Eagle Pt Bluff Scaling, Vorwald Ltr
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MEMORANDUM
December 12, 2006
TO:
The Honorable Mayor and City Council Members
FROM:
Michael C. Van Milligen, City Manager
SUBJECT: Letter of Concern from Mr. Richard Vorwald about the Eagle Point Bluff
Scaling & Tree Removal Project (CIP 1021825)
City Engineer Gus Psihoyos is transmitting a response to Mr. Richard Vorwald's
concerns submitted to the City Council on November 6 and 7, 2006, and recommending
that the City Council approve proceeding with the scaling and tree removal outlined in
the Eagle Point Bluff Scaling & Tree Removal Project.
I concur with the recommendation and respectfully request Mayor and City Council
approval.
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Michael C. Van Milligen
MCVM/jh
Attachment
cc: Barry Lindahl, City Attorney
Cindy Steinhauser, Assistant City Manager
Gus Psi hoyos, City Engineer
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MEMORANDUM
December 11, 2006
FROM:
Michael C. Van Milligen, City Mvn~
Gus Psihoyos, City Engineer) .
. ~
TO:
SUBJECT: Letter of Concern from Mr. Richard Vorwald about the Eagle Point
Bluff Scaling & Tree Removal Project (CIP 1021825)
INTRODUCTION
The purpose of this memo is to present the response to Mr. Richard Vorwald's
concerns submitted to the City Council on November 6 and 7, 2006.
BACKGROUND
On May 2, 2005, the City Council approved the selection of Kleinfelder, Inc. to
provide professional consulting services for the Eagle Point Bluff Study.
Kleinfelder found that there is a high level of risk of a large-scale failure; and the
risk has been increased because of the 2003 excavation that steepened the
slope from 75 to 80 degrees and increased the height from 35 to 60 feet. While
they found no fault with the actual blasting operation, striking the rock face with a
track hoe and wrecking ball "exacerbated the instability of the rock slope."
Kleinfelder made recommendations to stabilize the bluff based on the use of the
property below the bluff: commercial, residential, and undeveloped. Scaling
loose rocks and removing trees from the brow of the bluff is recommended
regardless of the use of the property below the bluff.
In a letter from Kleinfelder dated January 16, 2006, Kleinfelder recommended
that the City "scale the loose rocks from the complete bluff face to reduce the risk
of rock fall and remove trees from the brow of the slope to reduce the prying
action by trees" that can induce rock fall.
In a letter dated March 6, 2006, Kleinfelder's presents its professional opinion
that "there is a high probability that an additional rock fall event may occur."
Although the City has implemented Kleinfelder's recommendations to have the
area below the bluff fenced off to the public and Engineering regularly inspects
the site, Kleinfelder asserts that the possibility of injury (from a rock fall) remains.
They recommend that the City "scale the loose rocks from the rock cut. . . and
remove trees from the brow of the slope."
In May of 2006, the City Council authorized hiring Kleinfelder & Associates to
help develop bid documents to scale loose rocks and remove trees from the brow
of the slope and inspect the work as it is performed.
In October, the City Council initiated the public bidding process for the Eagle
Point Bluff Scaling & Tree Removal Project. The schedule for the project would
be as follows:
Advertisement for Bids
Notice of Hearing on Plans & Specifications
Receipt of Bids
Public Hearing
Award of Contract
Final Completion Date
October 6, 2006
October 20, 2006
October 26, 2006
November 6,2006
November 6,2006
December 31, 2006
The engineer's estimate to do the scaling and remove the trees (prepared by
Kleinfelder) is $61,000.
No bids were received for the bid letting on October 26, 2006.
DISCUSSION
Kleinfelder, Inc., the City's consultant, has reviewed each of Mr. Vorwald's
concerns; their rebuttal can be found in the attached letter from Kleinfelder, Inc.
to City Engineer Gus Psihoyos.
Mr. Vorwald's central opinions, as outlined in his letter, are:
1. Because only rock fall has occurred in the north end of the bluff, that is where
the focus should be.
Kleinfelder asserts that "tension fractures behind (portions of the rock mass on
the south end of the bluff face) indicate movement has occurred and may occur
again." In addition, some of the blocks are "overhanging in nature with no key
blocks below them for support and the risk of failure is high,"
2 & 3. The trees are actually helping to hold the bluff together.
According to Kleinfelder, "it is a misnomer that the trees hold rock mass together.
(Kleinfelder) observed tree roots wedged into fractures . . . in most cases there
was little soil apparent." They go on to say that "tree roots will tend to wedge
open fractures in the rock mass creating an unstable position." While it is easy to
imagine tree roots curling around and grabbing hold of the rock mass, in actuality
the tree roots push against the backside of the wedges making them unstable.
Trees also provide a "sail for the wind to catch and jack the rock from the slope."
Kleinfelder concedes that different species may react differently with the bluff.
However, following their field investigation, Kleinfelder observed that most of the
trees along the brow should be removed because they tend to exacerbate the
rock instability.
4. Except for a little minor assistance, can't the bluff be left alone to heal itself?
Kleinfelder believes that the rock scaling and tree removal identified in the Eagle
Point Bluff Scaling & Tree Removal Project is the minimum that should be done
to protect public safety. In their estimation, the project consists of minor
assistance. If the bluff is left alone, rock failure will persist over time as "the bluff
erodes back and seeks equilibrium."
RECOMMENDATION
I recommend proceeding with the scaling and tree removal outlined in the Eagle
Point Bluff Scaling & Tree Removal Project.
Prepared by Deron Muehring, Civil Engineer II
cc: Barry Lindahl, City Attorney
Cindy Steinhauser, Assistant City Manager
Deron Muehring, Civil Engineer II
Attachs.
III KLEINFElDER
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November 27,2006
Kleinfelder Project #66795fTask 1
Mr. Gus Psihoyos
City of Dubuque, Iowa
Engineerin~ Department
50 West 13 Street
Dubuque, Iowa 52001
RE: Letter Dated November 9, 2006 from The City of Dubuque to review letter
submitted by Mr. Richard Vorwald on November 4, 2006 attendant to the
scaling and tree removal project for Eagle Point Bluff.
Dear Mr. Psihoyos:
As requested we have reviewed the letter of concern submitted by Mr. Vorwald
attendant to scaling and tree removal on Eagle Point Bluff. The following is our
response:
Mr. Vorwald's comment:
1) Only 1/3 of 270-foot bluff section shown on above (F-I on photo exhibit submitted
by Mr. Vorwald), the portion to the north of the safety fence, has had any rock fall;
that's where any fix should focus."
Kleinfelder rebuttal 1 :
Although it is true that rockfall has been most active on the north end of Eagle Point
Bluff, rockfall has not been limited to the northern end of the bluff. Kleinfelder
identified several sections of the bluff as areas of potential instability in the Eagle
Point Bluff Study: Citizen Guide (Kleinfelder Project No. 58716), pages 5 and 6. The
risk of failure within these sections ranges from low to high. Table 1 provides a
summary of the rock mass information collected. The sections identified as Wedge
1, Tower 3, and Blocks 3 through 10 have a high risk of failure because of the
presence of tension fractures behind the blocks that indicate movement has
occurred and may occur again. Additionally, Blocks 3 through 10 are overhanging in
nature with no key blocks below them for support and the risk of failure is high. If
these blocks were to fail, a similar set of blocks above them on the slope would then
be exposed to potential failure. Furthermore, the results of our stability analysis
indicated a high probability of potential failure. In addition, loose rock from mass
66795/SEA6L349.doc Page 1 of 4 November 27, 2006
Copyright 2006 K~jnfelder, Inc,
kL[I~rFl DFR 140'j 140th Avenue N[, Suite Ai ()1, !:kllcvut', WA 9HOO') (42 r):'i6)-4200 (42':;', fit,J.'-LW i fdX
wasting of the rock slope mantels the bench on the south end of the bluff and open
fractures from solution and movement are evident. Under the present conditions the
slope is not stable.
Mr. Vorwald's comment:
2) The south 2/3 of the 270 foot section (A-F on photo exhibit submitted by Mr.
Vorwald), where historic steps are, are relatively stable except for a water runoff
problem towards CR Boats. Here the trees are actually helping to hold the bluff
together."
Kleinfelder rebuttal 2:
The southern end of the rockslope is also unstable. Refer to Figure 1, Section A; we
observed a large unstable wedge shaped rock mass just below the old observation
area and steps. Moreover, we have only identified the larger unstable rock blocks
that threaten to fall. Water runoff will continue to erode and open fractures in the
rock mass leading to additional rockfall. The area of the slope facing CR Boats was
not analyzed during our investigation. However, we visually inspected this slope in
order to get a three-dimensional view of the Bluff cut slope. We observed large
open sub-vertical fractures parallel to the bluff cut slope and sub-horizontal bedding
fractures. This indicates that the fractures visible. on the bluff slope face repeat into
the slope. We observed that trees were overhanging this slope face and that poison
ivy was present on the slope face.
It is a misnomer that the trees will hold the rock mass together. Trees can damage
the rock slope. We observed tree roots wedged into fractures in the rock mass on
the bluff. In most cases there was little soil apparent in the fractures around the
roots. The tree roots will tend to wedge open fractures in the rock mass creating an
unstable condition, which will lead to rockfall. Water from precipitation and run off
will enter the open fractures eroding the soil and small rock material created by the
wedging tree root. If the water is not drained, it will build hydrostatic pressures in the
fractures and further destabilize the rock mass. In addition, the water may freeze
forming ice wedges. Freeze-thaw action will loosen the rock mass. Moreover, wind
will exacerbate the unstable conditions by rocking. the trees and jacking the rock out
of place creating additional rockfall. The Federal Highway Administration (1998,
Rock Slopes Reference Manual; FWHA-HI-99-007) has found that over 60 percent
of the rockfall along California highways result from the action of rain, freeze-thaw,
wind and tree roots (singularly or in combinations).
66795/SEA6L349.doc Page 2 of 4 November 27, 2006
Copyright 2006 Ktelnfelder, Inc.
KLFINFElDER 240~; 140th Avenue Nc, Suitf' A 101, Bclll'vue, WA 98UOS (425) S62-42QO (425) 562-4201 fax
Mr. Vorwald's comment:
3) As noted above trees can help hold the bluff together or tree roots can pry a bluff
apart as the study indicated. It depends on things like rock/dirt ratio, slope, and type
of tree. As you go north along the bluff the slope generally increases."
Kleinfelder rebuttal 3:
Refer to Kleinfelder rebuttal No.2 second paragraph. The rock to soil ratio does not
appear to impact growth of tree roots into the fractures. The mechanical action of the
roots wedging the rock and breaking it down to soil provides a media for the small
rootlets to grow. We have observed trees growing from fractures and benches on
the steeper slopes. Larger trees along the brow of the bluff tend to provide a
broader sail for the wind to catch and jack the rock from the slope. The species of
tree may playa roll in the stability of the slope. However, it is our opinion that most
of the trees along the brow of the bluff tend to exacerbate the rock mass stability.
Mr. Vorwald's comment:
4) Can the bluff with just minor assistance from people be left alone to heal itself?"
Kleinfelder rebuttal 4:
No, in our opinion, the bluff requires at a minimum scaling of the loose rock and
removal of the trees along the brow. There is a high potential for small and large-
scale rockfall along the bluff cut slope face as identified from our report and the
blocks outlined in Table 1. If the bluff is left alone, rockfall will continue over time as
the bluff erodes back and seeks equilibrium. This Vlill create a public safety issue.
We hope this answers Mr. Vorwald's concerns. Please call us at (425) 562-4200 if you
have questions or require additional information.
Sincerely,
KLEINFELDER. INC.
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Chad R. Lukkarila. PE
Project Engineer
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William C. B. Gates, PhD, PE (WA)
Principal-In-Charge
66795ISEA6L349,doc
Copyright 2006 Klelnfelder, Inc.
Page 3 of 4
November 27, 2006
KLEIN FELDER 2405 140th ^venllp. NE, Suite A 101, Bellcvue, WA 9800S (425/562-4200 (425) 562-4201 lax
TABLE 1: POTENTIAL UNSTABLE BLOCKS IDENTIFIED ON BLUFF
::.;;jBfiei1ii'i'>'-'BI~t~>f;.oi_h?. "~f~~~t.2YB f.t'~._;"'...' Thickness
:~ifiiiit~i8;:':trQm)$ciUti12'EridT .. I.... . . '<..,'~ . (feet)
Wedge 1 100 feet 30 17 (top), 9
5 (bottom)
Block 1 120 feet 9 3 10 --
Tower 1 1 50 feet 55 25 (top), 5
9 (bottom)
Tower 2 160 feet 55 2 (top), 5
8 (bottom)
Block 2 160 feet 4 3 6
Tower 3 180 feet 66 18 (top), 5
5 (bottom)
Block 3 200 feel 1 1 5 7.5
Block 4 210 feet 12 5 8.5
Block 5 225 feet 5 4 5.5
Block 6 230 feet 5 4 8.5
Block 7 240 feet 10 2 4.5
Block 8 250 feet 9 2 14
Block 9 260 feet 8 4 4.5
Block 10 270 feet 1 1 4 5.5
Block 1 1 250 feet 5 2 6
Block 12 255 feet 6 3.5 4 ,
..
Refer to Figure 1 for the general location of unstable blocks and towers listed above.
FIGURE 1: GENERAL LOCATION OF UNSTABLE BLOCKS & TOWERS
66795JSEA6L349.doc
Copyright 2006 Kleinfelder, Inc.
Page 4 of 4
November 27. 2006
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HONORABLE MA YOR. COUNCIL. & STAFF:
I TI''''k the Eagle Point Bluff IS one of the key features of Dubuque - 'The Masterpiece on the
MIssissippi It has been a Sacred Spot for over 1,000 years, we need to return It as close
as possible to the way It was. The following are some factors to consider prior to starting the
scalir"g and tree removal proJect:
1) Only 1/3 of the 270 foot bluff section shown above (F-I),the portion to the north of the
safety fence, has had any rock fall: that's where any fiX should focus.
2) The south 2/3 of the 270 foot section (I>,..F) where the hlstonc steps are, are relatively
stabie except for a water runoff problem towards CR Boats. Here the trees
are actually helping to 110Id the bluff together.
3) As noted above trees can help hold the bluff together or tree roots can pry a bluff
apart as the study Indicated. It depends on things like rock/dirt ratio, slope, and
type of tree. As you go north along the bluff the slope generally Increases
4 i Can the bluff with Just some minor assistance from people be left alone to
heai itself?
Respectfully Submitted,
Richard Vorwald
2921 Washington
Dubuque, Iowa
583-6198
11/4/2006
11/7/2006
To : Honorable Mayor, Council, and Staff,
Subj: Eagle Point Bluff Stabilization (Bids for ScalinglTree Removal)
From: Dick Vorwald, 2921 Washington, Dubuque, rjvorwald@aol.com
I did not pass this Info on at last night's Council Meeting because
there was no formal hearing on the matter. Afterwards I thought
Staff may find some of this info useful. I found the northern most
90 feet of the 270 feet shown to be in most need of attention.
I did observe around the bend facing CR Boats a few areas where water
runoff has created instability on the bluff and trees are holding these
portions together. You may want'Klelnfelder' to take a look.
Thanks, Dick Vorwald