Wharekawa Estuary - Sediment Dynamics

Results show the variation of sediment dynamics in upper estuary sub-environments and with proximity to the head of the estuary. Sediments are most dynamic in the depositional environment of the river mouth. Sediment transport is less dynamic towards the middle estuary and the head of the estuary. The most upper reaches of the estuary are depositional environments. Fluvial processes clearly dominate and transport sediment seawards. Sub-environments closer to the middle estuary are net erosional. Tides here are the dominant control in channel and bare intertidal environments. The flora and fauna of the seagrass and mangrove environments clearly influence sediment dynamics. Sediments in the upper Wharekawa Estuary are readily reworked. Up to 134 mm of the surface sediment layer is actively turned over. Greatest re-working occurs at the Wharekawa River and Tawatawa Stream mouth where 17,348,000 m3/m of sediments was estimated to cycle through the estuary cross section. Purpose: This study investigates sediment dynamics in the upper Wharekawa Estuary, Coromandel Peninsula, New Zealand. Detailed sediment transport and hydrodynamic experiments were undertaken and combined with topographic surveys to develop an understanding of spatial and temporal variations on sediment mobility within the upper reaches of the estuary.

Surficial sediment samples, cross sectional topographic surveys, biotic surveys, upper estuary flora survey, detailed seagrass survey. Faunal survey, surficial sediment analysis, current measurements – flow direction and water depth measured at a number of sites, wave measurements, suspended sediment sampling, bed level monitored.

Upper Wharekawa Estuary

Field work 22/04/2007 to 6/05/2007. Bed level measurements taken 28/05/2007 to 28/11/2007. Seagrass survey 11/08/2007.

Three cross sectional topographic surveys to determine elevation of different sub-environments. Total station. Biotic surveys to distinguish between sub-environments and link geomorphology with ecology. Upper estuary flora surveyed. Zostera (seagrass), Avicennia marina (mangrove) and Juncus (saltmarsh) documented at each transect Detailed seagrass survey. Relationship between seagrass density, maturity and topography. Quadrats with density counts. Faunal survey – (sieved from 0.5 m deep excavation). Surficial sediment analysis (23 to 26 samples per transect). Top 5-10 cm of sediment. < 2mm portion of samples was analysed using a Malvern Mastersizer 2000. Current measurements – flow direction and water depth measured at a number of sites. Acoustic Doppler current Profiler (ADCP), Falmouth Scientific Inc. ,(FSI) current meter and two Interocean System electromagnetic current meters (S4) from 22/04/2007 to 6/05/2007. Wave measurements: five Keller Pressure System Inc. (KPSI) pressure transducers were used to measure wave heights in upper Estuary. Suspended sediment sampling in upper estuary. Sediment traps in upper estuary. Bed level monitored using depth of disturbance rods. All methods recorded in detail within thesis.

Data quality: Various

Printed thesis.

Study was undertaken as part of a Master of Science degree.

Sensitivity/Confidentiality: None known Thesis available from Auckland University Library.

Study complete