that would later become Aliso and Wood Canyons Wilderness Park. Up until the 1960s and 1970s, barely 15 percent of the watershed was urbanized, but by 1990, after doubling the rate of development in the past two decades, the watershed was roughly 60 percent urbanized. The cities of Mission Viejo and Laguna Niguel were incorporated in 1988 and 1989, respectively. In 1991 El Toro incorporated as the city of Lake Forest; Laguna Hills also incorporated in 1991, and Laguna Woods in 1999. By the early 21st century, more than 70 percent of the watershed was urbanized. The newest city in the watershed, Aliso Viejo, was incorporated in 2001. Flood control In the early 1900s, several significant floods wreaked havoc in southern California. The Orange County Flood Control District was created by Orange County Flood Control Act of 1927 in response to some of these flooding events. Over the following decades most streams in Orange County were channelized, with Aliso Creek being channelized to facilitate urban development starting in the 1960s. Although some parts of Aliso Creek were completely lined with concrete, it retains an earthen riverbed in most parts despite being confined to a narrow channel. A major weakness in the flood control system is at the south end of Aliso Canyon where the creek is confined by steep cliffs and the Aliso Creek golf course. This area has suffered severe flood damage several times in the 20th century. The 1998 flood was the largest on record. It inundated the Aliso Creek Inn and Golf Course, destroyed six footbridges across Aliso Creek and caused severe bank erosion in many places along the creek. Like most other coastal Orange County streams, the watershed of Aliso Creek is now heavily urbanized. With 70 percent of the original land surface now underneath impermeable surfaces such as pavement and buildings, far more runoff now enters the creek during storm events, greatly increasing the risk of flooding. Several tributaries of Aliso Creek—the Dairy Fork, Aliso Hills Channel, Munger Creek, and other smaller ones—have been replaced by storm drains. Parts of Sulphur Creek and English Canyon Creek have been channelized as well. The only tributary that closely resembles its natural condition is Wood Canyon Creek, although it is still affected considerably by urban runoff. There are several facilities capable of storing floodwaters, the largest of which is Laguna Niguel Lake formed by the Sulphur Creek Dam