Historical bed-level change at seven cross-sections along the lower Rakaia River

This investigation analyses historical bed-level change at seven cross-sections along the lower Rakaia River between around SH1 Bridge and the coast using data from ground surveys undertaken in 1976 and 1988/89 and from airborne LiDAR flown in 2010. It is concluded that with a few exceptions, mean bed levels along this reach appear to have been stable - at least within the level of detection and allowing for natural variation in bed levels associated with normal braided riverbed dynamics. A slight degradation trend of a few mm/yr is consistent with a response to long term coastal retreat, at least for the river within about 18 km of the coast. It is likely that much of the 0.75 m of degradation apparent over the active braidplain of the South Branch 10 km upstream from the coast between 1988 and 2010 is an artefact of errors in re-locating the section line. The investigation included: 1) Securing the historical ECan survey records and entering them into a spreadsheet. 2) Extracting the 2010 bed-levels from the LiDAR along the ECan section lines 3) Post-processing the LiDAR topography to remove remnant bias from returns off riparian vegetation. 4) Using flow-gauging data to develop a relationship between wetted cross-section area and river flow rate for use in adjusting the LiDAR mean bed-levels to include wetted bed areas 5) Plotting the overlaid sections and calculating changes in mean bed-level reporting.
 
Citation proposal
Jochen Bind (NIWA). .
 

Identification

Data identification

Citation

Date ( Creation )
2015-06-16T04:18:00
Date ( Revision )
2015-06-16T04:18:00
Purpose
To determine if the mean bed levels along the lower Rakaia River have changed between 1976 (or 1988) and 2010. 
Credit
Hicks, D. M., Bind, J. (2015). Bed level change in the lower Rakaia River, 1976-2010. NIWA CLIENT REPORT No: CHC2015-012, NIWA Project: SCJ15501/13. p. 17 + appendix. Work funded by William Southward. 
Status
Completed  

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Spatial representation type
Vector  
Topic category
  • Inland waters

Extent

Description
Canterbury Region 

coordinates

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N
S
E
W


TimePeriod
2010-07-01T00:00:002010-07-31T00:00:00 
TimePeriod
1988-01-01T00:00:001989-12-31T00:00:00 

Extent

No information provided.
  • Rakaia River, historical bed-level change, airborne LiDAR
NIWA Project Codes
  • SCJ155REG

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Other constraints
Data used in this report are owned by ECan. Contact NIWA point-of-contact (email details above) in the first instance. 

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Use limitation
Data owned by ECan 
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Restricted  

Associated resource

Title
Hicks, D. M., Bind, J. (2015). Bed level change in the lower Rakaia River, 1976-2010. Prepared for W. Southward. February 2015. NIWA CLIENT REPORT No: CHC2015-012, NIWA Project: SCJ15501/13. p. 17 + appendix. 
Association Type
Larger work citation  

Locale

Language
English  

Character encoding

No information provided.
Supplemental Information
First data were from 1976. 
 

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Scope

Hierarchy level
Dataset  
Dataset
Rakaia River bed-level change data 
 

Ref. system

Reference system

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Reference system identifier
OGP / urn:ogc:def:crs:EPSG::4326

Reference system identifier
NZST/NZDT

 

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Text

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Classification
Restricted  
 

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