Stream bank vegetation

Randomly selected 500 m lengths of waterway from all pastoral land were selected for the monitoring. The sites are stratified by management zones, land use, and waterway size (as measured by Strahler stream order).

The monitoring occurs every five years.

The regional riparian characteristics survey was completed for the first time in 2002 and has been repeated in 2007, 2012 and 2017.

The regional riparian characteristics survey employs a sampling approach to provide scientifically robust estimates of the state of observed riparian characteristics (e.g. the proportion of bank length fenced). A sample site is an approximately 500 m long stretch of waterway in pastoral land at which the riparian characteristics (such as fencing, vegetation, and stream-bank erosion) are observed along both banks. Sites and observations are spatially referenced by GPS and the data are recorded using hand-held computers.

The raw data is stored in Excel spreadsheets and saved in Waikato Regional Council’s electronic document management system. The GPS data is stored in GIS layers.

The length of each sample site (approximately 500 m) is walked, adjacent to the waterway, and the riparian characteristics on both banks are observed and the data captured using a hand-held computer with built-in GPS. Changes in characteristics from those observed at the start point are recorded together with the spatial location of the change. The resulting stream segment information allows for the length and proportion of total stream length or bank length with certain characteristics (e.g. effective fencing) to be calculated. Data were collected at 432 sample sites across the region during the 2017 survey.

Proportions of bank and stream length (with associated confidence intervals) were calculated, categories compared, variables correlated, and change over time determined using appropriate statistical analysis techniques. All analyses were carried out using purpose-built procedures written in R.

Survey results in terms of the state and trend in riparian characteristics are presented for the region as a whole (i.e. region-wide), by management zone, land use (dairy and drystock), and stream order (a representation of stream size). Proportions of bank length have been presented here as graphs.

The raw data are collected using hand held computers with built-in GPS and transferred to Excel spreadsheets. The data held in Excel spreadsheets are imported into specialised statistical analysis software (e.g. R) for analysis. The data have been saved in GIS and Excel files stored in Waikato Regional Council’s electronic document management system.

There are no technical documents showing how the indicator data is quality assured but calibration of field observations and checking procedures for data accuracy is built into the methodology.

This indicator is not an actual measure of stock access to streams at every length of stream. It is a stream length sample method that provides estimates for management zones and the region as a whole. Assumptions are made about fencing and how effectively it prevents stock access. The absence of a fence has been assumed as allowing stock access.

The amount of woody vegetation across the region's bank length has not changed significantly over the 2002-2017 period (26% in 2002 and 24% in 2012). However, a significant decrease in the proportion of bank length occupied by woody vegetation was detected over the last ten years (2007 – 2017). In 2017 approximately one quarter (24%) of bank length across the Waikato region was occupied by woody riparian vegetation with the remaining three quarters (76%) occupied by non-woody vegetation.

The pattern of change in the proportion of bank length occupied by woody vegetation for both dairy and drystock land uses over the past fifteen years was generally similar to that observed across the region as a whole.

Vegetation type is reported by catchment management zone in the graph below. The Coromandel, Lake Taupō and Upper Waikato management zones had the largest proportions of bank length occupied by woody vegetation in 2017 (48%, 52%, and 44%, respectively) and were significantly different to all other zones which had between 13% and 19% of bank length with woody vegetation

Over the previous 5 year (2012 – 2017), 10 year (2007 – 2007) and 15 year (2002 – 2017) monitoring periods, significant changes in the proportion of bank length with woody vegetation were restricted to the Waihou-Piako and Waipā management zones. In both zones, a reduction in woody vegetation was observed, particularly in the Waihou-Piako zone where the magnitude of change was significant for each of the monitoring periods (-8 to –12%).