The information collected is used for:
• Council to make informed decisions on the state of the region’s freshwater resources and manage its sustainable allocation and use through the development of the Natural Resources Plan for the Wellington Region, including determining how much water can safely be taken from a water body
• Informing whaitua to enable the creation of a unique vision and to prioritise objectives for land and water management
• Providing for flood warning and flood response duties to protect vulnerable communities from flooding
• Maintaining groundwater aquifer levels to protect the resource against degradation and saltwater intrusion
• Providing information on the state of our water resources and the baseline quantity of water
• Detecting long and short term trends in water resources and whether these can be related to things such as climate change or other pressures on the resource
• Providing drought warnings and advice
• Resource consent monitoring.
All GW rainfall monitoring sites are automatic and typically record rainfall amounts at 5 minute intervals. The majority of sites are telemetered back to the GW database to allow real time monitoring. There are two measuring devices are at each site; an automatic tipping-bucket rain gauge that records rainfall as it occurs, and a check/storage gauge that collects and stores all rainfall between site visits by the monitoring team. A number of rainfall sites have alarm levels that are automatically triggered if a high intensity rainfall above a certain threshold occurs. Alarms are received by flood-warning staff and a flood event will be monitored at any time of the day or night with warnings issued to authorities and landowners if dangerous flood levels are predicted.
River level sites were originally installed for a number of reasons including flood warning, public water supply and water resource monitoring. As such the network tends to concentrate on the larger rivers and the upper parts of catchments. This has been changing over time as GW undertakes more monitoring in agricultural and urban areas and in the lower reaches of the catchments to manage abstractions, maintain environmental flows and ensure regional plan rules are being met. All river sites are automatic and typically record river levels every 5 to 15 minutes. Data is stored on loggers at the site, as well as being sent back to the GW database via telemetry to allow for real time monitoring. GW staff also physically measure the amount of flow in rivers and streams by completing a ‘flow gauging’ using specialised equipment, and can measure from a trickle in a ditch to a major flood in the Ruamahanga River. The gauged flow and the water level at the time are used to build up a flow-rating relationship that is used to convert the continuously measured river water levels into flow values. The flow-rating relationships at each site change often due to events such as a flood which might alter the river bed level, therefore gaugings are undertaken regularly to ensure the correct flows are being calculated from the recorded water levels. Most river sites have flood alarm levels that are automatically triggered if a river level rises above a certain threshold. Alarms are received by flood-warning staff and a flood event will be monitored at any time of the day with warnings to authorities and landowners issued if dangerous flood levels are predicted.
GW monitor lake water level at various locations for a variety of reasons. A number of wetlands are monitored to gather information on wetland hydrology and to determine how they fluctuate over time due to environmental drivers. Lake level monitoring sites on Lake Wairarapa and Lake Onoke are key flood warning sites and allow the Lower Wairarapa valley flood scheme to operate during a flood event to minimize flooding and damage to surrounding areas.
The groundwater monitoring network covers principal groundwater areas three whaitua, Ruamāhanga, Te Whanganui-a-Tara and Kāpiti Coast. Continuous data on groundwater levels are collected at 56 sites. These are automatic sites where the groundwater level is recorded every 5 to 15 minutes and stored in a data logger at the site. The majority of sites are also linked to GW’s database via telemetry.
Historically, a number of groundwater bore levels were monitored manually (for example, one every six weeks) but this network was discontinued in 2020 due to Monitoring of manually measured groundwater levels ceased in 2020 due to the COVID-19 pandemic that affected resourcing. Some sites reported on in this 2022/23 year contain periods of missing data. Common causes of missing data are at-site issues such as measuring sensor failure, power failure, communications issues, or site vandalism. After the quality assurance process has been applied to the recorded data in the office, data may be deleted if it is considered erroneous.
Knowing the water content of soil is important for managing groundwater recharge, assessing agricultural irrigation needs and soil chemistry. It is also used for analysis of long-term climate trends, measuring how often plant growth is restricted by soil moisture and providing an indication for early intervention and drought management decisions.