The potential for debris flows from Karaka stream at Thames, Coromandel
Report: TR06/17
Authors: M.J. McSaveney and R.D. Beetham - Institute of Geological and Nuclear Sciences Limited (GNS Science)
Abstract
As part of the resource consent process for the new development proposed at Thames Hospital, Environment Waikato were concerned, given the recent Matata event, about the potential for debris flows to occur within the Karaka Stream catchment that could affect the hospital building and adjacent properties.
To address these concerns, it was agreed with the Waikato District Health Board and the Thames Coromandel District Council that a report be commissioned from Geological and Nuclear Sciences Limited (GNS) to investigate the hazard further. You can download a full copy of this report below.
The Potential for Debris Flows from Karaka Stream at Thames, Coromandel
(789 kb, 112 seconds to download, 56k modem)
Table of Contents
| Executive summary |
III |
| 1.0 Introduction |
1 |
| 1.1 Purpose and scope of the report |
3 |
| 1.2 The brief |
3 |
| 1.3 Terminology used |
4 |
| 1.4 Debris flows and lahars |
10 |
| 1.5 Relevant terms in New Zealand statutes |
10 |
| 1.6 Relevant New Zealand standards for structures (AS/NZS 1170.0:2002) |
12 |
| 2.0 Assessment of catchments and processes contributing to debris flows |
13 |
| 2.1 Geology |
13 |
| 2.1.1 Mantling deposits around Thames |
13 |
| 2.1.2 Kuaotuna formation |
13 |
| 2.1.3 Waiwawa formation |
13 |
| 2.1.4 Fans and stream deposits |
16 |
| 2.1.5 Anthropic deposits |
16 |
| 2.1.6 Source of the boulders |
16 |
| 2.1.7 Faulting in the Karaka Stream catchment |
16 |
| 2.1.8 Regional faulting and earthquakes |
16 |
| 2.2 Geomorphology of Karaka Stream |
17 |
| 2.3 Other streams at Thames |
18 |
| 2.4 Effects of geology on headwater slope stability |
19 |
| 2.5 Storm rainfalls |
19 |
| 2.6 Land cover and effect of vegetation on stability and erosion potential |
19 |
| 2.7 Sediment transport processes active during big storms |
20 |
| 2.8 Debris flows caused by damming of streams |
21 |
| 2.9 Channel erosion |
22 |
| 2.10 Previous debris flows, and debris-flow recurrence interval at Thames |
22 |
| 3.0 Quantity of solid material and debris likely to be delivered from Karaka catchment |
25 |
| 4.0 Likely response to future hydrological events |
26 |
| 4.1 In the immediate term |
26 |
| 4.2 In the short term (up to 10 years) |
26 |
| 4.3 In the long term (up to 1,000 years and beyond) |
26 |
| 5.0 Areas at risk from debris flows and debris floods from Karaka Stream |
27 |
| 6.0 Options to mitigate risk and minimise the area affected by future debris flows |
30 |
| 6.1 Regional and local warning systems |
31 |
| 6.2 Mitigation options at Karaka Stream |
32 |
| 7.0 Conclusions |
34 |
| 8.0 Recommendations |
35 |
| 9.0 Acknowledgments |
36 |
| 10.0 References |
37 |