STATEMENT OF PURPOSE
This manual has been developed for educational purposes by the Sonoma RCD and the Resource Conservation District of Santa Cruz County. The storm water runoff improvement practices included in this guide are meant to be used as general guidelines and are not to be used as professional engineered specifications. Prior to implementation of any practices, seek technical assistance from a licensed professional engineer or landscape architect, and/or certified professionals in erosion and sediment control for specifications for these practices. Site-specific designs that address each individual site’s needs and constraints are essential.
WHO WE ARE The Sonoma RCD is a special district organized under state law and a public resource agency with no enforcement or regulatory function. Since the 1940’s, the RCD has worked closely with local rural and agricultural landowners and partners in responding to natural resource and watershed management needs in Sonoma County. Our primary focus is to provide soil and water conservation technical assistance to landowners owning over 24,250 rural and agricultural parcels, including over 5,100 farms and ranches in our district.
Before Sonoma County and its incorporated cities became the developed, unique communities they are today, the diverse collection of habitats including redwood forests, oak woodlands, native grasslands, riparian areas, coastal dunes, and wetlands were virtually undisturbed. Rivers and streams, capturing and conveying rainwater, flowed from upland areas though rivers and creeks to the Pacific Ocean and San Pablo Bay along sinuous unchannelized corridors. Intact wetlands functioned as natural filters and buffers from major storms. Under these predevelopment conditions, as much as 50% of rainwater infiltrated (soaked into) the soil replenishing groundwater supplies, contributing to year-round stream flows, and sustaining ecosystem function. Another 40% was released into the atmosphere through evapotranspiration (evaporation of surface and ground water plus water loss from plants). Only about 10% contributed to stormwater runoff (rainwater that flows over the land surface). Our modern day urban centers and rural neighborhoods are made up of impervious surfaces (hardened surfaces that do not allow water to pass through) such as roofs, streets, and parking areas. When rain falls on these surfaces, it flows faster and in greater amounts than it would have under pre-development conditions significantly increasing runoff and decreasing infiltration and evapotranspiration. Runoff is typically conveyed by pipes, driveways, streets, and storm drains to creeks and rivers, where it contributes to flooding, road damage, stream erosion, and landslides. Runoff also carries sediment and other pollutants to beaches and rivers, making them unsafe for recreation and wildlife. Though it starts as relatively clean rainwater, runoff collects pollutants as it flows over the landscape. For example, excess lawn fertilizers, pet waste, soap from car washing, oil and grease from leaking engines, zinc from tires, and copper from brakes are just some contaminants that have been found in runoff in the county. It is important to note that nearly ALL storm drains in Sonoma County empty into local waterways UNTREATED.