A year in the Border Rivers catchment: 2022-23

This year no managed deliveries of water for the environment were made. Significant flows were observed throughout the catchment in both regulated and unregulated watercourses.

The Pindari Stimulus flow was triggered for use but was not delivered because natural flows negated its need. The Pindari translucency rule provided flows all year. The Pindari Dam was full and all inflows were passed downstream for the first 6 months of the water year.

Rivers and catchments complete cycles of change at many scales in their shape and habitat characteristics. The most observable changes are the progressive change from wet times to drought and the very rapid change that can occur during a floodplain inundation event.

Although these high flows are significant events, bankfull and smaller events are critical to the functioning of the system’s ecology. Environmental watering targets have been developed for the catchment through the NSW Border Rivers Long-Term Water Plan. Analysis of these targets has shown the vast majority of these have been met. However, the after-effects of the recent drought have impacted the ability to meet all targets completely. A small fresh is required annually (with ideal timing) at Goondiwindi to meet some ecosystem function, fish population and within-bank vegetation needs. Missing this annual event compromises the health, resilience and structure of populations and communities.

Some highlights from this year include wide-scale floodplain inundation, flows in Morella Watercourse and Boomi River, and many opportunities for aquatic and floodplain species to complete all or part of their life cycles. We have seen germination and seedling growth of notable species including coolabah, river red gum and lignum. Several species of frog have completed their lifecycles, such as barking marsh, salmon-striped and broad-palmed frogs.

Large flows critical to the natural cycling of rivers and floodplains

From early 2021 to the end of 2022, widespread large-scale change resulted from high-velocity flows and floodplain inundation. This was in contrast to the previous 8 years of low to moderate flows where generally smaller more gradual changes were observed with riverbanks and benches remaining stable, accumulating vegetation and then some loss during drought.

During this recent wet period, many rivers had within-bank benches turned over, moved and cleaned of leaf litter, grasses, shrubs and in some cases small trees. Some benches maintained part of their vegetation, which resulted in accumulation of trees and branches from flood flows.

Although these larger flows and floodplain inundation events can affect local communities and infrastructure, they are critical to the natural cycling of rivers and the ecosystems they support. These events can ‘reset’ the landscape and provide regeneration and regrowth opportunities for different communities and food web assemblages.

The effect of these events varies. Some areas undergo an immediate change and positive response, whereas others have a slower less obvious response. For example, the Macintyre floodplain vegetation and flood-reliant species grew and completed their life cycles, whereas within-bank vegetation was stripped in many places. Suitable species are starting to recolonise these bare bars and banks.

The impacts of current land and water management as well as historical practices and events are evident. Some older members talk of the water quality being vastly different to today – for example, near Mungindi water was clear most of the time – and some places have ongoing bed and bank erosion.

Environmental water managers are doing what they can to support and improve the resilience of remaining native species and communities such as instream aquatic vegetation communities and native fish species. This includes working with other agencies and the community to minimise further damage.