ALTERNATIVES ANALYSIS

lifegunbarrelcityUrban and Civil

Nov 26, 2013 (3 years and 8 months ago)

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ALTERNATIVES ANALYSIS


The purpose of this

project is to provide a safer, upgraded roadway network within Manheim
Township that meets PENNDOT design criteria. The existing structure, built in 1913, consists of
a two
-
span, reinforced concrete slab and concr
ete T
-
beam bridge that does not meet PENNDOT's
minimum sufficiency rating standard. There is visible deterioration of the concrete deck and
abutments and the structure is very narrow, consisting of two 11 foot lanes with no shoulders,
which does not meet c
urrent PENNDOT design criteria.

Four alternatives for the proposed
project were considered.


No Build Alternative


The first alternative i
s the No Build Alternative. This alternative would co
nsist of doing nothing
to

the existing bridge. However, this alt
ernative is not prudent because of the
insufficient size of
the bridge as well as its deteriorated condition.

Therefore, the No Build Alternative does not
meet the pr
oject need to provide

a safe roadway crossing.


Rehabilitation Alternative


The second alt
ernative i
s the Rehabilitation Alternative. This a
lternative would require extensive
rehabilitati
on to r
epair

the deteriorated concrete and corroded reinforcement

of the existing
bridge
. The advanced stage of deterioration makes rehabilitation unfeasible.

Also, the bridge
would need to be widened
to
safely
support two lanes of traffic

and to provide modern safety
shaped parapets
.
The extensive rehabilitation and widening is not cost effective for this project.
Therefore, since rehabilitation and widening

is not feasible, this alternative does not meet the
project need and was determined not prudent.


Bridge Replacement Alternatives


The next

alternatives are

bridge replacements
. These alte
rnatives would provide a

bridge which
meets PENNDOT requirements.




Replacement on

New

Alignment


A replacement bridge to the north could result in impacts to the black crowned night heron
rookery, the PEM wetland and prime farmland and a new structure to the south would impact the
National Register listed mill complex.
Because of the increased potential for environmental and
cultural impacts as well as acquisitions or displacements for off
-
line alternatives, only
replacements on the existing alignment in the same location were considered.




Replacements on Existing Alignm
ent


Replacement Alternative #1:

The primary alternative considered in the replacement of t
he
existing concrete bridge is the single
-
span concrete box beam structure. The existing profile
grade of the roadway will be approximately maintained for this
alter
native

with the
bottom

of the
proposed bridge beams set one (1)
foot lower than the bottom chord elevation of the existing
bridge. This is considered a reasonabl
e and feasible alternative and was

used as the proposed
structure for the hydraulic analysis.

By lowering the elevation of the stream through the structure
to account for the dam removal, the depth of underclearance from the bott
om of beam to the stream
bed

increased. The overall span

also increased from 25
-
feet to
50
-
feet in order to accommodate
the
removal of the existing secondary relief spillway. Since the span and the underclearance of the
bridge will increase, the waterway opening will consequently change
.

As a result, the water surface
elevations for all analyzed flood occurrences are the

same or reduced in the proposed condition.



Replacement Alternative #2:

The next

alt
ernative is similar to the last

except an adjacent
prestressed concrete box beam structure is used.

The only change from the last

alternate is that
the beam depth is red
uced 7”, providing a slighter larger waterway op
ening. However, since the
last

alternate is already meeting the hydraulic requirements, the additional waterway opening
does not justify the increased construction costs for this alternate. Therefore this a
lternate was
eliminated based on cost effectiveness.


Therefore, t
he most economical
and least damaging environmental alternative is

Replacement
Alternative #1

-

a single span prestressed concrete box beam bridge with a span of
50

feet. Existing
flood wat
er surface elevations will be significantly improved with this design. This bridge is
recommended for construction.


All of the detailed alternatives include
d

the removal of the dam
along with the bridge structure

since
the two are integral to each other.

During meetings and in correspondence, the Pennsylvania Game
Commission (PGC) expressed concerns that the dam removal could potentially alter the existing
backwater wading habitat created by the dam and utilized by the black
-
crowned night heron (an at
ris
k species). However, the Pennsylvania Fish and Boat Commission (PAFBC) expressed a desire
to continue their campaign to restore fish passage by removing existing dams on Pennsylvania
streams including Lititz Run. As a result, PENNDOT and RETTEW went to wor
k developing a
plan that provides fish passage restoration while still retaining the existing backwater habitat in the
stream for the herons. RETTEW developed a plan utilizing Rosgen principles and structures to
retain the existing backwater elevation at t
he rookery following the proposed removal of the dam.
The installation of the grade control structure (rock cross
-
vane) at the top end of the anticipated
headcut in the stream in concert with a second upstream grade control structure to insure that the
cur
rent normal water depth and stream configuration remains the same will preserve the riparian
condition favorable for the herons. The goal is to preserve the existing stream condition as is above
the anticipated headcut. The stream configuration is only pr
oposed to change in the area of the
anticipated headcut, the dam footprint (under the bridge), and the scour hole below the dam. The use
of a W
-
shaped rock weir is favorable over a single rock cross
-
vane for the uppermost grade
-
control
structure (near the
heron rookery) because it will have more of a tendency to keep the stream
channel wide.
Details are provided in the EA Enclosure D.


PENNDOT and RETTEW have developed a plan that results in the replacement of a functionally
obsolete structure while result
ing in the least amount of environmental damage. By incorporating
the concerns and suggestions of both the PGC and PFBC, the project goals of replacing an
unsafe structure, restoring fish passage on Lititz Run, and preserving the continuity of the
rookery
and the black
-
crowned night heron species in this area are all achieved.

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ALTERNATIVES ANALYSIS.doc