CHANOINE WICKET DAMS. 229 



until the whole dam was on the swing and the pool level greatly lowered. For these 

 reasons the axis was raised in all the later dams, as mentioned further on. Fixed, 

 and in some cases sliding, weights or counterpoises were attached to the wickets, to 

 regulate better the tendency to swing, but they did not prove very satisfactory. With 

 a view to minimize the evil, experiments were tried on the upper Seine dams about 

 1865, when several of the wickets on the weirs were provided with chains fastening the 

 butts to the sills, and were made wider at the same time in the heads so that they would 

 swing before the others. The chains were of such a length that when the pool rose 

 and swung the wickets, the latter could not pass an angle of forty-five degrees with 

 the vertical, and would therefore right themselves much sooner than when swinging 

 free. This method was in part successful, but it was soon found to give rise to another 

 objection, which was that the wickets by being chained reduced the full spillway of 

 the dam. In order, therefore, to pass rises which formerly could be disposed of by 

 putting the wickets on a full swing, it became necessary to lower several, or to 

 maneuver the heavy wickets of the pass. The operation of raising them again, which 

 had to be done from a boat exposed to violent currents, was found to be difficult and 

 dangerous. Finally, as the only solution of the problem, De Lagrene proposed placing 

 a bridge of trestles above the dam from which the wickets could be maneuvered, and such 

 a bridge has now come to be regarded as almost indispensable for proper operation. 



Dimensions, etc. A width of 3 to 4 feet has usually been adopted for wickets, 

 the latter having been used on all American dams. From this is deducted a space of 

 3 to 4 inches for clearance between each one, this being necessary to allow for warping. 

 The width of the pass and of the weir wickets is generally the same, although in a few 

 cases the former is less, owing to the greater height. On the upper Seine, for example, 

 certain of the passes have wickets n.8 feet high and 3.3 feet wide, while those of the 

 weir are 6.5 feet high and 4.3 feet wide. The angle of inclination to the vertical, 

 where Pasqueau hurters are used, is about twenty degrees; but on the earlier dams, 

 where the tripping-bar was relied on for lowering, the angle was much less. The lap 

 on the sill is 4 or 5 inches. 



The wickets are made of wood, framed and bolted. The only example of iron 

 wickets is to be found at La Mulatiere dam near Lyons, although others will shortly 

 be in existence. An iron wicket can be designed so that its skin-plate only, and not 

 its uprights, will overlap the sill, thus reducing one cause of leakage which is inevitable 

 with the wooden wicket. 



Hurters. The hurter consists essentially of a shoulder and of two grooves, one 

 of which guides the end of the prop when the wicket is being raised till it falls against 

 the shoulder, while the other guides it back when released and leads it into position 

 again ready for raising. Until 1879 all lowering had to be done by a tripping-bar, 

 or by pulling the props sideways till they cleared the shoulder. This was facilitated 

 by sloping the latter slightly in the horizontal plane, so the prop would bear against 

 a slanting surface. The safe maximum of this angle, as found by experiments made 

 some years ago at the dam of Conflans in France, is three degrees. 



