The eFlows Explorer webtool is designed to aid broad-scale river flow management planning across New Zealand
The increasing use of water resources in New Zealand cause changes to the magnitude, duration, timing, rates of change and predictability of fluxes of water in rivers, wetlands, and groundwater systems.
These changes impact important physical processes such as sediment disturbance and transport, biological processes such as removal of algae and plants, in-stream ecosystems, and the cueing of life-history stages.
The National Policy Statement for Freshwater Management states that every regional council must include rules in its regional plan(s) that set environmental flows and levels for each Freshwater Management Unit (FMU), and may set different flows and levels for different parts of an FMU. Environmental flows and levels must be set at a level that achieves the environmental outcomes for the values relating to the FMU or relevant part of the FMU and all relevant long-term visions, but may be set and adapted over time to take a phased approach to achieving those environmental outcomes and long-term visions. Rules in regional plans that seek to protect environmental flows may take different forms but often comprise a minimum flow and a total allocation of water abstraction.
EFlows Explorer is intended to aid understanding of how minimum flow and total allocation can be set for all river reaches across a catchment or region, by demonstrating how they interact with reliability of water supply and example environmental metrics representing losses in total area of aquatic habitat.
Six key variables are considered within the app:
- minimum flow: the river flow at which all abstraction must cease;
- total allocation: the maximum rate of water abstracted from surface or river-connected groundwater summed across upstream abstractions;
- management flow: the minimum flow plus the total allocation;
- partial reliability: the percent of time for which some abstraction may occur because river flow is greater than the minimum flow;
- full reliability: the percent of time for which the total allocation may be abstracted, which also equates to percent of time river flow is greater than the management flow;
- width at minimum flow: the wetted width at the minimum flow as a percent of wetted width at a specified reference flow (width at minimum flow/width at reference flow)*100.
Setting input values for various combinations of two input variables allows the other four variables to be calculated. For example, setting minimum flow and total allocation allows calculation of management flow, partial reliability, full reliability, and width at minimum flow. Alternatively, setting width at minimum flow and full reliability allows calculation of minimum flow, management flow, partial reliability, and total allocation. Some variables can be specified in a variety of ways. For example, minimum flow can be specified as a percentage of mean annual low flow (MALF) or in cumecs (m3/s).
This tool can provide managers and decision makers with well-characterised options for sustainable management of New Zealand's freshwater resources by demonstrating and quantifying links between water resource use and environmental consequences.