Rancho Palos Verdes City Council
   

TO: HONORABLE MAYOR AND MEMBERS OF THE CITY COUNCIL

FROM: DIRECTOR OF PUBLIC WORKS

DATE: APRIL 15, 2003

SUBJECT: INVESTIGATION INTO THE TARAPACA LANDSLIDE

RECOMMENDATIONS

  1. Authorize staff to contact the County of Los Angeles regarding project participation
  2. Authorize staff to investigate the feasibility of an assessment district as a potential funding source.
  3. Request staff to investigate additional funding sources and assemble a funding plan for the repair of the Tarapaca Landslide repair that minimizes the use of general funds
  4. Engage adjacent property owners to reduce the amount of surface drainage entering the head of the landslide.
  5. Authorize the expenditure of up to $5,000 for additional engineering services.
  6. Adopt Resolution 2003- , A Resolution of the City Council of the City of Rancho Palos Verdes Amending Resolution 2002-45. The Budget Resolution for fiscal year 2002-03, for a budget adjustment to the City’s General Fund.

BACKGROUND

The eastern slope of the San Ramon Canyon immediately to the east of the Palos Verdes Drive East switchbacks shows signs of failure. Cracks and other areas of distress have been clearly visible for some time. In late 2002, the City Council awarded a contract to GeoSyntec Consultants, Inc. (GeoSyntec) to investigate conditions, identify risks, and recommend solutions. This report presents that investigation.

DISCUSSION

Geologic Setting and Conditions:

The GeoSyntec investigation concluded that a landslide exists along the eastern side of the San Ramon canyon just east of the PVDrive East switchbacks. The landslide, named the Tarapaca Landslide, is an active landslide that borders the eastern edge of the larger and inactive South Shores Landslide. The Tarapaca Landslide is presently sliding westerly into the San Ramon canyon, partially blocking stream flow, and contributing sediment for transport to downstream areas of the canyon.

A landslide exists at this location due to a combination of the following factors:

  1. Naturally occurring geologic conditions; that is a bedding plane of a bentonite, with low strength, is unfavorably oriented in the eastern wall of the canyon
  2. Surface drainage enters the head of the landslide and reduces soil strengths.
  3. Storm flow in the San Ramon canyon erodes the toe support of the easterly slope.

These three factors have set up a cycle of

  • Movement of the easterly slope of the canyon
  • Temporary stability of the eastern slope
  • Erosion of the toe of the slope due to drainage in the canyon, and drainage entering the head of the landslide
  • Renewed landslide movement

Left unchecked this cycle will occur indefinitely, the landslide will grow in size, and a solution will grow in cost.

At the outset of this report it is important to note clearly that:

  1. The landslide currently threatens no homes.
  2. The landslide is limited to approximately 800 lineal feet of the eastern side of the canyon.
  3. The landslide does not currently threaten Palos Verdes Drive East

Risks / Adverse Effects

The cycle described above has the following adverse effects:

  1. The landslide, currently 2.5 acres in size, appears to be expanding onto the County of Los Angeles parcel involving an additional 2+ acres. If left unabated, the active part of the landslide could enlarge down San Ramon drainage and upslope toward homes at the end of Tarapaca Road. At the present, there is no recognized threat to homes, but enlargement of the landslide could cause future impacts.
  2. Large volumes of sediment are being transported from the landslide area of the canyon to points below. This sedimentation has raised the base level of the canyon at 25th Street to the roadway elevation such that there is little capacity available to store either storm water or sediment. This sedimentation has contributed to the blocking of a City of Los Angeles storm drain under 25th Street. The result is that during even mild storms, 25th Street fills with drainage and debris.
  3. The sedimentation has caused temporary canyon blockages, and therefore retention of drainage upstream of the Tarapaca Landslide. This retention could result in an increase of water infiltration into the South Shores landslide. The South Shores Landslide extends from the south end of San Ramon Drive to the coastline and encompasses Palos Verdes Drive East, Palos Verdes Drive South, 25th Street and the South Shores Community.
  4. Sedimentation causing temporary canyon blockages also has the potential to retain water that could suddenly breach the debris, causing a rapid discharge of water and sediment load onto 25th Street.
  5. The cinder block wall along the South Shores Community is the only protection preventing surface run off and mud from spilling into the trailer park in the City of Los Angeles.
  6. Fissures within the landslide continue to appear and widen allowing easier access to surface water infiltration.

Jurisdictional Issues:

The length of San Ramon canyon from the upper reaches of the landslide to 25th Street is approximately 1500 lineal feet. This project area involves two cities, and a County of Los Angeles parcel (Friendship Park), within the City of Rancho Palos Verdes. Approximately 450 lineal feet of the canyon is on property owned by the City of Rancho Palos Verdes, approximately 250 lineal feet is within the County of Los Angeles parcel, and 800 lineal feet is with a parcel within the City of Los Angeles.

The active part of theTarapaca Landslide is principally within the City of Rancho Palos Verdes on Lot 8 of Tract 20856. Part of the landslide, however, is within the County of Los Angeles parcel.

Most of the toe of the landslide is within the City of Rancho Palos Verdes.

Surface run off entering fissures of the landslide originates from private property within the City of Rancho Palos Verdes, Lots 7, 8, 9, and 10 of Tract No. 20856, and from the County parcel. The City of Los Angeles is a receiver of drainage in the San Ramon canyon.

The sediment that erodes into the canyon comes principally from within the City of Rancho Palos Verdes

The sediment plugs a storm drain, and washes onto a roadway owned by the City of Los Angeles.

In preparation of this report staff contacted both the County of Los Angeles, and the City of Los Angeles.

There have been only brief discussions with the County, however, given that a portion of the landslide is on County property, and because a significant amount of surface flow that enters the head of the landslide originates on County property, there is role for the County of Los Angeles regarding the needed improvements within the City of Rancho Palos Verdes. One of the recommendations of this report is to make additional contact with representatives of the County of Los Angeles.

There have been several in depth meetings with the City of Los Angeles regarding this project. Because the landslide impacts their roadway and storm drain the City is desirous of a solution. At one point in time the City of Los Angeles contemplated construction of a debris basis just upstream of 25th Street, however, in more recent discussion there is thought that if the City of Rancho Palos Verdes were to construct a canyon storm drain, the City of Los Angeles would consider extending that improvement downstream to 25th Street. Irrespective of their actions, staff does not see a role for the City of Los Angeles regarding the needed improvements within the City of Rancho Palos Verdes.

Solutions

Three solutions have been identified

    1. Continued maintenance
    2. Storm drain construction
    3. Slope Stabilization
  • Option One – continued maintenance: This approach assumes that no remedial actions are implemented to change the current conditions of the drainage system or landslide. This approach would provide periodic removal of mud and rock sediment from the canyon, storm drain, and roadway. This approach has risks associated with it including but not limited to continued traffic hazards on 25th Street, the possibility of a major storm event causing closure of 25th Street, water and mud possibly overtopping the block wall above the South Shores Community.

    Other risks that may increase with time are the increasing movement and enlargement of the Tarapaca Landslide and the risk of water retention upstream from the landslide raising groundwater levels within the South Shores Landslide (possibly destabilizing the South Shores Landslide). Enlargement of the Tarapaca Landslide could also extend down the eastern side of San Ramon drainage and cause upslope encroachment toward the homes at the south end of Tarapaca Road. As a consequence, if the Tarapaca Landslide enlarges, mitigation or repairs will be more difficult and more costly in the future.
  • Option Two – storm drain construction to control erosion This option includes the construction of an 800-ft long storm drain across the toe of the Tarapaca Landslide. The storm drain will control erosion at the toe of the landslide and bypass the source of erosion, thus removing one of steps in the current cycle of degradation that currently exists along the canyon. This approach would significantly reduce erosion, reduce the potential for enlargement of the landslide enlargement, and provide control of water retention to prevent infiltration of water into the South Shores Landslide.

    Construction would consist of installing a storm drain with fill at the toe of the landslide. This pipe/fill would create a resistive force to limit the potential of future landslide movement and enlargement. This approach does not provide a fully engineered stabilization of the Tarapaca Landslide but it does mitigate the causes of canyon problems, i.e. sediment loading downstream, erosion at the toe of the landslide and surface water infiltration.
  • Option Three - Slope stabilization: This option provides an engineered solution to stabilize the areas of active landslide movement in Lower San Ramon drainage. The engineered stabilization of the Tarapaca Landslide would require removal of much of the landslide and placement of an engineered fill buttress and sub drains at the toe of the landslide. Due to the size and geometry of the buttress required, it is anticipated that a storm drain (e.g. similar to option two, would be required to protect the new buttress and maintain flows in San Ramon drainage.

Cost Estimates:

  • Option One $ 40,000 annually
  • Option Two $ 1,200,000 initially / $ 3,000 annually
  • Option Three $ 2,800,000 initially / $ 3,000 annually

These costs include design and construction. However, the cost of permits, environmental documentation and approvals, re-vegetation of slope, and the management of the re-vegetation are all additional.

Staff recommends that the City pursue Option Two, construction of a storm drain system to control erosion. The reason is that the storm drain will control erosion at the toe of the landslide and bypass the source of erosion, thus removing one of steps in the current cycle of degradation that currently exists along the canyon. This approach will reduce the potential for enlargement of the landslide enlargement, and provide control of water retention to prevent infiltration of water into the South Shores Landslide. In addition, this solution together with a companion storm drain project in the City of Los Angeles will solve the problem of flooding and debris deposition at 25th Street.

CONCLUSION

Adopting the staff recommendations will begin the process to mitigate the Tarapaca Landslide. Staff will solicit proposals for engineering services to design the needed canyon improvements, and contact the County of Los Angeles for their financial participation. Staff will return to the City Council with a recommendation for award of contract for engineering services, and a progress report on discussions with the County.

This project faces many challenges, and processes to construct the needed and the improvements will be lengthy. Some of the challenges facing this project are:

  1. Several jurisdictions are involved
  2. The engineering principals are complex
  3. The project impacts sensitive canyon biology
  4. The project will require multiple permits
  5. The project requires the acquisition of rights of way.

FISCAL IMPACT

The recommended actions include the expenditure of an additional $5,000 for engineering services. Staff anticipates this expenditure for engineering services to meet with impacted property owners, and agencies in an effort to assemble a funding program.

Staff could identify no immediate funding sources for this project other than General Fund reserves. The cost estimates provided in this staff report are preliminary and should be considered as an indicator of significant future costs rather than a precise budget. For example the first estimate of costs for the San Ramon Drainage project was $700,000.

The FY2002-2003 estimated General fund revenues in excess of adopted expenditures are only $827. Therefore, the additional appropriation for this project cannot be funded within this year’s anticipated revenues and will have to be drawn from the General fund reserve. The calculation of the projected General fund reserve available for appropriation, which is below the reserve policy level, is summarized below.

Actual General fund reserve, 6/30/02

7,233,654

 

 

 

Less:

 

 

 

Policy Reserve Level

(6,451,870)

 

Discretionary Budget Items Adopted:

 

 

Master Planning

(200,000)

 

Citywide Drainage

(100,000)

 

Sewer Maintenance

(350,000)

 

Traffic Signal

(135,000)

 

 

 

General fund reserve available, 7/1/02

(3,216)

 

 

 

Less:

 

 

7/16/2002

View Restoration Tree Trimming

(35,000)

7/16/2002

Open Space/Recreation Task Force Consultant

(25,000)

8/6/2002

Weed Abatement (Parks Maintenance)

(21,500)

11/19/2002

Additional Student & The Law Classes

(9,118)

11/19/2002

Civic Center Modifications (transfer out)

(5,000)

12/3/2002

Open Space Land Purchase

(18,216)

12/3/2002

Additional PVIC Park Maintenance

(19,000)

12/17/2002

Storm Water Program additional funding

(3,200)

12/17/2002

Temporary Trailers at PVIC

(10,000)

1/7/2003

Traffic Calming on Via Rivera (transfer out)

(6,780)

1/7/2003

Open Space/Recreation Task Force Consultant

(40,000)

2/18/2003

RPV City Talk video-editing

(2,500)

2/18/2003

Reinstall computers for bldg mods and furniture

(8,000)

2/18/2003

Lobbyist for PVP Land Conservancy

(25,000)

2/18/2003

Permit Clerk full-time salaries

(14,000)

3/4/2003

San Ramon Drainage (transfer to CIP)

(491,067)

3/18/2003

Educational Access Channel Equipment

(10,000)

 

 

General fund reserve available, net

(746,597)

Respectfully Submitted,
Dean Allison
Director of Public Works

Reviewed
Les Evans
City Manager

Attachments:

Resolution 2003 -

Photographs of the Canyon

RESOLUTION NO. 2003-

A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF RANCHO PALOS

VERDES, AMENDING RESOLUTION 2002-45, THE BUDGET APPROPRIATION

FOR FISCAL YEAR 2002-03, FOR A BUDGET ADJUSTMENT TO THE CITY’S CAPITAL PROJECTS FUND

WHEREAS, Section 3.32 of the Rancho Palos Verdes Municipal Code provides that all expenditures in excess of budgeted allocations must be by supplemental appropriation of the City Council; and

WHEREAS, on June 12, 2002, the City Council of the City of Rancho Palos Verdes adopted Resolution 2002-45, approving a spending plan and authorizing a budget appropriation for the 2002-03 fiscal year; and

WHEREAS, it is necessary for the City to allocate additional funds to conduct additional engineering investigations into the Tarapaca Landslide; and

WHEREAS, a budget increase in the Capital Improvement Projects Fund is necessary to authorize the expenditure of additional funds for the project.

BE IT, THEREFORE, RESOLVED BY THE CITY COUNCIL OF THE CITY OF RANCHO PALOS VERDES:

The following adjustment be made to the Capital Improvement Projects Fund budget::

CIP Fund 330-930-35 Professonal/Technical Services $ 5,000

PASSED, APPROVED, AND ADOPTED THE 15th DAY OF APRIL, 2003.

 

___________________________

MAYOR

ATTEST:

______________________

CITY CLERK

Resolution No. 2003-

State of California )
County of Los Angeles )ss
City of Rancho Palos Verdes )

I, JO PURCELL, City Clerk of The City of Rancho Palos Verdes, hereby certify that the above Resolution No. 2003- was duly and regularly passed and adopted by the said City Council at regular meeting thereof held on April 15, 2003.