Gravity Irrigation - Subsurface Drainage

Gravity Irrigation - Subsurface Drainage

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Salinity and waterlogging issues can threaten farm productivity, cause impacts to fruit trees, annual crops and pasture.

Summary

Salinity and waterlogging issues occur when a shallow watertable rises to near the ground’s surface.These are important issues for you (our customers) as they can threaten farm productivity, cause impacts to fruit trees, annual crops and pasture.

Subsurface drainage is controlled pumping to lower the watertable and help reduce impacts of salinity and waterlogging on farms. Lowering watertables draws groundwater away from root zones of plants. It also improves the chance of salt - that may have built up in the soil - to be flushed downwards.

Within the Goulburn Murray Irrigation District (GMID) and pumped irrigation districts,we:

  • Allow approved, privately collected, subsurface drainage water to be discharged to GMW owned and operated gravity pipelines and surface drainage schemes, and
  • Own and operates a network of groundwater pumps to ensure adequate subsurface drainage is achieved.

To reduce the impact of salinity and waterlogging on horticultural crops and pasture in high risk salinity areas of the Shepparton Irrigation Region (SIR), we actively manage, operate and maintains a Public Groundwater Pump network.

This network has pumps concentrated in areas that have a greater salinity and waterlogging threat and is the basis for the current Subsurface Drainage Service Standard: Subsurface drainage is available 98 per cent of the time.

This service standard has been achieved in recent years, but it is not unreasonable that pump outages will occur.

Changes to high watertable and salinity risks and threats during the past 20 years, the SIR Public Groundwater Pump network will look quite different in the future. Work is currently underway to mothball pumps in areas of lower salinity risk and, as a result, the operational network is likely to be about 30 per cent of its current size.

This means GMW’s service standard for sub-surface drainage will most likely need to change.

Why is this topic being considered?

A drier and more variable climate, together with irrigation changes, has significantly reduced the threat of high watertables and salinity in parts of the SIR.

We have been adaptively managing pump operation for many years in response to the changing threats. However, we need to look at how many pumps to keep operating and when to operate them to ensure we’re providing the most cost effective service to you.

We are currently working with Macquarie University to develop new operational triggers for our pumps, and have started a process to assess and mothball a large number of pumps, which we’ve assessed are not likely to operate for the foreseeable future.

Mothballing operational pumps is the preferred option to keep pumps in operational condition when not being used, because it:

  • is the lowest cost option,
  • allows the pumps to be easily brought back into operation if conditions change,
  • aligns with our State and Commonwealth salinity management obligations, and
  • protects the large public investment made in installing the pumps.

What is the decision(s) to be made?

  • Is the current service standard measure still relevant, given the changes to the SIR Public Groundwater Pump?
  • The current service standard “Availability of Sub-surface Drainage” is not clear –should it be changed to “operational availability of sub-surface drainage pumps” to be more transparent?
  • Is there a better way of measuring this service standard?
  • Is “Five annually - Number of occurrences of pumps being unavailable for operation for greater than 30 days when triggered to operate” clearer?
  • Would you like more information on sub-surface drainage?
  • If so how would you like to access this information? Email, website, social media, other.

How does this matter affect customers?

As a result of the changing threats of salinity and high watertables the number of and operation of Public Groundwater Pumps is changing.

What is not-negotiable in this topic?

GMW cannot negotiate on occupational health and safety requirements, nor can we operate pumps outside of their licensed purpose. We also need to operate and manage the pumps in line with our State and Commonwealth salinity management obligations.

What is negotiable in this topic?

  • Whether the current service standard still applies in light of changing conditions and risks.
  • What suitable timeframes for pumps to be unavailable are before customers are impacted.

What are the known, viable options?

  • Aligning the service standard with changes to the pump network, and understanding what is appropriate based on the number of pumps and how those assets are operated

If other options are identified, can they be considered?

Yes,we are committed to working with you to achieve the best outcome for our customers, business and region in operating our Public Groundwater Pump network.