In the case of small ponds, nivellation and oonstructicti can be undertaken without 

 outside help and counsel. Larger plants call for the advice of an expert and of a con- 

 struction engineer, specializing in such Tfork. 



Take for example, the case that a pond is to be constructed in a valley through 

 which a small brook flows. The first requirement is that a sufficient flow is available. 

 Only then can good fishing be accoiaplishedj only then can diseases such as carp pox, con- 

 tagious abdominal dropsy, and others be ccmbatted. If this requirement is fulfilled, then 

 the dam is projected at a constrictioti of the valley, provided the pond can be made 

 sufficiently deep. The dam should be as short as possible. '.'.Tiere the brook will cross 

 the future dam, will be the deepest part of the pond, here the outflow arrangement (sluice 

 board) must be built in. From this point on, tlie vivellation is to be undertaken. Next 

 a pole is hammered down perpendicularly, so that it extends as far above the soil as the 

 depth of the pond is to be at the sluice (for carp ponds about 1 m. to 1.3 m. ). Over 

 this first and a second pole, (hammered in successively at different places in the circuit) 

 a leveling staff is laid horizontally v.ith the aid of a hydrostatic balance. 3y sighting 

 in the direction of the future shore line, a helper is given the exact location in which 

 to drive a marking stake. The procedure is continued by driving in the second pole at 

 other successive locations until the entire future shore line is marked by stakes. If it 

 is found that the pond is too small, or tliat the upper part of the pond t.111 be too 

 shallow, then a greater depth at the sluice must be chosen, or several ponds may be 

 terraced above each other. The banks should be steep, sloped everyivhere if possible, to 

 provide a depth of 30-/*0 cm. at the shores. Only then will good pasturage and flight 

 possibility be given to the fishes on the fertile shores. 



In the construction of several ponds, each should be provided with separate inflow 

 and outflow (see figu-^e 15 and 37). This is very necessary in trout ponds and hatching 

 ponds, because flowing water easily carries the most dangerous diseases, such as; gyrodac- 

 tylus, furunculosis, dactylogyrus, gill rot and abdominal dropsy. 



The dam is to be constructed so that the v;idth of the crown is about equal to the 

 height (a) of the dam. If the dam is to be used as a road for larger vehicles, it will 

 obviously have to be wider. The height (a) should be such that the crov^n of the dam is 

 about 30 cm. above the water surface; if the ground still sinks, the height of the dam 

 must be further raised another 30 cm.; if the pond depth at the sluice amounts to 1 

 meter, then a height of 1.50 meters at least, should be chosen. 



The normal profile of the pond dam is shown in figure 11, On the outer side, the dam 

 has a slope incline of 1:1, on the inner side of 1:2. In small ponds and also when heavy 

 ground is used, the inclination of the inner side can be increased up to 1:1. In large 

 ponds, with strong wave action and light ground, the inclination must in some instances be 

 lowered to 1:/J., Before filling up the dam, it is best to mark off the profile with laths. 



A loan core, such as was formerly used for every pond dam, is generally superfluous. 

 Moreover, every soil material which does not contain too much decon?)osable organic sub- 

 stances; wood, foliage, etc., may be used for dam building. Even peaty earth, contrary to 

 other statements, nay be used for dam building. Rotting wood causes holes which make the 

 dam leaky; also, stakes must not be driven into the dam. Clayey sand is the best material 

 for dam building; too permeable a soil may be made usable by a mixture with humus soil. 

 Vilien using loam it is advisable to cover it with other material, otherwise, on drying it 

 readily develops cracks and becomes brittle. 



Before the filling of the dam, the territory on which it is to rest must be freed of 

 grassy covering, of humus layers, and permeable soil, so that the Hatti rests firmly on the 

 subsoil and cannot shift later. The removed grass sods are set aside and later are placed 

 on the outer or inner sides of the dam. In the exposed subsoil along the median line of 

 the dan "sole" a further 50 aa. wide trench is excavated. This excavated material is 

 heaped on both rims of the trench. By tliis means the dam is more securely bound to the 

 underground and it has a better rigidity and density (see figure 9). 



63 



