The Black Sluice was created specifically for land drainage purposes though at some points in its history it was also used to transport local agricultural produce to Boston. The sluice is situated to the south of the River Witham in south Lincolnshire. There are no specific dates for its opening or details of its use as a navigation though it was controlled by the Black Sluice commissioners who (despite their name) were predominantly responsible for looking after the River Glen and Bourne Eau to the west of Spalding. The first date mentioned for either of these waterways was an Act of Parliament for Bourne Eau in 1781.
The Black Sluice is marked on all good road maps under the name of The South Forty Foot Drain. It begins at Guthram Gowt on the north side of the A151, Bourne to Pinchbeck road (west of Spalding). On the south side of the main road the River Glen heads north east to Pinchbeck but, although there is only a few feet between the river and the head of Black Sluice, there is no navigable connection.
The first 4½ miles of the sluice are absolutely straight in a northerly direction. Along this stretch, before the B1397 is reached at the 4 mile mark, there are a couple of tracks which cross the route near the village of Casswell’s Bridge. A number of other roads come to dead-ends at either side of the sluice all along this stretch but only the B-road actually crosses it.
The route now heads slightly east of north along the next 4½ mile stretch. It continues to follow the same theme as the previous stretch – dead straight, almost featureless with only the odd farm and dead end road coming close. One minor road crosses the route about one mile along this stretch and the A52 crosses after about 3 miles. At the 4 mile mark the Spalding to Sleaford railway crosses over and then the sluice takes a slight right curve to head north east into the next stretch.
The penultimate part of the route is 3 miles long and is completely isolated. As before, the odd road or track comes up to the banks of the sluice but there are no major crossings. Just before the end of this stretch there is a fork to the left where an unnamed drain heads off to the north for about 8 miles to connect with the Sleaford Navigation (Kyme Eau).
The final stretch of the Black Sluice begins with a sharp right turn to the east just as the Sleaford to Boston railway swings in from the west to run parallel on the north bank. Within about ¾ of a mile the sluice and the railway meet the A17. The road crosses the railway on the level and crosses the sluice on Swineshead Bridge. The next 5 miles are dead straight with just one “kink” to the right. The railway still clings to the north bank and now the A1121 clings to the north of the railway. The B1192 crosses at Hubbert’s Bridge and Boston Airport is past just before the A52 crosses at Chain Bridge. Past this bridge the sluice runs for a final 1½ miles, under the A16 and into the River Witham on the tidal side of Boston Grand Sluice. There used to be a sea-lock at the junction with the river but this was removed in 1971.