Dutch Flood Policy Innovations for California

F lood risk management is an important part of life in the Netherlands. The Netherlands is formed by the deltas of three rivers-the Scheldt (rain-fed, originating in southern Belgium), the Meuse (rain-fed, originating in northern France), and the Rhine (glacier and rain-fed, originating in Switzerland). The country also borders the North Sea, with the Scheldt River connecting the sea to Antwerp Harbor. The Rhine is the largest of the three rivers, splitting into three branches (the Ijssel, the Lek, and the Waal) as it crosses the border into the Netherlands (Tol et al. 2003). Two-thirds of the country lies below mean sea level (Voortman 2003). The Dutch have a long history of attempting to control floods. As early as the ninth century, the Dutch started building dikes to protect reclaimed bog land (Kaijser 2002). These dikes started as local, individually-owned structures, but communities soon realized that closed dike rings were necessary to protect all sides of the region. These dike rings eventually became waterschaps, or " waterships, " regional districts charged with water management including drainage and dike building. These districts are still the administrative body for flood defense (Voortman 2003). The 14 th century saw the first major recorded floods in 1313 and 1315, leading to the famine from 1314-1317 that killed 5-10 percent of the population. Periodic flooding continued through much of the Netherlands' history. As sediment settled between the dikes, dikes grew taller. During the 19 th century, reorganization of the water districts occurred and a national body was formed. Military engineers took over the construction and maintenance of the dike system (Tol and Langen 2000). During the 20 th century, as trained engineers and the central government took over flood control efforts, the analysis of appropriate techniques and construction increased. Prior to 1953 dikes were built to the height of the previously known high-water level plus a margin of safety (Jonkman et al. 2004). Following the catastrophic flood of 1953, the Delta Committee was formed to advise the government regarding flood control (Voortman 2003). One recommendation of the Committee was to establish an optimal exceedance frequency of the design water level based on risk of flooding and cost of protection. van Dantzig's 1956 paper described this risk-based calculation. He proposed that flood management required integration of three areas with noted problems: statistics, hydrology, and economics. In the past 50 years, significant effort has been devoted to …