ESTABLISHING THE HATCHERY 



where the earth is saturated with 

 water — the wetter, the better — and 

 where it would be impossible to use 

 other methods. Holes, 12 to 20 

 inches apart, should be driven down 

 to solid earth (rarely more than 16 

 inches below the surface). These 

 holes should be charjjed with dyna- 

 mite made of 50-percent nitro- 

 glycerine, and set off \vith an elec- 

 tric battery to obtain the greatest 

 possible lifting power. The "prop- 

 agation" method may be used where 

 the soil is very wet. By this 

 method, one cap is used to set off 

 the first stick of dynamite, and the 

 other sticks are exploded by the 

 shock of the first charge. If the 

 soil is not Avet, a cap should be used 

 for each charge. Less time is 

 needed to construct a ditch in this 

 way than is required for other 

 methods. 



By now the soil types should be 

 known Avith some degree of ac- 

 curacy. Only pure clay or clay 

 soils should be used to fill the trench 

 that has been excavated. This cut- 

 off wall, or core, shoidd be built up 

 several feet through the center of 

 the dam. The better, more im- 

 I)ervious soils tliat are available for 

 construction should be used directly 

 under the center of the dam and on 

 the upstream side. IjCSs desirable 

 or lower quality earths, such as 

 sand, stone, or gravel may be used 

 in the fill, hut they should be in- 

 corjK^rated only on the downstream 

 side of the liighest [)oint in the dam 

 and extend to the toe. So placed, 

 these poorei- earths provide weight 

 to prevent slipping and are at the 



maximum distance from the satura- 

 tion point of the water. 



With small dams or pure clay 

 soil, it is unnecessary to construct 

 a core through the dam. The same 

 result may be effected, after the 

 whole area of the base is plowed, by 

 removing the topsoil down to solid 

 earth on the upstream half of the 

 dam and properly placing it on the 

 lower half. The solid earth should 

 then be plowed so it will bind with 

 new earth moved in. Thereafter, 

 the builder should follow the 

 same construction procedure rec- 

 ommended for a dam in which a 

 core is made. 



After the base has been properly 

 prepared, the drain line should be 

 laid. A shallow excavation to solid 

 earth should be dug from the pro- 

 posed pond outlet to a point below 

 the dam. Earth, the best clay avail- 

 able, should be firmly packed 

 around the pipe, particularly on the 

 underside. Addition of water to 

 the soil to form a stiff mud will fa- 

 cilitate a firmer pack in the tamp- 

 ing process. At some central point 

 in the dam, a concrete collar should 

 be poured around the pipe. This 

 prevents water from following the 

 pipe and developing leaks; it also 

 prevents burrowing animals, such 

 as crayfish, from following the 

 pipe. After the pipeline has been 

 set up, construction of the dam may 

 go forward. 



Earth from somewhere within 

 the pond area can be used to pro- 

 vide dirt for the dam. Most of the 

 soil should be obtained in the vi- 

 cinity to save labor. The whole 



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