1997-Nov-11:
Summary of SCVWD decision, implications and follow-up:
likely to be posted here in increments over the next week or so
(relative to 11 Nov 1997)
Presentations made at SCVWD Board Meeting (partial collection)
Doug Graham's map of the flooding in January 1983 :
Small (101K)
or
Large (257K)
Note:
The flooding started and peaked in the middle of the night,
and many residents awoke to water that was already
receding.
This map is not based on data collected during
the actual event,
but compiled from questionaires returned by residents
subsequently.
Article: from 14 November 1997 issue
of the
History
Article from 15 March 1995 issue
of the .
Special SCVWD Board Meeting on Barron/Matadero Creeks Interim Fix
Monday 10 November 1997 at 7:30pm in at SCVWD Offices in San Jose
(from SCVWD's )
: only 20-year protection for Barron Creek!!!
(from SCVWD's );
copy cached here (BPA Web site)
From :
Sample Driving Directions:
Letters sent by BPA requesting that meeting be held in Palo Alto
to facilitate public attendance
Edited versions of tables presented at Public Meetings
Flow Rates for Storm Frequency
Flood Frequency (Probability)
Barron Creek
Matadero Creek
5-year (20%)
210
1460
10-year (10%)
320
1960
25-year (4%)
490
2590
50-year (2%)
620
3060
100-year (1%)
760
3500
500-year (0.2%)
1100
4480
Flows in cubic feet per second (cfs)
Barron Creek flow measured at Foothill Expressway
Matadero Creek flow measured at Louis Road
Graphical Representation of above table (20 KB)
Matadero Creek Interim Fix Alternatives
Level of Flood Protection
Option
Max Diversion from Barron to Matadero
Matadero
Barron
Number of homes affected by 100-year flood
1. Do Nothing
600 cfs
50-year = 2.0%
100-year = 1.0%
3,000 +/-
2. Fully block the diversion structure
0 cfs
100-year = 1.0%
5-year = 20.0%
1,000 +/-
3. partially block
300 cfs
100-year = 1.0%
20-year = 5.0%
1,000 +/-
4. less blockage
300-600 cfs
70-year = 1.4%
70-year = 1.4%
4,000 +/-
5. Raise flood walls at Waverley
600 cfs
50-year = 2.0%
100-year = 1.0%
3,000 +/-
Note: flooding levels are stated in the two common formats:
(1) average interval over the longterm,
(2) percent chance of that level of flood happening in
any given year.
For example, a flood that is projected to happen 10 times
in a 1000-year interval is referred to as a 100-year
flood or a 1% event.
The calculations of the size of these events is based
largely on mathematical models,
backed by some actual measurements and experience.
Notes from preparatory meeting involving BPA, SCVWD, and City of Palo Alto (on 10 October 1997)
Marking changes: changes since the original issuance
of these notes are indicated by introductory words in the color
blue.
These notes have been edited
to remove sections relevant only to the preparation for the public meetings
(which have now taken place).
These sections have been moved to a subsidiary page with links left here.
Option numbers updated:
the options presented in the sheet handled out at the public meeting were
numbered differently from the preliminary version.
These notes on the preliminary meeting have been updated to use the later
number scheme (with the earlier number in parentheticals).
These notes do not follow the exact order in which they were made, but have been reorganized for brevity.
Introduction (BPA)
Focus of this meeting: preparation for public meeting
Explore alternatives
Discuss presentation of alternatives, priorities and order
Meeting arrangements
Goals of public meeting
Feedback to SCVWD staff on options, and especially on how public views the various risks and benefits
Foster public understanding of the choices so that when a decision is made, people can see that there is fairness in the sacrifices/risks they are being asked to take
Side note: encouraging that SCVWD went public with the problem so quickly, rather than remaining silent and just hoping that they would "luck out" this year.
Scenario to be avoided:
Option 3 (previously #1) selected:
Matadero with 100-year protection, Barron with 20-year protection
25-year to 40-year flood: major flooding along Barron
If Option 4 (previously #2)
(Matadero and Barron at 70-year protection) or
Option 5 (previously #4)
(Matadero=50 year; Barron=100 year) had been chosen,
then there would have been no flooding.
Discussion: 300 cubic feet per second (cfs) of flow on Barron Creek
has major impact on flooding on Barron,
but far smaller impact on Matadero (BPA, supported by Zlotnick):
the difference between a 10-year and 100-year flood on Barron is
rough the same as between a 50-year and 100-year flood on Matadero
(440 cfs -- see table above).
General areas of concern
How quickly can the Water District respond to developing conditions?
Matadero and Barron Creeks rise and fall at different rates and times.
Typical:
Barron peaks during storm and has substantially receded
before the trailing edge of the storm has passed
Matadero rises slowly, often rising for a day or two after storm has passed.
With saturated soil and closely spaced storms, less difference
Conclusion: IF (repeat if) there is to be any restriction
on flow into bypass from Barron Creek,
the blockage should be at the top of the bypass gate
because Matadero Creek is likely to have additional capacity earlier
in the storm (when Barron needs it).
SCVWD Answer: good point.
Any restriction should be that way and adjustable.
Ability to put up barriers
Ability to predict peak of flow:
Lack of instrumentation:
There are no flow gauges permanently installed in Barron Creek
Hence, no historical data (would have to depend upon computer modeling)
Flow information of limited use because Barron Creek responds so
quickly to rainfall -- you also need to know whether the storm
is going to move on or stall over the area
(which can only be an educated guess).
Benefit analysis: different views
Water District staff: focus on number of homes protected from 100-year flood
Alternative: weight number of houses affected by risk, for example, a house with protection up to a 50-year flood would count less than a house protected only up to a 20-year flood.
Channel at Louis Avenue Bridge over Matadero is too small for 100-year flood
Breakout of flood is likely to occur at Waverley.
Additional details from public meetings:
The problem occurs when the water rises to just touching the bottom
of the bridge and the analogue of friction slows the water touching
the bridge, and that band of water slows the water below it, and
so on and so on.
This slowing of the whole stream of water passing under the bridge
causes water to rise in the area above the bridge.
Thus, when the water touches the bottom of the bridge at Louis Road,
the level of water in the channel quickly rises
and soon touches the bottom of the Ross Road bridge,
where the problem repeats,
moving up to the Middlefield Road bridge, then Cowper and
finally Waverley.
From night of 2-3 February 1998:
Observers who were on one of the bridges when the water touched
the bottom reported that the effect was not just noticeable
but quite dramatic:
they could see the water level suddenly rise upstream of the bridge
and when they looked to the downstream side, they could see
that the levels were noticeably lower than before the
water touched the bottom of the bridge.
Breakout would be a big surge, with the swiftly flowing waters
which would like do substantial damage to nearby houses
before spreading out over larger area.
The manner of this flooding is a significant part of the
Water District staff'’s recommendation about how to apportion risk.
BPA concern: speed of response since Water District HQ is in San Jose:
Answer: Dennis Ely (attendee) is manager of region and is based here.
Ely: will supply in advance various tools (e.g., hooks) to be stored by BPA
and used by residents to clear debris from choke points during storms
(traditional problem).
His teams will handle major problems.
The section of Matadero Creek with reduced flood protection is below Alma.
None of the section of Matadero Creek in Barron Park
will have any decreased protection under any of the options
being considered.
The fix for the problem appears to be straightforward:
by replacing the current sloping concrete walls with vertical walls
(as in the segment near Fry's),
enough additional capacity would be created.
This could be completed next summer.
Note as of April 1998:
The problem was discovered to be larger and more serious
than was thought last fall.
The fix is now estimated to cost $10M
and take more than one year.
Funding has not yet been allocated, so it is questionable whether
much (any?) work could be done this year.
Zlotnick: "traditional level of service from the Water District not enough"
City of Palo Alto will do additional cleanup along Barron Creek
Overhanging trees and branches that could fall into creek
Items that were too big for neighborhood cleanup (organized by Bob Moss, end of September)
Update: In the last week of October,
a city crew was observed removing large debris
(large fallen branches + ???) from Barron Creek (above Laguna).
Background: the Barron Creek flood of 1983
that flooded large portions of neighborhood is classified as a 17-year event.
No one knew what the classification of the larger 1955 flood was.
Sandbags:
City will provide sand and bags at Hoover School (as in previous years)
BPA question: many seniors who would need help with sand bags.
Answer: Water District does not have the resources to provide
that level of individual help.
BPA should attempt to identify in advance who would need help
and coordinate with various service agencies (e.g., Scouts).
Miscellaneous topics
Stanford ditch: the Stanford Ditch is a major source of water in Matadero.
Can anything be done to reduce this flow into Matadero during peak flows,
thereby reducing the need to restrict the use of the bypass for excess water
from Barron Creek?
Answer: none known (the areas being drained are uphill of lots of residences)
Is there any way that open space could be used as a temporary reservoir
to hold small excesses (and are any open spaces at appropriate places).
Note: during the planning stage of the flood control project,
the possibility of additional upstream storage basins were considered,
but the cost of land was prohibitive.
Any temporary, ad hoc storage basin would have very
limited capacity because of the available surface area and
the limited height of the containment walls
(Aside: if you want to do your calculations, an acre is 43,560 sq. feet).
For some flood control systems, even a small amount of water going over
the top of the channel walls can lead to
catastrophic failures of the wall.
Unasked question: is that a problem for the Barron &
Matadero Creeks, and if so,
would having such an option make any significant difference?
: these are large heavy-duty vinyl tubes
that are inflated with water and create temporary dikes
(as seen on TV during last years flooding in Napa/Sonoma).
SCVWD Answer: very vulnerable to vandalism (episodes where tens of
thousand of dollars damage done).
BPA Question: but what about for a day or two to handle a peak flow
just above capacity (either on the Barron sediment basin or
on the downstream channel).
Barron Creek sediment basin: cleanup of reeds would be useful -- can hold
large debris until later in storm (when it would be the most difficult
to handle).
However, since the reeds haven't yet gone into dormancy
(and are defended by Blackbirds), this may need to wait a little.
Additional information from
Wednesday 15 October 97 meeting:
this cleanup is awaiting approval from the US Fish and Wildlife Service.
Notes from Public Meetings (Wednesday & Thursday October 15-16)
The two meetings had very similar presentations by the Water District
(as they planned) and the set of topics covered by the audience
was very similar,
although the amount of time spent on each varied more than I would
have expected.
Most of the issues and concerns raised in the
meeting of Friday 10 October
(between the BPA Board and the Water District)
were echoed by the general audience in these meetings.
I will not repeat those here.
NOTE:The numbering of the options in the handout at
the general public meeting
was not the same as in the handout at the preliminary meetings.
So be careful with any document that identifies
options only by number.
When the SCVWD staff report on comments and suggestions
received during these meeting is completed,
they promise to post it on their
page
on their
.
The SCVWD Board of Directors will consider which option to adopt at
some subsequent board meeting.
This may be at one of their regularly scheduled meeting
(every other Tuesday, starting at 9am, at their headquarters in San Jose),
or it may be a special meeting.
There was strong sentiment (especially at the Wednesday meeting) to
try to have that meeting in Palo Alto
so that interested residents could attend.
Zlotnick was supportive of this (and he may have originated the suggestion),
but could not promise that it would happen
(it is a decision for the whole board).
Letters are being sent by BPA requesting that meeting be held in Palo Alto
to facilitate public attendance
(to Board of Directors, Santa Clara Valley Water District
and
to Mayor Huber and Councilman Rosenbaum (City of Palo Alto) requesting support)
The clean-out of vegetation in the Barron Creek sediment basin
(behind Gunn HS) is awaiting approval (being delayed by)
US Fish and Wildlife Service
(issue raised in preparatory meeting).
Other public officials present (observing) at the Thursday 16 October meeting
Mayor Joe Huber (City of Palo Alto)
Dick Rosenbaum
City Council member
Member of SCVWD's Northwest Zone Advisory Committee
staff member from 's office
Discussion of assignment of risk
Much more at the Wednesday meeting, only a little at Thursday meeting
From an article in the San Jose Mercury News of Wednesday 15 October 1997 (page B1):
Headline: El Niño summit stresses preparation over recovery
By Frank Sweeney
Mercury News Staff Writer
...
Ants Leetmaa, director of the
,
repeated earlier warnings that California will see
``fairly continuous rains'' from January through April.
The state, he said, will see
``double the number of storms, each carrying more rain'' than normal.
This year's El Niño is expected to be as severe as the 1982-83
event, the most severe on record, he said.
But, he added, ``It will not be bigger than that event.''
...
This prediction, and similar ones, argue that
our primary focus should be on the 10-25 year flood
(1982-83 was a 17-year flood, and this range is plus-or-minus 50%):
an option that allows 1000 homes to be flooded in a 21-year flood
makes no sense when compared to an option where no homes are flooded
until the 71-year flood.
Demolishing the Louis Road bridge
Idea 1: tear down Louis Road bridge now
Idea 2: prepare for demolition (for example, explosives) of bridge if
crisis arises (water about to touch bridge)
Questions:
Practical: can bridge be demolished safely,
for example, not doing excessive damage to flood walls.
How much excess capacity does that give us?
Who pays: cost of rebuilding the bridge is likely to come from
the budget of our section of the Water District
(the Water District is divided into five flood districts, each
with its own tax base).
Idea 3: remove sides from Louis Road bridge so that water could
easily pass over it during a large flood.
Based upon simple calculation using cross-sections,
this would provide enough additional capacity to provide 100-year
protection for both Barron and Matadero Creeks.
It has the potential advantage of substantially
reducing the amount of rebuilding needed and
the amount of time that the Louis Road
bridge would be unavailable.
Question: does the structure and construction of the bridge
make such an option feasible?
Note:
this option was raised at Thursday meeting,
belatedly added here on 28 October.
Sediment build-up in lower creek channels,
and problems with US Fish and Wildlife Service
(no problems with California Fish and Game)
Water District: We have measured and
it is typically about one foot of sediment
(within range not requiring dredging).
This (and vegetation) will wash out with first storms.
Local residents: deeper than this. Worry about it not washing out.
Personal opinion: having seen the power of water,
it is hard to believe that a concrete channel would not have
a large capacity for self-scouring
(supporting the Water District's approach),
but it is hard to reject local observation
(although in this meeting, it was hard to judge the level of
experience of the speaker with living along the creek during
high flows).
Update: In week of Oct 27th,
bulldozers have been working in lower Matadero Creek removing
silt and vegetation.
Concerns about how high the water got in lower Matadero in 1995-6.
Motivations of SCVWD directors representing districts other than ours.
Option 4 and 5 in the table above are not favored
by the Water District staff because they would cause flooding for
homes not currently in the 100-year flood zone,
and they have a dictate of "First, do no harm."
This leads to the conclusion that it is better to leave 1000 homes in
a 5- or 20-year flood zone,
than to add 20 homes to a 50- or 70-year flood zone.
Reading between the lines: the district seems to more concerned about
successful litigation by homeowners placed into the flood zone
than litigation by homeowners left in the flood zone.
These priorities of the staff may well reflect the priorities that the
Board of Directors bring to the meeting that decides this issue.
Aside: the people affected by this problem vote for only one of
the five board members representing districts and for
one of the two at-large members.
Version Info: $Revision: 1.14 $ $Date: 2003/11/24 23:41:34 $
