Otama catchment. Geology, soils, and sedimentation.

As a sink point for waterflows through the catchment, wetlands will be influenced by the geology and associated soils of the catchment. Sedimentation processes are a natural resutlt of weathering, erosional cycles, volcanic events, and extreme weather events. Harbour infilling through sedimentation is a natural process, especially in a wetland partially constrained by dunes. However, human activities and land use within the catchment, removal of native vegetation, and fire events have all to some degree contributed to increased sedimentation whereby it may be considered a contaminant.

A wetland can be defined by hydrology, vegetation, and the way the two interact in a variety of “planting zones”, as outlined in the vegetation section. Hydrology and wetland types are influenced by the geographical location of the wetland in the context of surrounding landscape, ie. coastal, palustrine (inland or pastoral), floodplain wetland, etc.

Sedimentation issues may be compounded by the nature of sediments entering waterways and wetlands, for instance phosphorous, considered a contaminant at elevated levels, binds to soil particles that are then washed into waterways and lead to excessive nutrients encouraging algal and weed growth. Changes in hydrology of waterways can increase sedimentation, eg. changes in streamflow causing bank erosion. A further controlling factor on sedimentation rates in the wetland is the flushing action of freshwater inputs, and tidal cycles.

The Otama River catchment occupies the eastern sector of the Kuaotunu Peninsula, an area associated with a historical legacy of goldmining. Though mining activity has long ceased, historical mines and mineshafts may still be contributing to pollution of waterways and geo-chemical contaminantion of sediments.

The main freshwater input into the Otama wetland is the Otama River, therefore to understand sedimentation in the wetland and its associated waterways, we will define and research the wider catchment, its geology, geomorphology (the surface features in relation to the underlying geology), land cover, and land uses. Parameters for investigation, and recommended baselines may be derived from the Whangapoua Harbour Catchment Management Plan (Waikato Regional Council, 2015). and The Coromandel Zone Management Plan (Waikato Regional Council, 2011).

Recommended actions

An overview of the geology and geomorphology (the surface features in relation to the underlying geology and hydrology) of the area specific to this project will be compiled from current geological research, reports, and land data, in addition to on-ground field-work and aerial survey. Recommended actions will build on this overview and provide a clearly defined set of issues and direction for management and mitigation.Define catchment of restoration area. At a starting level this would involve defining and mapping the catchment of the Otama River, however further research and analysis is recommended to record and map areas of influence that may sit outside the specific boundaries of the Otama River catchment. REC dataset may be used to define waterways and the associated area of the catchment.

Construct multi-layered map of catchment defining

Recommended methodology

Define major landowners in the area, and their primary activities. Engage with landowners to ensure activities (eg forestry and agriculture) are compliant with local and regional catchment/management plans, and aspirations for wetland and dune restoration. Establish working relationships with landowners relating to land access for monitoring, flyover of private land for aerial surveying, and sharing of data.

Conduct regular ground and aerial surveys of the area, enabling monitoring of changes within the catchment such as changes in vegetation condition, changes in hydrology and condition of waterways, land-use, and other factors.
Instigate monitoring regime for water condition and chemistry, sediment concentrations, presence of pollutants and contaminants, excessive nutrients. Establish monitoring points both within the wider catchment, and within the wetalnd itself, thereby enabling tracking of changes from source to the final destintation.

Geomorphology Resources

The central activity of this module is constructiing a multi-layered map, utilising three sets of data available from the New Zealand Land Resources Inventory (NZLRI). This map will combine data on geology, soil types, land cover, and a value known as Land Use Capability (LUC) derived from the previous paprameters described. This map will serve to define areas of land and activities likely to be having a detrimental effect down-stream. It will also serve to define suitable monitoring and data collection points, and to also define areas for mitigation activities that are likely to have the highest return on investment (time, labour, and monetary). Resources linked to hear provide an overview of datasets, and downloadable data.

New Zealand River Environment Classification User Guide, by T. Snelder, B. Biggs, & M. Weatherhead, 2004 (updated March 2010). Published by Ministry for the Environment & NIWA.

NZ REC2 v.4 database
Land Use Capabilty survey handbook. A New Zealand handbook for the classification of land. Published by AgResearch Ltd., Landcare Research New Zealand Ltd., & Institute of Geological and Nuclear Sciences.

LUC data for Kuaotunu, including .kml shapefiles viewable in Google Earth.

New Zealand Landcover Database LCDB version 4.1, mainland New Zealand

LCDB data for Kuaotunu, including .kml shapefiles viewable in Google Earth.

Data for soils of Kuaotunu, including .kml shapefiles viewable in Google Earth.

Coromandel Zone Management Plan (2011). Published by Waikato Regional Council.

Harbour and Catchment Management Plan Whangapoua (2015). Published by Waikato Regional Council.

Natural Character study of the Waikato coastal environment (2016). Part C, Waikato’s East Coast marine and terrestrial areas. Published by Waikato Regional Council.

Dynamic processes in New Zealand land-water ecotones. Clive Howard-Williams, 1991. New Zealand jouyrnal of Ecology; Vol 15, no. 1; pp 87-98.

Holocene record of gradual, catastrophic, and human-influenced sedimentation from a Backbarrier Wetland, Northern New Zealand, by Scott Nichol et al. (2007). Published in Journal of Coastal Research, 23(3), pp. 605-617.