Ministry considers Lower Rakaia ‘unattractive’

Press, 25 October 1984, Page 6

Ministry considers Lower Rakaia ‘unattractive’

The Lower Rakaia River was considered “unattractive” by people surveyed by a Ministry of Works and Development hydrologist, the Planning Tribunal heard vesterdav. Dr M. P. Mosley, the leader of the environmental hydrology group at the Ministry’s hydrology centre, at Christchurch, was one of three Ministry witnesses to give evidence at the hearing of appeals against the Rakaia River draft conservation order yesterday. Dr Mosley said that he had recently conducted a survey of 315 people from 14 groups about their preferences for river scenery. The results showed that the wide, open bed of the Lower Rakaia was considered “unattractive." Some parts of the river, such as the Rakaia Gorge, were regarded as better than average. while others like the

wide, upper valley were considered less attractive than average. The headwaters were regarded as scenically attractive, but markedly less so than other mountain scenDr Mosley presented submissions on the physical characteristicss of the river and made some predictions about how the river might change in response to changing river discharge. He said studies showed that increases in discharge were accompanied by increases in depth and velocity, minimum passage depth, water surface width and cross sectional area, and areas of riffle, run and pool habitat types. Other factors appeared.to be independent of the river discharge. These included an index of potential fish habitat, the character of the riverbed sediment, and the

percentage of total flow in the three largest channels. He said the relationship between the number of branch channels and discharge was uncertain. Dr H. R. Thorpe, the leader of the ground water group at the Hydrology Centre, gave evidence about a study of the groundwater resource between the Ashburton River and Rakaia River. He said there was sufficient groundwater for a major expansion of irrigation, but conceded that the chances of successful wells became less further from the coast and rivers. This factor, combined with the greater costs of digging deeper wells and lifting water further in these areas, would be the constraints on development, he said. Dr E. M. Valentine, one of two Ministry scientists who

have begun a study of the stability of the Rakaia River, mouth, told the tribunal that it was unlikely that the river outlet would ever close, but even if a combination of low flows and high seas led to this he believed it would only be for a period of less than a few hours while the lagoon level rose sufficiently to over-top and breach the berm. On April 12 and July 3 this year there were reports that the Rakaia Mouth was closed. Dr Valentine said that while one outlet did close on April 12, a second outlet was open. Although an outlet closed again on July 3, he believed another opened simultaneously or shortly afterwards. The hearing, before Judge Skelton (chairman), Mrs N. J. Johnston, and Messrs H. M. Dodd and R. A. McLennan, will continue today.