Stage 4: River Management Applications

Stage 4: River Management Applications and Implications: Catchment-Based Vision Building, Identification of Target Conditions and Prioritisation of Management Efforts

Stage Four of the River Styles framework uses information from Stages 1-3 to identify target conditions for river rehabilitation for different River Styles. A prioritisation procedure is applied to identify where activities should start and where they are likely to have greatest success. These assessments are framed around the type of river, its condition and the river recovery potential. The philosophical perspective which underpins the prioritisation strategy for management efforts in the River Styles framework is as follows (see Brierley and Fryirs, 2005):

Conservation precedes rehabilitation.
Tackle strategic reaches irrespective of their geomorphic condition.
Work in those sections of the catchment with high natural recovery potential.
Consider more difficult tasks

Rehabilitation measures

T-jacks installed along a meandering gravel bed River Style
Wood installed along a partly-confined valley with bedrock controlled discontinuous floodplain River Style

Revegetation along a meandering fine-grained River Style

Stage 4 Step 2: Identify target conditions for river rehabilitation and determine the level of intervention required

Use information derived through application of Stage Two to determine the types of manipulation required along a reach and the types of geomorphic structures that must be enhanced. Condition provides information on the types of manipulation needed and level of intervention required. Good, moderate and poor condition reaches of each River Style can be used as short-medium term target conditions.

Use information from application of Stage Three to determine the likelihood that each reach will recover along a creation or restoration pathway. Assessment of recovery potential provides a surrogate for the time it will take a reach to recover given its catchment position and response to limiting factors operating within the catchment.

Nested within an over-arching vision are a suite of short-medium term target conditions which are used as stepping stones along a creation or restoration pathway. These target conditions are defined for particular time periods for each reach of each River Style in the catchment. As target conditions are achieved, the catchment vision is reappraised in an iterative process.

If target conditions for each River Style are to be sustainable over the long term they must be framed in light of the character, behaviour, condition and recovery potential of a reach, recognising how these interactions operate at the catchment-scale and related concerns for the overarchingvision. Due regard must be given to potential off-site impacts. River rehabilitation strategies undertaken in each reach must not compromise the catchment-framed goal.

Determining target conditions involves assessing what is realistically achievable for each reach in the catchment over a short-medium timeframe (i.e. over years to decades). The assessment of river condition and recovery potential undertaken in Stages Two and Three of the River Styles framework provides the tools and scientific information needed to identify target conditions for river rehabilitation. Creation and restoration goals equate to the natural or expected condition of a River Style operating in a sustainable manner under the prevailing boundary conditions. Information on minimally impacted reaches of each River Style is used to guide the target conditions for channel alignment, geomorphic structures, vegetation character, sediment distributions and channel-floodplain relationships for reaches in poorer condition. Hence, reaches in good geomorphic condition are used to design the target conditions for river structure and function of reaches in moderate or poor geomorphic condition.

Information on the condition and recovery potential of each reach in the catchment is used to determine the level of intervention and the type of manipulation required to attain a sustainable river structure and function, and the level of risk associated with applied rehabilitation measures. The timeframe of recovery is related to the recovery potential of the reach, and the level of intervention required is directly related to the condition of the reach. Reaches in good condition with high recovery potential will require minimal intervention, with visible results occurring relatively quickly. As the condition and recovery potential of reaches deteriorates the required level of intervention increases and the rate of recovery decreases. In poor condition reaches, direct intervention and manipulation may be required. The scientific insight provided through application of the condition and recovery potential framework is used to define, for each reach, the parameters that require manipulation to enhance recovery towards the target condition. These analyses are used as a benchmark against which to assess whether improvement has occurred.

Stage 4 Step 3: Prioritise management efforts based on geomorphic condition and recovery potential

Based on the condition and the recovery potential of each reach, priorities each reach according to its conservation/rehabilitation status.

Develop a catchment-wide plan of attack (a program/schedule of works) for tackling the river conservation/rehabilitation issues in the catchment.

A prioritisation framework determines the sequencing of actions that can be applied to achieve the catchment-based vision. Prioritisation frameworks for river rehabilitation and conservation programs can be used to ensure that the most cost-effective and efficient reach based strategies are employed that work towards the catchment vision.

In developing catchment-wide river rehabilitation programs, critical decisions must be made on where in the catchment to start and the associated plan of activities. While economic, cultural and social values place obvious constraints on how this is undertaken, a physical template forms a critical basis for decision-making. Application of a physically-based prioritisation framework, can be used to identify where the greatest likelihood of success is likely to be attained within the catchment. In many cases, the rehabilitation of strategic reaches triggers a positive feedback whereby enhanced recovery is achievable throughout the catchment. Identifying those reaches where “tweaking” is required is an underlying premise of the prioritisation framework developed in the River Styles framework.

The flow diagram in Figure 1 highlights how an understanding of river condition and recovery potential has been merged to provide a scientifically based framework for prioritising efforts at river rehabilitation in the River Styles framework.

 

Figure 1 Prioritisation of river reaches based on their geomorphic condition and recovery potential

Stage 4 Step 4: Monitor and audit adjustments to geomorphic river condition

This stage involves selecting appropriate techniques for river rehabilitation problems faced in the catchment. The most suitable treatment will vary markedly for different problems and for different river types. Adopted techniques must fit the character, behaviour and condition of the river if they are to minimise offsite impacts (Fryirs and Brierley, 1998 b). By determining the target condition of a reach, and the required treatment, the rehabilitation group must match resources with actions to initiate on-the-ground implementation.

As management strategies are implemented and the operation of biophysical processes adjust, it may be necessary to revise the target conditions and priorities for conservation and rehabilitation. The vision/goals must be reappraised once a certain target condition is achieved, and as pressures such as climate change, major flood/drought events or other unexpected consequences arise. Adoption of adaptive management principles is vital if flexibility is to be achieved in the rehabilitation process. Ongoing monitoring and maintenance programs allow the rehabilitation group to learn from mistakes and document successes, enabling continual progress towards the vision to be made, thereby maintaining momentum within the community.