If you look on the Oldmap site at Avebury (1889) the river seems to fold back on itself here, or at least may have been enlarged for some reason; the pond? which could have meant dredging. This river after all is a winterbourne one, and the farm would have needed lots of water. Also the spring line, can be followed by the line of wells that appear from the cottages at the entrance to WKLB to the Manor Farm ......