Hydrology

Otama Saltwater Estuarine Wetland & Lagoon.

The Otama Wetland and Lagoon is formed where freshwater discharge from the Otama watershed mingles with saltwater. Water levels and salinity and quality change in response to tidal cycles and the constituent nature of freshwater inputs.

These interactions between saline marine waters and freshwater drive ecological processes ranging from the microscale to the entire ecosystem.

A wetland is an example of an ecotone, a transition area between two biomes, where two ecological communities meet and integrate. In this case the land biome, and water biome.

Recommended actions

The first step to understanding the most fundamental processes underlying all other aspects of the functioning and condition of Otama wetlands is to obtain a general overview of hydrological cycles, hydrological inputs, and hydrological outputs.

  • Conduct visual assessment of flow regimes, tidal cycles, and hydrological processes as affecting fluctuating water levels and physical condition and structure of wetland. This may be achieved through on-ground survey and field-work, in conjunction with aerial imagery obtained through the use of Unmanned Aerial Vehicles.
  • Obtain any data held by relevant agencies, or available through online databases, relating to the wetland itself and the wider catchment. If necessary convert data to map display for ease of communication to wider group.
  • Obtain basic data through monitoring water levels at specified points in the wetland. It is suggested to use water markers that are easily visually monitored. This will enable monitoring of water levels in response to tidal cycles, weather events.
  • Conduct professional water quality monitoring at discharge locations and along the river and lagoon to record, salinity, sediment levels, ecoli etc. Build a model of catchment factors to identify forestry and agricultural activities and seasonal variations.
  • A minimum monitoring period of a year is recommended in order to establish baselines and cyclical processes that may have a strong component of lag.
  • Define boundaries of catchment. Investigate utility of River Environment Classification2 (REC2) dataset. Is council able to supply map of catchment boundaries using this dataset?
  • Construct a multi-layered map of the wetland in the context of the catchment. Display all inputs and outputs, ie streams, tributaries, and rivers feeding into wetland, freshwater discharge into coastal waters, and marine ingression. Map discrete areas of wetland defined by hydrological regimes and species assemblages. Map should include as many layers as possible relating to hydrology, including all data collection points clearly marked by geographic co-ordinates obtained on ground.

Hydrology Resources

Definitions

Wetlands are defined primarily by their hydrology, and the species assemblage that is best adapted to hydrological conditions of a wetland. In refering to hydrology, we are discussing the abiotic (non-biological) and hydrodynamic processes which affect a wetland.

According to NIWA the three following factors combime to form a range of hydrodynamic processes shaping estuaries:

1) The shape and volume (morphometry) of the water body

2) The quantity of river flow entering the estuary

3) The quantity of exchange of seawater between the estuary and the ocean.

Links

Hydrology Monitoring

On site activities undertaken by reserve group

August 15 2018Hydrological Snapshot Water quality monitoring report undertaken by Thomas Everth. Includes turbidity, disolved oxygen, slainity etc

August 20 2018 – Submission to WRC Coromandel Catchment Committee by Chris Twemlow requesting hydrological data and support to reduce silt discharge from forestry run off. (above report submitted)

Degraded Discharge Location - Otama Reserves

September 2018 – Corespondence led by Paul Kington with Waikato Regional Council

Summarised response from Elaine Iddon , WRC Catchment Management Officer, Whitinaga.

  • Getting some more rigorous samples analysed usually by some organisation such as RJ Hill for E coli, phosphorus or nitrogen levels.
  • As wetlands can be anaerobic by nature in their natural state some indicators may not be useful.
  • For areas like the Coromandel the problem is tyranny of distance so getting these types of samples over to labs within the required timeframe is tricky for communities (e.g. meeting up with couriers etc.).
  • NIWA have SHMAK kits (stream health monitoring assessment kits) which go for about $500 and have a probe amongst other equipment so some citizen science can be undertaken if you wanted to consider these.
  • Septic runoff would be a public health issue/compliance issue so TCDC would investigate concerns around septic tanks being a pollutant.
  • There is a sediment monitoring station at Opitonui measuring sediment discharge after large rainfall events.

 

October 25 2018 – Aerial & ground survey to identify freshwater inputs to wetland.