Recovery after the February 2004 Manawatu floods
Alistair and Bo Polson and Donald and Liz Polson, are the Waipuna Farm Partnership, with 4000ha hill country sheep and beef farm, a sheep stud and 4ha of kiwifruit in the Mangamahu Valley near Wanganui.
In February 2004, a once in a 200 year flood came down the Whangaehu and Mangawhero rivers, which meet near the Polsons large hill country farm. The river level rose 13 metres, 4 metres above the river flats and an estimated one million tonnes of silt was deposited on the farm. About 200ha of river flats had up to one metre of silt.
Damage was immense and included:
3500 trading sheep (lambs) lost
Estimated 180ha of hillside slips
Between 40-50km of fencing severely damaged.
Alistair and Bo Polsons historic homestead lost
Don and farm worker, Blair Gibson, trapped in a tree above floodwaters for a full day before being rescued by helicopter.
A jet boat and a heading dog lost.
A one year plan of reconstruction was drawn up within days of the flood, although Alistair and Bo were living in a Wanganui motel. That programme has nearly come to an end, 12 months later.
Reconstruction work has been needed on the flats, hills and orchard. More than 200ha of flat country was resown during the past year, much of it twice.
Where a paddock was half covered with silt, the whole paddock had to be sprayed out and sown. The first pass was with ryegrass and clover by helicopter only one week after the flood, with whatever seed could be rustled up from seed stores around the region. It went on with 150kgs/ha of DAP and was followed up with 80kg/ha nitrogen every four to five weeks. A very good strike resulted and the Polsons had healthy pastures throughout the winter. However the fertility of the soil was still low (pH 5.7, about 7 Olsen P) and more quality feed was needed for the greater number of lambs born last spring. The Waipuna Partnership had 35,000 lambs, up 6000 on the previous year, because of higher fecundity in ewes and good mating and lambing seasons.
Where the silt coverage was shallower, and deep ploughing could bring up black soil, cover crops were established in November, mainly pasja, which was fertilised with 550kg/ha of Ammophos mix (46 N/ha, 92 P/ha , plus sulphur and calcium). This has been set stocked throughout summer and will now be sprayed out and resown to permanent pasture around the end of April.
Where the silt cover was deeper, the initial cover of grass was sprayed out again in spring and cultivated with a grubber, chisel plough, leveller and roller before being drilled with Samson ryegrass and Huia white clover as permanent pasture.
The flats were fenced into larger paddocks than before, with some reconfiguring and new metalled laneways. Up to four fencers have been employed at times, putting up 8-wire, 10 gauge, No 1 round and batten permanent fences. Some patches of silt are still wet, preventing work by machinery, and the Polsons have not run any cattle on the flats, because of the poor soil structure no porosity, no earthworms and possible compaction problems.
Up to $2000/ha has been spent on the reconstruction of the flats, $1500 of which will qualify for relief assistance, which all has to be finished by May 2005.
The more lightly covered flats, where black soil was brought up from below, will be every bit as productive as before the flood, Alistair believes. The deeper silt deposits are an unknown.
Some 200ha of slips on the hillsides were seeded with clover after the floods, against the official advice from MAF that such sowing would be useless. About 6 tonne of coated clover seed was flown on which, Alistair believes, was hugely successful because it was done in autumn, and therefore had several months of growing before onset of dry summer. About half of the slip areas are very serious, eroded down to clay, and the hill damage was exacerbated by further heavy rains in early spring. There is widespread damage to fences and access tracks also. Two diggers were in working within 10 days of the big storm and one machine has never left, continuously working.
The kiwifruit block was buried with up to one metre of silt on places. This all had to be dug out and dumped, because the weight of extra soil suffocates the roots. Initially it was thought that all vines would be saved, but now up to 40% have died and have to be replaced. This work is being carried out by the Polsons horticultural partners Tim Wells and his son Peter.
The river banks are still choked with willow and poplar debris, which must be dealt with before another major flood event. The debris is growing again, where it is above the normal waterline, which creates a massive tangle of undergrowth on the banks, and sometimes extends into the river. It has to be sprayed and then ripped out with a skidder, cut into lengths on the bank and stockpiled for burning in the future. Stumps have to be poisoned also and this work is being done by Taskforce Green teams.
In February 2004, a once in a 200 year flood came down the Whangaehu and Mangawhero rivers, which meet near the Polsons large hill country farm. The river level rose 13 metres, 4 metres above the river flats and an estimated one million tonnes of silt was deposited on the farm. About 200ha of river flats had up to one metre of silt.
Damage was immense and included:
3500 trading sheep (lambs) lost
Estimated 180ha of hillside slips
Between 40-50km of fencing severely damaged.
Alistair and Bo Polsons historic homestead lost
Don and farm worker, Blair Gibson, trapped in a tree above floodwaters for a full day before being rescued by helicopter.
A jet boat and a heading dog lost.
A one year plan of reconstruction was drawn up within days of the flood, although Alistair and Bo were living in a Wanganui motel. That programme has nearly come to an end, 12 months later.
Reconstruction work has been needed on the flats, hills and orchard. More than 200ha of flat country was resown during the past year, much of it twice.
Where a paddock was half covered with silt, the whole paddock had to be sprayed out and sown. The first pass was with ryegrass and clover by helicopter only one week after the flood, with whatever seed could be rustled up from seed stores around the region. It went on with 150kgs/ha of DAP and was followed up with 80kg/ha nitrogen every four to five weeks. A very good strike resulted and the Polsons had healthy pastures throughout the winter. However the fertility of the soil was still low (pH 5.7, about 7 Olsen P) and more quality feed was needed for the greater number of lambs born last spring. The Waipuna Partnership had 35,000 lambs, up 6000 on the previous year, because of higher fecundity in ewes and good mating and lambing seasons.
Where the silt coverage was shallower, and deep ploughing could bring up black soil, cover crops were established in November, mainly pasja, which was fertilised with 550kg/ha of Ammophos mix (46 N/ha, 92 P/ha , plus sulphur and calcium). This has been set stocked throughout summer and will now be sprayed out and resown to permanent pasture around the end of April.
Where the silt cover was deeper, the initial cover of grass was sprayed out again in spring and cultivated with a grubber, chisel plough, leveller and roller before being drilled with Samson ryegrass and Huia white clover as permanent pasture.
The flats were fenced into larger paddocks than before, with some reconfiguring and new metalled laneways. Up to four fencers have been employed at times, putting up 8-wire, 10 gauge, No 1 round and batten permanent fences. Some patches of silt are still wet, preventing work by machinery, and the Polsons have not run any cattle on the flats, because of the poor soil structure no porosity, no earthworms and possible compaction problems.
Up to $2000/ha has been spent on the reconstruction of the flats, $1500 of which will qualify for relief assistance, which all has to be finished by May 2005.
The more lightly covered flats, where black soil was brought up from below, will be every bit as productive as before the flood, Alistair believes. The deeper silt deposits are an unknown.
Some 200ha of slips on the hillsides were seeded with clover after the floods, against the official advice from MAF that such sowing would be useless. About 6 tonne of coated clover seed was flown on which, Alistair believes, was hugely successful because it was done in autumn, and therefore had several months of growing before onset of dry summer. About half of the slip areas are very serious, eroded down to clay, and the hill damage was exacerbated by further heavy rains in early spring. There is widespread damage to fences and access tracks also. Two diggers were in working within 10 days of the big storm and one machine has never left, continuously working.
The kiwifruit block was buried with up to one metre of silt on places. This all had to be dug out and dumped, because the weight of extra soil suffocates the roots. Initially it was thought that all vines would be saved, but now up to 40% have died and have to be replaced. This work is being carried out by the Polsons horticultural partners Tim Wells and his son Peter.
The river banks are still choked with willow and poplar debris, which must be dealt with before another major flood event. The debris is growing again, where it is above the normal waterline, which creates a massive tangle of undergrowth on the banks, and sometimes extends into the river. It has to be sprayed and then ripped out with a skidder, cut into lengths on the bank and stockpiled for burning in the future. Stumps have to be poisoned also and this work is being done by Taskforce Green teams.