increases, the rate of evaporation also increases.

What factors effect the rate of evaporation?

Dam

The rate of evaporation is affected by the following factors:

  • Temperature: The rate of evaporation increases with an increase in temperature.
  • Surface area: The rate of evaporation increases with an increase in surface area.
  • Humidity: The amount of water vapor present in the air is called humidity. The rate of evaporation decreases with an increase in humidity.
  • Wind speed: Evaporation increases with an increase in wind speed.
  • Flow rate of air: On a calm day, the air close to the surface of the water in a storage becomes saturated with water vapour. So long as the layer of saturated air stays put, there will be little further evaporation. But if there is wind – the saturated air layer will be continually mixing with dry air and evaporation will continue

Record Levels of Evaporation

Dam pond evaporation

Annually, an estimated 261,530 billion gallons of water evaporates into the atmosphere.

The Bureau of Meteorology has revealed that, during October 2018, evaporation rates were the highest in 30 years.

Scientists worked out that the evaporation rate was as high as 12mm per 24 hour period in dam catchments.

At the same time last year it was 2mm to 3mm.

The total evaporation rate for the month of October was 222mm – while the average has been  179mm.

Evaporation rates are being fuelled by high temperatures, low humidity & strong winds.

How much volume does your dam lose?

Digging dam process

It is almost impossible to calculate the anticipated evaporation to be experienced by an individual  dam.

This is because there are so many variables – variables that can change on a daily basis.

Variables for measuring evaporation include:

  • wind speed
  • air temperature
  • water temperature
  • depth
  • atmospheric pressure
  • relative humidity
  • surface area
  • solar energy
  • wave action
  • amount of spray
  • roughness of the surface
  • vertical components of wind (wind direction)
  • solute concentration
  • fugacity
  • ambient air flow

Our evaporation management experiments

Evaporation scheme

“Evaporation losses from a storage are not constant and vary from month to month, and these losses can be a significant amount of total water volume” -www.industry.nsw.gov.au

To help you understand what volume of water is being lost to evaporation, we set up a micro simulation.

We filled a container with blue food dyed water

scheme of experiment with dam level

This container was chosen because to had the same proportional measurements regarding height, width and length of a typical farm dam

It would therefore produce proportionally similar results due to the same proportional surface area exposed to sun and wind.

During the course of the experiment, a data set that included date, total height vertical water height, total lost vertical water height and percentage total volume lost was maintained.

These photos show the progression of water loss due to evaporation over the experiment period

Over the course of ten days, losses due to evaporation exclusively totalled 30.7% of total water volume.

This represented a daily percentage loss of 3% of total water volume

The Cost Of Evaporation management. A Rough Calculation

Digging a dam

Evaporation reduction does not come cheap

Either you pay for ready-made fixes in money – or you pay for home-made fixes with less money but a lot of your time.

Using an example of a 1 megalitre dam with average annual evaporation of 2m – if the solution you use reduces the evaporation by 80%, costs $7000 and lasts twelve years – this is calculated as:

  • 800kL × 12 = 9.6ML;
  • $7000 for 9.6ML is $0.73/kL

This might be compared with using a big covered tank:

  • A 250kL tank will cost $15 000
  • Assuming a life of 15 years, we have 250kL × 15 = 3.75ML
  • $15 000 for 3.75ML is $4/kL.

How to stop evaporation

Dam
There has been a large number of approaches used to attempt to reduce evaporation losses from surface of water bodies.Every scientific approach tries to affect one of the 3 main causes of evaporation:
  • reduce the exposed surface
  • decrease the water temperature
  • decrease the wind effect

Since the meteorological factors affecting evaporation cannot generally be controlled under normal conditions, the focus has been placed on suppressing evaporation by physical and chemical means.

Evaporation can be reduced by either providing some sort of a barrier between the water and the air – or by somehow slowing the movement of the air near the water surface.

This can be accomplished a number of ways, but the effectiveness of each method varies

Some are far more efficient than others.

The Ultimate Evaporation Solution

aquaflo-underground-water-tanks-installed

Underground storage are one of the most if not the most effective way to drastically reduce evaporation by completely eliminating several factors such as wind, sun and air.

The main advantage of this method is that the loss of valuable land area is completely avoided.

However, the disadvantage of this method is that it requires high capital cost due to the size and engineering of the infrastructure used for the storage.

This can be diminished by storing the water in the aquifer. But by doing so, water needs to be pumped for use, which entails additional pumping costs and large energy consumption.

 

Deep Dam Design

 

Total-reservoir-storage-volume

Less water will evaporate if the ratio of the surface area to the volume is reduced.

The surface area can be minimised by building the dam as deep and as narrow as is practical.

This is highly effective but can be costly if the dam is already constructed.

The presence of a saline underground water table limits the depth to which a dam can be dug.

Another strategy is to construct the dam into cells so that independent areas of water can be managed to minimise surface areas.

For example, divide a dam into two or more equal sized cells of water.

Then, draw water from the first cell and, when possible, transfer the balance to the other cell(s) thus reducing the surface area of the remaining volume.

 

Windbreaks

Windbreaks

Wind breaks involve planting trees or other plants that act as wind breakers, thus reducing the movement of air over the water surface

This greatly reduces evaporation

Trees can also provide some shade which will further reduce evaporation.

However, wind breaks can only be employed on small water bodies.

On big dams, the wind break effect is limited to a short distance from the rim of the reservoir, leaving the inner water exposed.

 

Aquatain

Aquatain is a silicone based liquid that is spread in a very thin layer on top of bodies of water to form a barrier stopping contact between water and air – and therefore reducing the amount of loss to evaporation.T

The maker, Guyco, claims Aquatain will reduce evaporation by more than 50%

 

Waterguard

WaterGuard
WaterGuard is a unique liquid which spreads over the surface of water to form a very thin film and reduce evaporation. 
 
WaterGuard is produced from polymers which repel each other very strongly when they come in contact with the water.
 
This results in a strong spreading action across the surface, forming a liquid ‘blanket’ to reduce evaporation.
 
Water losses from evaporation are immense.
 
A single square metre of water surface can easily lose up to 8 litres to evaporation every day in summer, and a one hectare dam can lose up to 80,000 litres – water that is essential for animals and growing crops.
 
Trials in the US have achieved evaporation savings of 50% and above.

 

Vegetable oil

vegetable oil

This is also the principle behind using a floating liquid such as vegetable oil

A thin layer of vegetable oil will float to the surface and prevent water molecules from making contact with the air – thereby reducing evaporation

However, in many circumstances, it is not appropriate to use oil.

The problem with this method is that the wind can break the vegetable oil up & blow it to shore

 

Chemical WER

Chemical WER

Chemical WER (fatty alchohol) forms a thin film that has been found to be effective for reducing evaporation

Some studies cite a 46% reduction

Chemical WER is also fairly safe to the environment as it is biodegrable and permeable to oxygen

However, wind velocities and temperature does affect Chemical WER, and it is generally not used when winds exceed 10-15 km/h – or when the temperatures exceed 40-42C.

Chemical WER is also expensive to purchase and apply – and it is only a short term measure.

 

Dam plants

Waterplants

You can add free-floating water plants, such as water lilies and duckweed, in quantities that block approximately 40 to 60 percent of the dam’s water surface.

The floating plants’ flowers and foliage help to shade the dam effectively to keep it cool and reduce sun exposure, and in turn minimise the risk of algae blooms and weed invasions.

Choose plants that grow below the surface of the water.

Submerged plants have the largest contribution to water quality.

They function as oxygenators during daylight hours, providing oxygen for fish, and they supply fish with excellent cover.

Water lillies are an excellent solution

They reduce surface temperature  & the area exposed to wind

The growing of dam reeds would have same effect – although greatly impeding flow of water

 

Depth Segmentation

Depth segmentation; dam dead storage

Reducing the exposed water surface works best if some shallow portions in the reservoirs can be easily separated from the rest of the lake.

The method consists in building dykes to isolate the shallow portion of the reservoir and divert the water to deeper area – and is somewhat effective in drought prone areas.

Evaporation losses are eliminated in those sections, thus reducing the evaporation losses over the entire reservoir.

Unfortunately, it is dependent on the reservoir topography, and can be somewhat costly to implement.

 

Dam covers

Dam Cover

Floating cover systems were first introduced over 60 years ago.

Many advancements in design and materials have been made over the years.

Some of the newer materials includes hypalon, polypropylene, PVC, HDPE, LLDPE, geotextile, XR-5 and XR-3

Despite having a higher capital cost than wind breaks, complete reservoir covers offer the best cost /efficiency ratio out of all the existing methods to effectively reduce evaporation.

While quite as not effective as enclosed underground storage (99+% reduction in evaporation losses), some modular floating covers are getting very close (98%)

These covers are very similar to those used in swimming pools.

The downside of this method is cost.

To cover a dam of 4.5 Ha, the cost would be approximately $250,000 – or about $5.55 a square metre.

 

Assessment criteria for dam covers

Assessing dam criteria
When considering dam covers, there are a number of questions that have to be weighed up:
  • How stable will the cover be in high winds?
  • How long will it last?
  • Will it be stable when the dam is dry?
  • Will it leach toxic substances into the water?
  • How will it stand up to what is a corrosive environment – continual contact with water and air and some level of salinity; exposure to ultra-violet light that can degrade some plastics?
  • Some products are easily and cheaply installed by the land owner, others require expensive installation by specialists.
  • What warranty is there – and is the company likely to be around in five years if you need to call on the warranty?
  • Does the product need to cover only the water, or does it need to be large enough to allow for anchoring beyond the lip of your dam – making a big impact on the final price?
  • If your dam wall is vegetated? How much damage will be done to this during installation?
  • Many of the products on the market are flammable. The probability of a bushfire during the life of the cover must be considerable; in some areas more than others.

 

Dam cover drawbacks

relaxing in front of dam

Despite progress in material and manufacturing process, geomembrane and solid covers in general still present several drawbacks:

  • Can not use this method if you have fish in your dam
  • Geomembrane can tear, resulting in expensive repairs costs.
  • High maintenance cost
  • They must be custom designed to match the exact shape of the dam or reservoir.
  • They are affected by rain, ice, frost and snow.
  • They cannot be installed on full ponds.
  • Insurance cost associated with those type of covers are high.
  • They block access to the liquid.
  • Limited warranty: 5-10 years.
  • Overtime, vegetation growth appears on top of the cover.
  • Install requires specialised equipment and trained crew.
  • Cannot be easily reused or transferred to a different liquid containment.
  • Are not easily compatible with certain type of surface aerators.
  • Price becomes substantially higher for long lasting, thick, heavy duty geomembrane.

Below are some of the products that fall into the category of modular floating dam covers

 

E-Vap Cap

Evap Floating cover
E-Vap Cap is a floating polyethylene sheet cover
 
The floating cover consists of a unique, multi-layered, polyethylene membrane 540 microns in thickness that contains its own buoyancy cells.
 
It carries a 5-year pro-rata warranty against UV breakdown due to sunlight exposure (independent NATA laboratory testing indicates a much longer “life” expectancy than 10 years).
 
Optional thicker material, up to 1000 microns is available giving greater warranty and a design life of 20 years
 
For a dam measuring 20m x 30m, the quantity of material required – including allowances for top of banks, anchor trenches, welding overlaps – would be approx. 1011.84sqm
 
This would indicate an approximate price of $10,175 – or $20 per sqm
 

 

Evap-Mat

Evaporation mat

Evap-Mat is a product of DeVere Mining Technology Limited

Evap-Mat  is comprised of laminated 20 micron, stainless steel mesh and 0.4mm bubble HDPE sheet.

The cover is anchored to the storage floor by cables attached to a buried polyethylene pipe.

It is designed to only cover 90% of the water surface area.

Evap-Mat is easy to install, heat reflective and self-protecting in high winds (up to 150 kph) whether empty or full.

The cover is also suitable for all storage sizes, shapes and profiles up to 2 km wide.

It is claimed that Evap-Mat may reduce evaporation by up to 90 per cent  -depending on the water level of the storage.

Costs: $3.50/m2 for complete installation.

Life expectancy is 30 years.

Resistant to UV light and oxidation.

 

Hex Dome

Hex Dome

Hex Dome is an independent modular system made from UV resistant recycled plastic – with a life expectancy of 25 years

Each module covers one square metre – and it has been shown to greatly reduce the effects of wave action

Hex Dome claims to reduce evaporation by up to 90%

Costs: the anticipated cost is $4.50-8.00/m2

 

Quit Evap

quit evap

Quit Evap is a rectangular modular floating cover, manufactured from 0.5-0.75 mm thick polypropylene sheet with polystyrene floats.

The modules are interconnected by Velcro straps.

The full scale modules are up to 5 m x 25-30 m.

Quit Evap can cover 90-95 per cent of the water surface and reduce evaporation by 85-90 per cent.

Durability:

The cover has a minimum life span of 5 years with a potential life of 8-10 years – the cover is also UV stabilised.

Costs: the estimated cost is around $6.00-8.00/m2 plus transport and installation.

 

Raftex

Raftex
Raftex is a product of F Cubed Australia Pty. Ltd.
 
The Raftex units are hexagonal and link together – with sufficient space between units to allow proper aeration of the water and for rainwater to get into the dam.
 
Each panel weighs 16kg, covers 16m2 of water and is made of galvabond steel tubing, polystyrene foam, and polyethylene film.
 
It has a 10 year guarantee.
 
Apparently a minimum of 30cm of water should be left in the dam at all times to anchor the panels.

 

Modular floating covers

Modular floating cover

The need to overcome these obstacles has lead to a new type called modular floating covers.

Those covers are slowly replacing geosynthetic membrane for most applications not requiring gas to be trapped, and where the cover permeability is a priority.

Below are some of the products that fall into the category of modular floating dam covers

 

ArmourBall Shade Balls

balls-fusion

Armor Ball hollow ball cover systems offer a highly effective solution to evaporation in dams

High surface area coverage is achieved by placing a sufficient amount of balls on the surface of the liquid.

The balls arrange themselves to provide coverage of up to 91%.

The result is a thermal insulation barrier which combines the insulation factor of the air held in each ball with the poor heat conductivity of plastic.

While the air pockets between the balls are not sealed, they also contribute to this insulation system, which dramatically reduces heat loss and light transfer.

The Armor Ball cover does not represent an obstacle to moving equipment.

The balls can be easily pushed aside and the cover reforms itself as the basin and obstacles change configuration

 

Rhombo Hexoshield

Rhombo Hexoshield

Rhombo Hexoshield is another modular shade ball currently on the market

It is suitable for most dams in windy areas with fluctuating water levels

Compared to other modular floating covers, it is ideally suited for larger reservoirs because it will resist high winds and does not stack even with strong water currents.

This cutting edge cover is similar in simplicity as other sphere covers except that it does not have the gap in between the sphere.The Rhombo cover offers the following properties:

  • Up to 99.9% coverage of the surface
  • Up to 98% reduction of evaporation from water surface
  • Up to 96% emission reduction
  • Up to 90% odor reduction
  • Over 75% reduction in heat loss
  • Over 90% reduction in algae growth

 

The Aussie Shade Ball Solution

plastic-bottles-floating-on-water

Aussies have come up with a cheap and practical version of dam

shade balls cover the dam surface with capped floating milk cartons or sealed empty bottles.

Cheap. But not pretty.

Still, it has the same effect as shade balls. 

 

AgFloats

Ag Floats

A system that uses recycled tires as an evaporation barrier, with polystyrene to make the tires float

Early indications are that it results in an 80% reduction in evaporation.

A disadvantage to the new system is that the polystyrene is exposed to sunlight and will gradually degrade – although the tires will provide some protection from the UV light.

Also, since the system uses polystyrene, it is less environmentally-friendly

This system costs approximately $10 per square metre – about $7000 for a 700m2 dam

 

Aquacap

Aquacap

It is claimed that Aquacap reduces evaporation by 85%.

The product is a circular floating disc made of polypropylene – 1.15m in diameter, 200mm high and weighing 3kg each.

They are claimed to have been tested to wind speeds of 130kph.

Lifespan is claimed to be five years plus.

Other benefits claimed:

  • UV and wind proof
  • Allows rain water to enter the storage facility
  • Preserves water quality
  • Easy to transport
  • Wind, hail and debris resistant

Cost of using Aquacap in 700m2 dam :

  • 600 discs at a price of $23.50 each plus GST
  • $15 500
  • $26 per square metre

 

Pumice

Big Ditch Dam Company. Pumice for dam evaporation

Pumice is a light-colored, extremely porous igneous rock that forms during explosive volcanic eruptions.

It is used as aggregate in lightweight concrete, as landscaping aggregate, and as an abrasive in a variety of industrial and consumer products.

We are the first company globally to be testing pumice for evaporation management.

Pumice is 100% organic, has no toxic effects on fish life, and the irregular shape allows oxygen and rainfall into the water body.

It is more wind stable than duckweed, and has excellent buoyancy ratings

The tiny holes in pumice caused by volcanic gases encourage the growth of water cleaning microbes

Small volume tests in 10,000 litre micro dams have performed extremely well, and we are now moving to large installation tests with 2 year windows


Contact us about your evaporation control needs, and we can advise you on the best solution for your situation.

We have tested all products above