Carters Creek

Community concern about water quality and flooding issues initiated an investigation into the Carters Creek catchment.

Carters Creek is a small stream that originates at springs near the Ashburton River, flows through rural farmland and lifestyle blocks, into urban Tinwald, out through more farmland and eventually drains into Lake Hood. Along the way, it collects surface water, overland flows and stormwater run-off and has issues with water quality and flooding.

The report (PDF file 3.36MB) highlights the complex ecological and management challenges facing Carters Creek, including water quality, riparian vegetation, and stock exclusion, highlighting the need for targeted remediation efforts and ongoing monitoring.

Water quality

Water quality in Carters Creek has been deteriorating for many years. It has high levels of faecal contamination (E.coli), high nitrate levels and problems with sediment and erosion.

This poor water quality is one contributor to the growth of toxic algae in Lake Hood, a popular recreation spot for locals.

We met with Carters Creek residents on 29 November 2023 to carry out a creek walk - the first since 30 January 2020. Many new community stakeholders and neighbouring residents had been carrying out work on Carters Creek and we wanted to see if actions taken on this section of the creek were improving water quality.

The creek walk covered the lower Carters Creek catchment between Tinwald and Lake Hood and focused on:

water quality, particularly E. coli and phosphorous
stock exclusion
overland flow pathways
critical source areas
and weeds.

Key issues

Damage from erosion:

Four main locations had significant bank erosion or areas of bank slumping. The longest section of steep and eroding banks stretched for around 700 metres, which represented that whole reach.

Part of a 700 m long section of bank scoured out from water flow with little to no stock access

Very steep undercut bank with historic stock access and de-vegetated bank margins

A collapsing bank - erosion potentially caused during flood events

Damage from spraying:

Two areas of banks were lacking vegetation from blanket spraying, and one length of the creek had exposed soil running on the outside of a narrow grass buffer.

The lack or reduced capacity of vegetated buffers means that sediment and nutrients are more likely to enter the waterway here. The exposed banks also increase erosion potential during storm events.

The first section of the creek lacks vegetation from blanket spraying

The second section of the creek lacks vegetation from blanket spraying

A thin grass buffer with exposed soil, which runs for a significant length

Flooding

Landowners adjacent to Carters Creek have been experiencing flooding issues for several years. Because we manage Carters Creek as a designated drain within the Ashburton Hinds drainage scheme, much of the flooding issues within Tinwald township fall outside the scheme's limitation and likely require additional long-term planning and funding.

A creek walk through Tinwald on 7 December 2023 focused on the flooding issues, particularly within the Tinwald township area.

Work to further investigate and carry out upstream rural overland flow stormwater diversion is scheduled in the draft Long-Term Plan 2024-2034.