As the excavations were being carried out, an enormous amount of excess soil was produced, . The French initially dragged the soil to an adjacent valley where the soil was dumped. This itself caused many problems during the rainy season and was the cause behind many of the earthquakes.
When the Americans started work on the canal, the engineers decided to reuse this soil for the building of the Gatun dam. This dam held back the water from the Chagres river and thus creating the Gatun lake. As time passed, the soil would continue to settle thus, increasing the strength of the dam.
The dam is 1.5 miles in length and is nearly 0.5 mile wide at its base. The construction of the dam involved constructing 2 walls along its length using the excavated rock from the Culebra Cut. The space between these 2 walls was then built up with impervious clay. This clay gradually dried and hardened into a solid mass almost equal to concrete in its water-resistant properties. This dam contains 16.9 million cubic metres of rock and clay, equivalent too about one tenth of the entire excavation of the canal.
The dams at Pedro Miguel and Miraflores are small in comparison to Gatun. Their foundations are on solid rock and are subjected to a head of water of 12 meters, whereas the Gatun dam is subjected to a 24meter head.
The dam at Pedro Miguel is an earth dam approximately 300 meters in length with a concrete core wall.
At Miraflore there are two dams forming a small lake with an area of about 2 square miles. One of the dams is constructed of earth and is 210 metres in length. The second of the dams at Miraflores is 150 metres in length and is made from concrete.