HomeMy WebLinkAboutAgenda Report - November 5, 2008 K-02aAGENDA ITEM KOL06
&0� CITY OF LODI
COUNCIL COMMUNICATION
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AGENDA TITLE: Receive Report on Mokelumne River Erosion Near Pigs Lake
MEETING DATE: November5,2008
PREPARED B Y Interim Parks and Recreation Director
RECOMMENDEDACTION: Receive presentation regarding the condition of the Mokelumne
River bank erosion and its potential effect on Pigs Lake.
BACKGROUND INFORMATION: On February 6, 2008, staff provided informationto Council related to
the status of the Mokelumne River bank in the general vicinity of
Pigs Lake within the Lodi Lake Nature Area. Civil Engineering firm
of Kjeldsen, Sinnock & Nuedeck was contracted to provide, as best
possible, a detailed report on the effects cf erosion of the river bank
in the vicinity of Pigs Lake.
On August 13,2008, staff received Mr. Sinnock's Preliminary Reportthat outlines the initial findings and
recommendations regarding the erosion that is occurring on the south bank of the Mokelumne River
adjacent to Pig Lake in the Lodi Lake Nature Area.
FISCAL IMPACT The fiscal impacts are varied and complex. Temporary measures
range in cost from $10,000 to $25,000, excluding permits and
monitoring, which are an additional $25,000. Permanent repair
costs may be greaterthan $2 million. If the embankment fails, this passive recreation area may be lost
permanently as the cost of permitting and reclamation will be significantly higher.
FUNDING AVAILABLE: None
James M. Rodems
Interim Parks and Recreation Director
APPROVED:
Blai�King, City Manager
KJELDSEN,SINNOCK& NEUDECK,INC.
CIVIL ENGINEERSAND LAND SURVEYORS
STEPHEN K. SINNOCK
CHRISTOPHER H. NEUDECK
KENNETH L. KJELDSEN
RETIRED
711 NORTH PERSHING AVENUE
POST OFFICE BOX 844
STOCKTON. CALIFORNIA95201-0844
TELEPHONE (209) 946-0268
FAX (209) 946-0296
E-MAILksn@ksninc.com
2088-0010
Mr. Steve Dutra
Parks & Recreation Department
City of Lodi
125N. Stockton Street
Lodi, CA 95240
August 13,2008
Re: Lodi Lake Nature Area Erosion Along Mokelumne River, Preliminary Report
Dear Mr. Dutra,
Kjeldsen, Sinnock& Neudeck, Inc. submits herewith our Preliminary Report that outlines
the initial findings and recommendations regarding the erosion that is occurring on the south
bank of the Mokelumne River, adjacent to "Pig Lake" in the Lodi Lake Nature Area. This letter
report has been prepared pursuant to the scope of work described in our proposal to the City of
Lodi dated October 17,2007. The purpose of this letter report is to communicate to the City of
Lodi our preliminary findings and recommendations relative to 1) the probable causes of the
erosion, 2) permitting requirements for construction of repairs, 3) options to repair erosion sites,
4) preliminary quantity estimates for repair options, and 5) preliminary cost estimates for repair
options.
I have included as attachments to this letter report, the following exhibits:
Exhibit A - Aerial Map and River Bank Cross -Sections
Exhibit B - Photographs of Active Erosion Sites
Exhibit C - Annotated Photographs
Exhibit D - Typical Repair Section
Probable Cause Of Erosion
There are several conditions occurring in this segment of the Mokelumne River that may
be contributing to the aggressive erosion of this particular section of riverbank. Based upon our
site inspections and preliminary evaluation of site conditions, there appear to be three
mechanisms contributing to the active erosion of the riverbank, 1) hydraulic erosion on the lower
slope, 2) wave erosion on the upper slope, and 3) bank instability due to the annual draining of
Lodi Lake.
First, there is hydraulic erosion occurring below the waterline that has undermined and
washed out a previous repair project that was completed in 1994. The erosion area that is the
subject of this report is located on the outside bend in the river, where the flow velocities will be
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August 13,2008
the greatest. The 1994 repairs consisted of stacking a grid of tree roots and logs along the eroded
bank and cabling them to existing live trees along the riverbank. The remnants of the trees and
logs installed during the 1994repair project are scattered throughout the river bottom and the
lower slopes of the bank as shown in the attached photos in Exhibit B. The remnant trees and
logs may be aggravating the hydraulic erosive action of the river in this area, as they could be
creating eddies and turbulence that are contributing to the erosion of the lower portions of the
riverbank.
Second, there appears to be wave wash erosion occurring higher up on the slope of the
riverbank, at the summer water level when Lodi Lake is full. The waves are generated by both
boats and wind. This erosion is clearly defined and localized at the top of the waterside slope,
and is causing severe undercutting of the embankment crown. The wave wash was observed
during the August inspection when watercraft passed the site.
Third, the erosion of the riverbank may be aggravated by the annual draining of Lodi
Lake. The rapid drawdown of the lake in the fall could be contributing to the "erosion" of the
riverbank slope by not allowing adequate time for the saturated riverbank to drain. When soils
experience a rapid drawdown, the moisture that was trapped in the soils at the higher water levels
are not provided adequate time to drain. This trapped moisture destabilizes the soils and on steep
slopes can result in the sloughing of the cohesionless sands on the upper portions of the
riverbank.
Permitting Issues Related To Repairs
The permitting requirements will be primarily driven by the type of repairs made, and the
impacts that the project might have on the environment. As with all such projects, the repair
project will have to comply with the requirements of the California Environmental Quality Act
(CEQA). An initial study will need to be performed to address all of the impacts associated with
the project. That process will require a qualified Biologist to inventory the species present and
determine how the proposed project might impact those species. Once the impacts are
determined, the project scope might be modified to avoid or minimize impacts to the
environment. The results of these investigations and modifications to the project will result in the
CEQA determination and provide the basis for the permit applications to the regulatory agencies
listed below.
State Department of Fish & Game
U.S. Army Corps of Engineers
NOAA Marine Fisheries
US Fish & Wildlife Service
Central Valley Regional Water Quality Control Board
State Reclamation Board
Other Local, State and Federal agencies as necessary
Our office had various discussions with the regulatory agencies and biological
consultants that are familiar with current regulatory and environmental issues in the area of the
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August 13,2008
project. It was made very clear in the conversations that due to the backlog of permit
applications, the State and Federal agencies will not perform a site inspection to provide a
preliminary assessment of impacts until a permit application is submitted by the project
proponent. The project is in a biologically sensitive area where threatened and endangered
species are likely to be present, and will require careful consultation and consideration during the
development of the scope of work for this project. It should be noted that the permit application
process requires substantial detail in order to be processed so it actually occurs after the project
design and environmental issues are addressed. Estimating the costs associated with securing
environmental documents and permits were not included in our scope of work.
Erosion Repair Options
This location presents several challenges in terms of implementing a repair project. The
primary obstacles are that access to the repair site is very restrictive and that the top of the
riverbank adjacent to the eroded area is extremely narrow and will likely not support large
construction equipment. Access to the work locations is by way of narrow foot paths through the
Nature Area. The repair options presented below could be performed by either waterborne or
land based equipment, however the costs for both will be higher due to the access limitations.
Emergency Protective Measures
Due to the length of time that may be necessary to secure permit approvals for a major
project, it would be prudent for the City to investigate the possibility of placing plastic
sheeting or riprap on the upper slope of the riverbank, to stabilize and protect it against
further erosion,during the months when Lodi Lake is full. The City should consult with
the Department of Fish and Game and the Federal regulatory agencies to determine if the
placement of riprap on the upper slope could be performed under an emergency
notification. Another temporary option would be to limit boat speeds and wakes in that
area.
Repair the Entire 500 Foot Eroding Bank
Placing clean quarry stone riprap along the entire reach of eroded levee would be
considered the conventional repair for this location. Exhibit D illustrates a possible
scenario for a repair cross section at the narrowest point between Pig Lake and the
Mokelumne River. The embankment crown has been widened to 30 feet to allow for an
area where plantings of various types of native vegetation could occur, as is usually
required by the permitting agencies to mitigate project impacts.
Another option for repairing the eroding bank could include driving sheet piles to form a
bulkhead along the eroded area, and then backfilling the upper section as necessary.
Various configurations could be used to make this type of repair more user and
environment friendly.
Flow Diversion Structure
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August 13,2008
This site might lend itself to the installation of a water diversion flow structure that would
divert the high velocity flows away from the banks and force it down the center of the
river. This option would require that the hydrology of the project be studied in detail in
order to determine the feasibility and impacts associated with that type of concept.
Possible advantages of this concept is that it might be less invasive environmentally and
could require less material to construct. Potential disadvantages are the cost of the
analysis and the possibility that the eroding bank might require rebuilding and armoring
in addition to installation of flow diversion structures.
Preliminary Quantity & Cost Estimates For Repair Options
KSN performed field surveys of the site to determine the typical dimensions of the
project. A copy of an aerial photograph of the project site showingthe location of the 13
surveyed cross-sections of the eroded bank is attached to this report as Exhibit A. Photographs
showing the existing condition of the riverbank taken at the cross-section locations is attached as
Exhibits B).
The cost for riprap is based on unit prices developed from discussions and site
inspections by an experienced local contractor. The unit price for riprap "in place" is estimated to
be approximately $75 per ton. Obviously, market conditions could change that estimate due to
material demand, fuel prices, and changes in site conditions. Please note that these construction
costs do not include the costs to secure the necessary environmental documents and permits.
Temporary Emergency Protective Measures
Several options exist to temporarily slow the erosion on the upper bank caused by wind
and wave action when the lake is full. These measures could be implemented either by a
contractor or City of Lodi staff, and would only be temporary in nature. It should be
noted that placement or work on the channel bank could require that a Notification of
Streambed Alteration permit be filed with the Department of Fish & Game.
The first option would be to implement speed limits on boats in the damaged section of
the river. This would be a relatively inexpensive option and would require notifications,
buoys and possibly the costs of enforcement. We have limited experience with the costs
associated with these actions, but assume that the City of Lodi is already enforcing speed
limits in other areas of the lake so additional costs would be nominal.
The second option would be to place plastic sheeting or geotextile fabric, and sandbags
over the upper bank. This is a cost effective and easily installed measure. Plastic sheeting
costs range from approximately $60 - $100 for 100 x 20 foot rolls. Estimated need is 500
feet so materials are estimated at about $500. These materials could be installed by City
of Lodi employees. The installed cost of this temporary option is estimated at $10,000.
Page 5
August 13,2008
The third, and most expensive option, would be to hand place riprap in the eroded areas
at the "lake full" waterline. This option does have drawbacks due to access issues, high
labor costs and the potential for site preparation work. Due to the soil types at the eroded
sites, there is potential for the rock to slip down the slope. Estimated costs are based on
using $75 per ton unit price for rock, and filling a band approximately 3 feet high and 500
feet long to a depth of 18 inches, or 660 lbs per foot. Estimated cost for this item is
$25,000.
Permanent Repairs
As stated above, permanent repair options include placement of riprap on the entire
eroded area, driving sheet piles or developing a hydraulic flow diversion structure in the
channel. We are providing costs for armoring and sheet pile options. The flow diversion
structure would require hiring a hydraulic consultant to determine the feasibility of such
an option.
Based on our survey data, the preliminary estimates indicate that 15,500 tons of material
will be required to construct the structure illustrated in the attached Repair Exhibit
(Exhibit D). The material would consist of a combination of rock fill and riprap. The
total cost, based on $75 pre ton "in place" would be $1,116,000.
Driving sheet piling along the eroded stretch is another option. Recent project costs,
where there was good access, have been running about $40 per square foot, installed.
Due to the access issues, and that the pile driving equipment might need to be marine
based, we have doubled the square foot costs for installed sheet piles. Using 40 foot
sheets for the entire reach of eroded area result in an area of 20,000 square feet. At a unit
cost of $80 per square foot, the total estimate is $1,600,000.
Please note that these estimates are preliminary and are intended to give the City an idea
as to the magnitude of the costs associated with each repair option. The costs seem very high for
the relatively simple work that is being performed, but with escalating costs for materials and the
potential for double and triple handling of the materials, we feel they are a conservative estimate
given the limited information that is available on the project at this time.
If you should have any questions or require further information, please contact Bill
Darsie or me at (209) 946-0268.
Sincerely,
KJE SEN, S K & NEUDECK, INC.
L1
/Stephen K. Sinnock
w/enclosures
EXHIBIT B
EXHIBIT D
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44 �� � 44
3 0' .�
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40 2 40
� o RIPRAP
1
36 � 36
ROCK FILL 8'
32 � 0 32
o a
0
28 28
o a o O fl 1.5
24 24
GEOTEXTILE FABRIC
20 ' ` 20
0 20 40 60 80
TYPICAL REPAIR SECTION
K K ELpSEN LODI LAKE MOKELUMNE Design Sole Date
S S�N N OC K Post Office aox Baa LODI, CALIFORNIA wc� MAY 2008
711 w Pershing Avenue Drawn I" = 10' Sheet Number
N N E U D E C K §Officep' 20)g946� 268 LEVEE BANK EROSION CONTROL SAM Original Drawing Scale of 1
INC. Consulting Engineers Foxes: tl209} 946-0296 C V tJ l IT Check D W Project File No.
I and Land Surveyors E-mail: KSN@ksninc.com REPAIR G An" 1 D I I SKS I 2 ct File o.