Dingee Reservoir Final Seismic Report - East Bay Municipal Utility ...

Executive Summary
Seismic Stability Evaluation Report
Dingee Reservoir Dam
Oakland, California
This report presents the results of a seismic stability evaluation of the Dingee Reservoir Dam,
located in Oakland, California. This study is part of an ongoing dam safety program by the East
Bay Municipal Utility District (District) to assess the static and seismic performance of its dams.
Dingee Reservoir is a 4.2-million gallon (MG) open-cut reservoir and is located south of the
intersection of Estates Drive and Bullard Drive in Oakland, California. The reservoir is bound
by Estates Drive to the west and Bullard Drive to the north.
The reservoir was originally constructed in 1894 and was modified twice, once in 1931 for the
construction of a new roof and lining, and again in 1939 for the construction of a new west curb,
that parallels Estates Drive. The embankment fill was constructed using the excavated on-site
native soils and Franciscan Sandstone and Shale materials. The Hayward Fault zone lies about
1100 feet east of the reservoir (dam).
The objective of the study is to evaluate the performance of the dam during the Maximum
Credible Earthquake (MCE) on the Hayward Fault, the controlling seismic source for the site.
Although the dam is not under the jurisdiction of the State of California Division of Safety of
Dams (DSOD), similar evaluation standards were used for this dam as are used for jurisdictional
dams. The performance goal is to ensure that the dam withstands the MCE without an
uncontrolled release of reservoir water.
To evaluate the performance of the dam, we conducted field investigations including drilling and
logging of exploratory borings, and installation of an inclinometer. Laboratory testing included
identification, index and strength tests. Using this information, we performed engineering
analyses to estimate potential deformation of the dam when subjected to the controlling seismic
event.
No known active fault trace is present at the site; thus earthquake-induced ground rupture is not
anticipated. The embankment and foundation materials of the dam are stiff and clayey in nature
and are not likely to liquefy or undergo significant strength loss, due to a seismic event.
We conclude from the investigations and analyses that the fill and foundation materials of the
dam will perform satisfactorily when subjected to ground shaking from the MCE of magnitude
7.25 on the Hayward Fault. The results of the seismic analyses indicate less than one foot of
crest settlement under this scenario. Since the reservoir is operated with the average water level
at least four to five feet below the spillway level, uncontrolled release of water due to
overtopping is not expected.
The Dam is also deemed to be stable under rapid drawdown conditions, which would occur if the
reservoir needed to be lowered in case of natural or operational emergencies.
Seismic Stability Evaluation Report
Dingee Reservoir Dam
1
August 2008