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  Services » Publications » Technical Reports » tr200515

Soil conservation survey of the Pokaiwhenua catchment

 

Report: TR05/15
Author: Dr Douglas Hicks

Abstract

These notes summarise the results of a survey carried out in January 2005 at the request of Environment Waikato. The survey's purpose is to ascertain extent of vegetative soil conservation cover in the Pokaiwhenua catchment, and measure what changes in the percentage of bare ground have accrued from them. This information is required for a 5-year review of soil conservation's costs and benefits in the Middle Waikato sub-catchments.

The Pokaiwhenua has been selected by Environment Waikato staff because they regard it as typical of land in the Middle Waikato sub-catchments in terms of terrain, land use, and types of soil conservation measure. It is approximately 472 square kilometres in extent, draining westward from the Mamaku plateau past Tokoroa and entering the Waikato at Lake Arapuni. The headwaters are a high plateau of ignimbrite, dissected into narrow steep-sided gorges where streams descend its edge. Middle reaches are an undulating ignimbrite plateau mantled by pumice and ash. Lower reaches are moderately steep hill country; ignimbrite with patchy ash cover on slopes, and terraces of waterlaid pumiceous alluvium in valley bottoms.

Environment Waikato wishes to:

  • Identify how much land needs soil conservation in the Pokaiwhenua catchment,
  • Ascertain whether such land has vegetative soil conservation measures. These may be spaced tree plantings in pasture, close afforestation with commercial tree species, or natural vegetation (retained, reverting or planted),
  • Obtain measurements of any changes in soil erosion or disturbance where vegetative soil conservation measures are present.

Its brief does not entail mapping exact locations and types of measure on all land in the Pokaiwhenua - to do so would take a great deal of time - rather, to obtain reliable summary measurements for the catchment from 2002 and 1992 aerial photographs. These notes summarise the results of a survey carried out in January 2005 at the request of Environment Waikato. The survey's purpose is to ascertain extent of vegetative soil conservation cover in the Pokaiwhenua catchment, and measure what changes in the percentage of bare ground have accrued from them. This information is required for a 5-year review of soil conservation's costs and benefits in the Middle Waikato sub-catchments.

Soil Conservation Survey of the Pokaiwhenua Catchment
(139 kb, 19 seconds to download, 56k modem)

Table of Contents

Acknowledgements I
Introduction 1
1 Method 1
2 Results 2
  2.1 Landform stability 2
  2.2 Need for conservation measures 4
  2.3 Extent of Measures 7
  2.4 Soil disturbance under different standards of conservation measure 10
  2.5 Changes in soil erosion/disturbance between 1992 and 2002 14
  2.6 Comparison of Project Watershed Estimates with Point Sample Data 15
3 Conclusions 17
References 18
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