Description: Areas of potential recharge include areas of high to moderate infiltration capacity and low to moderate water holding capacity soils that overlie proven alluvial aquifers. These areas include Fort Ord/Seaside, parts of northern Monterey County, Carmel Valley, and the alluvial deposits along the Salinas River. Other areas include the alluvial fan deposits near Arroyo Seco. The alluvial fill in the San Antonio Valley area was also identified as highly favorable for recharge.
Overlain on recharge areas are isohyetals (rainfall contours) of average annual precipitation. Blaney (1933) suggested threshold rainfall amounts that must occur to result in meaningful amounts of recharge for semi-arid climates similar to Monterey County. Blaney suggested a value of 17 inches per year of rainfall on native soils and 11 inches per year on irrigated fields. However, Blaney's analysis does not account for the anomalous distributions of annual rainfall (for example, a year where the rainfall total was 9 inches but it all fell in January), modeling efforts have shown the generalization relatively accurate. With the exception of the northern portion of North County and the San Antonio area, most of the identified recharge areas in Monterey County receive less than 17 inches of rainfall. In consideration of Blaney's generalizations, in these areas, even if soils are favorable, recharge from rainfall must be considered a rare occurrence and the importance of these areas as recharge areas is therefore limited.