PORE WATER INFILTRATION AND DRAINAGE ON A MEGATIDAL BEACH IN RELATION TO TIDE- AND WAVE-FORCING

Abstract

A pressure and temperature sensor (pT sensor) was deployed at mid-tide level and at a sediment depth of 0.5 m on a steep, megatidal, mixed-sand-gravel beach in Advocate Beach, Bay of Fundy, Nova Scotia, for pore pressure monitoring at the beachface. The pT sensor was buried at a sediment depth of 0.5m centrally located in the intertidal zone. For comparison, another pT sensor of the same model was synchronized and mounted to an instrumented frame 0.5 m above the beachface at approximately the same location. The tidal range in this area is ∼10-12m. During the experiment, significant wave heights ranging from 0.1-0.9 m and wave periods ranging from 3-8 s were measured. The results demonstrated that the pT sensor was well suited for pore pressure monitoring with regard to tidal variations and wave action in the intertidal zone. A spontaneous infiltration of pore space with the uprising flood tide was observed, while the drainage phase was extended in response to low drainage rates. Regarding wave action, the wave signal was well reflected in the pore pressure records. However, the signal was damped and delayed compared to the in-water pressure signal. Also, wave skewness and asymmetry was more pronounced in the sediment. Despite the very coarse material (d 50 =0.3-18.5 mm), short phases of pore pressure build up were observed. Based on this data set, a more detailed analysis of pore pressure signals with regard to surficial grain size variations and hydrodynamics will be carried out.