Feedlot Drainage & Effluent Management: Planning Clean Water, Runoff and Storage
Drainage is one of the first systems to consider when planning a new or covered feedlot.
Every rainfall event creates water that needs somewhere to go. The important question is where that water has been before it reaches the drainage system.
Water falling on a clean roof is very different from runoff that has passed through an occupied cattle pen.
A well-planned feedlot drainage system aims to:
- Keep clean water clean wherever practical
- Prevent external runoff entering controlled areas
- Collect contaminated runoff
- Remove solids where required
- Provide sufficient storage
- Protect pen conditions and infrastructure
- Allow systems to be cleaned and maintained
- Meet environmental approval requirements
For covered feedlots, the roof can significantly change this water balance. It prevents rainfall entering part or all of the pen while creating a large new source of relatively clean roof runoff.
That needs to be considered from the beginning of the project.
Start by Separating Clean and Contaminated Water
One of the most useful ways to understand feedlot drainage is to divide water into separate streams.
| Water source | Typical approach |
|---|---|
| Clean external runoff | Divert around controlled feedlot areas where practical |
| Roof runoff | Collect and direct as clean water where appropriate |
| Runoff from occupied pens | Treat as contaminated runoff and direct into the controlled drainage system |
| Feed and manure handling areas | Assess as part of the controlled drainage system |
| Trough overflow and washdown | Manage according to where it occurs and whether it becomes contaminated |
The objective is to avoid unnecessarily increasing the volume of contaminated water requiring storage and management.
That is particularly important when introducing covered housing.
Understand How Water Moves Across the Site
Before designing drains or ponds, understand the site’s existing water movement.
A site investigation should consider:
- Natural contours
- Catchment boundaries
- Existing waterways and drainage lines
- Upstream runoff
- Soil characteristics
- Groundwater where relevant
- Low points
- Existing dams and drainage infrastructure
- Proposed pen locations
- Future development areas
A survey and site levels provide the basis for understanding where water currently flows and how the proposed feedlot will alter those flows.
This work should happen before the final building and pen layout is locked in.
Keep External Clean Water Out of the Feedlot
Water that has never entered the operational feedlot area generally should not be allowed to become contaminated unnecessarily.
Depending on the site, clean-water diversion may involve:
- Diversion banks
- Catch drains
- Channels
- Bunds
- Culverts
- Controlled discharge points
This reduces the volume of water entering the controlled drainage system and ultimately the amount requiring storage.
It can also reduce erosion and help protect roads, buildings and other infrastructure.
Plan How Pens Will Drain
Within open pens, the pen surface itself forms part of the drainage system.
The MLA Feedlot Design Manual identifies pen slope as an important design consideration, with typical open-pen guidance around 2.5% to 6%, and approximately 3% to 3.5% often providing a practical balance.
That means a 3% fall represents:
30 mm of vertical fall per metre
Across a 50 m pen:
50 m × 3% = 1.5 m of fall
These figures should not simply be applied to every project. Pen geometry, soils, climate, drainage, earthworks and operational requirements need to be assessed together.
The aim is to move runoff effectively without creating excessive erosion or making pen maintenance unnecessarily difficult.
Related Article: Feedlot Layout Design
Covered Pens Change the Drainage Equation
Putting a roof over cattle does more than provide shade or shelter.
It changes where rainfall lands.
Instead of rainfall falling directly onto the pen surface, a significant proportion may now fall onto the roof.
The basic relationship is:
1 mm rainfall × 1 m² roof = 1 litre of water
For example, a 5,000 m² roof receiving a 50 mm rainfall event receives:
5,000 × 50 = 250,000 litres
or:
250 kL of gross roof runoff
A 10,000 m² roof under the same rainfall receives approximately:
500 kL.
That water needs to be accounted for in the design.
Keep Roof Water Separate Where Practical
Roof runoff is potentially a valuable clean-water stream.
A covered feedlot should consider:
- Gutters
- Downpipes
- Lined catch drains
- Discharge locations
- Erosion protection
- Storage
- Water harvesting
- Overflow routes
Where appropriate, clean roof runoff can be kept separate from contaminated feedlot runoff.
This can reduce the amount of water entering the effluent-management system.
It may also create opportunities for water capture and reuse, subject to appropriate water-quality and storage considerations.
Related Article: Feedlot Roof Design
Covered Housing Can Reduce the Contaminated Catchment
This is one of the most important differences between open and covered feedlots.
MLA’s Feedlot Covered Housing Systems: Best Practice Design and Management Manual includes a worked 5,000 SCU comparison showing substantially smaller contaminated-water storage requirements for the covered system.
In the example, the covered system used approximately:
- 1.0 ML sedimentation basin
- 8.5 ML holding pond
The required storage was around one-fifth of the uncovered example.
That does not mean every covered feedlot can reduce its pond capacity by 80%.
The result depends on the site’s rainfall, catchment, roof coverage, drainage design, evaporation, operating system and approval requirements.
What it demonstrates is the principle:
Reducing the contaminated catchment can materially change the scale of the effluent system.
That can have significant implications for both site planning and civil works.
What Happens to Contaminated Runoff?
A typical controlled drainage pathway may look broadly like:
Pens → drains → solids/sediment removal → holding/storage → managed reuse or disposal
The exact system is site-specific.
Depending on the facility, infrastructure may include:
- Pen drains
- Catch drains
- Sedimentation systems
- Holding ponds
- Embankments
- Pumps
- Irrigation or reuse infrastructure
- Manure storage areas
The drainage and effluent specialist should determine the required configuration and capacity.
Sedimentation Is an Important Part of the System
Runoff from cattle pens can carry manure, soil and other solids.
Sedimentation systems help remove a portion of these solids before runoff enters downstream storage.
Their design needs to consider:
- Expected runoff
- Sediment load
- Capacity
- Cleaning frequency
- Machinery access
- Safe access
- Where removed material will be placed
A sedimentation system that cannot be practically cleaned will become increasingly difficult to manage.
Maintenance access should therefore be designed into the system rather than added later.
Storage Needs to Be Calculated for the Site
There isn’t one standard pond size for every feedlot.
Storage requirements can depend on:
- Controlled catchment area
- Local rainfall
- Evaporation
- Storm events
- Pen area
- Roof coverage
- Clean-water diversion
- Sedimentation
- Proposed reuse
- Operating conditions
- Environmental approval requirements
That is why the MLA covered-housing example should be treated as a benchmark illustrating the effect of coverage, not as a design specification.
A suitably qualified specialist should undertake the site’s water balance and determine the required storage.
Don’t Forget Manure and Bedding
Drainage and effluent cannot be designed independently from manure management.
Covered housing can change the characteristics of manure because rainfall is excluded from the covered area.
Depending on the system, the feedlot may also use bedding.
Planning therefore needs to consider:
- Pen cleaning
- Manure removal
- Bedding removal
- Manure storage
- Stockpile drainage
- Machinery access
- Nutrient management
- Final reuse or application
Drainage from manure and bedding storage areas also needs to be considered within the overall environmental system.
Troughs Create Their Own Wet Areas
Water troughs can create persistent localised wet areas if leakage, overflow or cleaning water is poorly managed.
During design, consider:
- Trough position
- Overflow
- Drainage
- Aprons
- Cleaning access
- Pen scraping and cleaning routes
- Pipe maintenance
A relatively small amount of continuous leakage can create a significant pen-surface problem over time.
Trough infrastructure should therefore be coordinated with both the pen layout and drainage strategy.
Drainage Needs Regular Maintenance
A drainage system only performs as designed if its capacity is maintained.
ALFA maintenance guidance recommends regular inspection of feedlot drainage infrastructure, including drainage channels, sedimentation systems and storage lagoons.
An inspection program should look for:
- Sediment accumulation
- Blockages
- Erosion
- Damaged drains
- Vegetation restricting flow
- Pond capacity
- Embankment cracking or slumping
- Damaged inlets and outlets
- Access problems
Records should document what was inspected, any defects identified and what action was taken.
Inspect the System Before Major Rainfall Periods
Don’t wait for a large storm to discover that a drain is blocked or a sedimentation system has lost capacity.
Before wetter periods or forecast significant rainfall, check:
- Drains are clear
- Diversion systems are functioning
- Sedimentation capacity is available
- Pond capacity is adequate
- Roof-water systems are clear
- Gutters and downpipes are functioning
- Discharge points are stable
- Erosion is controlled
This is particularly important after earthworks, construction or expansion because site drainage patterns may have changed.
Plan for Future Expansion
A drainage system designed around today’s feedlot may not have sufficient capacity for tomorrow’s.
Before finalising the design, consider:
Current capacity → next expansion → ultimate site capacity
Future development may add:
- More pens
- Additional covered areas
- Larger roof catchments
- Additional manure areas
- Roads
- Feed storage
- Hardstand
- New clean-water catchments
Some additions increase contaminated catchment.
Others, particularly additional covered housing, may reduce rainfall entering cattle areas while increasing clean roof runoff.
Both need to be modelled.
Related Article: Feedlot Expansion Planning
Environmental Requirements Need to Be Considered Early
Feedlot drainage and effluent management are closely tied to environmental approval requirements.
The exact pathway varies between states and according to feedlot size and location.
In NSW, larger feedlot developments may require planning and environmental assessment through the NSW planning system and may require an Environment Protection Licence through the NSW EPA.
Queensland feedlots may require an Environmental Authority for environmentally relevant activities depending on the operation’s capacity.
The drainage concept, controlled catchment, water balance, storage and effluent-management strategy may therefore need to be developed as part of the approval process rather than after approval has been obtained.
Related Article: Feedlot Environmental Requirements
Related Article: Feedlot Approvals
What Information Will Your Drainage Consultant Need?
Before detailed design begins, it is useful to have:
Site
- Site survey
- Contours and levels
- Soil information
- Catchment boundaries
- Existing drainage
- Nearby waterways
- Local rainfall data
Feedlot
- Current cattle capacity
- Future cattle capacity
- Pen layout
- Open pen area
- Covered pen area
- Feed and manure areas
- Roads and hardstand
Buildings
- Roof areas
- Gutter and downpipe strategy
- Proposed discharge locations
- Future building extensions
Water Management
- Clean-water catchments
- Contaminated catchments
- Existing ponds
- Sedimentation infrastructure
- Water-reuse opportunities
Operations
- Pen-cleaning method
- Manure-management strategy
- Bedding use
- Machinery access
- Maintenance requirements
Who Should Be Involved?
A feedlot drainage and effluent system will generally require input from several specialists.
Feedlot planner
To coordinate the overall operational layout.
Civil engineer or drainage specialist
To develop levels, drainage, earthworks and water-management infrastructure.
Environmental consultant
To coordinate environmental requirements, approvals and water-management documentation.
Geotechnical specialist
Where soil conditions, earthworks, embankments or pond construction require investigation.
Structural engineer
To coordinate covered structures with site levels, drainage interfaces and roof-water management.
TechSpan
To coordinate the covered structure with the agreed site, drainage and operational requirements.
Where TechSpan Fits
TechSpan does not design the complete feedlot effluent-management system.
Our role is to make sure the building does not get designed independently from it.
Through our 3C Advantage, we work with the producer and relevant consultants to coordinate:
Concept
Understand the site, cattle capacity, proposed coverage, drainage strategy and future development.
Configure
Coordinate building dimensions, levels, column locations, roof geometry, gutters, downpipes, operational access and drainage interfaces.
Construct
Detail, manufacture and construct the agreed structural package.
That coordination is particularly important with covered housing because the structure can fundamentally change the site’s water balance.
Before You Finalise the Feedlot Layout
Know where the water is going.
Identify:
Clean external water → clean roof water → contaminated pen runoff → sedimentation → storage → reuse
Then make sure the building, civil works and environmental systems have been designed around the same plan.
Getting that right during concept design is much easier than trying to redirect water after the feedlot has been constructed.
Talk to the TechSpan team about planning your covered feedlot.