D.—lc

6

Several small cracks have been detected in different structural parts of the intake. Either they must be effectively grouted or the intake must be rebuilt. I do not hesitate to recommend that the first of these two measures be taken. Even so, we may not be quite sure but that there may be also small cracks in the rock behind the intake, and if these should not be effectively filled with a resisting material they would obviously constitute a source of danger, if hydrostatic pressure were exerted from the headrace. Although less obviously, such cracks would if left open, be dangerous, even if an independent flume or a system of pipes were substituted for the present open headrace. The smaller the cracks are —if there are any —the smaller the quantity of water that would fill them ; and water percolating during a long period of rain might cause serious damage. It must therefore, at all events, be considered necessary to employ methods of grouting by which there is a fair prospect of reaching all cracks not only in the structural parts of the intake, but even in the rock under and behind the intake. Concerning the boreholes that must be made for the injection of cement mortar, the best method is, as is well known, to arrange the boreholes at an angle to the plane of the cracks, and, the cracks being in this case presumably vertical, the boreholes must be at an angle to the vertical plane. These circumstances make it seem possible to arrange at a comparatively small cost such reinforcement of the ground as would make it able to resist any conceivable stress that may be occasioned by the hydrostatic pressure against the side of the headrace. If the boreholes are arranged in a suitable manner, the extra measure to be taken will be limited to introducing into the boreholes steel rods, which, embedded in cement mortar, are capable of dispersing the pressure over an area large enough to resist the hydrostatic pressure from the headrace. A reinforcement of this kind, is, in my mind, very advisable all along the intake. It should under no conditions be omitted in places adjacent to the junction between the intake and the spillway. In connection with the grouting of the intake, all small-sized bodies between cracks in the concrete should be replaced by fresh concrete. I recommend, furthermore, that in front of the corner between the spillway and the intake a solid concrete block should be arranged from the first screen to the first dividing pier in the spillway, thus covering the first opening in the spillway. As to the details, I recommend that this block be not solidly jointed, but isolated from the spillway and the intake. The joints at the face should be cut out and filled with wedgeshaped strips of a plastic material to act as a seal and so effectively give a tight joint even if a small movement, due to compression or variations of temperature, should tend to open the joint between the spillway and the intake. As to the intake, I finally recommend that, after all the open spaces under, in, and behind the intake have been thoroughly grouted, all concrete surfaces facing the water in the headrace be thoroughly cleaned and provided with a very carefully applied gunite concrete lining. After this indication concerning the solidification of the intake and the rock behind it, I will now proceed to a closer. comparison between the different measures that may be taken in order to prevent the possibility of water in the headrace increasing the penetration of water into the ground. From this point of view there is no material difference between a flume and a system of pipes, but a flume would be by far the cheaper. I therefore discard the pipes in favour of the flume. When comparing the flume with the lining of the headrace, certain constructional features may be considered. I foresee that, in the case of the erection of a flume, difficulties would be encountered as to the jointing of the flume to the spillway, and to the intake, because the flume must of necessity be a more or less rigid structure, and yet must call for flexible joints in.places to allow for expansion and contraction. I also feel inclined to disapprove of the flume because special measures would have to be taken in order to make allowance for every conceivable change of the ground, no matter where or how small it be. For this reason, and also having regard to changes due to variations of temperature, the more the flume is calculated to transfer stresses from the intake to the spillway, and vice versa, the less it corresponds to my conception of an adequate solution.