Location: Hamilton, New Zealand
Type of Project: Field Data Collection, Hydrodynamic Modelling
Client: Environment Waikato
(Left) Aerial view of the Hamilton reach of the Waikato River and the locations of the two study sites. (Right – top) the river bed composition at Site 1 and (lower right) the river bed composition at site 2.
ASR investigated the effects of synthetic flood wave generation (ramping) on the transport of sediment and changes to the river bed.
To assess the effect of synthetic flood waves (the surge of water released from a dam that travels down a river reach) on sediment transport, ASR made direct measurements of the bedload transport at two sites in the Waikato River near Hamilton, New Zealand. The bed shear stress was found to be sufficient to transport the sand fraction continuously and, at peak flow, able to mobilise sediment over 10 mm in diameter. In general, the transport rates were correlated with the flow velocity and shear stress, as would be expected, and total loads were found to be between 23000 and 37000 m3/yr.
The measured sediment transport rates were far lower than rates predicted by the commonly-adopted sediment transport formula. This occurs because transportable sandy sediment is very limited due to the gravel lags covering the bed. This was supported by video observation of an armoured bed. Based on the measurements and observations, the bed is apparently relatively stable in the reaches studied. The bed is evidently evolving to an armoured state, which is slowing the rate of bed degradation. Without re-supply of sediment from upstream due to the presence of the dam, this process would be expected to continue under the present ramping regime.« Download Project PDF