Source: County of Santa Clara

Hydrology

• Since 1947, the addition of three reservoirs significantly reduced the probability of flooding in the lower Pajaro River.
• Neither current agriculture conditions nor potential agricultural changes have a significant effect on design discharge or flood impacts.
• Urbanization increases the runoff from frequent events (2-years to 25-year) but has little impact on runoff from large storms (50-year to 200-year).
• Soap Lake provides significant flow attenuation and flood storage benefits for the upper Pajaro River and is key to flood protection.

• The small, predicted changes in peak design discharges should not significantly alter sedimentation conditions within the Pajaro River channel.
• Significant growth of shrubby vegetation could increase hydraulic channel roughness and could be expected to cause an increase in sediment deposition.
• Changes in sediment load may have localized impacts at the confluence of the San Benito and Pajaro Rivers but do not affect the system as a whole.
• Soap Lake limits sediment discharge from the upper to the lower Pajaro River.

As currently calibrated, both models meet the goals of Phase 1. The models can be further refined in future phases if required. Also, Soap Lake operation and flood protection capabilities could be examined in greater detail.

The Pajaro River is the largest coastal stream between the San Francisco Bay and the Salinas Watershed with a watershed of over 1,300 square miles.

The watershed covers portions of Santa Cruz, Santa Clara, San Benito, and Monterey Counties (Figure ES-1). The largest size of the watershed contributes to the number of diverse environments, physical features, and land uses within its boundaries. Development within the watershed, both urban and rural, is clustered around the major cities of Watsonville, Gilroy, Morgan Hill, Hollister, and San Juan Bautista. Agriculture and grazing are the dominant land uses in these areas but represent a small portion of the total watershed land use. The majority of the watershed land cover is grassland, shrub land, and forest.

Aquatic System Research Paper
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