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U.S. Department of the Interior Bureau of Reclamation Technical Service Center Denver, Colorado August 2012
Facility Vulnerability Assessment for Imperial Dam and Desilting Works Invasive Quagga and Zebra Mussels Lower Colorado Region Yuma Area Office Boulder Canyon Project - All-American Canal System
U.S. Department of the Interior Bureau of Reclamation Technical Service Center Denver, Colorado February 2012
Facility Vulnerability Assessment for Imperial Dam and Desilting Works
Invasive Quagga and Zebra Mussels
Prepared for Reclamation’s Lower Colorado Region & Yuma Area Office
Mission Statements
The mission of the Department of the Interior is to protect and provide access
to our Nation's natural and cultural heritage and honor our trust responsibilities
to Indian Tribes and our commitments to island communities.
___________________________
The mission of the Bureau of Reclamation is to manage, develop, and protect
water and related resources in an environmentally and economically sound
manner in the interest of the American public.
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Disclaimer
The information provided in this report is believed to be appropriate and accurate for the specific
purposes described herein, but users bear all responsibility for exercising sound engineering judgment in
its application, especially to situations different from those reported. References to commercial products
do not imply endorsement by the Bureau of Reclamation and may not be used for advertising or
promotional purposes.
Cover Photo: View of Imperial Dam and Desilting Works
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Contents
Executive Summary .............................................................................................. 1 Findings............................................................................................................. 1 Recommendations ............................................................................................. 1
Introduction ........................................................................................................... 3 Purpose and Objectives ..................................................................................... 3 Brief Project Description .................................................................................. 3
Background on Potential Invasive Mussel Impacts .......................................... 3
Assessment Findings ............................................................................................. 6 Susceptibility to Infestation .............................................................................. 6
Recreation ................................................................................................... 7 Dam and Spillway ....................................................................................... 7
Drainage System ................................................................................... 8
Intake Structures ......................................................................................... 9 Gates ......................................................................................................... 11
Service Water Taps ................................................................................... 13 Pumps ........................................................................................................ 14 All American Canal Desilting Works ....................................................... 15
Bulkheads and Stoplogs ............................................................................ 19 Instrumentation ......................................................................................... 19
Reservoir Elevation Gauge ................................................................. 19
Flow Measurement.............................................................................. 20
Other ................................................................................................... 20 Laguna Dam .............................................................................................. 21
Conclusions .......................................................................................................... 21 Recommendations ............................................................................................... 22
Monitoring and Detection ............................................................................... 22
Response Planning .......................................................................................... 22 Facility Protection Options ............................................................................. 22
Intake Structure ......................................................................................... 22
Emergency & Regulating Gates................................................................ 23 Bulkheads .................................................................................................. 23
Instrumentation ......................................................................................... 23
Drainage Systems...................................................................................... 23
Pumps ........................................................................................................ 23 Desilting Works ........................................................................................ 24
Appendix A .......................................................................................................... 25 Facility Vulnerability Checklist ...................................................................... 25
2. Preparation (Step 1) ............................................................................. 25
3. In-house Review and Preparation for Field Visits (Step 2) ................. 26 4. Site Visits, Follow-up and Reporting (Step 3) ..................................... 27 5. Mussel Vulnerability Evaluation - Project Team Contact List ............ 27 6. Mussel Vulnerability Evaluation – Sample Facility Deliverables List 28 1. Instructions for Using this Document ................................................... 29
2. Walkthrough Checklist ........................................................................ 29
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Appendix B .......................................................................................................... 33 Management Options for Quagga & Zebra Mussel Infestations .................... 33 Actions to consider prior to detection of mussels: .......................................... 33 Actions to consider following detection of mussels: ...................................... 34
1
Executive Summary
The purpose of this assessment is to provide Reclamation management and project staff with
information regarding the vulnerability of facility features to invasive mussel impacts. This
report is not intended to be a risk assessment or prediction of the severity of the existing quagga
mussel infestation. Instead it is intended to assist project management and staff in anticipating
and planning for impacts should the infestation become exacerbated.
Findings
Imperial Dam and Desilting Works and appurtenances are relatively complex for a diversion
structure. The outlet works intake structure trashracks, All American Canal desilting works,
reservoir level measurement system, and sampling and irrigation water pumps appear most
susceptible to mussel-related impacts.
While it is currently uncertain, the potential for mussel settlement in drainage systems (including
structure under drains and drain outlets with the potential for back flooding) should also be
considered and closely monitored if a future infestation worsens.
Potential factors mitigating mussel impacts that were identified during the site visit included
extended high seasonal water temperatures and concomitantly low dissolved oxygen levels at the
outlet works. The validity of these and potentially other environmental factors remains to be
verified.
Initial recommendations and options for facilities protection are provided to assist with
preliminary planning and budgeting should the existing invasive mussel infestation worsen. It
should be noted that various options for facilities protection exist (this report is not an all-
inclusive list of possible options and new technologies may become available in the future).
Selection of the best option will depend on a number of considerations including operational
flexibility, design requirements, project constraints, and cost.
Recommendations
The following recommendations are provided for consideration:
Invasive mussels have been detected at Imperial Dam and Desilting Works since 2008, but
they have remained minor faunal constituents. This report is based on the hypothetical
assumption that mussels will become problematic at some future time. While there is no
precise way to foretell whether the Imperial infestation will become an issue without further
study, planning ahead will allow time for budgeting and implementation of response actions
if needed. It is important to build upon the Lower Colorado Region Invasive Mussel
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Response Plan by developing site-specific plans to address a potential future worsening of
the infestation. General information on management options have been included in
Appendix B along with links to other response plans and response planning guidelines
developed by the National Parks Service.
It is also recommended that a monitoring plan, via plankton net sampling, be established as
well as monitoring for settlement using either substrates and/or routine inspection of
underwater structures (e.g., outlet works intake structures) using quantitative methods. This
post-introduction monitoring provides information on the status and rate of development of
the infestation and allows for a rough idea of when certain facilities features will become
impacted. Typically intake structures will be impacted first followed by internal piping and
related systems and equipment. Continued monitoring can also be used to refine
maintenance schedules or to anticipate future changes in population dynamics as well as
ecological impacts attributable to mussels.
It is recommended that future water quality sampling and environmental parameter analyses
be conducted at regular intervals and include seasonal, if not monthly, calcium, pH,
temperature, dissolved oxygen (DO) profiling and possibly other variables at the Imperial
Dam impoundment to further ascertain the potential for mussel survival, establishment, and
mitigating factors.
3
Introduction
Purpose and Objectives
The purpose of this assessment is to provide Reclamation management and project staff with
information regarding the vulnerability of facility features to invasive mussel impacts. This
report is not intended to be a risk assessment or prediction of the potential for a future mussel
infestation. Instead, it is intended to assist project management and staff in anticipating and
planning for impacts should a future infestation occur.
Brief Project Description
Imperial Dam and Desilting Works, spans the Colorado River 18 miles northeast of Yuma,
Arizona. The purpose of the dam is to raise the water surface 25 feet and provide controlled
gravity flow of water into the All-American Canal (AAC) and Gila Gravity Main Canal
(GGMC). The desilting works remove most the sediment carried by the Colorado River
to prevent clogging of the AAC and subsequent extensive maintenance.
Imperial Dam is a reinforced concrete structure of the monolithic slab-and-buttress type
consisting of an overflow weir, canal headworks at each end of the dam for the Gila Gravity
Main Canal (east) and All-American Canal (west), and a sluiceway between the All-American
Canal Headworks and a central overflow weir. The dam is 3,475 feet long, including a 510-foot
rockfill dike at the Arizona end. The 1,198-foot-long overflow weir, in conjunction with the
California Sluiceway, is designed to pass a maximum flood of 185,000 cubic feet per second, not
including any diversions to the canal systems. The California side of Imperial Dam consists of
AAC headworks, trashrack and rake, service bridge, and inlet channels to the AAC desilting
basins. The Arizona side of the dam consists of trashrack, trashrake, desilting basin and GGMC
headworks.
Background on Potential Invasive Mussel Impacts
Quagga and zebra mussels (adult lengths typically average about 1 in) are unique in that they can
firmly attach to the underwater surfaces using byssal threads. They begin spawning by emitting
eggs and sperm into the water column when water temperature reaches around 10-12ºC (50-
54ºF). Though spawning has been observed at slightly lower temperatures in some case. On a
population-wide basis, egg production occurs in astronomical levels (on the order of 30,000
eggs/female/reproductive cycle). Depending on temperature and environmental suitability,
multiple reproductive cycles may occur in a single year. Fertilized eggs develop into freely
swimming larvae or veligers (ranging in sizes from 60 to 250 micron) which may be transported
by water currents for many miles. When water conditions are suitable, veligers will settle (i.e.,
attach to hard surfaces) and continue growth to adulthood within a few weeks.
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Successful settlement is mediated by a number of environmental conditions inherent in the
natural water system. These include calcium, alkalinity/hardness, pH, nutrients, dissolved
oxygen, temperature and conductivity. It should be noted that some of these parameters are
indirect measures of others. For example, alkalinity/hardness are presumptive for calcium. It is
generally accepted that highly successful mussel colonization occurs when calcium levels exceed
24 mg/L. Successful establishment is more in question when calcium values fall below 10 mg/L.
With the possible exception of nutrients (implied indicators of food supply) in high mountain
lakes, the remainder of listed parameters seems fairly well represented as having adequate levels
in Western waters where data are available. Table 1 provides water quality parameters suitability
criteria for invasive mussels. It should be noted that this information was obtained from various
sources involving primarily zebra mussel specific studies in Europe and Eastern portions of
North America and may not be entirely applicable to water bodies in the Western U.S.
Nevertheless it provides an approximate indication of suitability requirements.
Table 1. Presumptive infestation-level suitability criteria for invasive mussels.
Parameter
Low
Probability
of Survival
Infestation Levels
Low Moderate High
Calcium (mg/L) <10 (QM)
<8 (ZM)
10-12 (QM)
8-15 (ZM)
12-30 (QM)
15-30 (ZM) >30
Alkalinity/Total Hardness
(mg CaCO3/L)
<35 (QM)
<30 (ZM)
35-42 (QM)
30-55 (ZM)
42-100 (QM)
55-100 (ZM) >100
pH <7.0
>9.5
7.0-7.8
9.0-9.5
7.8-8.2
8.8-9.0 8.2-8.8
Dissolved Oxygen (mg/L) <3 5-7 7-8 >8
Dissolved Oxygen (% saturation) <25% 25-50% 50-75% >75%
Mean Summer Temperature (oF)
<64
>86
64-68
83-86
68-72
77-83 72-75
Conductivity (μS/cm) <30 30-60 60-110 >110
Salinity (g/L) >10 8-10 5-8 <5
Secchi depth (m) <0.1
>8
0.1-0.2
2.5-8 0.2-0.4 0.4-2.5
Chlorophyll a (μg/L) <2.0
>25
2.0-2.5
20-25 8-20 2.5-8
Total phosphorous (μg/L) <5
>50
5-10
35-50 10-25 25-35
It is also important to note that mean summer temperature does not imply temperature
thresholds. Adult mussels have been observed to survive at temperatures near freezing. The
low-temperature threshold for mussel growth is thought to be around 45 ºF. This would imply
that mussels are more likely to colonize systems with raw water temperatures greater than about
45 ºF, with a lower probability of colonization for sustained temperatures below this threshold.
On the upper end, temperatures greater than about 84-86 ºF for extended periods are normally
not expected to support mussel survival. However, there is reason to suspect acclimation to
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higher temperatures by mussel populations in the Colorado River upstream. Currently an
explanation is unknown as to why mussels are not problematic in the Imperial Dam vicinity at
levels seen upstream as near as Parker Dam. For additional information see Mackie G. & R.
Claudi, Monitoring and Control of Macrofouling Mollusks, 2nd
Ed., CRC Press, 2010.
Environmental and operational conditions of the structures themselves may also influence
veliger settlement and subsequent colonization. Within a facility, veliger settlement is prohibited
or greatly reduced in pipes where water velocities continuously exceed 6 feet per second (ft/s).
However, intermittent operations or slower velocities may lead to successful settlement. Once
attached, mussels can sustain that attachment even when flow velocities exceed 6 ft/s. Ideal
areas for mussel colonization are those areas with continuous flows of moderate velocities (<6
ft/s) and ample supplies of food and oxygen. Piped systems which are seldom utilized or idle for
prolonged periods and which have depleted oxygen are not generally supportive of successful
colonization. A major exception is a situation where leaking valves allow constant flows and
replenishment to such seldom used systems.
Invasive mussels pose serious threats to water resources infrastructure and operations. Of major
importance to facilities is the ability of mussels to rapidly colonize hard surfaces at densities of
tens of thousands per square meter. This heavy accumulation can lead to costly operations and
maintenance problems. Flow restriction is the foremost concern because mussels can clog water
intake structures, such as trashracks, pipes and screens, thereby threatening water delivery to
critical systems at hydropower plants and reducing pumping and conveyance capacities of water
distribution systems.
Major structural impacts caused by quagga and zebra mussels fall into the following categories:
Flow restriction or blockage – Light infestations can roughen water conveyance surfaces,
reducing the ability to deliver water in desired quantities and in a timely manner. If
accumulation is allowed to progress to extremes, pipes as large as 1-ft in diameter have been
blocked. Accumulations of shells from dead mussels are also problematic in screens, filters
and small diameter pipes, fittings, and valves.
Mechanical damage – Mussel shells can cause abrasive damage to soft materials such as
seals and over time, finely machined surfaces. Removal of attached mussels can cause
damage to surfaces by lifting of coatings.
Chemical degradation of structures – The accumulation of mussel fecal material, digestive
by-products and sediments next to uncoated or damaged coatings on metallic (ferrous)
substrates under large colonies is highly supportive of bacterial colonies which accelerate
corrosion processes.
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Assessment Findings
Susceptibility to Infestation
Water Quality Of importance for estimating potential infestation levels are those parameters necessary for
establishment and growth of mussel populations discussed above (namely calcium, pH, dissolved
oxygen, temperature and nutrients).
Table 2: Water quality data and suitability for zebra/quagga and mussel infestation at
Imperial Dam
Water Quality Parameter Level Infestation Potential
pH 8.34 High
Calcium 82 mg/L High
Total Dissolved Solids 670 mg/L High
Conductivity 1070 µS/cm High
Salinity 683 mg/L Low
Asiatic clam shells were observed in large quantities on the floor of the desilting works
clarifying basins (Figure 1). While there is no guarantee that the clam shells were not
transported from distant locations further upstream, this would appear to suggest the water
quality here is conducive to supporting large populations of zebra or quagga mussels. However,
it is worth noting that Asiatic clams, according to current literature, have even less tolerability to
high salinity. This may suggest local adaptation to salinity, or seasonal fluctuations in water
quality.
Figure 1: Asiatic clamshells found in Imperial Dam desilting works
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Zebra and Quagga mussels have also been observed in limited numbers in the reservoir (and
equipment surfaces) but have yet to experience the explosive population growth that has
occurred in nearby locations such as Parker Dam just a few hours to the north.
One question surrounding Imperial Dam and other facilities nearby is whether or not mussels
will eventually become established. One hypothesis is that the high summer temperatures are a
sufficiently effective mitigating factor in mussel reproduction. High water temperatures
(sustained > 90ºF) and low DO (sustained < 3 mg/L) may provide mitigating effects if other
water quality parameters are favorable for invasive mussel establishment. It is currently
unknown whether a temperature tolerant subpopulation will begin to growth and thrive over
time. An additional study is currently being proposed to evaluate the biological and
environmental factors mitigating population growth in this portion of the Colorado River.
Recreation Recreational boat traffic is considered a primary vector for the spread of invasive mussels.
Imperial Reservoir and the associated Colorado River has moderate boat traffic. Project staff
indicated boat ramps are accessible for launch year around. The management responsibility for
boat ramps and land-based recreation is shared among federal, state, and Native American
agencies. No boat ramps were visited during this assessment. If not already done, it is
recommended that signs displaying information about invasive mussels be placed in conspicuous
locations to increase public awareness and compliance with relevant guidelines.
Dam and Spillway Imperial Dam contains a weir which is utilized to pass flows that cannot be accommodated with
using the All American Canal, GGMC and California Sluiceway. Although the spillway was
observed to be partially wet during the site visit due to wave action, the spillway itself is not
likely vulnerable to significant impacts related to mussel fouling. Owing primarily to the design
and low frequency of spillway operation such that the crest are likely remain dry for extended
periods of time, little mussel fouling would be expected.
8
Figure 2: Overflow weir spillway at Imperial Dam
Drainage System
Although it is currently uncertain (i.e., hypothetical), structural drainage systems (including
formed drains and drain outlets with the potential for back flooding) may be impacted by
mussels depending on the design of the systems and size of seepage passages. If flow passages
from the reservoir are sufficiently large (>60 micron) and water chemistry is suitable for survival
then it may be possible for mussel larvae to enter, colonize, and clog portions of the drainage
system. Furthermore, back flooding of drain outlets, if possible, represents another route for
mussel entry and colonization. The overflow weir at Imperial Dam contains an inverted gravel
filter with 168 drains which are monitored on a regular basis as well as 68 pipe ejectors.
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Figure 3: Ejectors in the overflow weir
Figure 4: Drain piping underneath the overflow weir.
Intake Structures The intake structures at Imperial Dam and Desilting Works includes trash rack gratings on both
the California and Arizona side of the dam. Each structure also includes a trash rake cleaning
system. This equipment is perhaps some of the most vulnerable and least accessible features of
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the facility. Experience at Reclamation facilities along the Colorado River upstream which are
exposed to high levels of infestation suggests that intake structures, particularly those with
trashracks, can become fouled in a very short period of time, with mussel attachment on and
between trashrack bars resulting in reduced open area. Reductions in open area produce
increased headloss and decreased discharge capacity with some potential for trashrack failure.
The trashracks at imperial are particularly susceptible given the relatively narrow spacing and
thin bar stock used. On the AAC headworks, the trashrack panels consist of what appeared to be
¼” bar stock at 2.5” spacing. The spacing on the GGMC headworks trashracks is reported to be
4 5/8” on center. Velocities through the intake trashracks will vary, but are typically well below
the critical velocity of 6 ft/s, above which mussel attachment is unlikely. The trash rake may
provide some mitigation of macrofouling but is unlikely to provide complete removal due to the
fixed rake tine design. A rotating brush design may be better suited for mussel removal.
Figure 5: Trashrack Structure on All American Canal Headworks
11
Figure 6: Trashrack on All American Canal Headworks
Gates Imperial Dam and Desilting Works contains the following gates:
California Side:
Twelve (12) radial sluice gates.
Multiple radial gates used to control influent and effluent from the desilting basins.
Four (4) roller gates used to regulate inflow into the All American Canal headworks /
California Desilting Works.
Seven (7) radial gates present on check structures (not observed during visit).
Arizona Side:
Nine (9) radial headworks gates (3 gates are operable).
Eight (8) fixed wheel sluice gates
Eight (8) fixed wheel diversion gates which remain in the lowered position
Mussel attachment along gate guides, seals, and sealing surfaces has the potential to degrade seal
performance and may lead to reduced gate performance. Although these impacts are not
expected to render the gates inoperable, they will likely increase future maintenance
requirements to maintain smooth operation and adequate seal performance. A tile drainage
system provides drainage on the downstream side of the unused headworks gates on the Gila
Canal. In the event of an infestation, it is possible that these drains could become clogged by
mussels or shell debris rendering the drains inoperable or increasing required maintenance.
12
Figure 7: Radial gate on All American Canal Desilting Works
Figure 8: Roller gate on All American Canal Headworks
13
Figure 9: Sluice gate on All American Canal
Service Water Taps Any small diameter service water piping and hose taps that are connected to raw water lines are
also susceptible to complete blockage from mussel attachment or dead mussel shell debris. The
potential for complete clogging increases with decreasing pipe diameter. However, the service
water piping at Imperial Dam is taken from well water so no problems with fouling are expected
on this system.
14
Figure 10. Well used to deliver service water to Imperial Dam.
Pumps Pumping systems delivering raw water are subject to increased maintenance and clogging due to
mussel fouling and loading from shell debris. Sump pump float switches can also become fouled
and fail to operate properly. Imperial Dam contains an irrigation pump which takes water from
the reservoir and irrigates Phil Swing Park Lawn. Other pumps include a drain well on West
Pond and a sump pump in the sludge gallery. Severe mussel colonization in the sludge gallery
piping and pump is not likely due to the amount of sediment present in the water. The drainage
well in the West Pond is pumping seepage water from the canal which may or may not be subject
to mussel infestation depending on the passageway size of the seeps.
15
Figure 11: Irrigation pump used to water the lawn in Phil Swing Park.
All American Canal Desilting Works
Both the All American Canal and GGMC have desilting works to clarify the water before it
enters the canal. The AAC desilting works consists of 3 desilting basins and total of 72 clarifiers
which rotate slowly directing the sediment towards the center of each clarifier where it is drained
and discharged into the California sluiceway channel. The water enters each basin through an
influent channel where it passes through sets of 3-inch wide angled wall slots that direct water
into the clarifying basin (Figure 122).
16
Figure 12: AAC Desilting Works vanes
The slots are designed for a water velocity of 7 ft/s, just above the speed at which mussel
settlement typically occurs. In the clarifying basin, water velocity slows to nearly a standstill
which allows particulate matter to settle to the bottom of the basin. An empty clarifying basin is
shown in Figure 13.
17
Figure 13: Drained desilting basin at Imperial Dam All American Canal Desilting Works.
Clarified water enters the effluent channel by flowing over a weir (Figure 14). Consequently, the
weir is subject to constant immersion and hence is theoretically susceptible to mussel fouling.
However, the water is very shallow here and it is uncertain whether mussels would actually
colonize this area. If colonization were to occur on the weirs, one consequence would be
nominally reduced outflows into the AAC. One of the desilting basins had been drained for the
assessment and was accessible for inspection. Significant amounts of shell debris from Asiatic
Clams were observed in the bottom of the basin. The most susceptible portions of the clarifying
basin include the wall slots and the sludge drain piping and associated with flap valves.
However, it is unlikely that the mussels will colonize the drains due to the amount of sediment
loading present. Infestation of the clarifying arms could cause increase loading of the motors
due to increases in weight and flow resistance. Figure 15 shows the sediment encrusted walls of
the drained clarifying basin. Note that a single mussel is present and attached to the surface.
The amount of sediment present on the basin walls makes mussel attachment more difficult.
Furthermore, water velocities in the wall slots are currently believed to be too high for
attachment. However, if flows are permitted to stagnate for an extended period of time, mussel
settlement could occur and disrupt the desilting process.
The desilting works on the GGMC (Arizona side) are much simpler in design and are therefore
not intended to be nearly as efficient. No significant impacts are expected for this system.
18
Figure 14: Clarified water flows over the weir into the effluent channel on its way to the All American Canal.
Figure 15: Quagga mussel in Desilting Works
19
Bulkheads and Stoplogs In general, bulkheads are not directly susceptible to mussel fouling since they are stored in the
dry. However, mussel fouling along guides and slots can damage seals and sealing surfaces
during bulkhead installation or make installation more difficult. This can generally lead to poor
seal performance with the possibility for incomplete seating of bulkhead. Furthermore, bulkhead
vent and fill lines may become clogged by attached mussels if bulkheads are deployed for
extended periods of time (i.e., several weeks). According to the standard operating procedures
(SOP), there are stoplog guides or I-beams which can be used as guides present at the following
locations:
GGMC Headworks
GGMC Trashrack
California Sluiceway
Note that a severe infestation of stoplog guides could potentially result in difficulty deploying
stoplogs. Manual cleaning may be required to ensure trouble free operation.
Instrumentation
Reservoir Elevation Gauge
Although tubing from the inlets is not typically susceptible to mussel fouling because it is
usually constructed of copper (the only known material which inhibits mussel attachment) and
the line from reservoir to gauge is generally poorly oxygenated (except for situations were
frequent flushing or bleeding occurs), the inlet line for the spillway stilling well in this case may
be susceptible to clogging from mussel attachment or dead mussel shell debris. Depending on
levels of infestation, clogging of the inlet line has the potential to reduce sensitivity of the
reservoir level measurement system or render it inoperable. In general, any instrumentation
including stilling wells, floats, pressure transducers, gages, or bubbler systems that are directly
exposed to raw water will be susceptible to mussel fouling or shell debris accumulation leading
to the potential for measurement errors or inoperability. There are a variety of elevation gages
present at Imperial Dam and Desilting Works at locations including:
ACC Trashracks (upstream and downstream)
GGMC Trashracks (upstream and downstream)
Desilting basins
Check structures on the AAC
20
Figure 16: Reservoir elevation gage on All American Canal Headworks
Flow Measurement
It should be noted that, in general all flow measurement devices in contact with raw water are
susceptible to errors due to mussel fouling. This includes associated flumes, stilling wells,
acoustic flowmeters, and manometers. The sludge pipe flow on the AAC desilting works is
measured using a manometer which would normally be susceptible to impacts from mussel
fouling. However, severe fouling is not expected due to the high sediment loading in the sludge
pipes.
Other
Sample pump and salinity monitors are located on the AAC trashrack structure. These
instruments are susceptible to mussel fouling. Pumping systems delivering raw water are subject
to increased maintenance and clogging due to mussel fouling and loading from shell debris.
21
Figure 17: Housing for sample pump and salinity monitoring equipment.
Laguna Dam Laguna Dam is a simple structure located downstream of Imperial Dam. Due to its simplicity,
the structure was not visited during the assessment and is not expected to experience any
significant impacts in the event of the mussel infestation. The facility consists of 3 sluice gates
(two of which are currently operational) which are operated using an electric motor. The sluice
gates at Laguna Dam are subject to the same vulnerabilities as the gates at Imperial Dam.
Conclusions
Imperial Dam and Desilting Works and appurtenances are relatively complex for a diversion
structure. The outlet works intake structure trashracks, All American Canal desilting works,
reservoir level measurement system, and sampling and irrigation water pumps appear most
susceptible to mussel-related impacts. Initial recommendations and options for facilities
protection are provided below to assist with preliminary planning and/or budgeting should an
invasive mussel infestation occur at Imperial Reservoir. It should be noted that various options
for facilities protection exist (this report does not contain an all-inclusive list of possible options
22
and new technologies may become available in the future). Selection of the best option will
depend on a number of considerations including operational flexibility, design requirements,
project constraints, and cost.
Recommendations
Monitoring and Detection
It is recommended that a monitoring plan, via plankton net sampling, be established as well as
monitoring for settlement using either substrates and/or routine inspection of underwater
structures (e.g., outlet works intake structures) using quantitative methods. This post-
introduction monitoring provides information on the evolution of the infestation. Typically,
intake structures will be impacted first followed by internal piping and related systems and
equipment. Continued monitoring can also be used to refine maintenance strategies or to
anticipate future changes in population dynamics as well as ecological impacts attributable to
mussels.
Sampling should also include water quality analyses as well as temperature and dissolved
oxygen profiling to further ascertain the potential for mussel survival, establishment, and
mitigating factors in the reservoir.
Response Planning
It is recommended that this report be used in conjunction with the Lower Colorado Region
Invasive Mussel Response Plan to develop a site-specific Response Plan for the possibility of a
future invasive mussel infestation. In the event of an infestation, one specific action worth
considering would be the inclusion of mussel impacts and associated requirements into the SOP
and O&M schedules where possible. Appendix B provides some management options for
response planning, including links to various response planning guidelines and online examples.
Facility Protection Options
Intake Structure The intake structure at Imperial Dam and Desilting Works is the first choke-point from the
standpoint of mussel fouling and problematic due to the relative inaccessibility (i.e., submerged).
Various options exist including inspection and manual cleaning of the trashracks at regularly
scheduled intervals. However, due to depth and size depending on the level of infestation,
frequent cleaning may become expensive.
A second option is to retrofit the existing trash rake with a rotating brush designed to clean in
between the trash rack bars. This also is a reactive strategy but may be the least costly and
23
easiest strategy to implement. This option has yet to be tested in a scaled-up application for
mussel removal.
A third option involves the use of foul-release coatings (perhaps in combination with option 1) as
a proactive strategy to reduce the maintenance frequency and facilitate trashrack cleaning.
Various coatings are currently being tested at Reclamation’s Parker Dam which is heavily
infested with quagga mussels. Results to date are promising, but durability of best performing
systems appears to be low. Nevertheless, such coatings may perform adequately in situations
where there is a low probability for abrasion or heavy debris impacts.
Emergency & Regulating Gates Regularly exercising the gates can reduce mussel attachment along gate guides, stems, and seals
but doing so can also increase wear on seal elements. In general, increased maintenance will
likely be required to maintain gate seal performance should mussels infest Imperial Reservoir in
the future.
Bulkheads Use of alternative materials of construction that reduce fouling on guides, seats and sealing
surfaces may afford some measure of protection, but increased maintenance will likely be
required to ensure adequate seating and seal performance. A means for cleaning the guides and
seats prior to installation could also be considered to prevent or reduce the potential for damage
to seals or sealing surfaces and improper seating during installation.
Instrumentation The reservoir level monitoring system inlet will likely require frequent inspection and cleaning
to ensure unobstructed operation. If Imperial Reservoir becomes infested, consideration should
be given to retrofitting the inlet with copper materials of construction. Depending on location,
accumulation of mussel shell debris around the inlet may compound clogging problems for the
inlet port. In that case, moving the inlet port as high up in elevation as possible may be the most
practical solution. Another option includes replacing the measurement arrangement with
noncontact down looking acoustic water level sensors where possible.
Drainage Systems There are few options for protecting structural drainage systems aside from frequent cleanout of
accessible portions. All drainage systems should be closely monitored for changes and
consideration given to larval and water quality sampling and analyses of drain flows if mussels
ever become established at Imperial Reservoir.
Pumps A mussel infestation at Imperial may require more frequent cleanout of accessible portions of the
sump wells, pump intakes, and discharge piping to remove live mussels and/or shell debris. In
addition float switches should be inspected periodically to ensure they are functioning correctly.
Foul release coatings can help mitigate the settlement of live mussels on the pump intakes, float
switch, and piping.
24
Desilting Works Infestation of the desilting works may require more frequent outages for cleaning of the
clarifying arms and desilting slots. Foul release coatings may be an option for the clarifying
arms but would be difficult to apply to the slots.
25
Appendix A
Facility Vulnerability Checklist
Project Name: Imperial Dam and Desilting Works , Boulder Canyon Project - All-American Canal System, YAO
Prepared by: Nibling & Tordonato Date of Preparation: 2/07/2012
2. Preparation (Step 1) Item No.
Item Status 1
Comments /
Plan to Resolve
1 Planning
1.1 Has the project scope – including definition and
objectives – been prepared? Y
1.2 Has the Project Scope Statement been approved? Y
1.3 Is there a Project Plan against which to measure
progress? Y
1.4 Does the Project Plan address the following areas:
1.4.1 Project Scope and Deliverables Y
1.4.2 Project Schedule Y
1.4.3 Project Budget Y
1.4.4 Project Organization and Resources Y
1.5 Were key project stakeholders brought into the Project
Plan? Y
1.6 Were potential customers involved early in the
planning process? N/A
1.7 If there are vendors, have they signed off on the
Project Plan? N/A
1.8 If there is an independent oversight contractor, have
they signed off on the Project Plan? N/A
1.9 Is the Project Sponsor function identified and defined? Y
1.10 Are there alternate persons if key members of the
project are not available or become reassigned? Y
1.11 Other organization items (please list): N/A
2 Tracking & Monitoring
2.1 Are the various types of reports, their contents,
frequency, and audience defined and communicated to the Project Team?
Y
2.2 Are the input requirements from Project Team
members clearly documented and communicated? Y
3 Meetings and Input Data
3.1 Have the various meetings, purpose, context,
frequency, and participants been defined and communicated?
Y
1 Enter one of the following: C (Complete), P (Partially Complete), Y (Yes), N (No); NA (Not Applicable)
26
2. Preparation (Step 1) Item No.
Item Status 1
Comments /
Plan to Resolve
3.2 Have the drawings and documents from the facility
sites been requested? Y
4 Project Assumptions and Constraints
4.1 Are there any key assumptions upon which the
assessment is based and have these assumptions been
documented?
N
4.2 Does the Project have any Constraints such as:
4.2.1 Facility shutdown schedules? Y
4.2.2 Facility access limitations and ventilation requirements?
Y Outlet works intakes structure inaccessible.
4.2.3 Monitoring issues such as availability of reports from sampling plates set out in previous seasons?
N
4.2.4 Any training needed for key project staff? N
4.2.5 Any pre-project procurement needed for portable field equipment?
N
3. In-house Review and Preparation for Field Visits (Step 2) Item No.
Item Status 2
Comments /
Plan to Resolve
1 Reviewing
1.1 Have drawings and documents from the facility site
been reviewed? N
1.2 Have questions arising from the document review been
communicated to and discussed with the site experts? Y
1.3 Did the document review identify any pre-site-visit
activities that should be done such as video inspections
requiring divers or shutdown of equipment that needs
to be scheduled?
N
1.4 Are all pre-site-visit tasks needed to be done at site
completed? Y
1.5 Has the deliverables list been updated based on the
information from the site documents? Y
1.6 Have all system checklist sheets been prepared? Y
2 Enter one of the following: C (Complete), P (Partially Complete), Y (Yes), N (No); NA (Not Applicable)
27
4. Site Visits, Follow-up and Reporting (Step 3)
The general approach should be to follow the path of the water through the site facility. The water
path will become more complicated each time the water branches into a specific system. Follow
each system in turn and you will have covered the complete flow of water through the facility.
Item No.
Item Status Comments /
Plan to Resolve
1 Field Walkthroughs
1.1 Has the pre-meeting at site been completed? Y
1.2 Were all necessary site staff available? Y
1.3 Have follow-up discussions with staff not available
during the site visit been scheduled and completed? N/A
1.4 Have all the system walkthrough checklists been
completed? Y
1.5 Have all actions arising from the site meeting and
system walkthroughs been documented and
communicated to the person responsible for the action?
Y
1.6 Has the draft project report been reviewed by all
contributors? N/A Will be completed following site visit
1.7 Has the final report been approved for issue? N/A Will be completed following site visit
1.10 Has the final report been distributed? N/A Will be completed following site visit
5. Mussel Vulnerability Evaluation - Project Team Contact List
Project Name: Imperial Dam and Desilting Works , Boulder Canyon Project - All-American Canal System , MTAO
Project Lead: Kubitschek & Willett Some suggestions for the roles of the various team members and the skills or knowledge that would be helpful for each team member are contained in Appendix A.
Name Title Location Office Phone & E-mail
Fred Nibling Research Botanist
Reclamation, TSC – Ecological Research and Applications Group, Denver, CO
(303) 445-2202 [email protected]
David Tordonato
Materials Engineer
Reclamation, TSC –Materials Engineering and Research Laboratory, Denver, CO
(702) 494-2216
Frank Macaluso Civil Engineer Reclamation, LC Region, YAO, Yuma, AZ
Nick Heatwole Natural Resources Specialist
Reclamation, LC Region, YAO, Yuma, AZ
28
6. Mussel Vulnerability Evaluation – Sample Facility Deliverables List
Facility Name: Imperial Dam and Desilting Works , Boulder Canyon Project - All-American Canal System , MTAO
The deliverables are internal document packages prepared for each system or major structure. Once all deliverables are completed, they are then used to prepare the overall assessment report which would be the only external deliverable. It will be helpful when preparing this list to refer to Appendix D for additional detail about typical systems and components at risk that should be considered.
Major Structure or System
Reference drawings Used Deliverables
Dam & Appurtenances No dwgs provided at time of site visit
Continue with systems or structures until all areas in contact with raw water are covered.
29
System Walkthrough Checklist
System or Structure Name:
Imperial Dam and Desilting Works , Boulder Canyon Project - All-American Canal System , MTAO
Prepared by: Kubitschek & Willett Date of Preparation: 8/18/2011
1. Instructions for Using this Document Prepare one of these sheets for each system or major structure identified in the Deliverables list. For each Item No. below, complete all blank fields (see footnotes for Status and At Risk of Mussels columns).
For some of the components such as valves and strainers there may be several in one system. If more than one component needs to be considered add an extra sheet for that particular component group.
Refer to Appendix C for additional information and suggestions about various systems and components.
Add additional rows as required where you identify items that need to be considered and are not covered elsewhere in the list.
2. Walkthrough Checklist Item No.
Item Status 3
At Risk
(yes/no) Comments
1 General for Dams, Reservoirs, Aqueducts
1.1 Are there any membranes, control joints, permeable
construction media, drains, etc. that will let raw water
pass?
Y Y Structural drainage system – formed drains
Potential impacts to drainage systems are
currently unknown
1.2 Are there any air vents? N N None noted during site visit
1.3 Check if the spillway and appurtenances are always
wet or dry and record duration of dry period. Uncontrolled spillway which may remain
wet.
1.4 How much does the water level (i.e. reservoir water
surface elevation) fluctuate? Approximately 1 ft annually
1.5 Are all potential water seepage paths inspected on a
regular basis? Y Y
2 Water Intake Structures
2.1 Types of intake structures present (more than one may
be present):
2.1.1 Open Canal Direct into Facility (concrete) N
2.1.2 Open Canal Direct into Facility (other material-specify)
N
2.1.3 Forebay (specify lining material) N
2.1.4 Tower (specify construction material) N
2.1.5 Submerged Tunnel or pipe intake (specify construction material)
N
2.1.6 Penstock intakes (specify construction material)
N/A
2.1.7 Fish Barriers N/A
2.2 Is the floor of any intake structures likely to be covered
with silt or sediment? N
2.3 Are any structures duplicated to provide a back up? N
2.4 What is the flow velocity range in the structure?
2.5 Is the structure accessible for inspection or
maintenance? N
3 Enter one of the following: C (Complete), P (Partially Complete), A (Absent); Y (Yes), N (No); NA (Not Applicable)
30
2. Walkthrough Checklist Item No.
Item Status 3
At Risk
(yes/no) Comments
2.6 Are there any shutdowns to provide easy access and
what is their frequency? N
2.7 Are there scheduled maintenance cycles and what are
their frequencies? Y
3 Trash Racks, Grates, Screens
3.1 Record spacing, size and material of trash rack bars. 2.5-in spacing for outlet works intake
structure on the AAC, 4.625” spacing on
Arizona side
3.2 Are trash racks fixed or easily removable for
maintenance? Removable
3.3 Is there a planned maintenance frequency for the trash
racks? If so what is interval?
3.4 Is there a trash rake or other style of cleaning system? Y Automated trash rake
3.5 Are the rake fingers sufficiently large to remove
mussels from sides of trash rack bars? N Some mussel removal is possible but
complete mussel removal is unlikely.
3.6 Record location, material, size and grid spacing of any
small intake grates. N/A
3.7 Are grates fixed or removable for easy maintenance? N/A
3.8 Check if grates at bottom of pipes or channels get
covered with silt or sediment. N/A
3.9 Record location, material, size and grid spacing of any
screens. N/A
3.10 Are screens fixed or removable for easy maintenance? N/A
4 Wells and Sumps
4.1 Location and material of constructions of wells. N/A Sump wells present in sludge piping.
Drainage well is present in West Pond
4.2 Identify level fluctuations in pump wells.
4.3 Distance of pump suction from bottom of wells. Will
pump ingest shells that are transported along the floor
into the well?
Y
4.4 Location and material of constructions of sumps.
4.5 Is there a float or other instrumentation in sump that
could become covered with mussels? Y
4.6 Frequency of sump inspection by plant staff.
5 Pumps and Turbines
5.1 Is pump motor or turbine generator water or air
cooled? Water cooled motors are at risk. N/A
5.2 Can mussel shells get into wear ring gaps? N/A
5.3 Does pump have a mechanical seal? N/A
5.4 How is the seal flushed during start-up? N/A
5.5 How is the seal flushed during normal running? N/A
5.6 Does the turbine or pump have a stuffing box? N/A
5.7 Is there a stuffing box lantern ring or other cavity for
cooling and flushing water? N/A
5.8 How is the ring flushed during start-up? N/A
5.9 How is the ring flushed during normal running? N/A
5.10 Check if the motor bearings have water cooled
lubrication? N/A
5.11 Check if the pump has water cooled bearings? N/A
31
2. Walkthrough Checklist Item No.
Item Status 3
At Risk
(yes/no) Comments
5.12 Can mussel shells get into the water lubricated bearing
passages? N/A
5.13 Do seal or stuffing box cavities have a means of
monitoring or inspection? N/A
5.14 Can seals or stuffing box be cleaned without removing
motor? N/A
6 Piping
6.1 Identify materials of construction for piping. N/A
6.2 What is flow velocity range in piping? N/A
6.3 How much time is velocity above 6 ft/sec? N/A
6.4 How much time is velocity below 6 ft/sec? N/A
6.5 Are there any offsets or changes in pipe diameter? N/A
7 Instrument Tubing and Instruments
7.1 Identify any small diameter lines (2” diameter or less)
including material of construction such as: Y N Service water tap is run off of well water.
7.1.1 Flow measurement taps Y
7.1.2 Piezometer taps Y
7.1.3 Pressure taps N
7.1.4 Sample lines N
7.1.5 Pressure balance lines N
7.1.6 Other – Outlet works acoustic flowmeter N
Other – Reservoir El. gauge Y
8 Heat Exchangers
8.1 Identify material of construction of plenum. N/A
8.2 Identify material of construction of tubing. N/A
8.3 What is diameter of tubing? N/A
8.4 What is flow velocity range in tubing? N/A
9 Valves
9.1 Identify all normally open (NO) valves. N/A
9.2 Can NO valves fail to seal properly if valve seat or
valve face becomes mussel coated? N/A
9.3 Identify all normally closed (NC) valves N/A
9.4 Can NC valves fail to open if valve face becomes
coated with mussels? N/A
9.5 What is throat diameter of valve? Is it small enough to
become plugged by mussel shells? N/A
10 Strainers and Filters
10.1 Identify the style of strainer, material of construction of
strainer body and basket as well as the size of the basket pores. Typical styles are:
N/A
10.1.1 Fixed In-line strainer N/A
10.1.2 Duplex strainer N/A
10.1.3 Self-cleaning strainer N/A
10.1.4 Wye (Y) strainer N/A
10.1.5 Other type - specify N/A
32
2. Walkthrough Checklist Item No.
Item Status 3
At Risk
(yes/no) Comments
10.2 Identify the style of filter, material of construction of
body and filter element, as well as the size of the filter
pores. Typical styles are:
N/A
10.2.1 Self-cleaning filter N/A
10.2.2 Replaceable cartridge filter N/A
10.2.3 Other type - specify N/A
33
Appendix B
Management Options for Quagga & Zebra Mussel Infestations
Concurrent with Prevention & Public Outreach/Education Actions
Most water bodies in the western United States are now at risk of infestation by invasive quagga and
zebra mussels. While the actions taken to prevent or respond to infestation must be tailored to each
specific location, the following activities represent options for consideration as part of any readiness
planning as well as options for dealing with mussels following detection. Information on preventing the
spread of invasive mussels can be found at the 100th Meridian Initiative website http://100thmeridian.org/
and http://protectyourwaters.net. Procedures have also been developed by Reclamation and are documented in Technical Memorandum
No. 86-68220-07-05 Inspection and Cleaning Manual for Equipment and Vehicles to Prevent the Spread
of Invasive Species which provides guidance for inspecting and cleaning vehicles and equipment to help
prevent the spread of invasive species during Reclamation activities. The manual can be found at
http://www.usbr.gov/mussels/prevention/docs/EquipmentInspectionandCleaningManual2010.pdf
Actions to consider prior to detection of mussels:
1. Develop Coordinated Response Plan(s) - This plan would detail policies, command and
authority structure, strategies, communications, roles and responsibilities, and response actions to be
implemented – Involves multiple federal, state, and local agencies and stakeholders. An example
Response Plan for the Columbia River Basin may be found at the 100th Meridian website
http://www.100thmeridian.org/ColumbiaRT.asp. The National Parks Service also has information and
guidelines for prevention and response planning that can be found at
http://www.nature.nps.gov/biology/Quagga/index.cfm.
2. Perform Infestation Risk Assessment(s) – This activity may be completed as standalone or as
part of the Coordinated Response Plan. The purpose is to identify which water bodies are most at-risk
of infestation within the geographic region of interest or management jurisdiction. The likelihood of
infestation is typically based upon recreational usage, nearest known infestation, and the extent to
which environmental conditions (including calcium, pH, dissolved oxygen, temperature, etc…) are
likely to support mussel establishment. This information can be used to prioritize facility vulnerability
assessments (below). A variety of examples for risk assessments are available on the web.
Information specific to environmental suitability based risk assessments is available at the U.S. Army
Corps of Engineers Zebra Mussel Information System (ZMIS) website
http://el.erdc.usace.army.mil/zebra/zmis/zmishelp.htm.
3. Perform Facility Vulnerability Assessment(s) – This activity may be completed as standalone
or following the infestation risk assessment(s) and consists of a detailed inventory of critical water
related infrastructure at a water body and how each component is likely to be affected by mussels
should infestation occur. The results can be used to prioritize facility protection needs and actions. A
facility vulnerability assessment template can be found at www.usbr.gov/mussels/.
34
4. Implement Monitoring Program(s) – Monitoring programs should be considered for high
priority water bodies where infestation is either most likely or would cause significant harm to water
systems or other key resources. Monitoring programs, designed to provide early detection of mussel
larvae (through water sampling and lab analysis), potentially provide 2-5 years of lead time for
planning and implementing protective actions before the infestation impairs operations via adult
settlement on hydraulic structures or within critical systems. Additional information on monitoring
can be found at the U.S. Army Corps of Engineers Zebra Mussel Information System (ZMIS) website
http://el.erdc.usace.army.mil/zebra/zmis/zmishelp.htm.
Actions to consider following detection of mussels:
1. Execute Coordinated Response Plan – Involves notification, information exchange, and
implementation of containment and control actions (i.e., components of the response plan).
2. Increase Monitoring – Transition from monitoring for detection to monitoring with increased
frequency to confirm detection, identify or locate the presence of adults, and track infestation levels.
This activity may also include regular facilities inspections to determine when facilities are being
impacted by adult colonization. This information can guide facilities protection actions and assists in
anticipating ecological impacts for future mitigation planning.
3. Identify and Implement Appropriate Facilities Protection Measures – Identify which
actions or technologies are best suited for maintaining water operations and reducing O&M costs or
other expenses. Various conventional technologies have been used with reasonable success. The
table below provides some conventional as well as experimental options, each of which has
advantages and disadvantages. It should be noted that there are a number of commercial treatment
products that have not been listed, but may be applicable in various situations.
Table 1 – Control and facilities protection options for various applications
Technology Example Applications
Filtration to prevent mussel entry to piped
systems – self-cleaning 40-80 micron filters may
be adequate depending on exclusion requirements.
Exclusion avoids the need for treating infested
systems. †
Low volume systems - Facilities service
water, unit or transformer cooling water,
HVAC, pumped systems, and delivery
pipelines
Ultraviolet (UV) Treatment of water in piped
systems – In-line UV systems are being evaluated
to prevent mussel settlement. UV has additional
water treatment benefits and is not expected to
require discharge permitting †
Low volume systems - Facilities service
water, unit or transformer cooling water,
HVAC, pumped systems, and delivery
pipelines
Chemical Treatments – Injection or delivery of
chemicals (oxidizing and nonoxidizing) to kill
mussels or impair ability to attach to surfaces
Bromine
Chlorine
Chlorine dioxide
Low and medium volume systems - Facilities
service water, unit or transformer cooling
water, HVAC, pumped systems, and delivery
pipelines. Permitting often required for
chemical treatment methods
35
Hydrogen peroxide
Ozone
Potassium salts
Potassium permanganate
Sodium Hypochlorite
Salinity
Alternative Treatments – Alternatives to kill
mussels or impair ability to attach
Thermal
Biological †
Desiccation
Low and medium volume systems – Facilities
service water, unit or transformer cooling
water, HVAC, pumped systems and delivery
pipelines. Desiccation requires capability to
dewater system for extended durations
Coatings to protect exposed surfaces – Prevents
mussel attachment or facilitates cleaning (anti-
fouling & foul-release) †
Hydraulic Structures & Equipment - Gates,
valves, penstocks, intake structures,
trashracks, fish screens
Alternative Materials – To prevent mussel
attachment or facilitate cleaning
Copper
Galvanizing (requires high zinc content)
Intake grating, piping/tubing, heat exchangers,
HVAC systems
Mechanical Removal – For routine maintenance
Mechanical raking/scraping
Hydrojetting/water spraying
Pipeline pigging
Traveling intake screens (self-cleaning)
All structures, systems, equipment, and
instrumentation where access is possible –
Diversion structures, pipelines, trashracks,
intakes, fish screens. For instrumentation,
noncontact methods should be considered
where possible
Redundant Systems – Multiple intakes or
duplicate systems for switching during treatment or
cleaning to provide uninterrupted service
All systems for which retrofit is
possible/practical
† - Experimental - Under development or being field tested/demonstrated
Technologies selection for each application depends on a number of considerations including periodic
or continuous mussel exclusion requirements, operations and maintenance requirements, permitting
requirements, environmental impacts, and cost; to name a few. If conventional technologies are not
applicable then alternatives should be developed and demonstrated as early as possible to meet unique
facilities requirements. Operational strategies may also be available to reduce or eliminate mussel
impacts. However, such strategies are often limited depending on the type of system and available
flexibility. Additional information on control strategies and facilities protection methods may be
found in The Practical Manual for Zebra Mussel Monitoring and Control, R. Claudi & G.L. Mackie,
CRC Press, Inc. (2000) and at the U.S. Army Corps of Engineers Zebra Mussel Information System
(ZMIS) website http://el.erdc.usace.army.mil/zebra/zmis/zmishelp.htm
4. Identify Ecological Impacts – Involves developing and initiating actions to measure and track
ecological changes, develop mitigation plans, and implement long-term mitigation actions (considers
endangered species, food webs, aquatic weeds, water quality, etc…)