I took it off this site -I posted a couple of years ago;if you save it to your computer you should be able to increase but not sure how to increase resolution
the banks would be shown on any decent electronic chart; even in a rib you want to be careful at low water.I would get a paper chart as well
there is petrol on the Orwell at Levington Marina -expensive.Alternative would be a visit to Foxes further up the river and walk to the nearby petrol station .
take a look at www.hha.co.uk
-loads of info and a downloadable chart /map