Abstract

Waikato Regional Council commissioned a survey to assess soil intactness (soil disturbance and bare soil) in the Waikato region using a point sampling assessment of aerial photographs flown in 2002.

The survey and a final report were completed by September 2003. In August 2005 additional analysis of bare ground was carried out using an improved cluster sampling technique. The survey developed an innovative method to interpret orthophotos (aerial photographs rectified to fit a map grid) on-screen using a Geographic Information System (GIS) with direct entry of data to a GIS-linked database.

The survey estimates soil disturbance and bare soil from land use activities and natural erosion processes across the region. Additionally, measures of bare soil under naturally occurring and planted primary and secondary vegetation cover (including soil conservation) indicate land use pressures and responses to soil intactness.

The point sample is sufficiently representative to draw conclusions about soil intactness/disturbance region wide, for land uses within the region and for large subdivisions of the region such as districts. An additional analysis has been carried out for the Coromandel catchment management zone. This has enabled a procedure to be worked out for future sub-regional analyses. The results furnish some useful examples of what can be extracted from such surveys.

Soil Intactness Assessment of the Waikato Region: 2003 [PDF, 248 KB]

Contents
Acknowledgements		i
Executive summary		iii
1	Introduction	11
1.1	Background	11
1.2	Brief	11
1.3	Survey design	12
1.4	What has been recorded	13
1.5	Data storage, statistical analysis and data presentation	16
1.6	Survey concepts	17
2	Survey results - soil intactness and disturbance	19
3	Survey results - land use impacts on soil	19
4	Survey results - secondary vegetation	26
5	Survey results - vegetative soil conservation measures	32
6	Conclusions about state of the Waikato's soil	39
Technical conclusions about survey method		44
	Use of orthophotos	44
	Representativeness of results	44
	Photo-interpretation error	45
	Calibration of data for sample point size and cluster analysis of bare soil	45
	Procedure for extracting regional subsets	45
References		47
Appendix I: Field check of randomly selected sample points		49
	Type of disturbance	50
	Landform	50
	Overall comments on photo-interpretation error	50
Appendix II: Calibration of data for sample point size		52
Appendix III: Cluster analysis of fresh soil disturbance under various soil conservation covers		56
Appendix IV: Procedure for extracting regional sub-sets		59

Soil intactness assessment of the Waikato region: 2003

Abstract