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Lake Te Koo Utu Ecology, stormwater management and restoration options Prepared for Waipa District Council 3 April 2020 Document Set ID: 10372718 Version: 3, Version Date: 17/04/2020 Document Quality Assurance Bibliographic reference for citation: Boffa Miskell Limited 2020. Lake Te Koo Utu: Ecology, stormwater management and restoration options. Report prepared by Boffa Miskell Limited for Waipa District Council. Prepared by: Andrew Blayney Ecologist – Associate Principal Boffa Miskell Limited Mike Chapman Water Resources Specialist Te Miro Water Consultants Ecology Inputs Kieran Miller Reviewed by: Ecologist – Associate Principal Boffa Miskell Limited Status: Final Revision / version: [1.1] Issue date: 3 April 2020 Use and Reliance This report has been prepared by Boffa Miskell Limited on the specific instructions of our Client. It is solely for our Client’s use for the purpose for which it is intended in accordance with the agreed scope of work. Boffa Miskell does not accept any liability or responsibility in relation to the use of this report contrary to the above, or to any person other than the Client. Any use or reliance by a third party is at that party's own risk. Where information has been supplied by the Client or obtained from other external sources, it has been assumed that it is accurate, without independent verification, unless otherwise indicated. No liability or responsibility is accepted by Boffa Miskell Limited for any errors or omissions to the extent that they arise from inaccurate information provided by the Client or any external source. Template revision: 20180621 0000 File ref: BM19451_Lake_Te_Koo_Utu_report_draft_20200304_Final.docx Cover photograph: [Lake Tee Koo Utu, © Boffa Miskell 2019] Document Set ID: 10372718 Version: 3, Version Date: 17/04/2020 CONTENTS 1.0 Introduction 1 1.1 Ecological context 1 2.0 Lake Te Koo Utu’s Catchment 2 2.1 Catchment Geology 2 2.2 Land use 2 3.0 Habitat values 3 3.1 Vegetation 3 3.2 Fauna 4 4.0 Discharges/outlets to the Lake 7 4.1 Discharges 7 4.2 Lake outlet 7 5.0 Current water and sediment quality 12 5.1 Water quality 12 5.2 Sediment quality 12 5.3 Botulism 14 5.4 Lake health implications 15 6.0 Ecological restoration approach 16 6.1 Short-term approach 17 6.2 Medium-term approach 18 6.3 Long-term approach 18 6.4 Lake Te Koo Utu Reserve ecological enhancement 19 7.0 Conclusion 20 8.0 References 21 Appendices Appendix 1: Lake Te Koo Utu catchment map Appendix 2: Lake Te Koo Utu water quality data Appendix 3: Lake Te Koo Utu sediment quality data U:\2019\BM19451_JSo_Concept_Plan_for_Lake_Te_Koo_Utu_and_Memorial_Park\Documents\Ecology\Rep ort\BM19451_Lake_Te_Koo_Utu_report_draft_20200417_final.docx Document Set ID: 10372718 Version: 3, Version Date: 17/04/2020 Appendix 4: Sediment sample – Certificate of Analysis – Hills Laboratories. Appendix 5: GHD option analysis review and Boffa Miskell and Te Miro Water Consultants comments. Figures Figure 1: Lake Te Koo Utu reserve aerial and location. ................................. 1 Figure 2: Lake Te Koo Utu riparian edge showing sprayed grass to the lake edge (foreground) exotic tree cover (background) and aquatic emergent vegetation raupo (right background) and bamboo spike sedge (right foreground). ....................................... 4 Figure 3: Outlet for commercial catchment on south-western edge of Lake Te Koo Utu ............................................................................ 8 Figure 4: Outlet for commercial catchment on south-western edge of Lake Te Koo Utu – Looking along the flow path. .......................... 8 Figure 5: Outlet for large residential catchment on western edge of Lake Te Koo Utu............................................................................ 9 Figure 6: Outlet for commercial catchment on southern edge of Lake Te Koo Utu – Looking along the flow path. ................................... 9 Figure 7: Outlet for small residential catchment on north-eastern edge of Lake Te Koo Utu...................................................................... 10 Figure 8: Lake Te Koo Utu lake outlet. ......................................................... 10 Figures 9 a-d: Time series of aerial images of Lake Te Koo Utu showing the expansion of Raupo in the western end of the lake since 2006. Indicative of sediment accumulation from Large residential and commercial catchments. ........................... 11 Document Set ID: 10372718 Version: 3, Version Date: 17/04/2020 1.0 Introduction Boffa Miskell and Te Miro Water Consultants have been engaged by Waipa District Council to produce a concept plan for the Lake Te Koo Utu Reserve (Figure 1). As part of this project it was identified that the water quality, stormwater management and ecology of Lake Te Koo Utu should be a primary driver to guide reserve management objectives and actions. This report provides a summary of the ecology of Lake Te Koo Utu with an emphasis on the aquatic environment. The report also explores the water quality issues of the lake, the sources and contributors to these issues, and provides recommendations to begin to restore the Lake’s water quality from both an ecological, hydrological, and engineering perspective. There have been several iterations of recommendations for improving the water quality of Lake Te Koo Utu over the last 20 years ranging from “soft treatment” options such as wetlands to “hard treatment” options such as filters, desludging, and “nanobubble” technology. We intend to focus our recommendations on options that provide the most sustainable outcomes over both a short and long-term period with emphasis on solutions that act to reduce the long-term contaminant inputs to the lake. Figure 1: Lake Te Koo Utu reserve aerial and location. 1.1 Ecological context Lake Te Koo Utu is a shallow lake, with an approximate depth of 2.4m, within the Cambridge township and receives stormwater from the northern half of the town which is then discharged east to the Karapiro stream. It is located in the Hamilton Ecological District and the area surrounding the lake would have once been dominated by podocarp forest (primarily kahikatea in the lower lying areas and a mixed conifer-broadleaf forest on the elevated landforms (Deichmann & Kessels, 2013; Leathwick et al., 1995). It’s estimated that, since 1840, there is Boffa Miskell Ltd | Lake Te Koo Utu | Ecology, stormwater management and restoration options | 3 April 2020 1 Document Set ID: 10372718 Version: 3, Version Date: 17/04/2020 now less than 1% of wetlands, forest, and scrub remaining in the ecological district (Leathwick et al., 1995). The area surrounding the lake itself has a threatened environment classification of 1, which means there is less than 10% of indigenous cover left in the area (Walker et al., 2015). 2.0 Lake Te Koo Utu’s Catchment 2.1 Catchment Geology Deposition of the Hinuera Formation underpins the geology of the Lake Te Koo Utu catchment. The Hinuera formation is characterised by alluvium deposits of alternating layers of sand, silt and gravels which were deposited by the historical flow path of the Waikato River during the fan forming phase. This sand, silt, gravel formation is influenced by regular changes in the channel position as the Waikato River migrated across this surface. The Lake itself was once part of the main river channel but was then ‘cut off’ from the main flow by mass deposits from the Taupo eruption. The lake catchment soils range from highly permeable sandy loams to less permeable silty deposits in depression areas. The lake catchment (~177Ha including the lake reserve) includes a broad flat area of free draining soil which provides a significant groundwater recharge zone for the lake. There is low runoff from pervious garden and reserve areas and maximum rainfall infiltration can be expected. Groundwater discharge was observed around the southern and western perimeter of the lake during the site visits. It is expected a rapid increase in groundwater flow will occur around the base due to the increased piezometric gradient created by the steep lake sides. Tritium results for the Waikato show that waters from the shallow unconfined aquifers of the Hinuera Surface are of recent origin, originating as precipitation within the last 5 years. Water is discharged rapidly from these shallow aquifers. Similar age, well filtered groundwater is expected to be discharging into the lake. 2.2 Land use A map of the Lake Te Koo Utu catchment is provided in Appendix 1. 2.2.1 Residential Areas The overall catchment is dominated by residential land use. The houses within the catchment are typically low-density large lot residential with the majority of runoff going to private soakage systems some of which will overflow to the road via kerb outlets. These kerb outlets then connect to the reticulation network draining to the lake. Some runoff from residential areas is therefore expected to reach the lake although it is difficult to estimate the exact area as it depends on how well the private soakage devices are maintained and whether their overflows are connected to the road kerb. 2.2.2 Roads There are several high use and minor residential roads (total length approximately 7.2km) which connect to the reticulation network. Stormwater trunk lines underlay Victoria Street, Taylor 2 Boffa Miskell Ltd | Lake Te Koo Utu | Ecology, stormwater management and restoration options | 3 April 2020 Document Set ID: 10372718 Version: 3, Version Date: 17/04/2020 Street, Clare Street and Bowen Street as well as Lake Street through the southern commercial catchment. The road network will be a contaminant source for runoff to the lake with an estimated total impervious area in the order of 5.70Ha (assuming on average 8m wide carriageway). The typical contaminants for urban roads are suspended sediments, heavy metals, hydrocarbons as well as elevated temperature during summer months. 2.2.3 Commercial A relatively small commercial sub catchment (5.35Ha) is located to the south of the lake. A commercial land use has higher impervious surfaces compared to low density residential.

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