Acoustic Doppler Current Profilers (ADCP) are an amazing (and expensive) piece of kit. Mounted on to a float in this case, the unit works by sending acoustic ‘pings’ through the water, and then records the echoes that rebound off the sediment and other objects suspended in the water. The clever part of the ADCP is in its ability to identify not only the presence of items in the water, but also the direction that the water is flowing in down through the water column to the riverbed, as well as the speed at which the water is flowing. When linked to the differential GPS (dGPS) system built in to the unit (and a static GPS base station of the river bank) you can then see a cross-section of the river and identify exactly what is happening below the surface.
In a dynamic and volatile environment like an estuary, water currents direction and speeds are complicated. With salt water and fresh being different densities, you can have a situation (particularly on rising tides) where fresh water is flowing down the river, whilst the heavier salt water is driving upstream beneath the fresh water.
The level of discharge of the river (the physical volume of water flowing down the river) and the tides state will all affect how quickly and how thoroughly these two distinct water bodies mix and combine. Whilst the ADCP cannot tell us the salinity of the water being analysed, the direction and speed of flow can be a good indication of the waters source, especially when combined with salinity readings from the water samples already collected.
Once surveyed, the data collected is downloaded in to GIS (Geographical Information Systems) software. This allows the data collected to be overlaid on to a three-dimensional map, so that visual presentation of the processes underway beneath the surface is straightforward and easy.
Through the support of Dr Annie Ockelford, my supervising professor for my project, and her contacts at the University of Hull, I was able to use their equipment on two separate occasions in May and June of 2018.
The data collected supplemented and built on the data provided by the water sampling and will hopefully help to produce a more insightful and complete analysis of the processes underway in the estuary.