was , with a high of in March and a low of in June. The largest flow recorded at the Laguna Beach gauge was during the El Niño event on March 1, 1983. Urbanization is the main cause of increased winter flooding, due to the covering of land with impervious surfaces. From 1931 to 1960, the average annual peak flow at the El Toro gauge was , and between 1960 and 1980, the average peak flow was . Watershed The Aliso Creek drainage basin lies in the south central part of Orange County, roughly halfway between the Santa Ana River and the border of San Diego County. It is an elongated area of , ranging from about a mile (1.6 km) in width in the north to wide in the south. The watershed is characterized by rolling hills, with very little flat land except in the alluvial valleys along Aliso Creek. The portion of the Santa Ana Mountains in the Aliso Creek watershed top out at approximately , while the San Joaquin Hills rise to at Temple Hill, locally called "Top of the World", in Laguna Beach west of Aliso Canyon. Aside from Laguna Niguel Lake, an impoundment of the Sulphur Creek tributary, there are no major bodies of fresh water. The watershed experiences a dry Mediterranean climate. As of 2001, the average annual precipitation in the San Juan Hydrological Unit, which Aliso Creek is part of, was . The watershed borders five major Orange County watersheds: Santiago Creek to the north, San Diego Creek to the west, Laguna Canyon to the southwest, Salt Creek to the southeast, and San Juan Creek to the east. As of 2018, the Aliso Creek watershed had a population of 144,000 divided among seven incorporated cities, or a population density of 4,100 persons per square mile (1,600 persons per km2). Nine communities were established in the creek's watershed as it was developed in the 20th century. By 2001 seven of them had become cities (from mouth to source, Laguna Beach, Laguna Niguel, Aliso Viejo, Laguna Hills, Laguna Woods, Lake Forest (formerly El Toro), and Mission Viejo), and the last two, Foothill Ranch and Portola Hills, were incorporated into the city of Lake Forest in 2000. The largest land use in the watershed is residential, which as of 2009 accounted for 39.6 percent of the total area. Other urban land uses are commercial (10.7 percent),