Floods create steep learning curve for Horizons district farmers

September 2006
The Manawatu-Wanganui region encompasses 8% of New Zealands land area. There are 6000 farms in the region, half of them on 1.3 million hectares of hill country drained by five major river systems. Horizons estimates that approximately 300,000 hectares of hill country is highly erodable. Some 75% of the regions population live downstream of this country on the fertile Manawatu Plains.

Gravity, naturally high rainfalls, soft bedrock, farming practices that exacerbate erosion and the potential for increasing intensification of hill country farms all contrive to produce aggrading rivers and reduced capacity in flood protection schemes.

The February 2004 storm affected 70% of the region causing

o Severe erosion on 120,000 hectares of hill country

o 200 million tonnes of soil loss

o $66 million worth of repair works to the roading network

o $112 million in insurance claims

o $300 million worth of damage to the regional economy.

Erosion removes grass and topsoil which affects farmers' productivity, silt build-up in rivers causes them to overflow and slips often impede access to critical farm areas.

Further flooding in July of this year caused widespread damage to hill country around Palmerston North and Wanganui, serving as a reminder of the priority of protecting land from flood damage. In some parts of the region, the extent of erosion was even greater than in 2004. Because this was a winter rather than summer flood, the implications are particularly serious with lambing just around the corner.

Horizons Regional Council is now seeking up to $40 million from Government over the next 10 years, as a contribution to its $90 million Sustainable Land Use Initiative.

The Sustainable Land Use Initiative, an overview

Horizons Sustainable Land Use Initiative (SLUI) takes a non-regulatory whole farm approach to improving the resilience of the regions landscape to extreme weather. Whole farm plans have been drawn up for 14 properties, with those located on highly erodible land targeted first.

Erosion control is a prime focus of these plans but nutrient management, water quality and biodiversity is also addressed.

Tools for protecting land from soil erosion range from care with cultivation to developing forestry plantations or shutting up areas for regeneration. Plans include a one-year operational plan and five-year strategic plan.

Horizons has set a target of half the regions most at-risk farms operating under a whole farm plan by 2015.

Hazelhurst Hills

Tony and Lynda Grays 620 hectare property, Hazelhurst Hills, is working towards meeting goals set out in a SLUI farm plan. With areas to be taken out of livestock production, the aim is to better use remaining areas to protect income. Inputs such as fertiliser will be concentrated on areas where they will achieve the best return on money spent.

The Grays purchased the property just prior to the 2004 floods and settled just afterwards, with 2% of the property still scarred by slips including part of a 65 hectare QEII covenant in native bush.

Stock units are around 50% sheep and 50% cattle and deer.

In February 2004, there were eight slips across the road between the house and woolshed.

This has been a wet winter, with areas of the property having slumped with cracks opening up in the July floods.

Matching land type to use

A key to the Farm Plans is matching land type to use, says FarmVision consultant Lachie Grant who has worked with the Grays on drawing up their SLUI farm plan.

A farmer cant optimise his farming business without an understanding of his land resources, the strengths and limitations and how they respond under different conditions.

A first step to drawing up a farm plan for Lachie is identifying soil types. A lot can be learned by digging holes, with land not always what it seems on the surface.

Managed retirement

Farmers in the region accept that there are areas where they might not be able to keep running livestock, says Lachie. Many have already been retired from grazing in the past, as at the Grays where around 40 hectares of regenerating scrub fenced off by past owners will be left untouched, with Tonys original plans to clear some of this area put aside.

The scrub provides useful shelter post winter shearing, and will eventually close up and return to bush, Tony acknowledges. Ive observed that where theres scrub cover, theres virtually no erosion.

The farm also has a 65 hectare block of native bush, under a conservation covenant to the QEII Trust.


When looking at options for Hazelhurst Hills most erosion-prone country, Lachie talks about a change of land use rather than retirement.

The beauty of forestry for protecting against soil erosion is that the roots of old trees take six or seven years post-harvest to break down, says Lachie. Providing the block is re-planted immediately post-harvest, young tree roots will then take over their role of holding the soil together.

Tree type should be matched with land type, says Tony. Cypress species and macrocarpa for example, could be planted in shady areas, redwoods on alluvial sites and pines on drier areas. On some sites, regenerating native scrub can be used as a nurse crop for high value timber species like blackwoods or native totara and rimu, for example.

Tony and Lynda are planning to plant not only pines but also lusitanica and leyland cypress and macrocarpa, having been advised that these will be able to be milled for useable timber any time between 20 and 70 years versus around 20 years for pines.

But what of soil effects when the block is harvested?

It is important to plan ahead to minimise the environmental impacts of harvesting, says Lachie. Care needs to be taken when building tracks and in stormwater systems to channel run-off where it will not do any damage.

Soil conservation planting

The planting of poplar poles is an option to stabilise areas of active erosion, especially to protect infrastructure such as fences, tracks and buildings.

This is a way of future-proofing our investment.

Last year the Grays planted poplars above a main track, to protect it from slips. They now have 300 poles ready for planting, purchased from Horizons with 30% of their reclaimed as an environment grant, once they are in the ground.

The remaining 70% of this and other farm plan flood-proofing costs come out of income, which hasnt been substantial of late.

The poles are planted 10 to 12 metres apart, in and around gully systems and on areas that are actively eroding.

Mid slope tracking is a major cause of soil sip erosion in the Horizons district, magnified where tracks have inadequate storm water drainage. In some areas, slipping has resulted from pasture lacing the rooting density to hold soil on steep terrain.

Willow removal

Forty to fifty years ago, a 300 to 400 metre wide strip of willows was planted along a creek at Hazelhurst Hills. These trees are now massive, and are blocking the stream when branches fall off and form dams.

In December, when the willows are leafed up, they will be sprayed then removed with a digger. The waterway will be fenced and planted in more appropriate species.