Hydrology

Definition

Wetland  hydrology is the science concerned with how the storage and movement of water into and out of a wetland affects the plants and animals and the soils on which they grow.

Hydrology is the most important factor that determines wetland type and function and changes in hydrology are the leading cause of wetland degradation. Many wetlands in NZ have become degraded because they have been drained to provide land for farming and urban development.

Hydrologists need to define the size and shape of the catchment, which is the area of land that contributes water to  the wetland either as streams or groundwater in the form of seepages and springs. 

The upland parts of the catchment are integral to the health of a wetland and their water quality and quantity can be affected by land use practises surrounding the wetland.

For successful restoration an integrated approach involving the entire water catchment water quality and quantity issues needs to be implemented. This may involve restoring natural water flow, fencing and riparian planting of the wetland and surrounding steams, implementation of siltation controls and  modification of farming practices, as well as the monitoring of water quality.

The Otama Wetland

The Otama wetland is approximately 36ha and is ranked as 376 in the top 500 of DOC’s national prioritisation system for ecosystem and species.

The wetland and lagoon are formed where freshwater discharged from the Otama catchment area mingles with saltwater. Water levels, salinity and water quality change in response to tidal cycles and the changing nature of freshwater inputs. This wetland is an example of an ecotone – a transition area where two ecological communities merge and integrate- the land biome and the water biome. The interaction between saline marine water and freshwater drive ecological processes ranging from the microscale to the entire ecosystem.

The water level is also affected by inundation from weather events and drainage being cut off via the lagoon entrance from marine tidal cycles. The ORG believes that connectivity from the surrounding catchment and hills through the wetland and dune and foreshore is an important value for Otama.

A study in Nov 2917 conducted by Lucy Roberts (Distributed Technical Advisor) and Catherine Beard (Science Advisor) Terrestrial Ecosystem Unit described Otama wetland as degraded. It’s natural water courses have been altered by historical farming practices which have impacted on the health of the wetland and its inhabitants. It was  identified as home to significant nationally threatened native plants and bird and fish species. It is threatened by lack of silt control from forestry in the hills above the wetland, farming practices causing an overgrowth of salt water paspalum and reduced water quality, as well as other invasive weed and predator species. It is also faces potential subdivision despite the entire low-lying area being flood prone.

Our intentions 

Our intention is to re-establish and maintain the natural ecosystem processes and the indigenous character of the Otama Wetland. From a hydrological perspective this involves restoring and retaining higher water levels within the wetland, fencing the wetland boundary along with integrated  planting and weed control programmes, water quality monitoring and controlled drainage when necessary, with the aim to improve the quality and quantity of our wetland habitats.

 The Otama Reserves Group is developing a restoration plan for the Otama Wetland. 

We have engaged the services of Jim Dahm and Meg Graeme wetland ecologists from  Natural Solutions to prepare an integrated wetland restoration plan.

It is our aim to engage the cooperation and active participation of the key stakeholders; landowners, DOC, WRC, TCDC, and IWI and residents in the restoration plan with a holistic view to restoring and managing the wetland.

In relation to hydrology this will involve:

-Identification of natural boundaries of the wetland and relevant landowners

-Assessment of controls/influences of wetland hydrology

-Assessment of wetland values and functioning including plant communities and hydrologic controls

-Assessment of historic modification of the water flow in to the wetland

-Identification of existing and potential future threats to the wetland, including drainage, bunding, anthropogenic modification of wetland hydrology, plant and animal pests and potential effects of climate change on sea levels and water flow  from the catchment area into the wetland

-Identification and prioritisation of the various desired actions required to protect and restore the wetland and wetland hydrology

What we have done so far

Aug 15th 2018

  • Water Quality Monitoring Report by Thomas Everth (LINK)

Aug 20th 2018

  • Submission to WRC Coromandel Catchment Committee by Chris Tremlow requesting  hydrological data and support to reduce silt discharge from the forestry runoff

Oct. 25th  2018

  • Aerial and ground survey undertaken to identify freshwater inputs to wetland