Baxter’s Bush is at risk in drains row

Press, 28 March 1979, Page 21

Baxter’s Bush is at risk in drains row

By

STAN DARLING

No matter who wins the persistent Mount Pleasant drainage wrangle, an unusual stand of native bush will still be the loser if a better way of guiding stormwater is not found. Natural erosion in the steep gully — planted earlier this century in a profusion of native plants from both islands -— has been speeded up by residential and road developments around it. But complaints about the damage would have been fewer and less justified if the gully had been acquired as a public reserve years ago. There would ~ have been no homes to be threatened by the sudden, high-velocity runoffs now coursing downhill. Unfortunately, the former native plant nursery was divided up. Rights-of-way were created, houses were built on the slopes,

and driveways were laid in switchbacks down the hillside. From then on, the “gentle stream’’ was headed for trouble. Land further up the hill had also been developed, or was available for development. It was a classic case of water flowing faster and easier off sealed roads and the roofs of houses. The natural way for water to leave the hill was down the gully, and it was only natural for a drainage system to make it easy for the water to get there. Unless the natural

drainage gully had been blocked off or piped, it never had a chance. The dn-again, off-again stream was destined for bigger things even if no building had been allowed below the road. Houses placed near it meant that a rowdier future during storms would lead to bigger headaches for people living there. Hill dwellers take risks. One issue in the long legal battle is whether local bodies or the homeowners themselves have the financial responsibility to provide protection against inevitable changes in stormwater flows. Far homeowners in the bush gully, the inevitable has happend more than once since 1970, when Mount Pleasant Road was widened and a stormwater culvert at the head of the gully was replaced with a bigger one. More water than in previous years has come through the culvert, coursed through the bush and gouged out the stream channel. Tree roots and even a sewer pipe have been exposed by the rough water. Perhaps the worst problems — the ones emphasising the dangers of hillside building — came dun ing the April, 1974 storm. Flood water tore away part of a private drive, and sandbags had to be placed across the drive to divert water away from a home further down. Vehicle access to that house was cut off for months after the storm. Even today, the driveway across the gully shows signs of breaking up in places. Hillside housing problems were virtually unknown in the 19205, when Mr John Matthew Baxter started planting native seeds on the tussock slopes. The entire area, more

than two acres, was handgrubbed after the nurseryman found that digging separate holes in the tussock did not work very well. His son, Mr Hugh Baxter, remembers that water in the holes seeped down and the ground dried out. Cultivation was the only answer. Mr Baxter brought thousands of plants to the hillside, collected from most parts of the South Island and many places in the North Island. He supplied his Tawhai Native Nursery in Papanui Road with plants grown on Mount Pleasant.

Many plants were sent overseas, and London’s Kew Gardens got some of them.

Mr Lance McCaskill, the Christchurch naturalist, helped collect and plant some of the bush after trips with Mr Baxter to the high country. “It was one of the finest native gardens ever made in New Zealand,” he said. One of the bush features was a fernery built at the gully bottom, with an archway and stone wall across the front of it. Remnants of that fernery are still there. Mr McCaskill remembers it as having "a trickle of a stream running through it, a wee stream that did nothing like it does now.” The archway’s keystone was brought back by the two men from one of their plant gathering trips in the foothills. It used to be in an old fireplace at the foot of Porter’s Pass, where there was a horseholding stable on the West Coast route. Mr McCaskill thinks it is a shame that the bush was not protected after Mr Baxter sold it. “In the old days, the water was all dissipated,” he said. “But when you seal things and gutter them, the water flows at a terrific rate.” He said the bush gully was a natural place for a park, where water would be a fact of life and man would simply stay away when it was running in flood. Much of the original bush is still there, although mostly in dominant plants that held sway when it was no longer looked after as a nursery. Mr McCaskill said the slopes had “many thousands” of ferns, shrubs and trees in their heyday, a perfect example of how even a dry and rocky hillside could be transformed into a native bush that

seemed to belong there. He said Mr Baxter knev the exact age of hit plants. In some places, he had planted after trenching two or three feet down.

Even the uncultivated areas produced well. In 1940, after the bush had been going about 13 years, Mr McCaskill made a tour of it to measure some of the trees. In an uncultivated part, there were kowhai at 18ft, tainui at 17ft, black beech at 24ft and red beech at 16ft. There were also black pine, mountain beech, silver beech, white pine, toothed lancewood, totara, broadleaf, ake ake, lemonwood, ribbonwood, ngaio and cabbage trees among the profusion. A ngaio hedge had been planted along one boundary, and it is still distinctive today from Soleares Avenue, across, the Valley. Mr Baxter made special provisions for bird life, and some made the bush their year-round sanctuary. Flax fuchsia, kowhai and ivy trees were planted to provide nectar. Poroporo, broadleaf, coprosmas and others had berries. Near the fernery were other attractions, a bird bath and drinking trough. The growth canopy provided by South Island native trees protected North Island pohutukawa, puriri, kauri, kohekohe, pukatea and other plants. As long as the drainage deadlock continues, the remaining bush will remain at the mercy of man’s developments up the hill. Testimony given to a 1973 court hearing on the issue said that homeowners near the gully’s head bought their property in 1970, when the lowflow stream channel was no more than a foot deep in places, and from a foot to 18in wide. They said there were no signs of water flows outside the channel.

By 1973, some pools along the channel were more than three feet deep from scouring, even though a concrete base with velocity obstructions had been placed below the large culvert. The court opinion was that there had been a small, insignificant increase in the gully’s stormwater catchment area, but a definite increase in water velocity from the road culvert. If the smaller culvert had not been replaced, the court said, the channel was not likely to have been eroded.

But the court added that property owners who deepened the channel themselves to ward off flooding problems could also have contributed to the erosion.