sr-032481-11eSanta Monica, California, March 17, 1981 ~`~ F~
SAAR 4 4981
T0: Mayor and City Council
FROM: City Staff
SUBJECT: Approval of Preliminary Design for Relief Sewer for
Colorado Street Sewer
Introduction
This report presents information and recommendations for
alignment and size of the sewer proposed to relieve the Colorado
Street sewer.
Background
On February 11, 1981, City Council awarded a design contract for
the relief sewer and adopted sewer connection fees to finance the
project. The consulting engineer with the assistance of the
staff has studied several alternative alignments and capacity
requirements and desires confirmation of these prior to beginning
final plans and specifications.
Alignment - The relief sewer can be built in Colorado Street in
the same location as the existing sewer, but this would require
pumping of all of the sewage during construction and is not
recommended. The sewer can be constructed on any parallel street
north of Colorado Street, allowing the existing sewer to carry
the flow during construction and allowing the area between the
new sewer and the existing sewer to be carried by the existing
sewer, after the new sewer is completed.
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Santa. Monica, California, March 16, 1981
It is recommended the new sewer be built in Broadway from 1st
Court to 20th Street, as shown on the attached drawing..
Capacity-,and Size - ?o properly provide for existing development,
as weld as development which may be reasonably expected within
the anticipated life of the improvements and making provision for
infiltration of storm water* and anticipated water conservation
measures, the consultant and the staff recommend a maximum design
criteria of 24 inch diameter sewer to augment the 18 inch
existing sewer.
The existing 18 inch sewer will remain in service to serve
several areas including that east of Cloverfield between Broadway
and Pico. Repair work will be required on the 18 inch sewer to
reinstate it to near original condition. This work is
recommended as a separate contract after the relief sewer is
completed and in use.
At the lower. end of the relief sewer (1st Court at Colorado
Avenue), the existing peak flow is 20.0 cubic feet per second
(CFS). The peak design flow for the new sewer is 20..9 CFS. The
peak design flow for the existing 18 inch sewer will be reduced
to 11.5 CFS.
e rues tributary to -the relief sewer
are 40 - 60 years old and in many cases
have leaky joints. During rainy weather,
flows are 2D% - 30% greater than in dry
weather..
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Santa Monica, California, March 16,1981
Recommendation
It is recommended City Council .app rove the alignment shown and
approve the 24 inch diameter size for the new relief sewer and
authorize preparation of final plans.
Prepared by: Stan Scholl
Attachment: Drawing
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