1. For ponded water inside the water-retaining dike, except where the longitudinal undulation of the ground is relatively large, transverse blind drains should generally be provided. The blind drains shall be constructed of dry-laid rubble, but a sand-gravel filter layer should also be provided at the ends connecting to the sand embankment to prevent sand from clogging the blind drains.

2. During hydraulic filling of the water-retaining dike, the removal and dewatering of water inside the dike should be properly carried out, and drainage outlets should be left at appropriate locations. The size of the outlets may be calculated as 2 to 4 times the area of the drainage pipes. The water-retaining dike on both sides of the outlets should be reinforced; wooden or metal frame-type openings may be installed on the inner side of the dike, with movable gate plates and 1 to 2 discharge pipes leading through to the outside of the dike.