What makes storm water runoff unique in Hawaii area?
The unique characteristics of Hawaii ‘s topography, climate and geology result in a highly variable and complex surface hydrology. Most streams originate in the mountains of Hawaii and terminate in the ocean. In general, each of Hawaii ‘s islands can be divided into two regions, windward and leeward, relative to the prevailing northeasterly trade winds and mountains. On the windward side, orographic rainfall results in high mean annual rainfall sometimes 15 times greater than the mean for Hawaii (25 to 30 inches annually). Consequently, the majority of Hawaii ‘s perennial streams are located on the windward side of islands. Mean annual rainfall on the leeward side can be in the single digits and intermittent streams that are dry during most of the year are more commonly located in leeward watersheds. Variations in ocean tides, rainfall, soil type, and geology can result in streams having both gaining and losing reaches (Oki, 2003). Streams in Hawaii also experience extreme flash events
