draft revised kaihu river management plan - Northland Regional ...

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Northland Regional Councilpotentially compromised by sediment accumulation due to trapping ofsediment in ricegrass on the banks. Removal of bed sediments is notpractical, given constraints of the reach of available machinery andcost implications.In Section 1, machine cleaning will be done on both banks annuallyexcept for a section on the left bank where the floodwall exists and asection on the right bank where a slump compromises machineaccess. In Section 2, machine cleaning will be done annually on bothbanks. In Section 3, machine cleaning will be done on one side of theriver annually, commencing with the left bank in Year 1, and alternatingbetween right and left banks on subsequent years.3.3. Clean Inside BendsFrom Rotu Bottle Neck to Waihue Road the channel meanders andthe river gradient is low. Excavation of accumulated sediments fromthe inside bends is proposed for this section. This river work requiresan annual assessment prior to commencement to prioritise removal forthose bends that would contribute greatest to stream bank erosionand/or loss of assets.3.4. Spray WillowsWillows in the channel which reduce the capacity of the flow and/orresult in potential for debris blockages or streambank erosion requiremaintenance. The maintenance plan provides for three years ofspraying in the three upstream sections of Kaihu River.3.5. Remove Fallen Debris That Dam The RiverThe significant debris that dam the river specifically in the section fromWaihue Road to Ahikiwi are the fallen mature poplar trees, shootscoming from the exposed roots of the poplar trees along the channeland willows. This river maintenance is done annually on the two uppersections of the channel, with an annual assessment undertaken at thecommencement of the works season to identify blockages andprioritise removal.3.6. Gravel ManagementLarger gravel is accumulated upstream of Ahikiwi, reducing in sizedownstream.Where the accumulation of gravel in the channel causes flowobstruction or flow diversion that introduces streambank erosionwhich in turn risk damage to assets, gravel management may berequired.Any person who wants to extract gravels from the channel ispermitted as long as the activity falls within the scope of the permittedKaihu River Maintenance Plan 2010-2016 - 5 -
Northland Regional Councilactivity rules set by the Regional Water and Soil Plan for Northland 2 .Activities which fall outside the rules such as extracting quantities ofgravel greater than 100 cubic meters in 12 months among othersneed to seek consents from the Northland Regional Council or rely onexisting consents for gravel extraction such as that held by theNorthland Regional Council.3.7. River Cross Section SurveyEvery five years, a river channel cross section survey will beconducted on fifteen locations in the river from SH Bridge to RotuBottleneck. This will provide a basis for assessing the effectiveness ofthe maintenance programme and assessing changes in river capacityover time. The proposed cross section locations are shown in Figure6.4. Proposed Annual Work Programme and Indicative CostingsThe proposed annual work programme and cost estimates provideinformation on the forecast Kaihu River Maintenance Work. It isessential that there is an annual pre-works assessment of the river toconfirm priorities for river works that are required. Figures 2-6 andTable 2 show the summary annual programme for each of the riversections.2Rule 31.01.01, Regional Water and Soil Plan for Northland, Page 31-1Kaihu River Maintenance Plan 2010-2016 - 6 -
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draft revised kaihu river management plan - Northland Regional ...

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