Rural catchment sediment yields from the Auckland region. State of the environment reporting

Author:

D M Hicks, N Holwerda, C M Grant

Source:

Auckland Council Research and Evaluation Unit, RIMU

Publication date:

2021

Topics:

Environment

Extract from the executive summary:

The many rivers, streams, estuaries and harbours in the Auckland region provide extensive recreational, cultural, food harvesting and aesthetic values, but they can be degraded by elevated delivery of sediment from the land and from stream channel erosion during storm event runoff. Concern with sediment impacts on Auckland’s coastal receiving environments has spanned the past several decades. For example, with targets set for reduction in coastal sediment delivery to priority marine receiving environments under the previous Auckland Plan. More recently the Ministry for the Environment’s National Policy Statement for Freshwater Management has drawn attention to also limiting sediment impacts in in-stream environments.

Acknowledging ongoing sediment management issues and drivers, over the past decade Auckland Council has pursued a programme (the “Auckland Council event-based sediment monitoring network”) to monitor predominantly rural stream sediment yields (derived from storm events) at a selection of river sites across the region. This knowledge will provide scientifically robust and defensible information to service multiple planning instruments and forms part of the state of the environment sediment management assessment through time. This programme supports Auckland Council’s role in managing rural catchments to create a sustainable balance between environmental protection and rural production.

This report provides updated results to 31 December 2019 on sediment yields from 10 state of the environment sites across the rural Auckland landscape (information from an additional three sites outside this programme is also presented). At these sites, suspended sediment loads are sampled continuously during storm runoff events using automatic samplers operated on a flow-proportional basis. ’Rating’ relationships between event sediment yield and event peak water discharge are used to estimate the sediment yields of any unsampled or inadequately sampled events. ...

Auckland Council technical report, TR2021/12