Lower Pilarcitos Creek Groundwater Basin Study - Coastside ...

• Urban: urban, urban residential, and schools
• Open space: natural vegetation, recreation, idle agriculture, and urban vacant
lands
• Irrigated agriculture: flowers, field crops, and truck crops.
Figure 5 illustrates land use in the groundwater basin, while Table 1 summarizes the
extent of the land use categories based on the DWR land use maps for 1977 and 1987
and the field reconnaissance for 2002. The areal extent of the groundwater basin is
1,765 acres or about 8 percent of the Pilarcitos Creek watershed. As indicated, urban
areas have increased over the period 1977 to present, with the greatest increase since
1987. As shown in Figure 5, lands undergoing urbanization generally have been urban
infill and have changed from open space (specifically, idled agricultural land) in 1977 to
urban in 2002. Irrigated agriculture acreage declined slightly between 1977 and 2002.
The open space area includes phreatophytic vegetation along the riparian
corridor of lower Pilarcitos Creek; this area is estimated at 28 acres (6,000 linear feet
along the creek and 200 feet wide on average).
Figure 6 shows the City of Half Moon Bay land use plan map developed for the
City’s general plan update (EMC Planning, June 2000). Comparison of Figures 5 and 6
reveal the following:
• Current agriculture areas within the groundwater basin are urban reserve
• Medium-density residential land uses account for nearly half the urban area
within the groundwater basin; the remaining area is primarily mixed commercial
and residential uses and public services areas (e.g., schools)
• Areas along the coast now mapped as open space are shown to continue as
open space, in some cases protected by transfers of development rights
• Natural vegetation open space areas east of Highway 1 are planned for urban
uses, primarily medium-density residential.
Impervious Areas. An important land use characteristic for a water balance is
the proportion of impervious area (paved areas and buildings) within a land use
category. Representative proportions of impervious areas for selected land use
categories in the San Francisco Bay area and Santa Clara Valley are shown in Table 2.
For this study, the urban area within the groundwater basin was estimated to be
half medium-density residential and half a mixture of commercial, public service, and
medium- to high-density residential. The medium-density residential area was assigned
6