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Restoration of Ohinemuri River ]

The bird call heard on this page: Tui

The restoration of the Ohinemuri River provides an opportunity to bring back some of the nature of a place whilst also improving water quality. The corridor of a stream provides links for people, as well as links for nature, making the Ohinemuri River an ideal backbone in the creation of a network of walks linking attractions and areas of interest within Waihi and its environs.

Proposed design guidelines

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Always seek to imitate nature, natural patterns and processes.

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Reinstate natural stream or river processes and patterns, i.e. meandering, gentle banks and wetlands, as far as is practical, to allow the stream to function as nature intended.

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Take full advantage of the natural features that currently exist, i.e. gorge like river habitat in the Mill Stream Walkway, existing Totara groves, past mining remnants.

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Return "life" to waterways by encouraging and re-establishing some local indigenous flora and fauna patterns, processes and connections.

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Remove potentially invasive exotic and non-local vegetation.

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Future plans could involve the expansion of river plantings to link up with remnant native vegetation, to enhance the habitat value and diversity of the stream corridor.

The major impacts that were seen as an ecological threat to the Ohinemuri River were erosion and flood damage, working together the result is severe habitat degradation. Traditionally the method for removing storm water etc has been to remove it as quickly as possible. The direct entry of storm water into the river and an increase in the development of hard surfaces (guttering, roads etc) has led to an increase in the magnitude of flood events. The magnitude of flood events can be reduced by:

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The creation of back waters, pools and wetlands, these hold water in the system for longer after wet weather, slowly releasing water back into the stream, keeping river levels at a more constant level during summer and winter. Wetlands are also the richest habitat in a waterway.

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Restoring riparian vegetation, which helps to reduce floodwater velocities by impeding river flow, it is imperative for flood flow retardation that a dense close ground cover is maintained. Also by absorbing excess water during wet weather preventing surface run off and further erosion.

A reduction in riparian vegetation as a result of stock browsing right to the water edge is the main factor contributing to the increase in soil erosion, especially along Riverbank Terrace. Erosion can be reduced by:

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Restoring riparian vegetation, which softens the impact of rain on the soil structure, plant root systems help in stabilising banks.

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Vegetation also prevents sedimentation by having a filtering effect on runoff entering the stream.

Proposed planting guidelines

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Plant densely for total dense cover and good weed suppression low cover plants (sedges, rushes etc) at about half metre spacings (4 per. sq. m.); shrubs at about 1 metre spacings (1 per. sq. m.); small growing trees at 2-5m spacings; and large trees at 6-1O m spacings, with shrub and lower cover species massed between.

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Plantings should be done in sections that are undertaken and maintained separately. Do not try to cover an area too large for the available resources, it is better to have a small area done well than a large area that is sparsely planted and weed-ridden.

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Identify the different types of sites along the stream, the wetter and the drier sites, sites often and sometimes flooded, the north facing slopes and the south facing.

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Plant drier sites in late winter when the threat of flood damage no longer exists, very wet sites e.g. wetlands, river bed to be planted in summer, plant right into the river bed with the native rushes and sedges (Zone 2) that naturally belong, i.e. locally sourced plants.

Carefully phase out non-local cover and re-establish native plants. However make use of existing exotic and non-local vegetation that may be beneficial to wildlife, and may provide shelter for re-establishing local native plants during a transition period.

Back swamps

Back swamps or wetlands are created by damming drains, ditches and any sources of water that flow into the river during rain, and allowing the water to follow the contours of the riverbank, residing in any low points and seeping slowly into the river. Thus reducing flood/drought magnitudes and filtering out sediments and harmful pollutants. At points where the walkway needs to cross these wetlands some minor earthworks may be needed to restrict the wet area into a culvert, and raise the walkway above the natural water level of the wetland, excess soil created when scooping out wetlands can be used here. Once the natural wet areas form plantings of native sedges and rushes can be undertaken, this further increases water-holding capabilities of the wet area and filters out pollutants, nutrients etc.

Our thanks to Derek Hayes for this material.

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Waihi District Walkways Inc. PO Box 241 Waihi New Zealand

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