In the spring of 1901 , this core wall cracked in five places within a length of 100 feet . This caused the writer to believe that some serious disturbance had taken place , as in his opinion the cracks were too close together to be caused by contraction . After close study of the condi- tions , there was no conclusion to be arrived at except that there was a fundamental weakness here , and , therefore , it would be unsafe to proceed with the work . This close study brought to view objectionable features of the plans of the embankment and core wall , the most conspicuous of which were three . First the excessive height , narrow base and unstable foundation of the embankment ; sec- ond , the great height of the core wall , and , third , the double means afforded the water to reach the core wall . To take up the first , the embankment : It was to be 150 feet high , and only 650 feet thick at the base . This section , would be not only about 40 per cent . higher than any heretofore built , but in comparison with other high embankments its base was narrow for its height . As an example , the Amawalk dam , which forms one of the upper Croton reservoirs , while only about half the height , 85 feet , yet has a base even wider than that of this embankment of unprecedented height . And further , this embankment was hazardous because of the unsta- ble nature of its foundation . It was founded over a great refilled pit , which was 360 feet wide at the top , 170 feet at the base and 70 feet deep ; this pit was a necessary ex- cavation for the foundation of the end of the stone dam , which was 164 feet wide at the base as before stated .