Shankland Island found and confirmed as below:
Shankland Island is another one of the many frustrating research projects encountered in genealogy. When I first started I thought this would be a "no-brainer", after all how difficult could it be to find a 60+-acre Island in the middle of a well known creek?
Unfortunately, for us, the long proposed Lewes-Rehoboth canal became a reality (built between 1893 and 1916), and according to the local historians Shankland Island "was dredged away".
William Shankland bought this island of marsh in the early 1700's and the survey still exists. It was approximately 16 acres then, but being a sand bar it kept growing in size over the years. I have yet to find an early map of the area that shows the exact location. In a resurvey by William Shankland (a descendant), he shows the various resurveys, probably occurring at probate, with tick marks. The Island was passed down through the family over several generations. Note that the compass rose is not set to due North and the orientation of the island in the survey nearly matches the map.
I have revisited this problem in recent times and have found the area of this Island and possibly the Island itself. The key here is the Island is located in the Lewes Creek (now the canal) but in the area of Cape Henlopen as indicated above. Looking at modern computer maps shows an Island that approximates this survey. It may not be Shankland Island but the Island was definitely in this area. Further research using the old surveys of both Shankland Island and the neighbors' Islands could pinpoint it. The area of the asterisk to the right is likely Shankland Island, and the asterisk to the left is William Shankland's original homestead in Lewes for reference.
This picture is of the Lewes Rehoboth Canal and the land on the North side taken east of Lewes route 9. It is representative of the marsh land in the area. Marsh hay was valued for livestock feed.
Subsequently John N Shankland and Simon Grundy discussed further the possible location of Shankland Island, and Simon believed he had positively located them as the shaded areas on these two maps: