Farm Dam Construction - Mornington Peninsula
When it comes to Dam Construction & Earthworks Braidak's experience makes the difference
A dam is not just a hole in the ground – it is a water storage structure requiring design, survey and construction.
To be effective, a dam wall must remain stable during large storm events and the soil must be relatively impermeable to minimise seepage loss. Consent may be required from your local council, and if so, a Development, Application must be lodged.
Choosing a dam site
A poorly sited or constructed dam can be very expensive to build, of little long-term use, and may cause severe land degradation problems. If you are in doubt, seek further advice from an experienced contractor.
What should you consider when looking for a dam site?
• A dam built in a gully or depression is generally the most favoured, due to its excellent storage to excavation ratio.
• Steep sites (steeper than 15 per cent slope) should generally be avoided because there is not usually enough suitable soil material to build a satisfactory wall.
• Ensure there is sufficient suitable soil material for wall construction. Sampling and evaluation of the subsoil is essential to ensure the quality and quantity of soil material. Rock, sand, gravel and soils prone to tunnelling failure are generally unsuitable, unless specialised construction techniques are used.
• The size-of the catchment must be considered when planning dam capacity and spillway size.
For instance, in coastal areas a 5 hectare catchment of moderate slope should provide sufficient catchment area to fill a small dam, say up to 1,000 cubic metres capacity. On the other hand, in large catchments it may be difficult to locate and maintain an effective spillway.
• Dam spillways must be located and designed to handle major storm flows safely.
• When surplus water flows through the dam spillway, ensure there is a suitable place to return it to its normal flowline without causing erosion. If it is near a property boundary, ensure flows leave the property in the same place that they did before the dam was built.
Licensing Requirements for Private Dams (Domestic & Stock Use) in Victoria
Under Victoria’s Water Act 1989, you may need a license to construct or operate a private dam for domestic and stock use, depending on the dam’s location and size.
Dam Construction Mornington Peninsula
Advice should always be sought first from Southern Rural Water to determine whether a licence is required for the development of a dam, or to take and use water from the dam.
If a licence from Southern Rural Water is required
If Southern Rural Water confirm that a licence is required for the development of a dam, or to take and use water from the dam under the Water Act 1989, the Mornington Peninsula Planning Scheme is only binding on the removal of vegetation necessary to accommodate the dam, and any ancillary works or structures not directly associated with construction of the dam itself. Further advice should be sought from Council about whether a Planning Permit will be required for these components of the project.
Licensing Requirements for Private Dams (Domestic & Stock Use) in Victoria Under Victoria’s Water Act 1989, you may need a license to construct or operate a private dam for domestic and stock use, depending on the dam’s location and size.
Licenses That May Be Required:
• Works License to Construct – Required to build or modify a dam on a classified waterway. Determines if construction plans meet regulations.
• Works License to Operate – Required to operate a dam on a waterway after construction finished. Confirms safety for water storage and release.
A dam refers to any structure that collects or stores water through excavation, barriers, or other built features.
A Works License to Construct is mandatory for dams built on identified waterways to ensure no harm is done to river health or flow. Contact your local water authority to assess if your proposed dam site is on a classified waterway.
For dams not on waterways, a license may still be needed if:
• Wall height exceeds 5m and capacity exceeds 50 megalitres
• Wall height exceeds 10m and capacity exceeds 20 megalitres
• Wall height exceeds 15m regardless of capacity
• Dam classification requires licensing for safety reasons
Check with the water authority to confirm license requirements if your private dam for domestic and/or stock use meets any of these criteria. Proper licensing ensures your dam is built and functions safely and sustainably.
Construction method
Generally a bulldozer with rippers is the most appropriate machinery for building dams larger than 250 cubic metres in capacity.
Peg out the dam site carefully, indicating the location of the proposed excavation, dam wall, top water level and spillway:
Clear all vegetation from the area that will be disturbed, ensuring .that natural vegetation below the spillway outlet and on the inflow areas is not disturbed by machinery, vehicles or livestock.
Remove topsoil from the excavation and dam wall site, and stockpile it below the wall for later respreading.
Construct a cut-off trench – a trench dug below ground level at least 300mm into the impervious material the embankment will be placed on. Clay from the excavation must be placed into the trench and compacted, forming a
watertight barrier preventing seepage passing
under the dam.
Build the wall layer by layer. Spread clay evenly in layers no greater than 150mm to obtain adequate compaction. Do not dump or spill clay over the back of the dam wall. Place any unsuitable soil material at the downstream toe of the wall.
Don’t place rocks over 75mm in size, logs or trees in the constructed wall.
Rock exposed on the floor of the dam during excavation should be covered with impervious clay at least 300mm thick and compacted to control seepage.
All excavation should be within the area that will be covered by stored water. If not, all exposed subsoil to be topsoiled and seeded.
Construct an earth spillway. This is a channel of sufficient capacity to safely convey surplus flows past the dam wall. A level sill should be constructed in natural ground at the end of the spillway.
At least 1 metre of freeboard is required. Freeboard is the height from the top of the water level (i.e. spillway level) to the top of the wall.
Stockpiled topsoil should be spread over the dam wall and spillway and seeded immediately with grasses to promote stabilising vegetation.
Specifications Spillway size
For stable soils, the following general minimum spillway sizes are recommended:
Trickle pipes – Continuous trickle flows kill vegetation, keeps the soil wet and encourages spillway erosion. A small diameter sewer class pipe or stronger (usually 15Omm diameter, but varied according to flow rate) can be built into the end of the dam wall during construction to accommodate trickle flows. The pipe is normally installed with fall in gradient between its inlet and outlet, with the inlet generally 300mm below spillway level. Anti-seepage collars should be fitted to the pipe and the outlet extended to the floor of the downstream flowline.
Glossary of dam building terms
Batter The excavated or constructed sloping face of a dam wall or embankment, produced as a result of earthmoving operation involving cutting and filling.
Cut-off trench – trench excavated into impervious material
under the wall to prevent seepage. Pervious
material is removed and replaced with clay.
Sill – A level section at the outlet of a spillway which
converts channelised water flows to sheet flows,
to prevent erosion of the outlet.
Spillway – Generally an excavated level channel extending from the end of the wall embankment to a level sill or outlet. The height of the outlet in relation to the structure governs the top water level if pipes are not included.
After care of your newly constructed dam
- – Maintain grass on all areas of the dam, especially the inlet and outlet.
- Don’t grow trees on the embankment, as they cause seepage and damage the structure.
- Check trickle pipe inlet for blockages.
- Avoid driving through or damaging the spillway.
BRAIDAK Bobcat & Excavation Berwick & Beaconsfield
Braidak Bobcat and Excavation has been operating successfully since 2017.
We provide a range of services including site cuts, site clean ups, gravel driveways, small or large excavations, bush or access tracks, demolition, auger drilling, top soil spreading, shed site cuts, dams and drainage, concrete pipe installs for crossovers, tree stump removal and brush clearing.
We are also experienced in developing Equestrian Arenas.
We also supply and deliver quality lawn soil, sands and gravel in 17 cubic metre semi tipper or 4m tipper.
We now also offer low loader haulage with a maximum capacity of 30 ton and up to 3m wide.
In addition to years of experience in the construction industry we believe quality equipment is important to ensure we provide the best service.
All our equipment is all either brand new or low hours to help us deliver a quality and reliable service.
Our motto is “the customer must be happy with the service we supply”.
I really appreciate your professionalism and promptness. You turned up when you said, did the job you said you’d do and charged what you quoted – rapt.
Cheers Roger
Braidak Bobcat & Excavation Areas Serviced
We are based around Pakenham but work in and around Berwick, Beaconsfield, Warragul, Mornington, Monbulk, Dandenong, Trafalgar, Grantville, Longwarry, Bunyip, Officer, Garfield, Tooradin, Warragul, Drouin, Belgrave, Gembrook, Emerald, Ferntree Gully, Lysterfield and Leongatha areas.
