River management can be seen as distinct from flood protection and soil conservation, although in some ways it links to both.
Most landowners are capable of undertaking river and stream maintenance, and under Project Watershed it is proposed that this continue. Most landowners manage stock to prevent damage, maintain trees and vegetation along riverbanks, and undertake minor levels of work to maintain the channels in their present form.
Issues arise when the work is undertaken to differing standards or when the type of work undertaken needs particular expertise or experience. Most river improvement work is outside the normal maintenance activities done by landowners, and in many instances, requires a resource consent. It is also essential that river and stream work in a catchment be undertaken to a consistent standard so that any damage or loss from river processes is minimised.
Routine river maintenance includes undertaking inspections, liaison with landowners, and completing an annual work programme to maintain river and stream channels in their present form. It does not include any improvement work or capital work. The intention of routine river maintenance is to ensure channels remain free of vegetation and obstructions so efficiency is maintained. It also includes undertaking small erosion control work to maintain channels in their present locality, as well as reduce the sediment input caused by streambank erosion. River management includes:
- Annual inspections of the main rivers and streams and responding to enquiries.
- Removal of isolated whole trees, stumps or limbs that have fallen into the channel, or are likely to and could create an obstruction to flow or exacerbate erosion.
- Assisting with fencing of eroding portions of channels.
- Planting and maintaining vegetation to help prevent erosion.
- Undertaking simple erosion control work within channels.
- Spraying vegetation.
Routine river maintenance work involves landowners by liaison before the work is done. In most cases, the work would be undertaken with assistance from the landowners and in conjunction with the landowners’ normal river and stream maintenance work.
It is intended that landowner involvement in proposed river management work continue. Environment Waikato’s involvement would be to provide advice, ensure that maintenance within a catchment is undertaken to a consistent standard, and undertake work which is beyond the normal capabilities of landowners, or requires a resource consent.
It is proposed that routine river maintenance be undertaken in all of the larger rivers and streams where lack of maintenance is likely to have a significant effect on other properties or values, or where streambank erosion is having a significant input to the sediment load within the stream. Streams in this category may include:
- Rivers and streams of a significant size (say, greater than 3-5 m top width) and where there is benefit within the catchment from consistent maintenance.
- Rivers and streams that suffer from significant erosion and where there is regional benefit in controlling the erosion.
- Rivers and streams of a significant size that have different property owners on opposite banks.
- Rivers and streams that are within a property where maintenance is required to avoid significant adverse effects on upstream property or values.
At this stage, only limited mapping has been undertaken to assist in scoping the possible extent of work proposed under routine river maintenance. If the work fits this description then it is likely to be noted and prioritised.
River improvement involves works of a more significant capital nature. In some cases this will involve large-scale intervention. In most cases, the work aims to control bank erosion and stabilise the river channel. Proposed river improvement works are restricted to a few specific areas where major intervention is required.
The type of intervention will depend on the requirements of the site, but could include:
- Willow revetment (revetment refers to the armouring of stream banks).
- Rip rap (or large rock) revetment.
- Channel realignment.
- Construction of groynes.
- Gravel management.
- Sand Management
Landowners adjacent to the works are likely to receive the most benefit from river improvement work. Where direct benefit can be attributed, a differential rate may apply. A percentage of cost is attributed to the wider catchment in recognition of sediment reduction and other contributing effects.