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Background

VIEWS: 2 PAGES: 28

  • pg 1
									Introduction

This report describes the preliminary engineering investigation, conducted by the
Department of Water Resources’ Northern Region Office, of the construction of
four brood ponds within the Thermalito Afterbay (Afterbay).

According to the Settlement Agreement for the Oroville Facilities Relicensing
Project (FERC Number 2100), Article A122, DWR shall construct four new brood
ponds in the Afterbay. Moreover, the USFWS Terrestrial Biological Opinion (BO)
denotes the brood ponds (totaling a minimum of 245 acres) shall be constructed
within the first four years of the new FERC license to compensate and offset
potential adverse effects to giant garter snakes from Afterbay water-level
fluctuations. The construction of the brood ponds will also minimize the effects
of project operations on waterfowl reproduction and rearing.

Background

Water level fluctuations in the Afterbay related to hydropower generation can
adversely affect brooding waterfowl. During power generation, the water surface
elevation in the Afterbay increases thus potentially drowning waterfowl nests and
eggs. When less power is being generated, less water is discharged into the
Afterbay and the water surface elevation of the Afterbay decreases, resulting in
extensive barren, exposed mud flats. Waterfowl broods are subject to high
predation rates when the Afterbay is drawn down because the distance from
open water to cover increases.

Over the past 24 years, the Department of Water Resources (DWR), California
Department of Fish and Game (DFG), California Waterfowl Association, and
other stakeholders have worked cooperatively to increase waterfowl production
on the Afterbay. These cooperative efforts have included implementation of
measures to improve reproduction and brood survival. During the summer of
1986, the first waterfowl brood pond was constructed. Currently, there are five
existing waterfowl brood ponds located on the Afterbay. Figure 1 identifies the
existing five ponds with existing culvert and spillway elevations.

The waterfowl brood ponds are constructed to reduce brooding waterfowl losses
and increase production by providing a refuge from the effects of Afterbay water
level fluctuations. The existing brood ponds provide improved habitat conditions
for a variety of terrestrial and aquatic species including special status species. A
few of the special status species observed on or near the existing brood ponds
include bald eagles, osprey, black tern, American bittern, American white pelican,
white-faced ibis, black-crowned night heron, double-crested cormorant, and
short-eared owl. Further, these ponds also provide potentially suitable habitat for
giant garter snake and red-legged frog.




                                         1
Figure 1. Existing Brood Ponds With Design Elevations.

Project Description

A preliminary design and cost estimate has been completed for five potential
brood pond sites within the Afterbay. Figure 2 shows the five potential brood
pond sites with design features and potential borrow locations.

                                        2
Figure 2. Proposed Pond Locations With Design Features and Potential Borrow
Areas.

Similar to the existing five waterfowl brood ponds, the new ponds will be created
by an earthen dam across an inlet of the Afterbay. A conduit through the dam

                                        3
will terminate at reinforced concrete headwall structures on each side of the dam.
A slide gate located on the pond side structure will be used to control the flow of
water into the pond from the Afterbay, thus regulating the water surface elevation
and volume of water stored within the ponds. The spillway design will include
culverts to facilitate access to the dam sites when the water surface elevation in
the ponds or Afterbay is higher than the spillway elevation.

Description of Investigation

In March 2009, NRO staff began collecting field data at the five proposed brood
pond locations. The work performed for all site locations include topographic
surveys and mapping, analysis of hydrologic data, reconnaissance of potential
construction material borrow and spoil areas, examination of access and
construction constraints, and a reconnaissance-level geologic investigation.

Surveying
The initial topographic surveys for all sites were performed in June 2009. Global
Position System (GPS) equipment was used to survey control monuments at
each of the proposed project locations. The purpose of the control survey was to
locate each site within the California State Plane Coordinate system (North
American Datum of 1983, Zone 2, Survey Feet) and establish elevations relative
to the Afterbay datum.

Total stations, automatic levels, and survey grade real-time kinematic GPS
equipment were used to collect survey data at each site. The data included
ground measurements for topographic and hydrographic mapping of dam sites,
ponds, and potential borrow areas. This data was used to create site maps and a
1-foot interval contour map of each project site. Existing features, facilities,
access roads, vegetation and sensitive areas that will not be disturbed were also
identified.

Hydrologic Data
During normal operations DWR maintains the water surface elevation in the
Afterbay between 124 and 136 feet. To maintain the water surface elevation in
brood ponds the USFWS BO requires a water surface elevation of 133.5 feet for
at least 12 consecutive hours at least once a month annually during the giant
garter snake active period (May 1 through October 1). This will ensure that the
brood ponds have sufficient water in them throughout the active season of the
snake.

Geologic Investigation
An initial review of geologic maps of the surrounding area indicates the soil has a
high clay content which is generally suitable for dam construction. However, it is
deemed necessary to conduct a geologic investigation to ensure the soil is
suitable. It should also be noted that paleontological resources have been found
in the surrounding areas of the Afterbay.

                                         4
A geologic reconnaissance was performed in December 2009 by a NRO
Engineering Geologist. Potential borrow areas were investigated for the
construction of an earthen dam for the proposed brood ponds (Figure 2).
Several borrow areas investigated include:
    Site E1 – the hill southwest of the potential dam site.
    Site F1 – the hill west of the potential dam site.
    Site G1 – the hill west of potential dam site.
    Sites J2 and J3 - top of the highest hill on “Big Island”
    All sites - the borrow area northeast of the intersection of Hwy 162 and
      Wilbur Rd.
    All sites - the borrow area south of existing pond 1A.

As a result of this reconnaissance, it was determined that it is likely that the
undisturbed areas near ponds E1, F1, G1, and 1A could be excavated to
produce suitable dam-building material (Figure 2). The top of the hill on Big
Island is a mix of material excavated from the Afterbay during its construction,
and though material from this location has been used to construct at least one of
the existing ponds, a more detailed investigation of this site is needed. The
potential borrow area northeast of the intersection of Highway 162 and Wilbur
Road is a mix of a wide range of materials collected from both onsite and offsite
and may not be suitable for dam-building.

A more detailed geologic investigation will be needed at all project locations. In
addition to verifying or disproving the suitability of borrow material for dam-
building, it is recommended that soil be excavated at selected representative
dam sites to determine the depth of hardpan or other suitable dam foundation
material.

Design Criteria

The design drawings shown in Sheets 1 through 23 depict the conceptual layouts
for the proposed dams. The locations of the dams within the Afterbay inlets are
based on requirements set forth by the Division of Safety of Dams (DSOD).
Where feasible it is desirable to keep the height of the dams and the volume of
water impounded behind the dams less than the amount that would require them
to be regulated by DSOD. In order to not fall under the jurisdiction of DSOD,
reservoirs between 6 and 25 feet deep must impound less than 50-acre-feet of
water. Subdividing a larger reservoir with an intermediate dam to keep the
individual pools of water less than 50 acre-feet is not an option. The DSOD
stated that the toe of a dam needs to be dry for the majority of the time for the
dam to be considered a viable water impoundment structure. A dam subdividing
a larger reservoir would be wet all of the time and would not meet this standard.

The following criteria were used for the design of the brood ponds:
     Dam height must be less than 25 feet tall.

                                         5
       Ponds must impound less than 50-acre-feet of water.
       Spillway design includes culverts or other water crossing structure to
        improve access during times of high water.
       Design Water Surface Elevation (WSEL) in ponds is 133.5 feet.
       Dam crest elevation is 137 feet where practicable. The relatively low
        elevation of the terrain around the southernmost ponds means that there
        is no existing ground of equal elevation to tie into without dramatically
        increasing the earthwork volume. A dam crest elevation of 135.5 feet
        was used for ponds J2 and C2-J3.
       Headwall structure in the pond will be fitted with a slide gate.
       Islands will be constructed within the ponds to create additional secure
        nesting habitat.

Table 1 shows the design dimensions for each site. The earthwork quantities
listed in Table 1 include the earthwork needed to construct the proposed dam
including a 12-foot wide, 6 feet deep key that daylights to original ground at the
toe of the proposed dam.

Table 1. Site Design Dimensions.
 Site    Dam        Dam      Earthwork        Perimeter @      Surface      Water
Name Height        Length     Volume           El. 133.5        Area       Storage
         (Ft.)       (Ft.)       (CY)             (Ft.)        (Acres)    (Acre-Ft.)
 E1      10.0       1,300      24,000            4,675          17.1        42.4
 F1      10.5        850       14,600            6,280          17.1        46.2
 G1       9.0       1180       13,800            4,030           9.6        18.2
  J2      6.5       1,100      8,000             1,865           4.5         7.2
C2 J3     7.5       1,890      3,500             4,840          14.2        17.5
                   C2 + J3    C2 + J3

Unlike the first four sites listed in Table 1 which are new sites where no previous
brood pond construction has occurred, the C2-J3 project involves making
modifications to an existing brood pond. By raising the existing C2 dam, its
spillway, and a roadway to the west of the C2 pond, the size of the existing pond
can be significantly increased. See Table 10 for specifics regarding the change
in perimeter, surface area, and water storage volume.

Cost

A budgetary cost estimate has been generated for each proposed project site.
Each cost estimate assumes that DWR’s Division of Engineering will develop the
final design plans and specifications and that the projects will be awarded for
construction with a competitive bid process.




                                         6
Construction Activities

Construction must occur during the giant garter snake active period from May 1
to October 1. The BO calls for all four ponds to be built within four years of
license issuance, but at the interest of saving time and money, it may be
beneficial to construct all four ponds in the same year. Construction of the dams
may require a drawdown of the Afterbay water level which requires planning and
scheduling by DWR Operations and results in lost revenue from power
generation for the Thermalito Pumping-Generating Plant; therefore, such
activities should be planned accordingly. If the brood pond dam sites can be
economically dewatered through the use of coffer dams or similar structures,
then construction could occur over the course of several consecutive years.

Based on an average of the dewatering cost of the five sites, since only four of
the five may be built and we do not know what pond might be eliminated from
consideration, the difference in dewatering cost can be characterized as follows:
     $720,000 – approximate dewatering cost using coffer dams (either all
        dams in the same year or spread over several years).
     $1,400,000 – approximate lost power revenue if ponds are constructed in
        four consecutive years and the Afterbay is drawn down each year for
        construction between May and October.
     $350,000 – approximate lost power revenue if ponds are constructed at
        the same time and the Afterbay is drawn down only once between May
        and October.
Because these dollar figures are averages and based on the energy market, they
subject to change. If, for example, four of the largest (or smallest) ponds are
selected for construction, the cost for using coffer dams will increase (or
decrease). Additionally, depending on fluctuations in the power market, or if the
price spread between flat-rate generation and on-peak generation exceeds
projections, then the figure for lost power revenue could increase.

Basic construction activities are as follows:
    Coordinate work with DFG Oroville Wildlife staff. If the Afterbay water
       surface elevation must be lowered for an extended period it may be
       necessary to coordinate pumping to fill existing brood ponds during
       construction of new ponds.
    Construct coffer dam (if necessary for dewatering).
    Excavate keyway trench at proposed dam location to suitable foundation
       for dam.
    Material excavated from the keyway shall be used for island construction
       within the pond at that site as shown on the plans.
    Construct and compact dam using locally available material where
       possible.
    Excavate center of dam, construct headworks and culvert through the
       dam, backfill, and compact.

                                        7
   Armor each side of the finished dam with riprap or cobble.
   Remove coffer dam (if necessary).
   Periodic monitoring will be required to fine tune operational criteria for
    recharge events.




                                       8
Pond E1

Location
Proposed pond E1 is located in the northern part of the Afterbay and east of the
Monument Hill Boat Launch Facility on Highway 162 at 39°29’53”N, 121°39’41”W
and can be found on the USGS 7.5 minute series Biggs Quadrangle (see Sheet
1, Location Map). Access to the site is an existing dirt road on the north side of
Highway 162, two tenths of a mile east of the Monument Hill Boat Launch
Facility. The area is open to the public, but there is a locked gate at the entry of
the dirt road restricting public motorized vehicle access.

Existing Conditions
The site generally consists of gently sloping terrain covered by low vegetation
with a small hill to the west of the pond. There are some mature trees around the
south eastern edge of the pond site, but construction activities will largely avoid
these trees. Several environmentally or culturally sensitive areas have been
identified near the project area and access routes, but not within the project
footprint (see Sheet 2). Multiple vernal pools have been identified alongside the
pond. The pond site is considered habitat for two species protected under the
federal Endangered Species Act the red-legged frog and giant garter snake.
Vernal pools, which are also considered habitat for federally listed species, have
been identified near the borrow area. Environmental and cultural site clearance
will be required prior to construction.

Constraints
Proposed pond E1 has minimal constraints to the site. There is good existing
road access as well as a locked gate and fence prohibiting motorized vehicular
traffic to the public. The most notable project constraints are listed below:
     Many of the vernal pools that have been identified in the area are located
         on the southern and eastern side of the project site. The vernal pool on
         the eastern side of the pond will need to be staked out and identified in
         order to avoid during construction. Also there are a couple of vernal pools
         identified on the western side of the access road, which should be out of
         the construction zone (see Sheet 2). Action will need to take place to
         prevent vehicular traffic from driving through pools and dust mitigation
         measures may be required. Where road improvement is necessary near
         vernal pools, action will be taken to prevent fill material from entering a
         vernal pool.
     Because of the possible presence of giant garter snakes, construction will
         need to occur during the giant garter snake active period (May 1 to
         October 1).

Project Description
This project calls for the construction of one main dam across an inlet of the
Afterbay and two islands within the pond. These islands (elevation 137.0 feet)
will remain dry on the top when the Afterbay is full (see Figure 3).

                                         9
                                                           Culvert
                    Main Dam
                       and                                 Spillway
                    Headworks
    Culvert
   Spillway                                                            Keyway
                                                                        Spoils
                                                                        Area



                                               Constructed
                                                 Island
              Constructed
                Island




        Existing                                 Pond
         Road                                  Perimeter


Figure 3. E1 Dam and Pond Features.

The crest height of the dam will be 137.0 feet. Much of the area surrounding this
pond is at elevation 137 or higher and the access roads to the site are dry when
the Afterbay water surface elevation approaches its normal maximum of 136.0
feet. It should be noted that based on the CDEC period of record for daily data
for the Afterbay (1/1/2008 to present), the Afterbay water surface elevation rarely
exceeds elevation 135.0 feet and has only exceeded elevation 135.5 feet for two
days (3/27 and 3/28, 2010).

A keyway will be excavated at the proposed dam location approximately six feet
below the existing ground as indicated in the design drawings (see Sheet 4).
Material excavated from the construction of the keyway will be used to construct
two islands within the pond. The islands will provide waterfowl with refuge from
predation by terrestrial species. Because of the relatively large size of this pond,
two island approximately 95 feet wide by 130 feet long and 190 feet wide by 120
feet long was selected for this site (see Sheet 3). The shape and size of the
islands can be modified so that all suitable material from the keyway excavation
can be used. All unusable material will be spoiled at the location indicated on the
map in Sheet 2. The spoils will be spread out on an upland area and graded to
create an area suitable for future planting of waterfowl forage or nesting plots.

                                        10
The actual size needed for the spoils area will depend on amount of unused
material.

Material needed to backfill the keyway trench and construct the main portion of
the dam will come from the borrow area identified in the design drawings (see
Sheet 2). If geologic investigations of E1 borrow area shows that the material is
not suitable, then another potential source location has been identified near pond
1A, though a geologic investigation of the 1A source location will also be
necessary. Rock slope protection will be used on the side slopes of the dam to
help with the effects of wave-wash and erosion. The rock slope protection
material will come from an outside source and will be trucked to the site. The
cost estimate outlines the quantity of each type of material required for
construction.

A concrete headworks structure will be constructed within the dam and fitted with
a 30-inch diameter culvert and slide gate to control the flow of water into and out
of the pond. The invert elevation of the culvert will be 127.0 feet. The headwall
structures are equipped with flashboard slots to allow for the installation of a fish
screen and/or flashboards for operation and maintenance of the structure (see
Sheet 4).

Two spillways consisting of two 24-inch corrugated metal pipes (CMPs) will be
constructed at each end of the dam (see sheet 5). The CMPs will be set at an
invert elevation of 133.5 feet with a minimum of 12 inches of cover. The spillway
will allow the pond to be recharged automatically when the Afterbay water
surface elevation rises above that level as well as release water if the pond
becomes overcharged by rainfall within the ponds watershed.

Details
Table 2 describes some of the details of the proposed pond including earthwork
quantities, pond volume, perimeter, and surface area.

Cost Estimate
The cost estimate in Table 3 was generated by using unit costs listed in Saylor
Publications, Inc 2009 Current Construction Cost Manual. The dewatering cost
was based on the assumption that the site will be dewatered by coffer dams or
similar structures. It is important to note that the cost estimate does not include a
cost for loss of power generation.




                                         11
Table 2. Basic E1 Dam and Pond Details.
                           Feature                                           Quantity
 Keyway Excavation (material will be used for creating
                                                                     8,600 Cubic Yards
 islands within new pond)*
 Total Fill Required (backfill keyway and construct dam)             24,000 Cubic Yards
 Dam Height (downstream toe to spillway invert)                           6.5 Feet
 Dam Height (downstream toe to dam crest)                                 10 Feet
 Dam Crest Length                                                        1,300 Feet
 Wetted Perimeter                                                        4,675 Feet
 Surface Area                                                            17.1 Acres
 Water Storage                                                         42.4 Acre-Feet
 Travel Distance From Highway 162                                         0.3 Miles
 Travel Distance From Borrow Area (E1 Borrow)                             0.1 Miles
*All islands will be created using keyway excavation material. Material not used in island
creation will be disposed in spoils area identified on Figure 3 and Sheet 2.

Table 3. E1 Cost Estimate.
ITEM             DESCRIPTION               QUANTITY     UNIT       UNIT COST TOTAL COST*

               MISCELLANEOUS
  1         Mobilization/Demobilization         9.00   ACRES $       4,800    $    43,000

                 DEWATERING
  2            Install and Removal               1       LS    $    272,000   $    272,000

                 EARTHWORK
  3          Excavation (key trench)         8,600       CY    $       12     $    103,000
  4             Backfill for Dam             24,000      CY    $       30     $    720,000
  5        Concrete Headwall Structure         27        CY    $      800     $    22,000
  6              30" Slide Gate                 1        LS    $     2,300    $     2,000
  7              Headwall Pipe                 26        FT    $       45     $     1,000
  8               Spillway Pipe                70        FT    $       45     $     3,000
  9                Road Base                  290       TON    $       41     $    12,000
  10         Rock Slope Protection            870       TON    $       23     $    20,000
                                                                              $    883,000

  11           Construction Cost                                              $   1,198,000
  12          Contingency @ 20%                                               $    240,000
  13       Construction Cost Subtotal                                         $   1,438,000

  14   Engineering and Inspection @ 20%                                       $    288,000
  15     Contract Administration @ 10%                                        $    120,000
  16                 Total                                                    $   1,846,000
*Total cost values have been rounded to the nearest $1,000.




                                           12
Pond F1

Location
Proposed pond F1 is located near Monument Hill Day Use Area in the Afterbay,
Oroville, CA. Pond F1 is southeast of the bridge crossing the Afterbay on
Highway 162 at 39°29’27”N, 121°40’4”W. This area can be identified on the
USGS 7.5 minute series Biggs Quadrangle (see Sheet 1, Location Map). Access
to the site is off Highway 162, at the Monument Hill Day Use Area turnoff. An
existing paved road leads to a large gravel parking area which can be used for
staging. A few mature trees along the access road might need trimming to allow
for large equipment access.

Existing Conditions
The site is a high public use area that has a paved boat launching facility,
restrooms, a day use area with picnic tables, and two large parking areas. The
gently sloping terrain is covered by low vegetation with trees surrounding the
edge of the pond site. Construction activities should avoid these trees if
possible. Several environmentally or culturally sensitive areas have been
identified near the project area and access routes, but not within the project
footprint (see Sheet 6). Multiple vernal pools have been identified alongside the
pond. The pond site is considered habitat for two species protected under the
federal Endangered Species Act the red-legged frog and giant garter snake.
Vernal pools, which are also considered habitat for federally listed species, have
been identified near the borrow area. Environmental and cultural site clearance
will be required prior to construction.

Constraints
The most notable project constraints are listed below:
    This project site is heavily used by the public. Precautionary measures
       will need to be taken during construction activities due to high volume of
       people and vehicles.
    Vernal pools exist near the project area. Action will need to take place to
      prevent damage to the pools and dust mitigation measures may be
      required. Where road improvement is necessary near vernal pools, action
      will be taken to prevent fill material from entering a vernal pool.
    Because of the possible presence of giant garter snakes, construction will
      need to occur during the giant garter snake active period (May 1 to
      October 1).

Project Description
This project calls for the construction of an earthen dam across an inlet section of
the Afterbay and two islands within the pond (see Figure 4). A 12-foot wide
drivable road will span the crest of the dam for maintenance access. A fence
with a gate crossing over the crest of the dam will be necessary to keep the
public off the dam. Other safety measures may be needed near the headgate
structures to ensure public safety.

                                        13
      Monument Hill                                  HWY
      Day Use Area                                    162

      Main Dam
         and                                              Constructed
      Headworks                                             Islands
        aand


        Borrow
         Area
         aand                                                      Pond
                                                                 Perimeter
                Culvert
               Spillway                          Keyway Spoils
             PillSpillway                            Area
                 aand                                aand
Figure 4. F1 Dam and Pond Features.

The crest elevation of the dam will be 137.0 feet. Much of the area surrounding
this pond is at elevation 137.0 or higher and the access roads to the site are dry
when the Afterbay water surface elevation approaches its normal maximum of
136.0 feet. It should be noted that based on the CDEC period of record for daily
data for the Afterbay (1/1/2008 to present), the Afterbay water surface elevation
rarely exceeds elevation 135.0 feet and has only exceeded elevation 135.5 feet
for two days (3/27 and 3/28, 2010).

A keyway will be excavated at the proposed dam location approximately six feet
below the existing ground as indicated in the design drawings (see Sheet 8).
Material excavated from the construction of the keyway will be used to construct
two islands within the pond. The islands provide waterfowl with refuge from
predation by terrestrial species. The islands will be built up to an elevation of
137.0 feet (see Sheet 7). The shape and size of the islands can be modified so
that all suitable material from the keyway excavation can be used. All unusable
material will be spoiled at the location indicated on the map on Sheet 6. The
spoils will be spread out on an upland area and graded to create an area suitable
for future planting of waterfowl forage or nesting plots. The actual size needed
for the spoils area will depend on amount of unused material.
Material needed to backfill the keyway trench and construct the dam will come
from the borrow area identified in Sheet 6. A geologic investigation of this area
will be conducted prior to construction to ensure the material is suitable. Rock
slope protection will be used on the side slopes of the dam to help with the

                                        14
effects of wave-wash and erosion. Rock slope protection material will come from
an outside source and will be trucked to the site. The cost estimate outlines the
quantity of each type of material required for construction.

A concrete headworks structure will be constructed within the dam and fitted with
a 30-inch diameter culvert and slide gate to control the flow of water into and out
of the pond. The invert of the culvert will be set at elevation 126.0 feet (see
Sheet 8). The headwall structures are equipped with flashboard slots to allow
for the installation of a fish screen and/or flashboards for operation and
maintenance of the structure (see sheet 8).

A spillway consisting of six 24-inch CMP’s will be constructed at the southern end
of the dam, furthest away from public access (see Sheet 9). The CMPs will be
set at an invert elevation of 133.5 feet with a minimum of 12 inches of cover.
The spillway will allow the pond to be recharged automatically when the Afterbay
water surface elevation rises above that level as well as release water if the pond
becomes overcharged by rainfall within the ponds watershed.

Details
Table 4 describes some of the details of the proposed pond including earthwork
quantities, pond volume, perimeter, and surface area.

Cost Estimate
The cost estimate in Table 5 was generated by using unit costs listed in Saylor
Publications, Inc 2009 Current Construction Cost Manual. The dewatering cost
was based on the assumption that the site will be dewatered by coffer dams or
similar structures. It is important to note that the cost estimate does not include a
cost for loss of power generation.




                                         15
Table 4. Basic F1 Dam and Pond Details.
                         Feature                                        Quantity
 Keyway Excavation (material can be used for
                                                                  5,000 Cubic Yards
 creating islands within new pond)*
 Total Fill Required (backfill keyway and construct
                                                                 14,600 Cubic Yards
 dam)
 Dam Height (downstream toe to spillway invert)                         7.0 Feet
 Dam Height (downstream toe to dam crest)                              10.5 Feet
 Dam Crest Length                                                       850 Feet
 Wetted Perimeter (full pond elevation 133.5 feet)                     6,280 Feet
 Surface Area (full pond elevation 133.5 feet)                         17.1 Acres
 Water Storage (full pond elevation 133.5 feet)                      46.2 Acre-Feet
 Travel Distance From Highway 162                                       0.2 Miles
 Travel Distance From Borrow Area                                       0.1 Miles
*All islands will be created using keyway excavation material. Material not used in island
creation will be disposed in spoils area identified on Figure 4 and Sheet 6.

Table 5. F1 Cost Estimate.
                                                                       UNIT            TOTAL
ITEM             DESCRIPTION               QUANTITY      UNIT          COST            COST

               MISCELLANEOUS
  1         Mobilization/Demobilization      200,000      SF     $      0.12     $     24,000

                 DEWATERING
  2            Install and Removal              1         LS     $    112,000    $     112,000

                 EARTHWORK
   3         Excavation (key trench)         5,000        CY     $      12       $     60,000
   4             Backfill for Dam            12,500       CY     $      30       $     375,000
   5       Concrete Headwall Structure         50         CY     $      795      $     39,750
   6                Gate Valve                  1         LS     $     1,500     $      1,500
   7            Headwall Culvert               26         FT     $      45       $      1,170
   8          Install CMP Spillways           250         FT     $      45       $     11,250
   9                Road Base                 125        TON     $      41       $      5,125
  10         Rock Slope Protection            800        TON     $      23       $     18,400
                                                                                 $     512,195

  11           Construction Cost                                                 $     648,195
  12          Contingency @ 20%                                                  $     129,639
  13       Construction Cost Subtotal                                            $     777,834

  14          Final Design @ 20%                                                 $     155,567
  15     Contract Administration @ 10%                                           $     64,820
  16                 Total                                                       $     998,220




                                           16
Pond G1

Location
Proposed brood pond G1 is located in the southern half of the Afterbay. The
pond can be identified on the USGS 7.5 minute series Biggs Quadrangle at
39°28’23”N, 121°39’39”W (see Sheet 1, Location Map). Access to the site is
from Wilbur Road south of Highway 162. An existing gravel road leads to the
day use area along the south-eastern edge of the site. Access to the western
side of the pond is through a locked gate. The area is open to the public, but
public uses of motorized vehicles are prohibited on the western side of the site.

Existing Conditions
The site generally consists of gently sloping terrain covered by low vegetation
with mature trees along the perimeter of the pond. Construction activities should
avoid the trees if possible. Several environmentally or culturally sensitive areas
have been identified near the project area and access routes, but not within the
project footprint. Multiple vernal pools have been identified alongside the access
road (see Sheet 10). The pond site is considered habitat for two environmentally
sensitive species, the red-legged frog and giant garter snake. Vernal pools,
which are also considered an environmentally sensitive area, have been
identified near the borrow area. Environmental and cultural site clearance will be
required prior to construction.

Constraints
The most notable project constraints are listed below:
    Moving people and equipment to the site includes traveling on a narrow
      gravel road with tight curves. These constraints, however, should not be
      difficult to overcome. Construction activities have occurred in the past
      using large construction equipment to construct two ponds southwest of
      G1.
    Many of the vernal pools that have been identified in the area are
      immediately adjacent to the existing project access roads. Action will
      need to take place to prevent vehicular traffic from driving through pools
      and dust mitigation measures may be required. Where road improvement
      is necessary near vernal pools, action will be taken to prevent fill material
      from entering a vernal pool.
    Because of the possible presence of giant garter snakes, construction will
      need to occur during the giant garter snake active period (May 1 to
      October 1).



Project Description
This project calls for the construction of an earthen dam across an inlet section of
the Afterbay and two islands within the pond (see Figure 5). A fence will be
necessary to keep the public off the dam. Other safety measures may be

                                        17
needed near the headgate structure to ensure public safety. The access road
along the northern edge of the pond will need to be raised approximately 2.5 feet
to ensure the pond gets inundated through the headgate structure only (see
Sheet 10).


            Borrow Area
                                             Pond Perimeter



                                              Constructed
                                                Islands




                                                       Culvert
                                                       Spillway


                                                 Main Dam and
                                                  Headworks


               Keyway Spoils Area




Figure 5. G1 Dam and Pond Features.

The crest elevation of the dam will be 137.0 feet. Much of the area surrounding
this pond is at elevation 137.0 feet or higher except for a small portion along the
northern edge of the pond as mentioned above. The access roads to the site will
remain dry when the Afterbay water surface elevation approaches its normal
maximum of 136.0 feet. It should be noted that based on the CDEC period of
record for daily data for the Afterbay (1/1/2008 to present), the Afterbay water
surface elevation rarely exceeds elevation 135.0 feet and has only exceeded
elevation 135.5 feet for two days (3/27 and 3/28, 2010).

Material excavated from the construction of the keyway will be used to construct
two islands within the pond. The islands provide waterfowl with refuge from
predation by terrestrial species. The islands will be built up to an elevation of
137.0 feet (see Sheet 11). The shape and size of the islands can be modified so
that all suitable material from the keyway excavation can be used. All unusable

                                        18
material will be spoiled at the location indicated on the map on Sheet 10. The
spoils will be spread out on an upland area and graded to create an area suitable
for future planting of waterfowl forage or nesting plots. The actual size needed
for the spoils area will depend on amount of unused material.

Material needed to backfill the keyway trench and construct the dam will come
from the borrow area identified in the design drawings (see Sheet 10). A
geologic investigation of this area will be conducted prior to construction to
ensure the material is suitable. Rock slope protection will be used on the side
slopes of the dam to help with the effects of wave-wash and erosion. The rock
slope protection material will come from an outside source and will be trucked to
the site. The cost estimate outlines the quantity of each type of material required
for construction.

A concrete headworks structure will be constructed within the dam and fitted with
a 30-inch diameter culvert and gate to control the flow of water into and out of the
pond. The invert of the culvert will be set at elevation 129.0 feet. The headwall
structures are equipped with flashboard slots to allow for the installation of a fish
screen and/or flashboards for operation and maintenance of the structure (see
Sheet 12).

Two spillways consisting of one 24-inch CMP each will be constructed at each
end of the dam. The culverts will be set at an invert elevation of 133.5 feet with a
minimum of 12 inches of cover (see Sheet 13). The spillways will allow the pond
to be recharged automatically when the Afterbay elevation rises above that level
as well as release water if the pond becomes overcharged by rainfall within the
ponds watershed.

Details
Table 6 on the following page describes some of the details of the proposed
pond including earthwork quantities, pond volume, perimeter, and surface area.

Cost Estimate
The cost estimate in Table 7 was generated by using unit costs listed in Saylor
Publications, Inc 2009 Current Construction Cost Manual. The dewatering cost
was based on the assumption that the site will be dewatered by coffer dams or
similar structures.




                                         19
Table 6. Basic G1 Dam and Pond Details.
                         Feature                                          Quantity
 Keyway Excavation (material can be used for
                                                                  5,300 Cubic Yards
 creating islands within new pond)*
 Total Fill Required (backfill keyway and construct
                                                                  13,800 Cubic Yards
 dam)
 Dam Height (downstream toe to spillway invert)                        5.5 Feet
 Dam Height (downstream toe to dam crest)                               9 Feet
 Dam Crest Length                                                     1,180 Feet
 Wetted Perimeter (full pond elevation 133.5 feet)                    4,030 Feet
 Surface Area (full pond elevation 133.5 feet)                        9.6 Acres
 Water Storage (full pond elevation 133.5 feet)                     18.2 Acre-Feet
 Travel Distance From Highway 162                                      2.2 Miles
 Travel Distance From Borrow Area                                      0.2 Miles
*All islands will be created using keyway excavation material. Material not used in island
creation will be disposed in spoils area identified in Figure 5 and Sheet 10.

Table 7. G1 Cost Estimate.
ITEM             DESCRIPTION               QUANTITY UNIT        UNIT COST       TOTAL COST*

              MISCELLANEOUS
  1        Mobilization/Demobilization          7      AC $       4,800     $      34,000

                 DEWATERING
  2            Install and Removal              1      LS   $    173,000    $     173,000

                 EARTHWORK
  3          Excavation (key trench)          5,300    CY   $       12      $      64,000
  4             Backfill for Dam             13,800    CY   $       30      $     414,000
  5        Concrete Headwall Structure          36     CY   $      800      $      29,000
  6              30" Slide Gate                 1      EA   $     2,300     $      2,000
  7              Headwall Pipe                  26     FT   $       45      $      1,000
  8               Spillway Pipe                 80     FT   $       45      $      4,000
  9                Road Base                   200    TON   $       41      $      8,000
  10         Rock Slope Protection            1400    TON   $       23      $      32,000
                                                                                  554,000

  11          Construction Cost                                             $     761,000
  12         Contingency @ 20%                                              $     152,000
  13      Construction Cost Subtotal                                              913,000

  14   Engineering and Inspection @ 20%                                     $      183,000
  15     Contract Administration @ 10%                                      $       76,000
  16                 Total                                                  $     1,172,000
*Total cost values have been rounded to the nearest $1,000.




                                           20
Pond J2

Location
Proposed pond J2 is located in the southern end of the Afterbay and east of the
Butte City Highway intersection with Highway 99 at 39°28’08”N, 121°40’17”W
and can be found on the USGS 7.5 minute series Biggs Quadrangle (see Sheet
1, Location Map). Access to the site is from Wilbur Road and then on existing
gravel roads through the Afterbay area. The area is open to the public but there
are two locked gates that restrict public vehicle access.

Existing Conditions
The site generally consists of gently sloping terrain covered by low vegetation.
There are some mature trees around the southern edge of the pond site, but
construction activities will largely avoid these trees, although a small amount of
trimming may be necessary. Several environmentally or culturally sensitive
areas have been identified near the project area and access routes, but not
within the project footprint. Multiple vernal pools have been identified alongside
access roads, nearly the entire area has been identified as red-legged frog and
giant garter snake habitat, and the remnants of the former Western Canal may
be culturally significant. Environmental and cultural site clearance may be
required prior to construction.

Constraints
The most notable project constraints are listed below:
    Moving people and equipment to the site includes traveling on narrow
      gravel roads with tight curves and crossing a relatively narrow bridge over
      a portion of the former Western Canal. These constraints, however,
      should not be difficult to overcome. Construction activities, such as the
      construction of the existing C2 dam, have occurred in the past using large
      construction equipment.
    Moving dam building material from the proposed borrow area on Big
      Island (see Figure 2) will require the contractor to drive across the existing
      C2 dam and/or proposed J3 dam. The C2 access route would need to be
      improved prior to use, the J3 route may not need much improvement, but
      both routes presently become inundated when the Afterbay water surface
      elevation reaches 132.5 feet.
    Many of the vernal pools that have been identified in the area are
      immediately adjacent to the existing project access roads. Action will
      need to take place to prevent vehicular traffic from driving through pools
      and dust mitigation measures may be required. Where road improvement
      is necessary near vernal pools, action will be taken to prevent fill material
      from entering a vernal pool.
    Because of the possible presence of giant garter snakes, construction will
      need to occur during the giant garter snake active period (May 1 to
      October 1).


                                         21
       Another constraint affects the height of the proposed dam. There is
        relatively little “high ground” around the proposed dam sites, so the
        proposed dam will have a lower dam crest heights than some of the other
        proposed dams.

Project Description
This project calls for the construction of a main dam from the ground outside the
Afterbay to a small island within the Afterbay. This island (elevation 134.4 feet)
can actually be a peninsula, an island, or be completely submerged depending
on the water surface elevation of the Afterbay. A smaller saddle dam would
connect this island back to the ground side outside the Afterbay (see Figure 6).


       Main Dam and                                                     Keyway
        Headworks                                                        Spoils
                                 Constructed                             Area
                                   Island




                                                                  Access
                                     Saddle Dam                    Road

    Existing                                            Pond
     Island                                           Perimeter
                  Culvert
                                       Existing
                 Spillways
                                        Road

Figure 6. J2 Dam and Pond Features.

The crest elevation of both the main dam and saddle dam will be 135.5 feet.
There is very little existing ground in this area that is higher than 135.5 feet, so
building this dam to elevation 137.0 feet is not practicable. Much of the area
surrounding this pond is submerged and access roads to the site are flooded
when the Afterbay water surface elevation approaches its normal maximum of
136.0 feet. It should be noted that based on the CDEC period of record for daily
data for the Afterbay (1/1/2008 to present), the Afterbay water surface elevation
rarely exceeds elevation 135.0 feet and has only exceeded elevation 135.5 feet
for two days (3/27 and 3/28, 2010).
A keyway will be excavated at the proposed dam location approximately six feet
below the existing ground as indicated in the design drawings (see Sheet 16).
Material excavated from the construction of the keyway will be used to construct
one island within the pond. The island will provide waterfowl with refuge from
predation by terrestrial species. Because of the relatively small size of this pond

                                         22
one island approximately 50 feet wide by 100 feet long with an elevation of 137.0
feet was selected for this site (see Sheet 15). Island construction will likely
require less than half of the material excavated from the keyway, so the
remaining soil will be spread on an upland area and graded to create and area
suitable for future planting of waterfowl forage or nesting plots. See Sheet 14 for
approximate location of keyway material spoils area. The actual size of the
spoils area will depend on how much material is actually excavated to construct
the keyway.

Material needed to backfill the keyway trench and construct the main portion of
the dam will come from one of two possible sources. If a geologic investigation
of Big Island shows that favorable dam-building material is located there, then
this will be the source location for the backfill and dam building material. If this
material is not suitable, then another potential source location has been identified
near pond G1, though a geologic investigation of the G1 source location will also
be necessary. Rock slope protection will be used on the side slopes of the dam
to help with the effects of wave-wash and erosion. The rock slope protection
material will come from an outside source and will be trucked to the site. The
cost estimate lists the quantity of each item required for construction.

If Big Island is used as the source location for dam construction material, we
recommend that the proposed improvements be made to the C2 and J3 ponds
prior to beginning construction of J2.

A concrete headworks structure will be constructed within the dam and fitted with
a 30-inch diameter culvert and gate to control the flow of water into and out of the
pond. The invert elevation of the pipe will be 129.5 feet (see Sheet 16).

One spillway consisting of three 24-inch diameter CMP’s with an invert elevation
of 133.5 feet will be constructed in the saddle dam to allow the pond to be
recharged automatically when the Afterbay elevation rises above that level (see
Sheet 17). These spillways will also allow the pond to release water if the pond
becomes overcharged by rainfall within the ponds watershed.

Details
Table 8 on the following page describes some of the details of the proposed
pond including earthwork quantities, pond volume, perimeter, and surface area.

Cost Estimate
The cost estimate in Table 9 was generated by using unit costs listed in Saylor
Publications, Inc 2009 Current Construction Cost Manual. The dewatering cost
was based on the assumption that the site will be dewatered by coffer dams or
similar structures. It is important to note that the cost estimate does not include a
cost for loss of power generation.




                                         23
Table 8. Basic J2 Dam and Pond Details.
                         Feature                                            Quantity
 Keyway Excavation (material will be used for
                                                                    3,900 Cubic Yards
 creating islands within new pond)*
 Total Fill Required (backfill keyway and construct
                                                                    8,000 Cubic Yards
 dam)
 Dam Height (downstream toe to spillway invert)                          4.5 Feet
 Dam Height (downstream toe to dam crest)                                6.5 Feet
 Dam Crest Length                                                      1,100 Feet
 Wetted Perimeter                                                      1,865 Feet
 Surface Area                                                           4.5 Acres
 Water Storage                                                        7.2 Acre-Feet
 Travel Distance From Highway 162                                       3.2 Miles
 Travel Distance From Borrow Area (Big Island)                          0.9 Miles
*All islands will be created using keyway excavation material. Material not used in island
creation will be disposed in spoils area identified in Figure 6 and Sheet 14.

Table 9. J2 Cost Estimate
ITEM             DESCRIPTION              QUANTITY UNIT           UNIT COST        TOTAL COST*

              MISCELLANEOUS
  1        Mobilization/Demobilization          10     Acre $       4,800      $       48,000

                 DEWATERING
  2            Install and Removal              1       LS    $    120,000     $     120,000

                 EARTHWORK
  3          Excavation (key trench)         3,900      CY    $       12       $      47,000
  4             Backfill for Dam             8,000      CY    $       30       $     240,000
  5        Concrete Headwall Structure         30       CY    $      800       $      24,000
  6              30" Slide Gate                1        LS    $     2,300      $      2,000
  7              Headwall Pipe                 30       FT    $       45       $      1,000
  8               Spillway Pipe               180       FT    $       45       $      8,000
  9                Road Base                  340      TON    $       41       $      14,000
  10         Rock Slope Protection            450      TON    $       23       $      10,000
                                                                               $     346,000

  11          Construction Cost                                                $     514,000
  12         Contingency @ 20%                                                 $     103,000
  13      Construction Cost Subtotal                                           $     617,000

  14 Engineering and Inspection @ 20%                                          $     123,000
  15   Contract Administration @ 10%                                           $      51,000
  16               Total                                                       $     791,000
*Total cost values have been rounded to the nearest $1,000.




                                           24
Pond C2-J3

Location
Proposed pond C2-J3 is located in the southern end of the Afterbay and east of
the Butte City Highway intersection with Highway 99 at 39°28’01”N, 121°40’05”W
and can be found on the USGS 7.5 minute series Biggs Quadrangle (see Sheet
1, Location Map). Access to the site is from Wilbur Road and then on existing
gravel roads through the Afterbay area. The area is open to the public but there
are two locked gates that restrict public vehicle access.

Existing Conditions
The site generally consists of gently sloping terrain covered by low vegetation.
There are some mature trees around the pond, mostly along the western edge
site, but construction activities will largely avoid these trees, although a small
amount of trimming may be necessary. Several environmentally or culturally
sensitive areas have been identified near the project area and access routes, but
not within the project footprint. Multiple vernal pools have been identified
alongside access roads, nearly the entire area has been identified as red-legged
Frog and giant garter snake habitat, and the former Western Canal may be
culturally significant. Environmental and cultural site clearance will be required
prior to construction.

Constraints
The most notable project constraints are listed below:
    Moving people and equipment to the site includes traveling on narrow
      gravel roads with tight curves and crossing a relatively narrow bridge over
      a portion of the former Western Canal. These constraints, however,
      should not be difficult to overcome. Construction activities, such as the
      construction of the existing C2 dam, have occurred in the past using large
      construction equipment.
    Many of the vernal pools that have been identified in the area are
      immediately adjacent to the existing project access roads. Action will
      need to take place to prevent vehicular traffic from driving through pools
      and dust mitigation measures may be required. Where road improvement
      is necessary near vernal pools, action will be taken to prevent fill material
      from entering a vernal pool.
    Because of the possible presence of giant garter snakes, construction will
      need to occur during the giant garter snake active period (May 1 to
      October 1).




                                        25
       Another constraint affects the height of the proposed dams. There is
        relatively little “high ground” around the proposed dam sites, so the
        proposed dam will have a lower dam crest heights than some of the other
        proposed dams.

Project Description
This project calls for the raising of the C2 dam and the existing J3 roadway to the
west of the C2 dam. The roadway is identified as “saddle dam” in Figure 7. The
C2 dam and J3 saddle dam will need to be raised by approximately 1.5 feet (see
Sheet 20) and 3.0 feet (see Sheet 19) respectively and rock slope protection will
need to be added to each side of the face of each dam.


                     Existing                                       Culvert
                      Road                   Pond                  Spillways
                                           Perimeter
       Saddle Dam
        (Existing                                                      Main Dam
         Road)                                                            and
                                                                       Headworks




                              Road                             Existing C2
                          Improvements                            Pond
                                                                Perimeter
Figure 7. C2-J3 Dam and Pond Features.

The crest elevation of both the main dam and saddle dam will be 135.5 feet.
There is very little existing ground in this area that is higher than 135.5 feet (see
Sheet 18), so building this dam to elevation 137.0 feet is not practicable. Much
of the area surrounding this pond is submerged and access roads to the site are
flooded when the Afterbay water surface elevation approaches its normal
maximum of 136.0 feet. It should be noted that based on the CDEC period of
record for daily data for the Afterbay (1/1/2008 to present), the Afterbay water
surface elevation rarely exceeds elevation 135.0 feet and has only exceeded
elevation 135.5 feet for two days (3/27 and 3/28, 2010).

Material needed to elevate the main portion of the dam and saddle dam will
come from one of two possible sources. If a geologic investigation of Big Island
shows that favorable dam-building material is located there, then this will be the
                                          26
source location for the backfill and dam building material. If this material is not
suitable, then another potential source location has been identified near pond
G1, though a geologic investigation of the G1 source location will also be
necessary. Rock slope protection, used to protect the side slopes of the dam
from the effects of wave-wash and erosion will need to come from an outside
source and trucked to the site. The volumes of each type of material required for
construction will be outlined in the cost estimate.

If Big Island is used as the source location for dam construction material, we
recommend that the proposed improvements be made to the C2 and J3 ponds
prior to beginning construction of J2.

The existing C2 headworks structure will remain in place and continue to be used
as the manual water control structure for the C2-J3 pond (see Sheet 21).

The existing spillways in the C2 dam will be raised to an elevation of 133.5 feet
(see Sheet 23). These spillways will allow the pond to be recharged
automatically when the Afterbay elevation rises above that level. These
spillways will also allow the pond to release water if the pond becomes
overcharged by rainfall within the ponds watershed.

Details
Of the five ponds described in this document, pond C2-J3 is the only pond
construction project that proposes to make changes to an existing pond. By
raising the C2 dam and the J3 roadway a new pond will be created that is larger
than the one that presently exists. Table 10 shows three of the significant
changes that will occur: increases in perimeter, area, and volume if the proposed
pond is constructed.

Table 10. Comparison of Site C2 With Combined Site C2-J3.
        Site         Perimeter @           Surface                     Water
       Name             El. 133.5           Area                      Storage
                           (Ft.)           (Acres)                   (Acre-Ft.)
      C2 + J3            4,840               14.2                      17.5
        C2               2,120               5.0                        7.6
  Size Increase          2,720               9.2                        9.9

Table 11 on the following page describes some of the details of the proposed
pond including earthwork quantities, pond volume, perimeter, and surface area.

Cost Estimate
The cost estimate in Table 12 was generated by using unit costs listed in Saylor
Publications, Inc 2009 Current Construction Cost Manual. The dewatering cost
was based on the assumption that the site will be dewatered by coffer dams or
similar structures.


                                        27
Table 11. Basic C2-J3 Dam and Pond Details.
                         Feature                                         Quantity
 Keyway Excavation (material will be used for
                                                                   0 Cubic Yards
 creating islands within new pond)
 Total Fill Required (raise C2 and J3 dams)                      3,500 Cubic Yards
 Dam Height (downstream toe to spillway invert)                       5.5 Feet
 Dam Height (downstream toe to dam crest)                             7.5 Feet
 Dam Crest Length (C2 + J3)                                          1,890 Feet
 Wetted Perimeter                                                    4,840 Feet
 Surface Area                                                        14.2 Acres
 Water Storage                                                     17.5 Acre-Feet
 Travel Distance From Highway 162                                     3.2 Miles
 Travel Distance From Borrow Area (Big Island)                        0.4 Miles


Table 12. C2_J3 Cost Estimate
ITEM            DESCRIPTION             QUANTITY UNIT         UNIT COST       TOTAL COST*

             MISCELLANEOUS
  1       Mobilization/Demobilization          10   ACRE $      4,800     $      48,000

                DEWATERING
  2           Install and Removal              1     LS   $    223,000    $     223,000

                 EARTHWORK
  3        Fill For Raising C2 Dam         1,700     CY   $      30       $     51,000
  4        Fill For Raising J3 Dam         1,800     CY   $      30       $     54,000
  5              Spillway Pipe              300      FT   $      45       $     13,000
  6               Road Base                 560     TON   $      41       $     23,000
  7      Rock Slope Protection For C2       590     TON   $      23       $     14,000
  8      Rock Slope Protection for J3       330     TON   $      23       $      8,000
                                                                          $     163,000

  9           Construction Cost                                           $     434,000
 10         Congtingency @ 20%                                            $     87,000
 11       Construction Cost Subtotal                                      $     521,000

 12 Engineering and Inspection @ 20%                                      $     104,000
 13   Contract Administration @ 10%                                       $     43,000
 14               Total                                                   $     668,000



*Total cost values have been rounded to the nearest $1,000.                                 Comment [m1]: Is the 30” slide gate and
                                                                                            headwall pipe needed for this work?




                                          28

								
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