Tracking geomorphic recovery in process‐based river management

Abstract

Human disturbance induces significant geomorphic changes to river systems. In eastern Australia, land-use practices such as clearance of forests and riparian vegetation, and removal of wood from channels in the 19th and 20th centuries induced widespread geomorphic impacts. However, since the 1970s, there has been a noticeable shift in the geomorphic condition of many rivers in eastern New South Wales (NSW). This transition to a recovery trajectory reflects a reduction in land-use pressures and improved farming practices on the one hand and adoption of recovery enhancement approaches to river conservation and rehabilitation by management authorities on the other. Monitoring and tracking changes in condition by state government agencies involves identifying when geomorphic recovery is occurring so that decision-support frameworks can determine whether river management is required, where, when, and how much to intervene to enhance river recovery and when to opt-out of management because the system requires little (or no) intervention. Here, we document procedures that are used to manage process-based, recovery enhancement in NSW. Following a brief review of river change in eastern NSW since European settlement, we outline an approach to identify and measure key geomorphic indicators of river recovery for different river types. We use case studies to demonstrate examples of geomorphic river recovery, prior to showing how state government agencies in NSW are monitoring trajectories and rates of recovery.Broader implications of this 'good news story' are discussed.

Engaging with research impact assessment for an environmental science case study

“…Similarly, how do you measure environmental, social, economic or cultural impacts of an initiative where the benefits can take many years (and in the case of rivers, decades) to emerge, and how do you then link and attribute those impacts directly with the design, development, use and extension of that initiative in many different places at many different times? For the River Styles Framework, on-ground impacts in terms of improved river condition and recovery are occurring 43 , but other environmental, social and economic benefits may be years or decades away. Impactful initiatives in themselves often reshape the contextual setting that then frames the next phase of science and management practices which leads to further implications for policy and institutional settings, and for societal (socio-cultural) and environmental benefits.…”

Simulating the effect of environmental flow duration on seedling emergence from riparian seed banks of the Upper Hunter River, New South Wales

“…This is due to the decoupling of the floodplain from the low‐flow channel as a result of channel incision and widening, the discharges required to inundate the floodplain (Hoyle et al, ) and the social and economic impacts of inundating agricultural property. Therefore, bench surfaces represent the most significant riparian habitat, and their presence is a key indicator that river recovery is underway (Fryirs et al, ; Fryirs & Brierley, ). This is particularly relevant in the Hunter catchment and along the study reach where vegetation communities on benches are targeted for revegetation and protection (Erskine et al, ; Fryirs, Spink, & Brierley, , 2018).…”

“…This is particularly relevant in the Hunter catchment and along the study reach where vegetation communities on benches are targeted for revegetation and protection (Erskine et al, ; Fryirs, Spink, & Brierley, , 2018). The practice of enhancing river recovery through bench formation and stabilization is now a common technique used in south‐eastern Australia as part of passive and proactive river rehabilitation practice (Fryirs et al, ; Vietz et al, ). This has traditionally been undertaken via fencing‐off and direct planting of vegetation.…”

“…Since the 1980s, greater attention has been paid to river rehabilitation projects that are process‐based and use recovery enhancement principles (Beechie et al, ; Brierley & Fryirs, , ; Fryirs & Brierley, ). In some places, geomorphic river recovery is underway (see Fryirs et al, ). One of the key indicators that geomorphic river recovery is underway is the formation of benches, step‐like inset floodplain features that occur along channel banks and act to reduce channel capacity in overwidened macrochannels (Erskine & Livingstone, ; Thoms & Olley, ; Erskine, Chalmers, Keene, Cheetham, & Bush, ).…”

Things we can do now that we could not do before: Developing and using a cross-scalar, state-wide database to support geomorphologically-informed river management

“…Using the River Styles Framework, rivers are characterised according to their present range of variability and diversity with process understandings and behavioural analysis undertaken through interpretation of form-process associations of geomorphic units [ 11 , 52 , 53 ] ( Fig 2 ). Condition is assessed in terms of what is expected for a particular river ( Fig 3 ; [ 44 ]) and recovery potential is determined according to what is realistically achievable given the character, behaviour and condition ( Fig 4 ; [ 45 , 54 ]).…”