A water sluice is a gold mining technique. Crushed ore and gravel are mixed with fast moving water and then channeled over a long trough with a series of perpendicular-to-the-flow slats. Each row of slats gets smaller as the water flows longer in the channel. Since gold is heavier than the surrounding rock, the gold nuggets collect at these slats. The larger nuggets collect at the bigger slats while the finer specks collect at the smaller slats. The sluice separates the valuable gold from the gravel, concentrating on the big nuggets first. The final product is a smelt of all the nuggets into one gold bar.
See Figure 3.3 on page for a technical diagram of a gold sluice. Picture courtesy of RMS Ross Corporation [#!RMS97!#].
Similarly, the WaterSluice software engineering methodology separates the important aspects from the less important and concentrates on solving them first. As the process continues, finer and finer details are refined until the product is released. The WaterSluice borrows the iterative nature of a cyclical methodology along with the steady progression of a sequential methodology.