What is Managed Aquifer Recharge (MAR) and Near River Recharge (NRR)?
MAR is not a new concept and has been used extensively overseas. Managed aquifer recharge in our context refers to the intentional recharge (infiltration) of clean water to aquifers for environmental benefit. Near River Recharge is a form of MAR that occurs in the floodplain of a river. In this situation the benefits occur in the river system and connected aquifers.
Infiltration basins and races, which act like big leaky ponds, are filled with high-quality clean water which seeps down and recharges the groundwater.
Clean alpine water from the Rangitata River is delivered to the MAR/NRR sites via irrigation races and pipes. Any silts carried by the water settle in a forebay (silt trap) before the water is allowed to flow through to the main infiltration basin. From there, the clean water seeps down to recharge the groundwater system.
Benefits include the natural treatment of water to enhance quality and the replenishing of over-allocated aquifers.
Why do we need constructed wetlands / bioreactors as well?
Most nitrates take many decades to travel through Hekeao/Hinds aquifers. These nitrates will continue to emerge in lowland springs for generations to come. Constructed wetlands and bioreactors are proven methods to manage nitrates in spring water, while requiring a much smaller land footprint than traditional wetlands.
Why do we need to do this?
Water quality in some rivers, streams and waterways in our catchment is not acceptable, with nitrate levels that exceed the New Zealand drinking water maximum acceptable value. We will not meet Plan Change 2 to Canterbury’s Land and Water Regional Plan (LWRP) requirement to reduce on-farm nitrogen losses by up to 36% by 2035 without taking a proactive approach.
This situation is not unique to our catchment and is an unforeseen consequence of historic farming practice alongside other community use of the water resource. Nutrients from land use activities take a very long time (decades to centuries) to travel through the groundwater system. We need to clean up these legacy nutrients in the groundwater while also significantly reducing the nutrients leaching from current land use.
The Freshwater National Policy statement and Plan Change 2 require a combination of reduced nutrient leaching from current land use, recycling of irrigation water nutrients, management of abstraction, and initiatives such as MAR to address legacy nutrients in groundwater.
We must act now. Leaving these issues for the next generation is not an option.
Where do the nitrates come from?
Although other industrial practices and leaky septic tanks negatively impact water quality, nitrates in Hekeao/Hinds waterways largely come from farming. Before we had our current knowledge about good farming practice the restrictions on farming were not as strenuous. Now we know more, our farming community is required to ensure good farm management practice, including reducing their nutrient/nitrate leaching by 36% by 2035.
Where does the water come from for MAR and NRR?
The project uses repurposed Rangitata River water from existing consents. It is important to note MAR and NRR do not use any additional water resource or consents but rely on existing consented water that is not used.
There is no unnatural mixing between waters, as recharge areas are designed to contain and recharge all supplied water. This water filters down through alluvium (loose clay, silt, sand, and gravel) before mixing with other groundwater.
Who oversees the Enhancement Projects?
The projects are governed by the Hekeao / Hinds Water Enhancement Trust (HHWET).
Trustees include:
- Peter Lowe – Chair
- Alister Argyle
- Neil Brown
- Craig Fleming
- Vince Lobb
- Ian Mackenzie
- Rab McDowell
- Marcus Murdoch
- Fleur Tompsett
- Carolyn Cameron
- Evan Chisnall
Observer and Advisor
- Mark Webb
Executive Director
- Dr Brett Painter
Will the Enhancement Projects achieve the required change?
The projects have achieved positive results to date. You can find the technical detail here. The governance group is confident that the projects will make a difference. However, it is important to remember that these projects are not the only solution. We all have a role to play in improving the quality and quantity of water. Farmers are making significant changes to the way they farm to help bring about improvements. Each farm must have an independently audited Farm Environment Plan and farmers must farm to good management practice, including reducing their nutrient leaching by 36% by 2035.
What if we don’t get nitrate levels down?
If we don’t reduce nitrate levels to those required by Environment Canterbury, then more drastic measures will need to be taken.