Hi, I've finally managed to do some more research for my Operation Sealion 1940 project. This time I decided to research some more about the German supply lines as these would be of vital importance for the German army and their possible victory. Surfing on the internet I've stumbled upon a huge amount of documents which contained lots of useful information. To make it possible to research the supply issue I narrowed the research to the ports of Dover, Ramsgate and Folkestone as these were some of the main objectives because of their proximity with Calais.

Dover, 1940
First of all I estimated the number of used German divisions for the 1940 invasion. These numbers were gathered from a number of sources including the internet and some publications. The first assault wave would probably exist out of eleven infantry division supported by a fallschirmjager division. The second wave would exist out of eleven divisions including four panzer divisions and one luftlande division. The third wave would exist out of six infantry divisions.
Another number I found was that an ordinary German division would use up to 300 tons of supplies a day including everything from fuel to ammunition. A Panzer division would probably need more so I roughly estimated 500 tons! So the first wave would consume 3600 tons, the second wave would use 4100 tons and the third wave would consume 1800 tons! The total of needed supplies for the entire invasion force (not mentionning reinforcements) a day would be 9500 tons a day!
Where would they unload these huge quantities? I found a short list with some of the British ports within the reach of the invasion forces. The numbers used are when the ports are fully operational but when the Germans would invade the ports would be destroyed together with the storage facilities, derricks and docks. These damages would probably cause that only 30% of the shown tonnage could be unloaded. The ports marked with a (*) are ports which are already partially destroyed by British engineers.

The ports of Folkestone, Dover and Ramsgate would be the primary targets of the first invasion force as these would enable the Germans to unload heavy equipment such as heavy artillery (such as 88's) and some much needed tank support (second wave). These ports however would not be sufficient to supply the invasion force so beaches would also be used for unloading supplies. The next picture shows some more number about the German capacity of unloading supplies.

The first wave would consume 3600 tons a day, the Germans would be able to unload 5200 tons (under perfect circumstances). The second wave would probably land within some days after the first wave so the total of needed supplies would be 7700 tons. As you can see there's already a shortage of 2150 tons! The third wave would probably land after a week, the total of needed supplies would be 9500 tons, the unload capacity would be 8400 tons. Again there's a shortage of 1100 tons! There's a small possibility to fly in some supplies using the Junkers but it would not be sufficient to fulfill the needs.
Edit, Thanks to the Angry Lurker, there's also the idea of Germans living off the land. As I don't think there was some sort of full scale scorched earth policy in Great-Britain. I guess some installations and supply depots would be destroyed but not all of them because of the surprise element of both fallschirmjager and some Brandenburg units.
I hope you found this an interesting read as always this "research" is purely made to be used as a base for my wargames. So there's the possibilty that the numbers aren't correct.
Greets,