It would be useless to consider any proposi- tion to increase the width of the embankment , because the means afforded the water to reach the core wall along the face of the dam would always remain ; this is a most dan- gerous feature , as the core wall would not have sufficient weight or strength to resist the pressure of the water that would come against it . A fourth objection might here be stated , namely , the permeable and light character of the earth of which the embankment was made , but even with the best of ma- terial , an embankment so constructed would be insecure . Thus it will be seen that the safety of this reservoir was dependent not only uponan embankment of a problematic section , resting upon an unstable foundation , but also upon a core wall of phenomenal height , unprotected and unsupported by original soil and attended with the great- est of all possible risks , that is the means afforded water to reach the center of the embankment against the core wall . Such a structure can not be regarded as anything but an experiment . It is abnormal and unprecedented in all its dangerous features . The engineer might apply in vain to science for aid in computing the efficiency of such a structures ; he could get no light , for he could find not even the slightest guaranty of safety in a structure so built . The failure of this embankment might not only create a devastating flood in the valley below , but also cause a current above , of such irresistible velocity , as would de- stroy the earthen part of the old Croton dam , thus at once cutting off the supply of water to the city until the old dam could be repaired and in addition postponing indefinitely the time when the city could have the addi- tional supply of water which the enlarged reservoir was to furnish .