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. I. INTRODUCTION The purpose of this report is to present the findings of a field investigation and to provide alternative techniques for emergency bank stabilization along Arroyo De La Guna Alameda County, California. This report and the information described herein were developed in order to assist landowners along the arroyo who experienced damaging erosion and flood problems following a flood disaster in February 1998. Due to heavy rains and significant runoff, the streamflow in the arroyo rose to a very high level and caused major erosion along the banks. It has been estimated that at least 10 feet or more of the bank has eroded along many properties in the affected area.. Highly unstable vertical cliffs, some nearly 30 feet high, are now the scenario in many areas along the arroyo. The eroded banks are dangerously close to a number of existing homes, garages, driveways, and other features. Any future flood events could easily prove to be devastating for the landowners. An emergency bank stabilization project will be required to mitigate the current loss of property and to prevent future catastrophic damages. II. BACKGROUND INFORMATION . Acknowledl!ements This study was completed by Thomas W. Browning on behalf of California landowners who experienced major flood and erosion problems in early 1998. Local, state, and federal officials in California have been extremely busy and overloaded with work due to the recent widespread flooding and devastating, and have been unable to address all concerns and needs. This study was undertaken in an effort to foster interstate cooperative assistance during times of need. The CWCB and the State of Colorado received much information and assistance from California officials and experts during the 1996 Buffalo Creek, Colorado flood event. The CWCB wishes to thank those individuals and agencies who provided information and assistance for this study and previous cooperative efforts. Study Area Description The study area lies within the northern portion of unincorporated Alameda County near the community of Pleasanton, California. The area is west of Interstate 680, east of Foothill Road, and in the vicinity ofthe Castlewood Country Club. The Arroyo De La Guna drains a very large area above the point of interest, and includes tributary inflow from Arroyo Valle, Arroyo Mocho, and a number of large streams that drain areas in Alameda and Contra Costa Counties. The Del Valle reservoir stores and releases water that eventually drains into Arroyo De La Guna. The average streambed slope in the study reach is on the order of 0.3% (0.003 ft/ft). . Floods of1998 Heavier than normal rains in northern California during February 1998 were partially caused by the phenomenon known as El Nino. The soils in the area became saturated which exacerbated runoff and significantly reduced soil stability along drainage courses and on hillslopes. A number of devastating events took place as a result of flooding, erosion, and slope failures. The massive streambank erosion along the subject property is one such example of mother nature's threat to human development. President Clinton declared Alameda and other California Counties as federal disaster areas as a result of massive flooding, mudslides, and other natural hazards.