The Department of Environment and Primary Industries study of new dams in NSW showed a 23 per cent failure rate due to the mistakes in dam building.

Furthermore, a high percentage of dams fail during their first filling — usually because of poor design or construction or a rushed filling rate meaning that earthmovers made some mistakes in dam building.

The answer, DEPI maintains, is to have your dam designed and built by a suitably qualified dam builder, not a general earthmover

Top 11 mistakes in dam building made by general earthmovers:

 

1. Selecting a poor location to site a dam

Site assessment is the first step towards successful dam construction and the first place where mistakes in dam building occur.

Dam building demands special considerations often ignored by traditional excavation companies.

The first of these is an extremely thorough site assessment. Just because you want a dam does not mean it is possible

Your land must conform to a few specific requirements – such as appropriate drainage area, efficient direct water source, an appropriate immediate impact area, efficient sun and shade profile throughout the day,  appropriate previous land use to ensure no contamination – and, most importantly, soils (availability and access).

Dams are too often placed in a low spot that collects water. This causes 2 problems

Firstly, low spots that collect water are challenging to build in and increase the build cost.

Secondly, dams in low spots can suffer from too much runoff, and pollutants tend to collect in low spots, therefore allowing the pollutants to enter the dam system.

Poor site planning can also lead to having little to no room to get in and out of the dam during the construction process – not to mention needing to move materials twice if they interfere with the building area.

This adds cost to the dam construction  

 

 

2. Illegal siting of dams

Many general earthmovers will site dams in streams and creeks.

Your dam should not be constructed in the path of an existing waterway. In many cases this is illegal, and usually this type of construction sets the course for extreme sedimentation and thus, a short dam life.

It is best if your dam is spring-fed from above or is fed from an existing stream running adjacent to the proposed site or is fed by purpose built water catchment swales.  

 

 

3. Incorrect soil composition

Dams require a heavy clay base – but not just any clay.

To seal properly, and for the years to come, a very specific type of clay should be used in the dam construction. We only use white clay – technically known as kaolinite clay.

Kaolinite is a clay mineral with the chemical composition of Al₂Si₂O₅(OH)₄.

It is a layered silicate mineral, with one tetrahedral sheet of silica (SiO₄) linked through oxygen atoms to one octahedral sheet of alumina (AlO₆) octahedra. 

Clay that is rich in kaolinite is known as kaolin – or china clay. 

If this is not available on site, we have our own mineral kaolin mine that we source the required kaolin from.

Many general earthmovers will simply use the soil they excavate – and this leads to many problems – such as seepage and collapse, which in turn leads to significant repair costs.

Without correct clay composition and preparation, dams usually devolve into expensive dry holes.  

 

 

4. Poor construction specifications

Many general earthmovers make dams too shallow (thereby losing excessive water to evaporation), or make the banks too steep (making maintenance down to the water level impossible, so the dam becomes unsightly and overgrown)

Once your chosen site has been deemed suitable – a second tier of requirements must be confronted – dam depth and shape, standpipe and overflow construction, aeration, habitat, access, bank stability and more.  

 

 

5. Poor construction techniques

There are many mistakes in dam building that plague general earthmovers when they build dams

Foremost among these is improper dam construction.

A correctly built dam is a well-compacted dam. To create an impervious levee, appropriate soils must be tightly compacted in thin layers or “lifts”, usually of 12” or less.

These lifts should begin several feet below the finished grade of the proposed pond bottom to form a key-way or “core”.

 

 

6. Not creating an impervious core in the dam wall

The core is essential for the dams strength and seal

Once water finds its way through or beneath a dam – major mitigation costs are soon to follow.

If you asked most general earthmovers, they could not tell you how to construct an impervious core inside a dam wall  

 

 

7. Incorrectly proportioned wall

Another one of the most widespread mistakes in dam building lies in-wall proportion calculations.

The dam wall must also be wider at the bottom than the top, much like a pyramid.

The generally accepted slope standards for both the front and back of a dam are 3:1 – and these should be adhered to by your contractor.

Most general earthmovers do not use this slope standard, and consequently, their wall slopes are too steep – and they are a recipe for neglect and failure.

Digging a deep dam with no provisions for shallow areas makes it a drowning danger for stock and young children.

It is illegal to build dams with a wall batter that makes an escape from drowning impossible

Steep dam walls also make it dangerous to get in and out of the dam for maintenance.

Plus, there’s no place or ledges for aquatic plants, the majority of which grow in less than 12″ of water.   

 

 

8. Incorrect overflow systems

Overflow systems are generally the next points of failure.

The purpose of overflows is to regulate water level, and provides an evacuation route for excess during extreme weather

Overflow notches are seldom placed in the center of the levee.

They should be oriented to one side or the other and constructed with permanence in mind.

In many cases an appropriately-sized ditch, armored with large stone (rip rap) over foundation fabric, is suitable.

For larger dams/lakes, or for dams that will double as roadways – concrete or buried drainage structures with head wall protection are advisable for overflows.

All should be engineered for your specific environment and circumstances.  

 

 

9. Lack of ability to control water levels

When general earthmovers construct a dam (and that is being generous, because all they really do is dig a hole) – they usually do not install the ability to lower the water level via stand-pipe making one of the most popular mistakes in dam building

Periodically lowering the water level can help compress sediment – and more importantly kill undesirable vegetation along banks.

This saves you money by lowering maintenance costs and cause one more of the mistakes in dam building.

Dams are maintenance structures that can’t be ignored for long intervals.

As much as possible, you want yours to manage itself.  

 

 

10. Lack of dam wall buffer

A healthy dam is one that creates a positive ecological impact, providing habitat not only for aquatic species, but nearly every type of creature – from bugs to birds.

A well-constructed dam must have a substantial buffer around the dam wall for the planting of native grasses and shrubs – firstly, for flora and fauna support, and secondly, for dam wall stabilization

Many general earthmovers will not create this necessary buffer – because they do not even know it is required

Remember, do not plant trees on your dam! Tree roots seek water and will perforate your dam!  

 

 

11. Permitting

Depending on where you plan to build your dam, and how it is to be constructed – you may require one or more permits.

Permitting takes into account not only the safety of those downstream but environmental impacts as well.

Permitting is usually much simpler on farms and in rural areas – but it is a legal requirement that the dam be within its approved EPA harvestable water rights.

Each state has different permitting requirements, so your dam builder should know what is needed before you invest too much in your dam building dreams.

Most general earthmovers are not aware of these permitting requirements adding to other mistakes in dam building– and this leaves the dam owner legally vulnerable to large fines  

 

In summary

Unless you dig dams for a living – it’s tougher and more technical than you think

And also – digging the dam is the easy part!

For more information about dam building or repair – contact us 

We will be happy to evaluate your proposal or existing site helping you fix mistakes in Dam building if they were made

We love dam construction – and each of our well-constructed dams is an oasis!