HomeMy WebLinkAbout1991-03-13 - AGENDA REPORTS - SAND CYN AREA DRAINAGE STUDY (2)NEW BUSINESS
DATE:
SUBJECT:
DEPARTMENT:
BACKGROUND
March 13, 1991
SAND CANYON
Public Works
AGENDA REPORT
City Manager Approval
Item to be presented by:
DRAINAGE STUDY
John E Medina
The Council has reviewed during recent Study Sessions our current design
treatment of floodplains as well as a river study for flood control and
recreational uses for the Santa Clara and the South Fork of the Santa Clara
River. In addition, a recent proposal for a building permit in Sand Canyon has
pointed out that the current design treatment allowing buildings within the
floodplain should be reconsidered. In order to determine the effects of
changing the design requirements for construction in the floodplain, we need to
provide an analysis of the depth and width of the water surface. in Sand Canyon
Wash during flood conditions.
In 1980, the Board of Supervisors approved maps indicating the depth and breath
of flooding in Sand Canyon, including its tributaries --Iron Canyon and Live Oak
Springs Canyon. They also designated an area within the floodplain that was to
be reserved for the construction of a concrete channel, both sides and bottom,
to be constructed at some future date. Buildings were allowed to be constructed
if they were outside this reserved area, and they. were elevated above the
expected flood water surface. The Council'sdesire to construct soft -bottom,
natural channels for flood protection widens the limits of the area to be
reserved for a channel. The width, design and effect on existing structures and
property can only be determined through an analysis of the hydraulics, water
surface elevation, of the wash.
Although there are other canyons which would require further analysis to address
the Council's desire for soft -bottom channels, we suggest -that Sand Canyon is
appropriate for the first study. Since Iron Canyon and Live Oak Springs Canyon
are tributary to Sand Canyon, the analysis would provide needed- information as
it relates to these two areas also.
A project report would be prepared which would include:
• The water surface elevation and width of flooding under natural conditions,
i.e., no improvements.
• The width, depth and possible location of soft -bottom channels to carry the
flood waters.
• The effects on existing. structures and property caused by the future
construction of the soft -bottom channel.
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�: Agenda Item:
SAND CANYON DRAINAGE STUDY
Page 2
• Detailed maps of all of the above conditions.
• Cost estimates for the construction of the channel's appurtenant
improvements.
• An analysis financing mechanisms for the proposed improvements.
The report would require from three to six months to complete for Council
review. Based on approximately six miles of channel to analyze, we expect the
cost of the study to be under $50,000.
With the slowdown in building construction activity, this would be an opportune
time to perform this study. It would also provide a basis for analysis of other
floodplains.within the City.
1. The Council direct the Public Works Department to prepare a floodplain
report on Sand Canyon Wash which includes Iron Canyon and Live Oak Springs
Canyon.
2. The Council transfer $50,000 from General Funds reserves to Account Number
01-6100-227.
ATTACHMENTS
Map
Floodplain
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z , IREOTION OF FLAW I
IRON CANYON I
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PLACERITA ar
CANYON
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FILL
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FLOOD
UMITS
MOST D E--LOJPMECNT
TYPES ALLOWED WITH PERMIT.
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IFLOODPLAIN
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101'
SO LIMITS
FLOOD FRINGE
FLOODWAY
(OPEN SPACE USE ONLY)
FLOOD LEVEL --7
TYPICAL CANYON DRAINAGE
2