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  Services » Publications » Technical reports - by year » tr200503

The effect on Waikato river water quality of changes to river flow and catchment land use, including the December addendum

Report: TR05/03
Author: Kit Rutherford (National Institute of Water & Atmospheric Research Ltd)

Abstract

Environment Waikato has requested NIWA to predict the likely effects on Waikato River water quality of:

1. reductions in the flow of the river at times of low flow; and

2. changes in nutrient loads to the river from dairy conversions;

by making use of an existing Waikato River water quality model (Rutherford et al. 2001). Results are provided in this report. Appendix 1 contains the contract details.

Originally 10 scenarios were detailed for modelling but subsequently an 11th scenario was requested (Appendix 2). Email correspondence to clarify assumptions made in these scenarios is attached (Appendix 2).

Subsequent to the presentation and acceptance of this report, EW requested that we run the model for 5 additional scenarios (cases 12-16). These are presented as an addendum in section 4.

The effect on Waikato River water quality of changes to river flow and catchment land use, including the December addendum
(989 kb, 141 seconds to download, 56k modem)

Table of Contents

1. Introduction 1
2. Methods 2
3. Results 3
3.1 Base case 3
3.2 Case 2: flows reduced by 10% 4
3.3 Case 3: flows reduced by 20% 6
3.4 Case 4: flows reduced by 30% 8
3.5 Case 5: nutrient inputs reduced by 10% 11
3.6 Case 6: nutrient inputs increased by 10% 13
3.7 Case 7: flows reduced by 10%, nutrient inputs reduced by 10% 15
3.8 Case 8: flows reduced by 10%, nutrient inputs increased by 10% 17
3.9 Case 9: 20,000 ha pines converted to dairy 19
3.10 Case 10: 40,000 ha pines converted to dairy 21
3.11 Case 11: 40,000 ha pines converted, 50% to dairy and 50% to mixed sheep/beef 23
4. Addendum 25
4.1 Introduction 25
4.2 Results 25
4.2.1 Case 12: 22,500 ha pines above Wharekaka converted to 10,000 ha dairy and 12,500 ha mixed sheep/beef 25
4.2.2 Case 13: 22,500 ha pines above Wharekaka converted to 10,000 ha dairy and 12,500 ha mixed sheep/beef PLUS 7,000 ha pines between Ohakuri and Maraetai converted to dairy PLUS 7,000 ha pines between Maraetai and Pokaiwhenua converted to dairy 28
4.2.3 Case 14: summer low flow with current land use 31
4.2.4 Case 15: 22,500 ha pines above Wharekaka converted to 10,000 ha dairy and 12,500 ha mixed sheep/beef. Summer low flow. 34
4.2.5 Case 16: 22,500 ha pines above Wharekaka converted to 10,000 ha dairy and 12,500 ha mixed sheep/beef PLUS 7,000 ha pines between Ohakuri and Maraetai converted to dairy PLUS 7,000 ha pines between Maraetai and Pokaiwhenua converted to dairy. Summer low flow. 37
5. References 40
6. Appendix 1 41
7. Appendix 2 43
8. Appendix 3 45
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