1) The diversion of the course of water using dams, to create dry conditions for masons to work on the foundations of bridge pillars.
This practice is alluded to in the contract of 1422 for Catterick Bridge, although it is not explicit about the means employed: Nicholas de Blakburne and his felaws schalle kepe the water wer [weir] and defende itt … to the tyme the branderethe be laide and the werke of masoncraft be passed the danger and the noiesance of the same said watir. In 1717,Brotherton Cawsey was being repaired and the workmen paid the millers and forge men for drawing the water of when they laid some low ground works. It is likely that the millers and forge men had the expertise to do this for they would have been accustomed to drawing dams. The purchase of a pump soon afterwards appears to confirm this.