Regional Estuary Monitoring Programme (REMP) intertidal sedimentation measurements, results and review of methodologies

TR 2019/04
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Report: TR 2019/04

Author: Stephen Hunt

About this report

Sedimentation within estuaries is a natural process but excessive sedimentation can lead to poor ecological health. To track patterns of contemporary intertidal sedimentation WRC has been monitoring SAR in the Firth of Thames and Whaingaroa (Raglan) Harbour since 2003 as part of an estuarine State of the Environment (SoE) monitoring programme. The programme measures sediment depth above plates buried in the intertidal flats. The purpose of these measurements is to track SAR in each estuary and to pair the measured SAR with monitoring of ecological health. This report analyses the WRC SAR monitoring to assess the suitability of the methodology including spatial distribution of plates, temporal distribution of measurements and longevity of the plates. Sedimentation rates at each monitoring site have also been derived from the measurements. This purpose of this analysis is to determine if the sedimentation monitoring programme has been effective and to establish principles around which a standardised sedimentation monitoring programme can be designed in the future, for the purposes of both SoE monitoring and for implementation of monitoring set out in Sea Change 2016. The analysis found that sedimentation rates are highly variable, with areas of both erosion and accretion and this spatial variation in SAR can be tentatively related to the spatial distribution of hydrodynamics in each estuary. Sedimentation plates are effective at measuring annual rates of SAR providing the plates are set out with an appropriate spatial array that take into account the spatial distribution of hydrodynamics and are measured annually at regular intervals for at least ten years. Simple guidelines for installing the plates and a standardised methodology are also outlined in this report.

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Regional Estuary Monitoring Programme (REMP) sedimentation measurements, results and review of methodologies  [PDF, 5.6 MB]

Contents
 1 Introduction
1.1 Estuarine and sedimentation processes
2 Methodology
2.1 Sediment plate methodology
2.1.1 Firth of Thames
2.1.2 Whaingaroa (Raglan) Harbour
2.2 Calculation of sediment accumulation rate
2.3 Plate elevation and water depths
2.4 Plate material and condition
3 Results
3.1 Firth of Thames
3.2 Whaingaroa (Raglan) Harbour
4 Discussion
4.1 Sedimentation trends
4.1.1 Firth of Thames
4.1.2 Whaingaroa (Raglan) Harbour
4.2 Effectiveness of methodology for measuring sedimentation
4.2.1 Plate subsidence
4.2.2 Plate material
4.2.3 Measurement technique
4.2.4 Temporal scale of measurements
4.2.5 Spatial configuration and coverage
5 Conclusions and recommendations
5.1 Plate setup
5.2 Plate positioning
5.3 Temporal frequency of measurements
5.4 Measurement method
6 References
Appendix A. Heights of plates from LiDAR and tide gauge data
Appendix B. Wave model