Sediment and River Care

April 2022

Horizons Regional Council’s sediment control initiative.

With more than 20 percent of New Zealand’s most erodible land in the Horizons region, a sediment control initiative is helping to keep valuable topsoil in the hill country, and out of the gullies and waterways. It is a voluntary scheme created by Horizons Regional Council, and so far 84 percent of the region’s hill country farmers are participating in it. 


Hill country farmers Justin and Mary Vennell are enthusiastic champions of the sediment control initiative set up by Horizons Regional Council following the devastating flooding of the Manawatu-Whanganui region back in February 2004. 


Immediately, they saw the council’s logic. Today, after some 15 years of retiring areas of native vegetation, fencing off streams to keep out stock and riparian planting on their farm near Hunterville, they believe the council’s Sustainable Land Use Initiative (SLUI) is the way to go for the entire country.


With 20-plus percent of New Zealand’s most erodible land in the Horizons region, the council’s intent with this forward-thinking programme was – and continues to be – to manage the land sustainably by keeping topsoil in the hills and out of the gullies and waterways. The aim was by doing this, to allow sufficient river channel capacity to cope with flooding events, while also enhancing water quality and increasing productivity on the land. 


The Vennells, fifth generation farmers on their 513 hectares, are amongst the 800 landowners involved in SLUI to date – about 84 percent of the farmers/landowners in the Horizons region who have whole farm plans in place, covering a total of some 600,000 hectares of highly erodible land.    


Justin first learnt of SLUI at a Beef + Lamb New Zealand monitor farm field day and says he saw the benefits right away, even as some of his fellow farmers were hesitant to invite the council onto their land as they were concerned about what they may be forced to do.


“The programme is completely voluntary though, and this is part of the reason why there has been such great uptake over the years,” he says. “Horizons is great to work with and never have any of our works been forced on us. We have been given the advice, both from the council and other sources, as well as the tools and resources to get the job done. It feels like a partnership.”


He believes the voluntary SLUI model is one that should be implemented nationwide to improve natural resources and the environment.


The Vennells graze approximately 400 hectares, running 1,700 ewes, 700 hoggets, 500 lambs and 100 beef cows. Their remaining land comprises 77 hectares of forestry, making for an alternative source of farm income in the future, plus native plantings; the remaining 36 hectares have been retired and include a large wetland area.  


SLUI-related work carried out over the years covers 130 hectares of the farm with the retirement of gullies, fencing off and planting Mangapipi Stream, which runs through the farm feeding into Rangitikei River, as well as afforestation and poplar planting to help stabilise hillsides. Nearly 60,000 trees have been planted and 11 kms of fencing constructed.


The Vennells were the supreme winners of the Ballance Farm Environment awards in the Horizons region in 2014 and Justin is a member of the SLUI Advisory Board, which includes farmers plus representatives of Horizons, the Ministry for Primary Industries and AgResearch.


Horizons land management advisor Brad Beatson says their farm is now much more resilient to weather extremes thanks to the work carried out.  “Through their whole farm plan all areas of their land have been identified, analysed and are now utilised to their full potential,” he says. “General day-to-day farming has been streamlined with areas that were difficult to muster now retired. Livestock have shade in most paddocks. Biodiversity has noticeably improved with many more native birds now seen – and greenhouse gas emissions have been greatly reduced. In all, the Vennells’ farm is now well set up going forward with them having already made good progress towards the changes central Government regulation will soon require.”


Horizons measures and monitors water quality in the region, tracking reductions in sediment levels, with the results informing what actions are prioritised in the SLUI programme.


Scientists at Horizons, with colleagues at Manaaki Whenua (Landcare Research), are working to estimate the amount of sand, silt and soil prevented from entering the waterways in the region from the implementation of the SLUI programme farm plans to date. This work will be complete by mid-2022.


While targets for annual sediment control works have been exceeded for the past decade, Horizons says the region’s rivers and streams are still carrying too much, and the council is now working alongside landowners to bring the remaining 16 percent – some 400,000 hectares – of the region’s highly erodible land into the SLUI programme. 


Water quality scientist Maree Patterson says too much sediment in a waterway not only discolours the water and carries a higher risk of illness for humans, but also impacts aquatic life smothering their habitats and making it difficult for seeing and feeding. “In the Horizons region, sediment build up in our rivers and streams also affects the ability of stopbanks to contain bigger flood events, which, of course, impacts land uses and our communities downstream.


“Given the scale of hill country in our region, we need to expand the reach of the SLUI programme to not only enhance water quality, but also maintain the flood carrying capacity of our rivers.” 


Horizons’ SLUI programme is funded by MPI’s Hill Country Erosion Fund, Horizons Regional Council rates and farmer/landowner investment. Total spend since the programme’s inception in 2006 is $57 million, of which $33 million has been fronted by farmers/landowners. SLUI is the largest hill country erosion programme in New Zealand.


For more information: Horizons Regional Council - Land