Mohaka, Waikari and Waihua Rivers An inventory of current knowledge of natural resources within the Ngati Pahauwera Rohe July 2010 EMT 10/18 HBRC Plan No. 4200 Environmental Management Group Technical Report Environmental Science Mohaka, Waikari and Waihua River Catchments. An inventory of current knowledge of natural resources. Prepared by: Brett Stansfield Freshwater Scientist Reviewed by: Adam Uytendaal –Team Leader, Water Quality Graham Sevicke-Jones – Manager, Science Approved: Disclaimer: Whilst the Hawke‟s Bay Regional Council has made every attempt to ensure the accuracy and reliability of the information and data provided, it is the responsibility of the data user to make their decisions about the accuracy, currency, reliability and correctness of information provided. The Hawke‟s Bay Regional Council, its employees and agents, do not accept any liability for any damage caused by, or economic loss from, reliance on this information. July 2010 l EMT 10/18 HBRC Plan Number 4200 © Copyright: Hawke’s Bay Regional Council Page i EXECUTIVE SUMMARY The Crown by way of its letter to Ngati Pahauwera dated 20 August 2008 has offered a “good governance initiative which would involve a scoping study on the health of the Mohaka, Waihua and Waikari Rivers, and a fund to contribute to the implementation of recommendations from that study.” The purpose of this report is to provide an inventory of current knowledge of natural resources of the Mohaka, Waihua and Waikari Rivers that fall within the rohe of Ngati Pahauwera. To this end the geographical extent of the inventory includes the lower Mohaka River – the main stem and all tributaries from the Te Hoe catchment downstream, the Waihua and Waikari Rivers. Where appropriate the report also extends upstream to include the entire Mohaka River catchment. This scoping study comprises a multi disciplinary input from various personnel of the Hawke‟s Bay Regional Council and the Ngati Pahauwera Trust. After discussions and briefs received from the working party, the following gaps in knowledge have been identified. Water quality – Good records exist for the Mohaka main stem for Willowflat and Raupunga however no information exists for the Te Hoe River. Information for the Waihua River is largely historical and would need the recommencement of monitoring to be made more up to date. Ecology - Riparian vegetation extent has been examined in combination with surrounding land use categories to gain a general understanding of likely effects on water quality and ecology of the rivers. This analysis was based on the LCDB2 geographic information systems database (defined in more detail in the body of the report). The current LCDB2 database gave an accurate depiction of conditions up to 2004. A more recent version of the database is not available. Fish population data is stored in the New Zealand Freshwater Fish Database however this data predominantly provides presence/absence data only and would not be considered reliable in determining the health of fish populations. More extensive fish monitoring surveys would be required to determine the age structure of fish populations and assess their abundance and viability. Macroinvertebrate surveys need to be undertaken in the Waihua and Te Hoe catchments to gain a better understanding of ecosystem health of these catchments. Cultural values – the cultural health of the catchments is poorly understood. Methods to assess cultural health of the catchments are briefly discussed. There is a clear knowledge gap of these catchments with respect to cultural values. Hydrology – hydrological records for the catchments are sparse however two hydrology sites (Mohaka River at Raupunga and Tahekenui Stream at Glenstrae) are maintained by NIWA for which reliable river flow records are available. In order to have a good understanding of flows within the Mohaka, Waihua and Waikari River catchments, it is recommended that a further 3 permanent recorder sites be installed as well as a concurrent gauging programme to develop correlations with existing gauging stations. Rainfall runoff modelling would also help improve our understanding of the hydrological character of the catchment. Biosecurity – the Maungaharuru Ecological District has the greatest terrestrial ecology value of the rohe and this is where intensive animal and plant control is focused by DOC in the scenic reserves that are scattered amongst the Mohaka, Waihua and Waikari Catchments. Animal pest control by Regional Council is largely confined to possums for the protection of animal health from bovine tuberculosis. While this measure is effective in protecting animal health, it is not effective in protecting biodiversity. In terms of plant pest control there are only two locations that are targeted for control of old man‟s beard (Mohaka and Waikari Catchments). Areas where plant pest control is not occurring are also identified. Land use pressures – other than general classifications of land use (e.g. Pastoral farming, plantation forestry, indigenous forest etc) little is understood in terms of localised land use Page ii pressures. It is possible that there are areas within these catchments that are subject to differing stocking rates, sheep/beef ratios and forestry planting densities. This is a recognised knowledge gap. Land use maps are provided and high risk slip areas identified. Erosion control plans have been scant and not well documented. However GIS capabilities are outlined on what is achievable to increase our understanding of land use pressures on conservation, ecology and water quality values. Commercial tourism activities within the catchments are summarised to gain an understanding of other economic values besides farming. Geological influences – No specific earthquake information is held by Hawke‟s Bay Regional Council for these rivers however small scale geological maps show active fault traces crossing the rivers. The Ruahine and Mohaka faults are the major active faults of the region. Ground shaking and liquefaction hazards within the catchments are outlined. Tsunami risks along the coast are also commented upon. Page iii Contents EXECUTIVE SUMMARY .................................................................................................... II 1.0 INTRODUCTION ....................................................................................................... 3 1.1 Geographical Extent of this Study ...................................................................................................... 3 2.0 CURRENT LAND USES WITHIN THE CATCHMENTS ........................................... 5 2.1 Introduction to the New Zealand Land Cover Database .................................................................... 5 2.2 Land cover of the Mohaka, Waikari and Waihua catchments. ........................................................... 6 2.3 Catchment Scale. ............................................................................................................................... 6 2.4 Riparian Scale. ................................................................................................................................... 8 2.5 Land use zones ................................................................................................................................ 17 2.6 Commercial activities ....................................................................................................................... 17 3.0 HEALTH OF THE RIVERS ..................................................................................... 22 3.1 Water Quality.................................................................................................................................... 22 3.2 Aquatic Ecology – macroinvertebrates and algae............................................................................ 27 3.3 Aquatic Ecology – fish ...................................................................................................................... 28 3.4 Terrestrial Ecology ........................................................................................................................... 33 3.5 Hydrology ......................................................................................................................................... 34 3.6 Cultural Health.................................................................................................................................. 35 4.0 LANDUSE PRESSURES ........................................................................................ 37 4.1 GIS Analysis Opportunities .............................................................................................................. 39 4.2 Extraction of Natural Resources ...................................................................................................... 42 4.3 Natural Hazards ............................................................................................................................... 45 4.4 Biosecurity Risks .............................................................................................................................. 46 5.0 BIBLIOGRAPHIC LISTING BY TOPIC ................................................................... 50 APPENDIX 1: CONSENTED ACTIVITIES OCCURRING WITHIN THE CATCHMENTS ...... .......................................................................................................................................... 54 APPENDIX 2: POLLUTION INCIDENTS RECORDED WITHIN THE CATCHMENTS.....