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  • Defining a ‘braided river’

    Posted on February 5, 2019 by in Advocacy, ECan, Ecology, Fresh water management

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    As an organisation, our overall view is that human activities (weeds, agriculture, river engineering, and built structures) have reduced the physical area of braided river ecosystems and damaged their hydrology. These historic activities and mismanagement should not now be viewed as a license to exploit these (often weed infested) damaged spaces in order to increase or protect personal or corporate profit margins. Allowing marginal/ephemeral spaces on braided rivers to be available for agricultural or other development will continue an ever-increasing cycle of contraction until braided rivers as ecosystems vanish, systematically squeezed into becoming ‘normal’ rivers.

    1. Our values reflect the priorities set out in the CWMS and in provision of section 6 of the RMA in relation to areas of national interest, including protecting the ‘natural character’ of braided rivers.

    2. Our values also reflect the priorities set out in the CWMS insofar as the environment, and cultural uses take first order priority over irrigation and power generation.

    3. As ‘braided rivers’ are natural landscapes that include springs, wetlands, and small streams that are hydraulically-connected to the river, i.e. the “lungs” & “kidneys” of those systems, they should be recognised in toto, as a landscape type that, for the sake of convenience, I would refer to as the ‘braidplain’.

    4. The dynamic nature of braided rivers is to change, primarily laterally over time, (what has been referred to as a fourth dimension). A defining feature of braided rivers is that high cumec ‘freshes’ fill the width of the braidplain, and active channels migrate across the braidplain (often following such events). Thus, the entire braidplain should be regarded as ‘riverbed’.

    5. We recognise that large sections of braided rivers (i.e., by the above definition, the braidplain) have been modified through built structures (town, bridges etc.), agricultural practices (irrigation pivots, permanent built structures etc.), and river engineering practices (stop bank, berms, willow planting etc.) to reduce the impact of floods.

    6. We support the proposed approach: recognise the ‘natural landscape’ of braided rivers, i.e. the braidplain as the ‘area that has been covered by active channels in historical imagery, while recognising the impact of river protection and other structures’.

    7. To this end, we would like to see the entire braidplain (as defined using, for example, the mechanisms proposed in recent reports by NIWA[1] and ECan[2] regarded as a single albeit complex landscape.

    8. Within this landscape, a two-tiered approach could be taken in terms of management:

    a. Currently active river channels and gravels/shingle
    b. Potentially active (currently ephemeral) river channels, i.e. the rest of the braidplain

    9. To this end, the ephemeral sections of the braidplain could be regarded as having the same values as wetlands, and treated as such under the RMA. Recognising that some sections have already been heavily modified, we support the idea that no further modifications be allowed in the braidplain, unless it is to restore the ‘natural landscape’ and/or ‘environmental/ biodiversity’ and ‘cultural’ values.

    10. We support the notion of a two-tiered approach to management, based on the entire width of braided rivers (the ‘braidplain’ for want of a better term) recognized as being composed of two alternating states in a 4D model:

    Tier A: Active river channels and gravels (which may or may not be weedy)
    Tier B: Ephemeral channels (historically active, which may be composed of ephemeral wetlands, turflands, drylands, and weeds, and possibly built and developed structures) that are, by definition, likely to once again become active river channels following a flood and/or as excess gravels building up in the currently active channels, leading to a re-directed flow.

    11. As a 4D model recognizes this naturally alternating state, most likely within a human lifetime, then we support the notion that there should be an adaptive management approach, that is, provision within the two-tiered approach for a locational change in the consented activities to be allowed within the total braidplain. Simply put, if the active channels (Tier A) abandon their existing location and migrate to Tier B areas, then the consented activities allowed in each tier should be able to ‘migrate’ with this movement.

    This adaptive management approach would also give effect to the RMA Section 7(i) the effects of climate change, which will vary considerably from river to river, and keep changing over time (i.e., 4D model).

    To answer the specific questions posed at the communty meetings, as  follows:

    Farming in the river bed – “undeveloped” land

    Q1. How intensively should the area (or parts of it) be farmed?
    A1. Areas defined as river beds should not be farmed at all, as they are, by definition ‘river beds’.

    As we support the notion of an adaptive 4D two-tiered approach to management based on the entire width of braided rivers (the ‘braidplain’) being regarded as composed of two naturally alternating states, then we would contend that no farming should take place in either Tier A or Tier B unless such activities can be shown to benefit or restore the ecological/biodiversity values. For example, in terms of braided river bird habitat, it may be beneficial at certain times of year to reduce, through grazing, weedy plants along the Tier B areas, as these serve as hiding places for mammalian predators on birds trying to nest in Tier A areas. Or it may be beneficial to remove, through grazing, exotic grasses and herbs around spring-fed streams, as a less toxic method than wholesale spraying, allowing endemic turfs and other native vegetation to flourish.

    Q2. How should vegetation clearance be managed?
    A2. (i) Exotic vegetation should be removed in the fairway of the active channels, to allow the river channels to migrate and re-arrange the shingle, as this is a defining feature of the ‘natural character’ of braided rivers.
    (ii) In an ideal world, exotic vegetation, including willows and poplars, should be removed/systematically replaced with natives, inside what are (as-yet-to-be) recognized ‘edges’ of the braidplain, where those trees do not serve the purpose of flood protection. The existence of weeds in many locations (including berms) interferes with the natural hydrology and ecology of the river. Floods are not sufficient to remove many of these woody weeds, and indeed, deep-rooted weeds including willows may exacerbate flooding and erosion by forcing water into narrower, faster flowing channels. We recognise that in some places there may be some ecological values in gorse acting as a refuge for invertebrates, reptiles, and some non-braided river bird species, but only in some sections of Tier B areas (hence ‘systematic; rather than ‘wholesale’ removal). Where weeds exist near braided river bird breeding habitats, they act as refuge for predatory mammals, not natives. Exotic vegetation removal in these areas should be prioritised.

    Q3. What about stock access or exclusion?
    A3. Stock access is problematic for other reasons, including adding nitrogen to waterways, eroding unstable banks, and increasing sedimentation. However, we recognize that there may need to be exceptions in some locations, for short periods. The exceptions may include the example in A1 and other circumstances outside our knowledge. In short, it should only be allowed under exceptional circumstances for ecological/environmental purposes (i.e. public good), and specifically not for private or corporate economic gain.

    Q4. What farming activities should be managed on the river bed (or part of it)? How might this be done?
    A4. None, except under circumstances that demonstrably benefit the environment, see A1 for example.

    Farming in the river bed – “developed” land

    Q1. Should there be any particular regulatory requirements on intensively farmed land that was historically river bed?

    A1: For activities that have been consented, we would support a phase-out over time (i.e., non-renewal of consents; capital investments be depreciated over the acceptable lifespan of the capital item), to ensure the ‘enhancement of the quality of the environment’ (i.e. public good) under the RMA.

    For non-consented activities, withdrawal and possibly remediation on a case-by-case basis.

    Q2: If a farmer has developed the braided river bed/margin should they be able to put in river control works to protect their land & associated infrastructure?

    A2: No, for non-consented activities, as this will interfere with the dynamic 4D movement of the river.

    For activities that have been consented, we would support a phase-out over time (i.e., non-renewal of consents) to ensure the ‘enhancement of the quality of the environment’ under the RMA.

    River protection

    Q. If the river establishes a new active (gravel) channel should we allow the river to be put back into its old channels? Does the answer differ if there is river control in place or not (and whether there is a town at risk)?

    A. No, if the new (active) channels fall within the Tier 2 section, i.e. the braidplain.

    Yes, if the channels fall outside the ‘braidplain’ and instead form on the ‘floodplain’.

    Yes, where sections of rivers have been engineered to protect critical infrastructure (as defined by Civil Defence, pages 11-35 [3]).

    We recognize ‘critical infrastructure’ values need to be protected ahead of other values, including environmental values, in some limited locations (for example bridges, roads, power lines). Similarly, we recognize the need to protect existing non-critical infrastructure including urban development, from flooding, especially as some built structures were built prior to the RMA or consented with little understanding of the potential for flooding or value of ‘braided’ rivers. These areas are relatively few and also confined to short sections of braided rivers.

    In some instances (and on a case-by-case basis), we suggest that a planned/strategic withdrawal over the coming decades be considered, via a write-off/relocation of assets or non-renewal of some consented activities, using a similar approach currently being considered for low-lying coastal communities and assets deemed vulnerable to rising sea levels. This approach will be necessary in areas where braided rivers reach the coast, thus the process for implementing a staged withdrawal and setbacks will be underway in some areas. This would also comply with the RMA Section 7(i).

    References:

    [1] Hoyle & Bind (2018) Braidplain-delineation-methodology, NIWA CLIENT REPORT No: 2017419CH_v2, for ECan

    [2] Gray (2018) Natural character assessment guidelines for braided rivers ECan Report No. R18/35 Gray et al (2018) Braided rivers: natural characteristics, threats and approaches to more effective management Report No. R17/13

    [3] https://www.civildefence.govt.nz/assets/Uploads/lifelines/National-Vulnerability-Assessment-Stage-1-September-2017.pdf

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