A Monday, Jan. 12, article in a Seattle newspaper correctly identified rampant development as a major casue of the massive flooding. The effects go beyond those listed. In summary, those effects include:
• Removal of natural vegetation which would slow runoff
• Replacement of natural vegetation with impervious surfaces (this includes lawns, which form a heavy mat that sheds water)
• Filling in the floodplain
• Building barriers to the flow of water
• Building in the natural floodplain, which increases flood damage
These observations are based in part on my extensive study of the Nov. 1990 flooding in the Upper Snoqualmie Valley in a city-sponsored survey. Comparison of flow rates between Nov. 1990 and Jan. 2009 show that the flow from the Cascade range in Jan. 2009 was much less than in 1990, while the flow in the Valley (where all the development has taken place) was much greater.
Kenneth P. McCarty