Nils F. Ambursen's main innovation in dam design was the development of the Ambursen dam, also known as the slab-and-buttress dam. This design introduced significant advancements over traditional dam structures, primarily through its use of reinforced concrete.

Key Innovations in Ambursen Dam Design:

1. Use of Reinforced Concrete: Instead of the massive stone or earth employed in conventional dams, Ambursen used reinforced concrete slabs supported by a series of buttresses. This reduced the amount of material needed, making construction more efficient and cost-effective.

2. Open Buttress Structure: The buttresses were hollow and open in design, which allowed for better water flow dynamics and reduced pressure on the structure. This design also made the dam lighter compared to solid counterparts.

3. Structural Efficiency: The slab-and-buttress system distributed pressure differently, making the dam more stable and resilient to various stress factors such as water pressure and natural forces like earthquakes.

This innovative approach not only reduced construction costs but also facilitated dam building in locations where traditional construction would not be feasible due to geological or economic constraints. Ambursen dams became popular in the early 20th century for their efficiency and modernization of water retention technology.

For further reading on the subject, including historical examples and impact, you might refer to engineering literature or resources dedicated to the history of dam construction.