The Las Vegas valley is the driest metropolis in the United States, with an annual rainfall of less than five inches. A large majority of the annual precipitation occurs between May and September in the form of high intensity thunderstorms. Since the founding of Las Vegas in 1905 until the formation of the Clark County Regional Flood Control District in 1986, the five jurisdictions that make up the Las Vegas valley: Las Vegas, North Las Vegas, Henderson, Boulder City, and Clark County, struggled to manage stormwater. The principal defect was that they reflected the particular whims of each government entity, largely ignoring the nagging geologic characteristics that made the valley so susceptible to flooding. Often, dikes and flood channels built in one city were not integrated with those in the adjoining city. After devastating floods in 1983 and 1984 exploited the gaps in the "patch-work" flood control system, a group of progressive minded politicians, engineers, and citizens aggressively campaigned for the formation of a regional flood control district. In 1986 Clark County residents approved a one-quarter of one-percent sales tax increase for the funding for the flood control district. Over the past quarter-century, the Clark County Regional Flood Control District funded a network of detention basins and flood channels throughout Clark County, which helped manage the massive physical expansion of the Las Vegas valley in the 1990s and early 2000s.