River Medway (mud flat, port in river)

River Medway (Kent)  28 Jan. to 29 Jan., 2019

Keywords: Tidal flat, Sedimentology, Land use, Port

I visited the mouth of River Medway to observe mud flat and the port along the river.

First, I went to Gillingham where a wide tidal flat spreads along the riverbank (Fig. 1).

Fig. 1. Location of River Medway.

The tidal range is around 5 m and the seafloor of the port was exposed when I visited there in low tide stage (Fig. 2). Meandering creeks develop in the tidal flat (Fig. 3), and dune develops (Fig. 4).

Fig. 2. Exposed seafloor in port.

Fig. 3. Meandering creeks and dune on the mud flat.

Fig. 4. Dune on the mud flat.

And I walked along the river to St. Mary's Island. It is not an typical island, but isolated point bar separated by a water channel (Fig. 5). There are four passages to the island, and all are water gates, and the water areas between them are used as marina or dock with the water level kept constant (Fig. 6).

Fig. 5. Location of St. Mary's Island.

Fig. 6. Marina inside the water gate. The water level then in marine is few meters higher than outside.

Many British important ports, included the port around here, are located at places where estuary changes nallow and to a meandering river like here. And most of the ports have water gates to keep water level constant.

On the other hand in Japan, the most of important ports are located along the sea and few are located along the river. In addition to this, Japanese ports are protected from strong wave and tsunami not water level changes due to tide. The differences are because tidal range is small and the river traffic is less developed due to the large river gradient in Japan, I think.

Navigation management is pointed out as a purpose in many international research papers about mud deposition in estuaries (and rivers). But in Japan, it seems not to be necessary in many rivers so I couldn't realize the importance before I saw such a ports in UK rivers.

The island is a high-end residential area, with many herbs planted along the garden and the road, with a lavender scent. The island is like a paradice (Fig. 7).

Fig. 7. Residential area in St. Mary's Island.

Along the island, River Medway is clear and blue, but the shore is a mud flat with ripple and a creeks which are perpendicular to the river. Many yachts are anchored on the river (Fig. 8).

Fig.8. River Medway and the mud flat on the shore.

I continued to observe along the river to Rochester, I found the small-scaled cuesta developed on the mud flat (Fig. 9).

Fig. 9. Small-scaled cuesta on mud flat. Strata are inclined steeper toward the river than present river bed.

The bedding surface of the sediments which are also modern are inclined steeper toward the river than the present river bed. To make such a structures, it have to be flatter at the erosional phases than depositional phases. Many cuesta in mud flat are opposite (only my experiences) so I felt this structure unusual.

It would be interesting to reconstruct the geological history by conducting a columnar sampling.

Appendix

As this area is a key area of transportation, it is also important for the military, and there are some forts, for example, Rochester Castle built in the 11th century and some early modern forts (Fig. 10).

Fig. 10. Forts around Rochester and Gillingham.

These buildings are open to the public and can often climb towers in many cases. From there, we can look quite far in all directions, and it helps to find out the places to observe, such as the distribution of outcrops, and glasp the summary of the topography (Fig. 11).

Fig. 11. View from Rochester Castle. The summary of River Medway and distributions of outcrops of chalk beds (right in the photo) are easily understand from here.

Rochester Castle is a tourist site not a geological site, so I visited there after I finished geological survey, but it was regrettable that if I went there in the beginning, I could grasp the whole picture before survey. After this survey, I decided to visit cathedrals or castles which are highest buildings in each area when I arrive new areas.