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Soil conservation survey of the Matahuru catchment


Report: TR05/39

Author: Dr Douglas Hicks


These notes summarise the results of a survey carried out in May 2005 at the request of Environment Waikato. The survey’s purpose is to ascertain extent of vegetative soil conservation cover in the Matahuru catchment, and measure what reductions have accrued from them. This information is required for a 5-year review of soil conservation in the Lower Waikato sub-catchments.

The Matahuru has been selected by Environment Waikato staff because they regard it as typical of the Lower Waikato sub-catchments in its terrain, land use, and soil conservation measures. It is 97 square kilometres in extent, draining west and south from the Hapuakohe range, then turning north-west to enter Lake Whangape. The headwaters are steep greywacke hill country. Middle reaches are easier greywacke hills, partly mantled by volcanic ash, separated by a broad valley floor of rolling ash-mantled downlands and flat alluvial terraces. Lower reaches flow along a narrow floodway, excavated through an undulating divide between the Hamilton and Huntly lowlands.

The survey brief is to :

Identify how much land needs soil conservation,

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.

Doing this does not entail mapping exact locations and types of measure on all land in the Matahuru - to do so would take a great deal of time - rather, to obtain reliable summary measurements for the catchment from 2002 aerial photographs. These should be in a format consistent with previous identification of target land for soil conservation (Project Watershed 2001), and comparable with an earlier survey from 1992 aerial photographs.

Soil Conservation Survey of the Matahuru Catchment [PDF, 87 KB]

Acknowledgments i
Introduction 1
Method 1
Results 2
Changes in the catchment between 1992 and 2002 12
Soil stability 12
Need for conservation measures 12
Extent of measures 12
Adequacy of measures 13
Erosion under different types of conservation measure 13
Erosion under different standards of conservation measure 14
Soil disturbance by land use 14
Conclusions 14
References 17
Glossary 19