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Journal op the Department op AoRicuLTUfiE. 



(a) The Section of the Dam. — The following section for dam 

 walls may be adopted with safety for ordinary good and properly 

 consolidated soils resting on good foundations. For depths of water 

 not exceeding 10 feet the top width of the dam must be 5 feet, the 

 up-stream slope IJ to 1 foot, the down-stream slope 1| to 1 foot, and 

 the top of the dam above the full-supply level 4 feet. For depths of 

 water from 10 to 15 feet, the top width of the wall must be 5 feet, the 

 up-stream slope 2-1 foot, and the down-stream slope 1\ to 1 foot, and 

 the top of the dam above the full-supply level must be 5 feet. 



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(b) Setting out Dajn Wall. — On each side and above the top level 

 of the dam the top width must be staked off, so that when the dam is 

 completed the up-stream and down-stream edges of the top will be in 

 line with these stakes. Stakes defining this line should also be put 

 in at the flanks of the dam marking the ends. The up-stream and 

 down-stream toes must be staked on the ground, and these stakes well 

 protected by beacons built up with loose stones, in order to prevent 

 tlem being interfered with during construction. 



(c) Cleaning Seat of Dam.- — The seat of the dam must be cleaned 

 from all vegetation and loose rock, and if the embankment has to 

 cross over a gully or donga, care must be taken to remove all silt 

 deposited there and to slope down and step the banks of the gully 

 or donga in order to ensure a proper bond with the new work. The 

 seat must now be deeply ploughed over. 



(d) Puddle Trench. — The trial holes described in section (d) 

 above will show whether or not an impervious core is required. In 

 the majority of cases it has been found that a layer of gravel and 

 sand underlies the surface soil, necessitating the construction of a 



In many cases good retentive clay can be procured in the 



core. 



neighbourhood where the core may be constructed of clay. A trencli 

 is now excavated in the centre line of the dam and across the area 



