HomeMy WebLinkAboutCC AG PKT 2003-09-22 #V AGENDA REPORT
DATE: September 22, 2003
TO: Honorable Mayor and City Council
THRU: John B. Bahorski, City Manager
FROM: Douglas A. Danes, P.E. Director of Public Works /City Engineer
SUBJECT: WINTER SAND DIKE (BERM)
SUMMARY OF REQUEST:
Receive and file the September 2003 Winter Dike Assessment Report by Moffatt &
Nichol Engineers and direct staff to use the recommendations presented in the report.
BACKGROUND:
The First District Councilmember forwarded concerns from citizens along Seal Way and
Ocean Avenue regarding the construction, schedule and configuration of the annual sand
dike. A community meeting was held on August 26, 2003 in the council chambers.
Approximately 75 people from the area attended along with the First District
Councilmember, a representative from Moffatt and Nichol Engineers, Director of Public
Works /City Engineer and the Lifeguard Lieutenant.
Staff used a computer slide presentation to explain the sand cycle, history of the dike,
groin and jetty at the Naval Weapons Station. During the question and answer section of
the presentation, the majority opinion of the residents was that they were dissatisfied with
the current construction and removal of the winter sand dike.
❑ Residents overwhelmingly expressed that the dike should not be constructed prior
to November 1 and should be removed no later than the end of March.
❑ Many voiced strong opinions that they did not desire the extra protection of the
dike constructed early.
❑ Opinions were expressed regarding the dimensions of the dike and how could it
be lowered to preserve views.
❑ Opinions were expressed how the dike should be constructed year to year with the
same standard.
The residents at the meeting were fully informed of the risks and the new limitations to
provide emergency services to the residents if flooding occurred. In response to citizen
concerns, the Department explained that it was already in the process of examining their
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concerns and had retained Moffatt Nichol Engineers who were finishing an assessment
report regarding the configuration dike and the probabilities for flooding with tropical
storm events via computer modeling. It was also explained that construction of the dike
was a matter of risk management. The flooding event September 1997 somewhat shaped
a more conservative philosophy regarding this issue. At present, the Department has
reduced its workforce significantly. Overtopping events put a physical and financial
strain on City resources. Response to any event would be a combination of in- house,
contract and regional resources such as the Orange County Fire Authority.
Given these parameters and given the results of the study, it was now possible to address
the concerns and opinions of the residents. Section 5 of the report details the
recommendations regarding dike construction. If adopted by Council, these would
provide for the following:
Timetable Recommendations
❑ Start construction of the dike after November 1 with completion anticipated by
mid November.
❑ Remove the dike by March 31.
❑ During El Nino years, start construction of the dike so it is complete by
November 1 and leave in place until mid April.
Dike and Location Height Recommendations
❑ Construct the dike to a set profile as illustrated on the Winter Dike Concept Plan
provided within the report. These include limits of the dike, the minimum widths,
height and slope.
❑ One of the major issues expressed by residents was the height of the dike. Using
the model, it was determined that the dike should be 20' elevation from
approximately 12 Street to 150 east of Dolphin which is approximately 9 feet
higher than the sidewalk elevation of 11 feet. The dike could be reduced to 18'
from the Pier to 12 and from 150 East of Dolphin to the end of the dike. The
profile of the summer beach profile is recommended at an elevation of 15 feet that
is approximately 4 feet higher than the elevation of the sidewalk. This reflects a 1-
foot decrease in elevation compared to the previous 1984 Winterization Study and
should alleviate some view concerns.
These recommendations addresses the majority of the concerns expressed during the
meeting. The dike is constructed later and taken down earlier than previously performed
within the last few years, the configuration has been changed to reflect flood protection
but also lowered by 2 feet during the winter and 1 foot during the summer, and a plan has
been developed that can be followed by the City's contractor so the dike is constructed in
the same standard from year to year. Additionally, the Department will use Moffatt
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Nichol Engineers to provide initial inspection services during the construction of the dike
during the first year of implementation and some monitoring to adjust to natural
occurrences.
The only differences than that expressed by the citizens is that Moffatt Nichols Engineers
recommend that during El Nino years it is recommended to place the dike about 2 weeks
earlier and take down 2 weeks later. This appears to be a prudent choice of action but
may meet with some resistance from the public.
It is important to note that any policy involving natural occurrences involve risk. Often
elected officials have to set policy and protection based upon probability of occurrence,
funding availability and geographic locale. This report analyzed the probability of
tropical events and does make a recommendation that will be perceived as more
favorable by the public. Note that the information analyzed is not exact and there always
looms the occurrence of future events similar to September 1997. Staff has also received
input from a small minority that they desire the additional protection. The current plan
intends to strike a balance with community desires and protection from unpredictable
natural events.
As a side issue, a proposal was brought up the meeting to construct a seawall along Seal
Way instead of constructing the winter dike. Moffatt Nichols analyzed this in a separate
attached memo. The approximate cost of constructing a 2000 linear foot, 4 -foot high, 50-
year design life sea wall would cost up to $4,000,000. Given the current prevailing
opinion of many of the resource agencies against "armoring" the coast and lack of funds,
this option is not recommended at this time.
FISCAL IMPACT:
None at this time. Should a wave - overtopping event occur prior to dike construction, the
City would incur response costs. As an illustrative example, if an event occurred, the City
would need to procure a dozer to construct an emergency dike and provide crews to
respond to the situation. Assuming the cost of a dozer at $1,300 to $1,500 per day plus
mobilization and cost of a 5 to 10 man contracted crew with trucks and equipment would
range from $1,000 to $3,000 per day. An event lasting 3 to 7 days may cost up to and
over $30,000. This cost would be reduced depending upon the amount of aid provided by
the Orange County Fire Authority if available. Although the City currently has
emergency contracts with contractors and mutual aid agreements with other agencies, the
situation becomes less certain if multiple events are occurring countywide at the same
time.
RECOMMENDATION:
Receive and file the September 2003 Winter Dike Assessment Report by Moffatt &
Nichol Engineers.
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Prepay ' y.
Douglas AJDancs, Director of f ublicWorks /City Engineer
NOTED AND 'PROVED
John B c ah • rski, City Manager
ch hments
1. September 2003 Winter Dike Assessment Report by Moffatt & Nichol Engineers
2. September 2003 Memo regarding 4 foot High Sea Wall by Moffatt & Nichol
Engineers
3. Southeast Old Town Drainage Area Map by Seal Beach Department of Public
Works GIS
4. Correspondence
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Attachment 1
September 2003 Winter Dike Assessment Report by Moffatt & Nichol Engineers
Provided as separate bound report and posted in PDF format on www.sb-
publicworks.coin .
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Attachment 2
September 2003 Memo regarding 4 foot High Sea Wall by Moffatt & Nichol Engineers
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l MOFFATT N & NICHOL
E N G 1 E E R S
Date: September 16, 2003 Memorandum
To: Doug Dancs, City of Seal Beach
From: Allan Charteris
Re: Winter Dike Assessment
Discussion of 4 -Foot High Seawall Alternative
It is our understanding that the feasibility of constructing a 4 -foot high wall along Seal
Way has been suggested in lieu of the winter sand dike for coastal flooding protection.
This structure in effect would be considered a seawall and would have to be designed to
withstand ocean wave forces. The following provides a brief discussion of advantages
and disadvantages of this seawall alternative:
SEAWALL ADVANTAGES
• Seawalls can provide a more long -term solution to coastal flooding than a winter sand
dike, and provide backland flooding and erosion protection during extreme storm
events. ,
• A vertical seawall takes up less beach footprint area than the sand dike, thereby
enhancing access.
• A vertical seawall can be constructed at a lower elevation than a sand dike and
provide greater and more reliable protection.
• The outer face of the seawall near the crest can be curved to help direct wave energy
away from the wall and reduce overtopping.
SEAWALL DISADVANTAGES
• A four -foot high wall would have a crest elevation at approximately +15 feet MLLW.
This elevation is lower than most seawalls on the coast and could be subject to rare
but significant wave overtopping. Most seawalls on the coast range in elevation from
+16 feet to +20 feet MLLW, based on our experience. A higher wall would come at
the expense of blocked views along Seal Way.
• Seawalls are expensive. Vertical seawalls typically cost a minimum of $1,000.00 to
$2,000 per foot to construct.
• Seawalls are extremely difficult to permit given concerns regarding beach impacts
and the general "hardening" of the shoreline
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Attachment 3
Southeast Old Town Drainage Area Map by Seal Beach Department of Public Works
GIS
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Attachment 4
Letters and petition from Residents
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