20140916 Late CorrespondenceCITY OF RANCHO PALOS VERDES
TO:
FROM:
DATE:
SUBJECT:
HONORABLE MAYOR & CITY COUNCIL MEMBERS
DEPUTY CITY CLERK
SEPTEMBER 16, 2014
ADDITIONS/REVISIONS AND AMENDMENTS TO
AGENDA**
Attached are revisions/additions and/or amendments to the agenda material presented
for tonight's meeting:
Item No. Description of Material
2 Report from Robert Douglas
Respectfully submitted ,
Teresa Takaoka
W :\AGENDA\2014 Additions Revisions to agendas\20140916 additions revisions to agenda .doc
r
Abalone Cove Landsl i de Abatement District (ACLADL
Report to RPV City Counc i l; Misc . Rept ., Sept . 16 ,2014
To: Mayor and City Council members, City of Rancho Palos Verdes
From: Robert Douglas, Abalone Cove Landslide Abatement District
Date: September 16, 2014
Re: Use of GPS Data collected in the Portuguese Bend Area
Comments: The Global Positioning System (GPS) was established in 1994 to
replace the ground -based engineering survey which lacked high precision and the
ability to measure the low-end rates of the landslide movement. Currently the
GPS network employs over 70 stations widely distributed across the four active
landslides, Abalone Cove, Portuguese Bend, Klondike Canyon and the Flying
Triangle , and the non -active Ancient Altamira Canyon landslide . The survey
measures the horizontal movement, vertical movement and direction (azimuth)
of each station relative to a fixed location. Prior .to the early 2005, many of the
GPS measurements lacked acceptable precision and were considered of low
confidence. With the appointment of Michael McGee Surveying Consultant,
these problems were solved and since 2007 the annual data results are of both
high precision and high confidence.
The GPS surveys are critical to the Abalone Cove Landslide Abatement District
(ACLAD) and the City Geologist in assessing and analyzing the landslides in the
Portuguese Bend area. With this data they were are able to:
1. Determine the horizontal movement, including rate and distance;
2. Determine vertical (elevation) movement
3. Determine the direction (azimuth) of movement
at rates of 0.01 feet (hundreds of feet) with accuracy and precision.
1
Abalone Cove Landslide Abatement District {ACLAD),
Report to RPV City Council; Misc. Rept., Sept. 16 ,2014
PowerPoint Presentation:
LANDSLIDE MOVEMENT
·······. GPS Stations
0 0
• • • 0 • 0 ~ I r • I••
•• ··; :: .:. ·.,: "c11so 'CRS i AB = Aba lone Cove . •
PB = Portuguese Be nd Ancient AJtamiro
I ' KC = Klon d ike Canyo n Landslide
Cr = Crenshaw Ex1.
Fl = F lyi~g Triangle
~R52 ', ~,,
Al56
Al57
ADU
Al17
Landslide
Total Horizo I Movement ' ,, /based on-.GPS m~asur
.05 \
---.. ~-20
05
1994-2012 "stable"F, ' contours in feet
AS55 • ' \ 0 0 < 6.0 In .so ",, \ 0 . Sft = .6in
PVDS
Ab a l one Cove LS
, 0 .20 ft = 2 .4 in
', \ 0 .50 ft = 6 in
\ 1.0 ft = 12 in
\
'
~
/
I
PP . 1 Distribution of GPS stations
r elative to the major landslides in
the Portuguese Bend area . All of
the landslides have adequate
coverage except for the Flying
Triangle Landslide which mostly
lies outside the City of Rancho
Palos Verdes.
PP 2 The horizontal
movement between 1994
and 2012 based on GPS,
portrayed in a contour map
of total movement. The 1 .0
contours{= 12 inches of
movement) approximately
describes the outline of the
Abalone Cove and
Portuguese Bend landslide
{shown here in blue). All of
the area has undergone
some movement but it
varies considerably . The
brown area has moved less than 6 inches over about 20 years and is considered "stable" while
the active landslides have moved several feet to several tens of feet . The most active area is in
the core of the Portuguese Bend landslide, the toe of which has move over 100 feet. Station
locations are shown as red dots.
2
"\
Total vertical (elevation) change
GPS Height )
199 4-2013
(A B stations only)
measurements in feet
PVDS
.01
-.02
Abalone Cove Landslide Abatemel")t District (ACLADL
Report to RPV City Council ; Misc. Rept ., Sept . 16 ,2014
/ ~ -, C RSO ~Cl!Sl
PP 3 The change in surface
elevation (vertical component of
PGS measurements) for the greater
Abalone Cove a r ea . (The surface
elevation in Portuguese Bend
landslide area was d i sturbed when
landslide remediation removed
over 10 million cu. yds . of top soil
from the middle of the area.) Note
that all of the measurements are
hundreds to tens of a foot and
negative, meaning the area is
subsiding with the greatest drop
\.
', Cl!07 •
(disturbed \
area >
occurring in a small depression in the center and in the landslide (shown in darker blue). The
greatest change is the area of the toe of the landslide . At the edges , the movement is very
small to nil.
/ ._.
GPS Height
lffr.:·MIU
tAfM.U•on1o"IYI
PVDS
Abalone Cove
Landslide
... •• ... ~ catl
Landslide
Movemen
Horizontal
c
Down
PP 4 The area of the landslide
is located on the flank of the
Palos Verdes Peninsula which
slopes towards the ocean .
Nearly all of the Portuguese
Bend area is sloping so it is no
surprise to learn that the
horizontal movement is
accompanied by a downward
vertical component. The
landslides in the area are
slowly subsiding while moving
towards the ocean with the
greatest subsidence in the
center and toe areas. (The same is occurring in the Portuguese Bend landslide). The movement
outside of the landslide area is due to two possibilities: Slow downhill creep due to expansive
soils and gravity or very slow deep movement in rupture surfaces at depth. Either way, the
areas around the landslide are very slowly moving into the depression. I want to emphasize
that the vertical change is a few hundreds to tens of inches over many years.
3
Abalone Cove Landslide Abatement District (ACLAD},
Report to RPV City Council; Misc. Rept., Sept. 16 ,2014
GROUNDWATER REMOVAL AND LANDSUBSIDENCE
ACLAD is often asked what effect the removal of groundwater from the area has on the land
surface . Does the removal of the groundwater cause subsidence? The GPS data allows us to
answer this question . We begin with data on the total removal of groundwater from the area
si nce 1994 (date the GPS survey began) and compare it to the subsidence in the area.
· ois
. 4246 ·: . :;~{$
.ww 12 12575 -t, .• ..,. . ~ . ·/f-~~ ~13 .. ·~~~· -
2443 .. ,_ 1766 : • -Ww~1006
NS 00°)-.. •. • W'f/1 483
a / .~WW 6 WW11
/ 473 • WW .H e 3000
~uC·l .
./
. -" •.. WW .1 ' 70 5 .
i ACLAO
('' / 13 ~ 3 , "· .. / • PrOd u ctl o n well s
pewatering Well • t ./ · ·
./ -ww 4 • Monitoring wells
1569 ,544,_.·
(140) I/NI 9 •
WW19
1281
ww 1a . .
• WW2
WY'/ 5 • (4 5)
Total i'99,4~2013
· ti:odutti~n -, . 'Kl;if
. ·-~
. ' . .
. . ..
Wwl9 C-1
' ..
PP 5 The total volume of groundwater at
each dewatering well is shown in red next
to the well locations. Remember the
numbers are in thousands of gallons so that
the 8025 at the top of the page (WW16} is
actually 8,025,000 gallons . Wells that were
not in production for the entire period are
not included (these are mostly in the toe
area of the landslide) .
< 500 t o sa ,
......... /' _,., Monitoring wells
PP 6 The total groundwater
removal contoured . There are two
notable areas, one in the northern
area where the wells have
produced over 5 million gallons and
one, WW 13, over 10 million
gallons. In contrast there are wells
in western area that have produced
less than 500 thousand gallons in
the same time period .
~140 t WW9
.. . ;w19
. ' wws • (45)
i2~1 /
WWl8 • 2·
Total fg .4-io13
4
Area of greatest groundwater
extraction (>5 million gallons)
Area of least groundwater extraction
(< 500 thousand gallons)
GPS Height
. . ·· -...
/
..... j
19~4-20 1 3 ,. ... -... C HO C R$1
IAB sut1on1 o nly}
rf'.ODSurt1T'.tnl"tf"'~1
-0 .
.01
" . .. ~0 7 -.
Abalone Cove Landslide Abatement District (ACLAD),
Report to RPV City Council; Misc. Rept., Sept . 16 ,2014
• . ....
(1 40) ""' • -·· . ...,, . . .
l•:.J 12111 / W'# 11
• 2
Wlot.'t!i C I ..
• Mo11>1onng.....,U1
PP 6 A comparison of
the groundwater
removal and the areas
of subsidence in the
Total 1994.2013 Abalone Cove area .
Production
Kgal
1•1, 00,00011
2 • 2,000.000 11
3 • 3.000.000 II
5 • 5.000,000 9
PVDS '-r'---..~d Areas of greatest subsidence ,
0 .4
Abalone Cove
Landslide
Area of greatest groundwater
extraction (>5 million gallons)
Area of least groundwater ext action
(< 500 thousand gallons)
GPS Height
1994-2013
(AB ste tionsonly)
IYWl$Ufemenb lt'I fH'\
..... Cfl07
/
...... /
~CRS l
greater than -0.40 feet
•
(140) "'"'' • -·· • ""'' ..
(4S)
U~t / ....,,,
~ 2
(4 .8 inches)
.. Monitoring wells
Total 1994-2013
Pr~du.ction
Kgal
'. 1.f>00 .000 g
2 • 2,0QO.o6o g
3 " 3,&0o.ooo 11
5 • 5,000 ,000 g
PVDS ..,_ __ ._..;.._1 Areas of greatest subsidence,
-0 .4
Abalone Cove
Landslide
greater than -0.40 feet
(4.8 inches)
5
PP 7 The areas of
greatest groundwater
removal do not
coincide with the areas
of greatest subsidence.
This is particularly
noticeable in the
northern area where,
if groundwater
removal was causing
subsidence, the
greatest subsidence
would have been
expected. The two are
not unrelated .