Dissertation equipment and practicalities.

Sampling the river at fixed depths and positions was the first major hurdle to overcome. The equipment I needed, a Van Dorn sampler, is an open tube that descends in to the water, and when it reaches the specified depth, releases the catch to seal the tube trapping the water from that specific depth within it. The issue I had with this was that the equipment cost in excess of £1000.00, money I didn’t have.

After some consideration, modification and improvisation, I built my own. Made from clear PVC piping, bungee straps and toilet plungers, the finished product was effective and had cost a tenth of the professional equivalent.

Because of the limited depths and strong currents within the estuary, lowering the sampler on a rope and hoping that the depth would be correct seemed unscientific and would add too big a margin of error to the results to be satisfactory. Again, online retailers came to the rescue, and a 5 metre long decorators retractable pole provided the perfect combination of lightweight manoeuvrability and precise depth monitoring. So, we were set.

Out on the survey vessel Capella, provided by the port authority, we began sampling. Logging location, time, total depth and sample depth, I began collecting samples to then analyse in the lab (I also added salinity and water temperature to these readings after the first sampling trip). The process was straightforward, aided particularly by the skills of Felix, the pilot of the vessel (an employee of the port authority, and a good friend of mine) and his ability to keep the boat steady and stationary whilst sampling was underway.

Dependant on the condition of the tide, and therefore the total depth of the water, we could collect between 20 and 40 samples in total.

To add a further baseline comparison sample, each time I collect samples from the estuary I also collected a water sample from Bramber Village, approximately 8 Km upstream. Whilst Bramber is still a tidally influenced part of the River Adur, Its distance from open ocean meant that it would provide an interesting comparison to the suspended sediment levels found further downstream.

So the sampling began in May 2018 with regular trips to the river expected over the next eight to ten months.

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Where and what. Dissertation takes shape.

Having had a boat in the marina for six years and having worked at the marina for a year prior to starting my bachelor’s degree, I knew the management team. We had an informal chat about the possibility of a research project to define and monitor the currents within the marina, and the quantity of suspended sediment entering and leaving the marina at different states of the tide. Unfortunately, Premier Marinas felt the administration and bureaucracy that they would have to adhere to would make the project unworkable for them. A blow for me as I really wanted to try to make a difference to the marinas functionality and environmental impact.

Undaunted, and using contacts I had gained from working at Brighton Marina, I contacted a friend at Shoreham Port Authority about my idea. To my surprise he told me that Shoreham Port was already trying alternative methods of sediment management, and following a few emails, I sat down with the harbour master and it became obvious to me very quickly how enthusiastic and helpful the team at Shoreham would be.

Over the course of a few months I developed a sampling project that Shoreham Port Authority would help me complete. The enthusiasm and positivity of everyone at Shoreham was energising and gave me renewed vigour in the project and in the hope that the project really could make a difference.

Now that I had an idea of the direction I wanted my dissertation project to take, and I had managed to secure support from the port authority, I needed to define what the project would consist of?

To research and design an alternative to backhoe dredging was completely beyond the scope of a bachelor’s degree, and I had to keep reminding myself of this as lecture after lecture inspired me to do more and more. The quality and enthusiasm of the teaching staff at the University of Brighton made deciding exactly what the scope of the project would be incredibly difficult.

As I discovered the amazing characteristics of salt marshes (of which Shoreham has many) and their ability to capture and lock away carbon, out performing even the Amazon rainforest per square metre, I wanted to bring this in to the project. As I learnt about the strength, and complexity of ocean currents, tides and amphidromic points, I wanted to explore and develop these inputs. As I discovered the unique and varied flora and fauna that lives in estuary environments, I wanted to bring this magical world and its distinct battles that it wages every tide in to my project. But I had to keep reminding myself of the constraints and expectations of a bachelor’s degree dissertation project.

So it was that the final project was devised. Using three transects on the western arm of the stretch of the River Adur up to almost to the Sussex Yacht Club from the mouth of the river. I would take samples of water at one metre intervals of depth in three places across the river. This would allow me to build up a picture of the volume of suspended sediment at three distinct locations within the estuary. By sampling at different times of the year, at different states of the tide, and after differing weather phenomenon, I could expand the picture of suspended sediment to try and identify key inputs and factors affecting the type and volume of sediment being carried and deposited in the estuary.

With the boundaries of the project decided it felt like I had moved away from the original concept completely, but upon reflection I realised I could not look at what to do with the sediment until I understand completely the origin, volumes and dynamics of the material I hoped to control.

Following discussions with what became my supervising professor, I also added Acoustic Doppler Current Profiling (ADCP) to the project. This compact and portable piece of equipment can analyse a cross section of the river and show you the direction and speed of the flow. This additional information would allow me to show what the currents in the estuary are doing and help to expand on the energy regimes present in the water. (More to follow on the ADCP in another blog piece.)

My dissertation project origins

Having lived and worked in Brighton Marina for over five years, I had seen at first hand the problems of silting-up of a marina. Accumulation of silt is a problem that almost every port, harbour and marina the world over suffers from.
When the high energy ocean waters enter the calm sheltered safety of a port, the drop in energy levels of the water means that it can no longer carry the same amount of suspended sediment, and therefore deposits its suspended load on to the bed of the port.

It’s important to differentiate here between dissolved and suspended. Content that is dissolved in the sea water has undergone a chemical reaction and will remain dissolved regardless of the energy levels of the water. Suspended material however is merely carried by the water and will be deposited as soon as energy levels drop.
In the few years since moving on to my boat, the silting at Brighton Marina has become progressively worse with access to the marina becoming more and more restricted as the attempts to dredge the fairways and berths fails to keep pace with the sediment build-up.

Currently the standard solution to sediment build-up is to scoop it out using a large excavator (backhoe dredging) and dump it in to a specialised (split) barge, that then transports it out to sea and drops it somewhere they think won’t matter.

This method of sediment management raises a number of issues:-
I} discharge of sea toilets, engine grease, litter, and antifoul are all deposits that are particularly concentrated in marinas and ports. None of these contaminants are positive for the marine environment, and in their often-concentrated forms in port silts can be devastating to marine life.
Ii}as silt builds up, anoxic (low or no oxygen present) mud is produced as there is no penetration of the top few centimetres of the mud. This dark, stinking mud is almost devoid of life, but when disturbed (during the dredging process) quantities of methane can be released; a gas that can be over twenty times more effective as a greenhouse gas than CO2.
Iii} a typical split barge (a vessel that is amazing in itself, as it literally splits in two and allows its load to fall down through the gap), can carry up to 600 tonnes of silt in a single load. When dropped on to the sea bed, away from the marina, this sudden and dramatic inundation of silt can be catastrophic to filter feeders and benthic (bottom dwelling) species.
In Brighton the above considerations must be viewed whilst remembering that the marina lies at the western edge of a marina conservation zone, and that all the silt being removed from Brighton marina is then being dumped in to what should be a protected and conserved area.

Backhoe dredging is not a cheap process, with a typical annual bill of £300,000 to £500,000 not being unrealistic, and at these levels of expenditure silt is still accumulating quicker than it is being removed.
With my personal experience of trying to get my own yacht in and out of the marina, with her 1.8 metre draft, and the knowledge I was gaining during my University of Brighton Earth & Ocean Science Bsc (Hons) course, I felt that there had to be a better solution?
I began to read research papers on sediment management, I learnt about the intricacies of suspension times, currents, coastal littoral cells, and particles sizes. With this growing knowledge and interest in how sediment built up, I approached the marina management at Premier Marinas Brighton to discuss a potential dissertation project for my bachelor’s degree.