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Contents of Botany Assessment Section
PROPOSED PARAPARA RIVER HYDRO SCHEME
A Report on the Vegetation

Dr Philip Simpson

Uruwhenua Botanicals
Pohara. July, 2003

1. INTRODUCTION

1.1 The location of the site and its general features.

The site is located on the lower reach of the Parapara River and a minor tributary, Glen Gyle Creek. All is Conservation land but none is included in the Kahurangi National Park. It ranges in elevation from 40m a.s.l., at the junction of these two streams, to about 180m at Richmond Flat just above the Parapara River Gorge. Much of the Parapara River catchment drains the steepWestern slopes of Parapara Peak (1252m) composed of old siltstone and quartz (Ordovician/Silurian, aged about 400 my). The site is located mainly within a tilted block (a peneplain) of schist into which the streams have cut steep valleys and gorges. The two geological systems interfold via faultlines. The streambed of Glen Gyle Creek contains boulders of white quartz, grey siltstone and reddish iron-stone, the last formed in situ. The quartz parent material contains gold and silver, which attracted locally intense mining activity during the late 19th and early 20th centuries. These old rocks are coated in places by much younger (Pleistocene) outwash gravels, weathered to a red-brown, clay soil.

The rainfall is high, about 2400mm per year, and the area is located below a locally extremely wet mountain area centred on Parapara Peak (5500mm). This means that the rivers and streams can flow very high during heavy rain. It also means that soil leaching is characteristic, leading to low fertility once the original protective forest is removed, resulting in large areas of 'pakihi': regenerating shrubland dominated by acid tolerant species. On the other hand, the high rainfall also means that in more fertile areas, regeneration of forest is a rapid process. Owing to surrounding farming, and mining, fires have cleared most of the lower slopes, leaving patches of original beech/podocarp bush in the gullies and widespread bush on the upper slopes. The strong coastal influence from the north results in a zone of lowland vegetation at the downstream end of the site.

The site can be entered from two directions. The lower part is approached from Parapara Road, which ends in an area of private dwellings, beyond which an informal track leads up the valley towards the confluence of the Glen Gyle Creek. The upper part of the site is approached via Plain Road, the left branch of which crosses farmland at Appos Flat, then rises steeply through pakihi to the ridge above Glen Gyle Creek. A former access road then descends to Richmond Flat.

Richmond Flat is a very distinctive landform. The river forms a wide meander across a former basin in-filled by alluvium above the entrance to the Parapara River Gorge. The basin appears to have been formed by the confluence of several fault-lines and the exposure of an outcrop of hard Waingaro schist forming the gorge immediately downstream. The entrance to the gorge was dammed by the Parapara Hydraulic Sluicing Co. about 1900 and the resulting lake water was diverted into a race that led to a pipeline through old alluvium

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