The most common explanation I have found is that it means swallow stream or spring. The explanation given is that the first component of the name is derived from the Anglo-Saxon word “swealwe” meaning “swallow”¹. However, the only proffered explanation of the salience of swallows to the topography and location of Swalwell is that it is located on the River Derwent joins the Tyne and the that the “junction of two rivers is a likely place for swallows to swarm”¹.
Further research regarding place names though suggests that there are three schools of thought re the meaning and origins of the “swal” component of the surname i.e.:
- Anglian “swalwe” or Anglo Saxon “swealwe” meaning swallow² and is interpreted as meaning the bird. It is also suggested that this may be indicative of a nickname for someone who darts quickly or indicative of a place where there are a lot of swallows.
- Old English “swealwe” or Anglo Saxon/German “swalm” meaning a rushing stream or whirlpool. As such its use as a place name is believed to be based on local topography. Relate to this is the suggestion is that the English words, swallet and Swallow-hole, which apply places where streams disappear underground in limestone or chalk country could explain the name of Swallow in Lincolnshire. In this context, the meaning of swallow as a noun appears to mean an “abyss or hole in the ground” and an association with water is frequent, often in allusion to whirlpools² ³.
- “Swale” as opposed to “swal” is described as meaning “low, hollow place, often boggy 
I cannot pretend to understand in any depth the nuances of etymology so deciding which of the above explanations are most salient to Swallow is difficult. Further understanding the topography of Swalwell at the time when the surname originated is almost impossible given industrial development and a reservoir that has changed the nature of the river.
There are possible hints within historical writings about the place that makes me think the “water” interpretation of the surname may be more appropriate than that of the bird i.e.:
- Swalwell is described as being at the end of the tidal reach of the Tyne
- Swalwell bridge is described as being no longer navigable by boat
- There are early references to a mill here & therefore presumably a mill race
- The Boldon book indicates there was a fishery here & this could imply that there was weir and a pool or pools in which to catch fish as this was common practice by the Romans
- there are references to historic incidents of flooding which may belie the calm and peaceful descriptions of the River Derwent in contemporary writing
- some of the descriptions do suggest that the land here was quite marshy
- it is also possible that the longmeadow at Swalewelles described in the early property transfer may refer to a water or flood meadow.
My hypothesis at this point in my research and understanding would be that Swalwell is a locational surname but a toponymical one based on the historical characteristics of the river at this point but clearly more work needs to be done to confirm this.
Of course, Swallowell has also been used in fiction as a surname for individuals who exhibit characteristics of gluttony so perhaps it could also have originated as a nickname but I know which interpretation I prefer!