Okaro Catchment Lake Restoration

June 2008

The Birchalls are dairy farmers involved in a number of water quality initiatives on their farm

Lake quality has become an issue in the Rotorua area with increasing levels of nitrogen and phosphorus discharging from urban and rural areas. The Rotorua Lakes Protection and Restoration Programme was set up to address these issues. It is a strategic partnership made up of Environment Bay of Plenty, Rotorua District Council and the Te Arawa Lakes Trust.  They have undertaken to oversee a programme of returning the lakes to a target quality agreed in Environment Bay of Plenty’s Water and Land Plan.

Action plans are being written for all of the Rotorua lakes stating the actions to be carried out to return the lakes to their target quality. Lake Okaro’s action plan has been completed.

Shane and June Birchall’s 234 ha property is close to Lake Okaro.  It has three separate pastoral land uses:

A dairy unit milking 420 cows on approximately 160 ha milking platform of rolling to strongly rolling land predominantly in the central and south-eastern part of the property. The cows are milked once a day. Aiming for 120,000 kgMS this season (target was 140,000 kgMS before the drought). The Birchalls changed entirely over to once a day milking during the 2005/2006 season. Cowshed effluent is disposed of by irrigation to land. Cows are excluded from all streams and drains.

A deer unit with 60 breeding hinds on 21 ha of strongly rolling to moderately steep land in the northern part of the property. Fawns are finished on the property.

Of the 234 ha, approximately 60 ha of the property drains to Lake Okaro, which subsequently discharges to the Haumi Stream, which flows into Lake Rotomahana. Approximately 99 ha of the property drains directly to the Haumi Stream and around 31 ha of the property drains to the Waiotapu Stream.  A new block of 44 ha was added to the property in June 2006 which is all in the Waikato catchment.

The Birchalls have been working collaboratively with Environment Bay of Plenty since 2005.

This partnership has been formalised in several signed agreements.

The environmental works on the Birchall property were designed in 2005 by Environment Bay of Plenty in conjunction with Shane and June. They were subsequently formalised and permanently protected (covenanted) by an Environmental Programme.

This has enabled planning, expertise and funding assistance to be provided for most of the riparian margins around the Birchall property (five specific areas). Around 75% of the cost is paid for by Environment Bay of Plenty, as it was recognised that these works have benefits for the wider community. The constructed wetland (Area 6) in particular has long-term mitigation benefits serving a wider catchment than the Birchall’s own property. These works in particular have been mostly funded by Environment Bay of Plenty.

It is generally acknowledged that the loss of nutrients (nitrogen and phosphorus) from pastoral farming contributes to the deterioration of lakes water quality.

This property has been formally assessed for its nutrient status as part of the Lake Okaro Action Plan being coordinated by Environment Bay of Plenty.

The primary aims for this programme are to minimise the nutrient loadings (N and P) leaving the property and protect soil and water values within the catchments of Lakes Okaro and Rotomahana and the Waiotapu Stream

To achieve a reduction in sediment and nutrient flow to Lakes Okaro and Rotomahana and the Waiotapu Stream the following works have now been mostly completed:

Permanent exclusion of stock from all drains, streams, wetlands and seepage areas by 7.6 km of fencing around Environmental Protection Areas 1, 2, 3, 4 and 5.

Revegetation and pest plant and pest animal control of these fenced off areas.

Re-routeing the two streams flowing into Lake Okaro through a constructed wetland (Environmental Protection Area 6) specifically designed for nutrient removal.

Engaging agKnowledge Limited to apply their Total Nutrient Management (TNM) system to the property to identify and prioritise the most cost effective management options to reduce N and P loadings to an acceptable level, whilst achieving the landowner’s production objectives.

Research has indicated that the Best Nutrient Management Practice (BNMP) with the greatest potential to reduce nitrate leaching is limiting winter stock grazing. This can achieve N-loss savings of from 30 to 60%.

The Birchalls are farming on a soil type called Rotomahana Mud. While relatively fertile this soil is particularly difficult during wet periods of the year.

Rotomahana is not free draining. During the winter and spring, paddocks being grazed by cows can become severely pugged and muddy with a high proportion of pasture trampled in and wasted. These wet winter and spring soil conditions also make movement about the farm with tractor and feedout wagon particularly hazardous.

Also a high proportion of any supplements fed onto the muddy surface are wasted.  These conditions motivated Shane and June to consider a stand off pad system that would reduce personal risks and wastage of pasture and supplements.

Environment Bay of Plenty has also set up a Memorandum of Understanding with the Birchalls. This enables an ongoing study and demonstration of the environmental benefits of this facility in relation to the economic performance of the farm.

This arrangement runs for five years. It is about to become integrated into a more detailed Sustainable Farming Fund research project on off-pasture wintering structures and their environmental benefit. This will focus on nutrient loss savings to groundwater as well as the issue of Green House Gas emissions.

The trial includes a regular sequence of demonstration days. Local farmers are invited to come along and hear updates.

Birchall’s experience with the Herd Home (HHS)

Cows took a while to learn to lie down. Half a dozen wouldn’t lay down so they were put out in another mob. Generally after the first month they appeared very content, moved well to paddock, four hours graze, moved well back to the herd home where they were all happy to lay down, 90% by 9 pm at night.

Later on in early spring used the HHS for the Colostrum herd. “Colostrum cows are always the least settled” but are very good in the HHS whereas out in the paddock they would be moving around and at the wettest time of year wrecking the pasture – not happening now. The colustrum cows are just in for the night (12-14 hours) with ad lib silage. “HHS Bloody magic for colostrum herd”.

Only had two down with metabolic problems which is very good. Some lameness but otherwise pretty good. Cows came through winter very well.

Shane and June say that during winter the pasture savings in paddocks was particularly noticeable. The cows were not there all the time trampling it and they were not on with the tractor dragging the silage wagon around in mud – so much less pasture damage. Have historically had 30-40% wastage of supplementary feed in the paddock – now not the case as any feeding is done on the concrete (apron) feed strip of the HHS eliminating wastage of both feed and Mg. With less pasture damage there is more feed for the cows and it will also allow more supplements to be made. As we had half the herd running out on pasture full time and half using the HHS you could see the difference in the paddocks with much more pasture damage in the former grazing system.

“The existing HHS can only accommodate about half of the cows in my herd. Ideally I need another shed but this will have to wait as there are other priorities. With the single HHS only taking half my herd, I still had to have two ‘Springer’ herds which complicated stock management which makes me more motivated for getting a second HHS built.“

Shane estimates that there should be enough nutrient in the HHS bunker to cover 35 ha.

By September production was up 25% on best ever for this farm. In November still 16% up for season and 13% for month. Shane thinks this mainly due to less pasture damage. He’s still 10% ahead for the season despite the big dry.

The reduced pasture damage from winter (cows off in HHS) has made a big difference going into the drought as well as the ‘once a day’ operation and good cow condition.


A constructed wetland was an early proposal as Shane and June Birchall were keen to be involved for a number of reasons. They provided an area of 2 ha for the wetland. Around 0.3 ha was part of the Rotorua District Council reserve and forming a wetland fitted with their development plans for the lakeside reserve.

De-nitrification is the key process by which wetlands remove nitrogen. This involves bacterial conversion of nitrate to nitrogen gas which is returned to the atmosphere. Wetlands only provide low levels of phosphorus removal. Cycling of phosphorus through growth, death and decomposition eventually returns much of the uptake to the water column.

Around 60,000 plants were used. The wetland was planted in spring 2005 by Wildland Consultants with the planting contract including a year of supervision and weed control.