Project A: Streamflow, Water Quality, and Sediment Transport and Budgeting in the Colorado River Ecosystem
The primary linkage between Glen Canyon Dam operations and the characteristics of the
physical, biological, and cultural resources of the Colorado River ecosystem (CRe) downstream
from Glen Canyon Dam is through the stage, discharge, water quality, and sediment transport of
the Colorado River. This project makes and interprets the basic measurements of these
parameters at locations throughout the CRe. The data collected by this project are used to
implement the High-Flow Experiment (HFE) Protocol (i.e., trigger and design HFE
hydrographs), to evaluate the reach-scale sand mass-balance response to the HFE Protocol (U.S.
Department of Interior, 2011; Grams and others, 2015), and to evaluate the downstream effects
of releases conducted under the Long-Term Experimental and Management Plan (LTEMP)
Environmental Impact Statement (EIS) (U.S. Department of Interior, 2016a, b).
The data collected by this project are also used by many of the other physical, ecological, and
socio-cultural projects funded by the Glen Canyon Dam Adaptive Management Program
(GCDAMP). In addition to supporting the LTEMP sediment goal, the basic data collected by this
project supports the following nine LTEMP goals: aquatic food base, archaeological and cultural
resources, humpback chub, hydropower and energy, invasive fish species, natural processes,
rainbow trout fishery, recreational experience, and riparian vegetation. Most of the project funds
support basic data collection at USGS gaging stations, with the remainder funding data
interpretation. Roughly 64% of the proposed budget covers basic data collection, with the
remaining 36% supporting salaries for serving the data and for interpretive work (i.e.,
publications). The funds requested under this proposal cover ~75% of the costs required to
collect data at the network of U.S. Geological Survey (USGS) gaging stations used by this
project. An additional $203,000 to support this network is provided directly to the USGS
Arizona Water Science Center from funds appropriated by Congress for the USGS, the Bureau
of Reclamation, and the Bureau of Land Management, and from funds provided by the Arizona
Department of Environmental Quality (AZDEQ), the Navajo Nation, and Peabody Energy.
Project A is designed to provide measurements of stage (i.e., water-surface elevation), discharge
(i.e., streamflow), water quality, and suspended sediment at sufficiently high temporal
resolutions (~15-minute) to resolve changes in these parameters and to allow accurate
determination of suspended-sediment loads for use in sediment budgeting (Grams and others,
2019; Topping and others, in press). The proposed monitoring under this project is similar to that
conducted over the last 18 years. Work conducted under the previous workplan, currently
provisionally accepted at the Journal of Geophysical Research pending minor revision, indicates
that sand storage in the channel and sandbars of the CRe is not likely sustainable unless tributary
sand inputs remain well above average and dam releases remain slightly below average. The
work proposed in this current workplan is therefore that required to address this important
conclusion.
Project B: Sandbar and Sediment Storage Monitoring and Research
The purposes of this project are to: 1) track the effects of individual HFEs on sandbars and
campsites (funded), 2) monitor the cumulative effect of successive HFEs and intervening dam
operations on sandbars (funded) and sand conservation (partially funded), 3) investigate the
interactions between dam operations, sand transport, and channel dynamics (funded as Project
O.2), and 4) develop predictive models for streamflow and sandbar changes that can be used for
evaluating dam operations scenarios (not funded).
One of the stated goals in the Record of Decision (ROD) for the LTEMP (U.S. Department of
the Interior, 2016) is to "increase and retain fine sediment volume, area, and distribution...for
ecological, cultural, and recreational purposes." Expectations of improved deposition on
sandbars and conservation of sediment were among the criteria used in the selection of the
preferred alternative. One of the central components of the selected alternative is the continued
implementation of HFEs for building sandbars. The LTEMP extended the program initiated with
the Environmental Assessment for Development and Implementation of a Protocol for HighFlow Experimental Releases from Glen Canyon Dam (HFE Protocol; U.S. Department of the
Interior, 2011) which asked the question, "Can sandbar building during HFEs exceed sandbar
erosion during periods between HFEs, such that sandbar size can be increased and maintained
over several years?" In other words, does the volume of sand aggraded into eddies and onto
sandbars during controlled floods exceed the volume eroded from sandbars during intervening
dam operations? In addition, condition-dependent experiments were included in the preferred
alternative, with objectives related to sandbar building and sediment conservation. Project B
includes elements that are designed to evaluate whether the sediment-related goals of the
LTEMP are met (partially funded), provide the information that is needed to proceed with or
abort LTEMP experimental activities (funded), evaluate the effectiveness of implemented
experiments (funded), and develop predictive models for future planning efforts (not funded).
The sandbar monitoring program described here was outlined in the LTEMP Science Plan and
provides the data required to answer the fundamental question of the HFE Protocol and LTEMP
by monitoring changes in sandbars over many years, including a period that contains several
controlled floods. The program is a continuation of the monitoring implemented in previous
work plans and is based on annual measurements of sandbars, using conventional topographic
surveys supplemented with daily measurements of sandbar change using ‘remote cameras’ that
autonomously and repeatedly take photographs. These annual measurements and daily
photographs are included in Project Element B.1 (funded). Because these long-term monitoring
sites represent only a small proportion of the total number of sandbars in Marble and Grand
canyons, Project Element B.2 (partially funded) includes periodic measurements of nearly all
sandbars within individual 50 to 130 km sediment budget reaches (see Project A for description
of sediment budget reaches).
The other critical information that is needed to evaluate the outcome of the HFE Protocol and the
LTEMP is the change in total sand storage in long river reaches. HFEs build sandbars by
redistributing sand from the low-elevation portion of the channel to sandbars in eddies and on the
banks. The sand available for deposition is the sand that is in storage on the channel bed, which
is the sum of the sand contributed by the most recent tributary inputs, any sand that may have
accumulated since Glen Canyon Dam (GCD) was completed, and any sand that remains from the
pre-dam era. The goal of the HFE Protocol is to accomplish sandbar building by mobilizing only
the quantity of sand most recently contributed by the Paria River, thereby preventing depletion of
pre-dam era sand. For this reason, conservation of sand was one of the criteria used to evaluate
and select the preferred alternative in the LTEMP ROD. Measured trends in sand storage along
the channel bed combined with trends in exposed sandbars will provide the necessary
information on which to base future decisions about dam operations and other potential
management options. If sand storage is maintained or increased, we expect the response to future
HFEs to be similar or better than that observed following recent HFEs. In contrast, depletions of
fine sediment in the active channel are potentially irreversible if sand supply from tributaries is
consistently less than downstream transport. This situation would threaten the long-term ability
to maintain sandbars. These long-term trends are measured in Project Element B.2 (partially
funded), which includes two channel mapping campaigns. In 2021, we propose collecting a
baseline map for the segment between RM 87 and RM 166, which has never been mapped. In
2023, we propose making a repeat map in Upper Marble Canyon to collect data that will be used
in the 10-year assessment of LTEMP to be completed in future work plans, however this field
work is not supported in the current project budget. Project Element B.3 includes work on the
control network in support of this project, the remote sensing overflight project, and other work
plan projects.
Project B also includes two research components and several experimental components. The first
research component is proposed to investigate river channel adjustment to HFEs and
redistribution of reservoir delta sediment on the Colorado River within the CRe in western Grand
Canyon. This project was initially proposed as Project Element B.4 but is now included in this
draft of the work plan as Project Element O.2 (experimental fund). Project Element B.5 (not
funded) is a modeling project to produce flow models that predict the inundation extent and flow
velocities for dam operations and HFEs in Marble Canyon and improve capabilities for
predicting sandbar response to dam operations. Although this element is not supported in the
current budget, we will attempt to make progress on modeling objectives if other funding sources
are found. Project Element B.6 (experimental fund) describes studies that will be conducted to
monitor and evaluate the condition-dependent experiments that affect sandbars and sediment
resources, including extended duration HFEs, proactive spring HFEs, and variations in HFE
downramp rate.
Project C: Riparian Vegetation Monitoring and Research
Riparian vegetation affects physical processes and biological interactions along the river channel
downstream of GCD in ways that are integrally linked to flow regime. Reduced peak flows and
increased base flows resulting from GCD operations have promoted riparian vegetation
expansion close to the river (Sankey and others, 2015), but favor some species over others. Daily
fluctuating flows have been shown to decrease germination and growth of riparian plants
(Bejarano and others, 2020; Gorla and others, 2015) and is likely impacting the species
composition in the CRe. Flow patterns designed to enhance other important resources, such as
HFE’s, have a collateral impact on riparian vegetation cover and composition (Kennedy and
Ralston, 2011; Ralston, 2011; Rood and others, 2005). Changes to species proportions and cover
result in altered ecosystem functions, since riparian plant species differ in their structure (e.g.,
tall trees vs. short grasses), morphological traits (thorns, leaf size), and function (shade, soil
stabilizer) (Butterfield and others, 2020; Merritt and Bateman, 2012). Through vegetation
changes, dam operations can impact wildlife habitat (Ralston, 2005), sediment scour and
deposition (Butterfield and others, 2020), visitor experience (Hadley and others, 2018), cultural
resources (Cook and others, 2019), and many other natural processes.
The purpose of this project is to monitor the status and trends of riparian vegetation, examine
mechanisms behind trends in riparian vegetation change as they relate to LTEMP flows, and
apply existing and new knowledge to LTEMP vegetation management. The four elements of this
project assess riparian vegetation status in the CRe (Element C.1, partially funded), test
mechanisms by which flow regime impacts species of interest (Element C.2, fully funded),
synthesize data to anticipate changes to vegetation (Element C.3, fully funded), and assist nonflow management actions directed by the LTEMP (Elements C.2, C.3, C.4; fully funded, Figure
1). For a description of budget cuts to Project C, see section 8. Elements and Activities Proposed,
but not Funded in the Work Plan.
Project D: Effects of Dam Operations and Vegetation Management for Archaeological Sites
The construction and subsequent 50+ years of operation of GCD has profoundly altered the
downstream aquatic and terrestrial ecosystem of the Colorado River corridor in lower Glen
Canyon, Marble Canyon, and Grand Canyon. Among many effects, dam construction and
operation have affected geomorphic processes responsible for the formation and preservation of
the Holocene age, fluvially-derived sediment deposits in which numerous archaeological sites
and other resources of cultural importance are embedded. The affected archaeological resources
are valued not only for their information potential to archaeologists, but also as the homes and
resting places of the ancestors of several Native American Tribes who reside in the region today.
They are also valued as tangible records of indigenous peoples’ tenure in this landscape.
Other resources of cultural value in the CRe include the plants that grow on the Holocene
deposits, the birds that nest in the vegetation, the reptiles and mammals that inhabit the riparian
zone, as well as the myriad kinds of aquatic life that live in the river. This project focuses
specifically on studying and documenting the dam’s effects to the terrestrial riparian
environment of the CRe and its associated archaeological resources, while recognizing the
linkages this work has for other culturally valued resources as well.
During the past three decades, researchers affiliated with the USGS and various academic
institutions have monitored and researched GCD effects on cultural resources in the CRe,
including specifically the dam’s physical effects on archaeological sites. While it is recognized
and acknowledged that the dam and its operation are not the only sources of change affecting the
CRe and associated archaeological sites, this project focuses on researching and monitoring dam
effects, in keeping with the mandates of the Grand Canyon Protection Act (GCPA).
Furthermore, while it is also recognized and acknowledged that Native American Tribes
affiliated with Grand Canyon view the effects of dam operations as being broader than just
physical impacts to the ecosystem, and they believe that dam effects can potentially include
impacts to traditional spiritual values as well as indigenous societies more generally, this project
focuses on impacts which are amenable to investigation by scientific methods, with the
understanding that those impacts which are not amenable to scientific investigation are best
identified and addressed by the specifically-affected cultures at risk.
From a physical perspective, GCD has reduced downstream sediment supply to the Colorado
River by about 95% in the reach upstream of the Little Colorado River confluence and by about
85% downstream of the confluence (Topping and others, 2000). Operation of the dam for
hydropower generation has additionally altered the flow regime of the river in Grand Canyon,
largely eliminating pre-dam low flows (i.e., below 5,000 ft3/s) that historically exposed large
areas of bare sand (U.S. Department of the Interior, 2016a; Kasprak and others, 2018). At the
same time, the combination of elevated low flows coupled with the elimination of large,
regularly-occurring spring floods in excess of 70,000 ft3/s has led to widespread riparian
vegetation encroachment along the river, further reducing the extent of bare sand (U.S.
Department of the Interior, 2016a; Sankey and others, 2015). Kasprak and others (2018) report
that the areal coverage of bare sand has decreased by 45% since 1963 due to vegetation
expansion and inundation by river flows. Kasprak and others (2018) forecast that the areal
coverage of bare sand in the river corridor will decrease an additional 12% by 2036.
The changes in the flow regime, reductions in river sediment supply and bare sand, and the
proliferation of riparian vegetation have affected the condition and physical integrity of
archaeological sites and resulted in erosion of the upland landscape surface by reducing the
transfer (termed “connectivity”) of sediment from the active river channel (e.g., sandbars) to
terraces and other river sediment deposits in the adjoining landscape (U.S. Department of
Interior, 2016a; Draut and Rubin, 2006, 2008; Draut and others, 2008, 2010; Draut, 2012; East
and others, 2016, 2017; Kasprak and others, 2018; Sankey and others, 2018a, b; Cook and
others, 2019). Many archaeological sites and other evidence of past human activity are now
subject to accelerated degradation due to reductions in sediment connectivity under current dam
operations and riparian vegetation expansion which are tied to regulated flow regimes (U.S.
Department of the Interior, 2016a; East and others, 2016, 2017; Cook and others, 2019).
The GCD Long-Term Experimental and Management Plan Environmental Impact Statement
(LTEMP EIS) predicts that conditions for achieving the goal of preservation for archaeological
resources, termed “preservation in place,” will be enhanced as a result of implementing the
selected alternative (U.S. Department of Interior, 2016a). HFEs are one component of the
selected alternative that will be used to resupply sediment to sandbars in Marble and Grand
canyons, which in conjunction with targeted vegetation removal, is expected to resupply more
sediment via wind transport to archaeological sites, depending on site-specific riparian
vegetation and geomorphic conditions. However, HFEs have been shown to directly erode
terraces that contain archaeological sites in Glen Canyon National Recreation Area (GLCA; East
and others, 2016; U.S. Department of Interior, 2016a).
HFEs have also been shown by Sankey and others (2018b) to rebuild or maintain sandbars that
provide sand to resupply aeolian dunefields containing archaeological sites throughout Marble
and Grand canyons. Aeolian dunefields were resupplied with sand at deposition of rates of 2-8
cm per year from HFE deposits in half of the flood-site instances monitored after the 2012, 2013,
2014, and 2016 HFEs (Sankey and others, 2018b). Sankey and others (2018b) also found
evidence for cumulative increases in sediment resupply of dunefields when annual HFEs are
conducted consistently in consecutive years.
Project E: Controls on Ecosystem Productivity: Nutrients, Flow, and Temperature
Aquatic primary production is an important energy source for riverine food webs, converting
sunlight, carbon dioxide and water into simple carbohydrates via photosynthesis. In the Colorado
River downriver of Glen Canyon Dam, fish are food limited (Cross and others, 2011) and energy
(carbon) produced within the river is a preferred food source relative to energy from tributaries
and riparian inputs (Wellard Kelly and others, 2013). Aquatic primary production, and the
aquatic insect community this production supports, is the main source of fish production in Glen
Canyon throughout the year (Cross and others, 2011). Primary producers (specifically diatoms)
are also a preferred food source downstream, although the role of non-algal (tributary/terrestrial)
carbon sources can also be an important driver of the food availability during flood pulses such
as occur during monsoon season (Cross and others, 2011; Wellard Kelly and others, 2013; Sabo
and others, 2018).
There are several lines of evidence that link both nutrient concentrations and primary
productivity to higher trophic levels throughout the Colorado River. Outside of periods when
tributaries are flooding for extended periods, the availability of aquatic insect drift and the
condition of native fish are positively related to seasonal rates of gross primary production (GPP)
near the LCR, highlighting the important role for aquatic primary production even 120 km
downstream of the dam (Deemer, 2020). Primary production at Diamond Creek (235 km
downstream of the dam) also appears linked to juvenile production of flannelmouth suckers, the
most common species in this area, further highlighting the importance of in situ production to
fish communities in the western canyon (Yackulic, 2020). While total primary production is not
significantly related to metrics of fish production in Glen Canyon, the availability of phosphorus
(P), an important limiting nutrient, is correlated with chlorophyll a, a metric of diatom and other
non-macrophyte-based primary production. Furthermore, P predicts rainbow trout recruitment
better than flow-based metrics used to predict recruitment for the LTEMP EIS (U.S. Department
of Interior, 2016; Yackulic, 2020).
Understanding the controls on Colorado River primary production is an important step towards
better managing the aquatic food base. Disentangling the drivers of both rates and types of
riverine primary production, and their link back to fish production, is particularly challenging
given interactive and delayed effects and given different levels of information on the potential
drivers. For example, monsoonal storm pulses that place temporary light availability constraints
on rates of primary production (Hall and others, 2015) may also be delivering significant
amounts of phosphorus to the mainstem. In a second example, at times of high phosphorus
outflow from Glen Canyon Dam, elevated production of a dominant food source, diatoms, may
suppress macrophyte production (via shading) obscuring the link between overall productivity
and higher trophic levels.
This project aims to disentangle some of these drivers by combining the highly resolved longterm
information about riverine turbidity, silt and clay concentrations, solar inputs, discharge,
and gross primary productivity (via continuous oxygen and temperature measurements – data
that are collected as parts of the Interagency Lake Powell Water Quality Monitoring project
(Appendix 1), Project A.2, and Project E) with improved additional information about
phosphorus, gas transfer and the relative role of diatoms in affecting whole river production
(Elements E.1 and E.2). Project E is designed to capture and link changes in productivity to
changes in bottom-up drivers such as light, flow, and nutrients and to further develop links
between these bottom-up drivers and higher trophic levels.
Key to linking primary production to higher trophic levels is developing a better understanding
of how much production is required to meet fish metabolic demands. This understanding will
help us to develop ecosystem models that incorporate data collected at multiple trophic levels
(Element E.3). Element E.3 involves both laboratory work and ecosystem modeling. Laboratory
work will quantify the standard and active metabolic rates of the dominant native fishes in the
ecosystem (i.e., humpback chub and flannelmouth sucker). Past bioenergetics work done in the
2000s (Petersen and Paukert, 2005; Paukert and Petersen, 2007) assumed humpback chub had
metabolism like other Gila spp. because it has never been directly measured in humpback chub.
However, recent observations in both the lab and the field suggest that humpback chub may have
abnormally low metabolisms that enable them to persist through periods of food shortage (e.g.,
Dibble and others, 2017). By estimating these standard and active metabolic rates and absolute
fish population abundances for Colorado River reaches, we can determine how much carbon
(i.e., energy) is being consumed and how this relates to the amount of carbon produced by
primary production through an ecosystem model.
Project F: Aquatic Invertebrate Ecology
The primary focus of Project F is continuation of long-term monitoring needed to track
ecosystem response to “Bug Flows” and other LTEMP experiments. Research by our group has
demonstrated that the scarcity of mayflies, stoneflies, and caddisflies from the Colorado River is
partly due to acute mortality of insect eggs arising from hourly changes in discharge associated
with hydropower generation (Figure 1). In May–August 2018–2020, Glen Canyon Dam
operations were experimentally modified to try to increase the production and diversity of
aquatic insects in the CRe. These experimental Bug Flows involved hourly flow fluctuations for
hydropower generation during weekdays, coupled with steady, low flows on weekends to reduce
aquatic insect egg desiccation and mortality. In FY2021-23, our group will track ecosystem
response to the Bug Flows experiment and other ongoing or potential management actions using
citizen science monitoring of aquatic insects (F.1), monitoring of invertebrate drift (F.1 and F.2),
monitoring of invertebrate communities in Bright Angel Creek in response to fisheries
management actions (F.3), through diet and stable isotope analysis of fish feeding habits (F.4),
and through monitoring and research associated with spring flow disturbances (O.1).
Research and monitoring of invertebrates described in Project F also provides essential context
and data that are used by other projects. For example, invertebrate monitoring data are used by
Project E (controls on ecosystem productivity) to identify the extent to which changing nutrient
levels are propagating up through the food web. Invertebrate monitoring data also aid
interpretation of seasonal and annual trends in humpback chub (Project G) and rainbow trout
(Project H), because aquatic invertebrates represent the food base for both species of fish. Project
F also integrates and uses data from other projects, particularly Project A (streamflow, water
quality, and sediment transport), to identify how changing environmental conditions affect
invertebrate populations.
Project G: Humpback Chub Population Dynamics throughout the Colorado River Ecosystem
During FY2021-23, we will continue monitoring activities mandated by the 2016 Biological
Opinion (BiOp; USFWS, 2016) associated with the LTEMP EIS (U.S. Department of the
Interior, 2016), while focusing research on improving our understanding of abundance and the
drivers of humpback chub population dynamics throughout the lower CRe. In the proposed
budget, mark-recapture research in western Grand Canyon (G.6) would cease in FY2023,
making it less likely that we would determine drivers of chub dynamics there (missing an
opportunity to learn about this population while it is still thriving and potentially failing to meet a
conservation measure). However, the TWG recommended that this project be funded in FY2023
by prioritizing savings and carry-over for continuation of Project Element G.6.
The LCR-spawning portion of the population has been a stronghold for humpback chub since
emplacement of Glen Canyon Dam in the 1960s. This portion of the population experienced a
decline in the late 1990s and early 2000s but has been stable or increasing ever since then
(Coggins and others, 2006; Van Haverbeke and others, 2013; Yackulic and others, 2018).
However, monitoring of juvenile fish indicates the LCR-spawning portion of the population has
displayed decreased juvenile production since 2012. As a result, we expect adult abundance to
decline in the near term; however, the magnitude of this decline is less certain (Figure 1).
During FY2021-23, we will continue to estimate juvenile production and test hypotheses
regarding drivers of juvenile production. We will also continue to resolve our understanding of
how rainbow trout, temperature, turbidity, and food limitation drive growth, survival, and fish
condition in the mainstem Colorado River.
For many decades, humpback chub that spawned in the LCR formed the vast majority of the
overall CRe population. Since 2014, however, the catch of humpback chub in western Grand
Canyon has been increasing (Van Haverbeke and others, 2017) and it is likely a larger portion of
the overall CRe population is now found in western Grand Canyon. While our understanding of
the drivers of the LCR population has matured in recent years following intensive demographic
studies, we lack a similar understanding for the western Grand Canyon. Available data suggests
that recent increases may be driven by only a few years of high juvenile production. During this
workplan, we will continue studies of chub demography in the western Grand Canyon, which
will allow us to determine baseline rates of growth and survival and allow us to estimate
abundance in this expanding population segment. We are optimistic that we will continue to
learn about drivers of juvenile production and overall chub vital rates with an ultimate goal of
developing predictive models for chub in the western Grand Canyon that are similar to the ones
used in the LTEMP EIS for chub that spawn in the LCR.
To satisfy BiOp Conservation Measures, test hypotheses about drivers, and estimate adult
abundance, we will monitor humpback chub in the LCR-spawning population by sampling the
LCR and juvenile chub monitoring (JCM-east) reach in the Colorado River (G.2, G.3) in all
years. We also will monitor the western Grand Canyon population via continuation of mark
recapture in the Fall Canyon reach (JCM-west) during all three years, if funding can be made
available for FY2023 (G.6), allowing us to continue to meet an objective listed in the BiOp
Conservation Measures. Maintaining JCM-west is particularly important because we will be
discontinuing seining trips (not funded, G.8) in all years of the workplan.
Extensive sampling via the aggregation sampling (G.5) will continue in all 3 years, albeit with
less effort in FY2022 than originally proposed. Mark-recapture data from these trips will be
supplemented with data from autonomous passive integrated transponder (PIT) tag antennas,
such as the LCR multiplexer cross-channel array (MUX) in the LCR and portable antennas, as
these technologies have proven effective at detecting larger adults which are often difficult to
capture using other methods such as hoop netting and electrofishing (G.4). Lastly, since models
developed under the previous workplan suggest that Chute Falls translocations help augment the
LCR-spawning adult population, we propose continuation of Chute Falls translocations and
monitoring by the US Fish and Wildlife Service (USFWS; G.7). We do not currently plan to
analyze otoliths from incidental mortalities of age-0 fish collected over the last few years in the
LCR to improve understanding of hatch dates, which would have helped us understand the
degree to which LCR hydrology effect juvenile production. Data collected from the abovementioned
field efforts will be analyzed to help learn more about humpback chub life history and
to guide management efforts (G.1).
Project H: Salmonid Research and Monitoring
The LTEMP (U.S. Department of Interior, 2016) provides the necessary long-term framework
for assessing specific operations at Glen Canyon Dam (GCD), as well as other types of
management actions conceived during and implemented over the next 20-year period. For this
reason, the Salmonid Research and Monitoring Project was developed having the long view,
with a means to revise and respond to unanticipated and emerging risks (e.g., brown trout). The
study design described in the previous work plan remains relevant for the same management
questions posed in the LTEMP, and likely, other work plans developed in the future. As such,
this type of experimental approach is appropriate for understanding large and complex
ecosystems, particularly when quantifying trout population dynamics. Clearly, population
responses are sometimes confounded by extrinsic factors (e.g., nutrients, see Project E) that act
independent of flows or because of multiple management actions that have been applied
concurrently within a given year (e.g., 2018 ‘Bug Flows’ and fall HFEs).
These circumstances make it difficult for resolving cause and effect relationships in a timely
fashion. Although monitoring programs (e.g., Project Element H.1) are important for
documenting long-term population trends and characteristics such as catch-per-unit-effort, size
distribution, and occurrence and trends, monitoring as a sole method of data collection is not an
effective approach in time or cost for determining causation, particularly when quantifying and
separating out effects from complex interactions that occur among multiple factors (e.g., flow,
fish density, nutrients). In order to study multiple flow treatments and avoid potential
confounding factors, we propose to continue using a seasonal sampling design described in the
FY2018-20 Triennial Work Plan (TWP) with spatial replication to assess trout responses to
experimental flows and other factors within and across years (Project Element H.2).
However, due to budget constraints in the FY2021-23 TWP, we initially proposed decreasing
sampling effort from three Trout Reproductive and Growth Dynamics (TRGD) sub-reaches to
one sub-reach per trip starting in FY2022. Stakeholders raised concerns in the June 23-24, 2020
GCDAMP TWG Meeting about this approach and the loss of information related to the
increasing brown trout population. The TWG requested a revision of the work plan in their
motion to the AMWG, stating they: “Propose AGFD and GCMRC look to integrate work efforts
to allow for an additional TRGD site to be monitored. Cost estimate for going from 1 TRGD to 2
TRGD sites is approximately 67,000.” To accommodate this request from GCDAMP
Stakeholders, (Arizona Game and Fish Department) AGFD and GCMRC are currently in
discussions that will continue over this 3-year work plan to integrate the two programs to the
extent practicable, knowing that both programs will need to compromise to attain this goal given
the budget allotted in the FY2021-23 TWP for trout monitoring and research. Since an integrated
study design will be developed and tested based on discussions over the next year or so, we have
kept the narratives and budgets for Project Elements H.1 and H.2 separate in the final draft of
this work plan for the sake of clarity. Additional details on our initial approach to better integrate
these programs while retaining some of the study objectives for each program are outlined in
Section 5.4.
As a goal, protection of the endangered humpback chub near the LCR is one of the highest
priorities of the GCDAMP, but a concurrent priority is to maintain a high-quality rainbow trout
sport fishery upstream from Lees Ferry in Glen Canyon. As such, rainbow trout were an
important component in the development of LTEMP for GCD operations, and thus were a major
consideration in the flow decisions in the selected alternative in the LTEMP ROD (U.S.
Department of Interior, 2016b). Yet, high trout abundance is not the only factor that limits
humpback chub abundance at the LCR (e.g., temperature, prey, and turbidity) (Yackulic, 2018),
as a population has survived multiple periods of high trout abundance (1998-2001, 2008-2009,
2011-2014, 2017-2019) (Coggins and others, 2011; Korman and Yard, 2020).
Trout Management Flows (TMFs) proposed in the LTEMP were designed to limit rainbow trout
recruitment and dispersal out of Lees Ferry (Korman and others, 2011a; Korman and others,
2011b; Korman and others, 2016; Yard and others, 2016) with a goal of maintaining the balance
between the sport fishery and the humpback chub population downstream. However, ecosystems
are dynamic and there has been a large increase in brown trout recruitment upstream from Lees
Ferry over the past few years (2015-2019).
Given this new development, it is unclear whether the expansion of brown trout will disrupt the
balance between salmonids and endangered native fishes downstream, the rainbow trout fishery
in Glen Canyon, and the degree to which flow manipulations can be used to manage rainbow and
brown trout.
A major component of the proposed study elements, described herein, focus on how
experimental flows will influence recruitment, growth, survival, and dispersal of rainbow trout in
Glen and Marble canyons. However, management of the rainbow trout fishery cannot occur in a
vacuum given the recent increase of brown trout in Glen Canyon. Small numbers of brown trout
have been present in the canyon since the dam was built (Minckley, 1991), but have increased
following a time period associated with frequent fall HFEs (Runge and others, 2018). It is
currently unclear whether this flow relationship is causal or coincidental, but research is needed
to further examine if the proposed flow manipulations help or hinder the expansion of brown
trout.
Other aspects of the flow regime and non-flow factors can also explain recent increases in brown
trout. These include increases in macrophyte abundance due to reductions in diel variation in
flow starting in the early 1990s (McKinney and others, 1999), and warmer water temperatures
due to low reservoir elevations from the persistent 21st century drought may provide a
physiological advantage for brown trout as an apex predator (Korman and others, in review).
However, good comparative studies of temperature tolerances made between rainbow trout and
brown trout are uncommon, and at best thermal differences are nuanced (e.g., prey availability
and prey size).
Brown trout are superior competitors in other tailwater systems and typically are not stocked past
their initial introduction (Dibble, unpublished data), and are known to be voracious predators of
small-bodied native fishes (Yard, 2011). It is therefore prudent and necessary to not only
evaluate the effect of experimental flows on rainbow trout, but also to examine how brown trout
populations may respond to such flow manipulations. Furthermore, competitive interactions
between brown trout and rainbow trout may impact each other’s survival and recruitment rates.
Good growth and condition of rainbow trout occurred in late 2016 and 2017, which contributed
to high rainbow trout recruitment in 2017, and its likely downstream movement. The only year
since 2015 without a substantive catch of age-1 brown trout occurred in 2017, which was also
the year with elevated recruitment of rainbow trout. Therefore, it is possible that a larger or
healthier population of rainbow trout could help keep the brown trout population in Glen Canyon
in check. It could be that higher levels of rainbow trout spawning in winter and spring of 2017
reduced recruitment of brown trout by redd (i.e., spawning bed) superimposition or other
competitive effects (Scott and Irvine, 2000; Nomoto and others, 2010).
Thus, policies aimed at reducing rainbow trout recruitment in Glen Canyon have the potential to
backfire if they inadvertently lead to an increase in brown trout abundance. A better
understanding of the interaction between rainbow and brown trout in Glen Canyon is therefore
critical, and a major aim of the revisions made in the proposed work plan, herein.
Project I: Warm-water Native and Nonnative Fish Monitoring and Research
Maintaining self-sustaining native fish populations within the Colorado River and minimizing
the presence and expansion of aquatic invasive species are two specific resource goals outlined
in the LTEMP EIS and associated BiOp for the operation of Glen Canyon Dam (U.S.
Department of Interior, 2016a, b). These two resource goals are closely linked together in that
introduced warm-water fish are largely incompatible with Colorado River native fish (Marsh and
Pacey, 2005; Minckley and Marsh, 2009). Introduced warm-water sport fish prey upon juvenile
native fish, and once established, can cause rapid disappearance of native fish (Moyle and others,
1986). In both the upper and lower Colorado River Basins, warm-water predatory fish are
implicated in the lack of recruitment and subsequent population declines in native fish (Mueller,
2005; Martinez and others, 2014). Control methods are typically the most cost effective and
successful when invasions are detected early (Leung and others, 2002; Dawson and Kolar, 2013).
A robust monitoring program increases the likelihood that a new invasion will be detected early
and that management actions can be taken to control pest species.
Long-term monitoring allows the ability to detect trends and test hypotheses in regard to
temporal variation in fish populations, but its strength also lies in the ability to interpret and
detect unexpected trends or surprises (Lindenmayer and others, 2010; Dodds and others, 2012;
Melis and others, 2015). When designed properly, a long-term monitoring program is a powerful
tool for quantifying the status and trends of key resources, understanding system dynamics in
response to stressors, and investigating the efficacy of alternative management actions. Without
long-term monitoring, science-based decisions for fisheries management are often not possible
(Walters, 1986). This project will continue long-term, standardized monitoring conducted by
Arizona Game and Fish Department (AGFD) throughout the Colorado River from Lees Ferry
(RM 0) to Pearce Ferry (RM 281) for the combined purposes of tracking the status of native fish
as well as identifying new invasive aquatic species. This is the only project that tracks all native
and nonnative fishes throughout the length of the Colorado River in the project area.
AGFD will conduct one spring system-wide fish monitoring trip in FY2021, one trip in FY2022, and
two trips in FY2023 from Lees Ferry to Diamond Creek using electrofishing, angling and hoop
netting. For the monitoring that takes place in the Fall downstream from Diamond Creek, AGFD will
only monitor the last 15 miles of river upstream from Pearce Ferry (3 nights of sampling in each
year) because of budget constraints and the need to reduce logistics costs. Other fish monitoring
efforts which focus on humpback chub (Project G), and monitoring of small bodied fished
conducted by the NPS downstream of Bright Angel Creek (funded by the Bureau of Reclamation
outside of the GCDAMP also provide important additional detection information of new invasive
aquatic species, and all of these efforts together provide a robust monitoring program to track
changes in native fishes and detect new problematic invasive aquatic species.
Water levels in Lake Powell have decreased in recent years because of ongoing drought. This
causes warm surface waters to be entrained into the penstocks and released downstream. While
warmer water provides better thermal conditions for native Colorado River fishes, it also
increases the likelihood that warm-water introduced fishes will become established and
negatively impact populations of native fishes. Management and removal of invasive aquatic
species can be difficult once a species becomes established because problems typically become
large in scale quickly and few effective tools are available for managing aquatic invasive species
(Dawson and Kolar, 2013).
This creates the need to both detect invasive species early and understand which species pose the
greatest threats so that efforts can be prioritized. Assessing the risks posed by existing or new
warm-water invasive fish provides managers with the scientific information needed to make
decisions about what management activities are warranted. Hilwig and Andersen (2011),
compiled a literature review of the potential risks posed by individual species, but those risks
need to be validated and quantified based on existing environmental conditions, species
abundances, and expected future conditions in the LCR and CRe. In previous work plans risks
related to rainbow and brown trout were evaluated (FY2016-17) as well risks posed by other
invasive warm-water fishes (FY2018-20). Channel catfish and green sunfish were identified as
two invasive species that pose particularly high risks to Colorado River native fish (Ward, 2020).
In surveys conducted in FY2018-20, channel catfish were found to exist in higher abundance
within the LCR than previously known, with a majority of the fish being large in size, averaging
408 mm (Figure 1). There are no catfish species native to the Colorado River, therefore native
Colorado River fishes did not evolve mechanisms to avoid catfish predation. Native fishes are
particularly vulnerable to predation by catfish predators (Ward and Figiel, 2013), especially
under turbid conditions (Ward and Vaage, 2019).
Green sunfish were also identified as a particularly high-risk species because of their aggressive
nature, high piscivory and known ability to rapidly colonize new environments and displace
native fish (Ward, 2015). In this workplan we propose to focus specifically on quantifying the
risks posed by these two species.
Laboratory studies will be conducted to quantify size specific predation risk from channel catfish
and green sunfish. These laboratory studies in conjunction with abundance estimates for channel
catfish from the LCR, will allow managers to determine if invasive catfish present more or less
of a predation threat to juvenile chub than predation by trout or other warm-water predators.
This information gives context from which to evaluate potential management actions such as
mechanical removal and will ensure that any future aquatic invasive species removal efforts are
focused only on those species that pose the highest threat to humpback chub populations.
In addition to evaluating the risks posed by invasive fishes we will also continue to evaluate the
risks posed by infestation of Asian fish tapeworm (Bothriocephalus acheilognathi) in humpback
chub. Asian fish tapeworm is an invasive species that infests warm-water cyprinid fish. Asian
fish tapeworm monitoring took place in 2005 and 2006 and has occurred annually at a low level
within the LCR since 2015.
Additional monitoring will continue in this work plan to evaluate the prevalence of Asian fish
tapeworm in humpback chub inhabiting the mainstem Colorado River as identified in the 2016
BiOp. Asian fish tapeworm has been identified as one of six potential threats to the continued
existence of endangered humpback chub (USFWS, 2002). It is potentially fatal to new host
species (Hoffman and Schubert, 1984).
Asian fish tapeworm was first documented in the LCR in Grand Canyon in 1990 (Minckley,
1996) and was hypothesized to be a cause of long-term declines in condition of adult humpback
chub from the LCR (Meretsky and others, 2000). Monitoring Asian fish tapeworm infestation in
humpback chub in the mainstem Colorado River in addition to the LCR will provide a baseline
context and relative risk assessment with which to evaluate the potential impacts of this invasive
parasite on humpback chub populations.
In the FY2018-20 Triennial Work Plan (TWP) we identified the need to develop a new tool to
detect rare nonnative species invasions prior to population expansion. Responding quickly to
invasions before populations become large and established is the least expensive and most
effective way to control invasive species (Leung and others, 2002). Early detection tools are in
the process of being developed to detect the presence of rare species and their spatial extent
across a riverscape at a molecular level (Schwartz and others, 2007; Carim and others, 2016a). In
aquatic environments, fish shed cellular material into the water via reproduction and feces that
can persist in the environment for several weeks. This cellular material can be collected via water
sample and environmental DNA (eDNA) extracted from cells collected in the environment in
which an organism lives, rather than directly from animals themselves.
Since the quantity of eDNA in a sample scales with fish biomass, relative abundance metrics can
be calculated (Klymus and others, 2015). This approach can have higher sensitivity relative to
traditional sampling methods, since hoop nets and standard electrofishing may not detect rare
species at the early stages of invasion (e.g., smallmouth bass), species that may not be
susceptible to capture (e.g., channel catfish), or species residing in deeper areas outside of the
range of standard methods. Molecular analyses can also be associated with lower costs than
traditional staff-heavy sampling methods, since a filtered water sample is all that is needed
(Carim and others, 2016a). As such, this tool lends itself nicely to answering questions in the
Grand Canyon related to both the presence and distribution of rare nonnative species and is a
critical first step in early detection so that management actions can be targeted to prevent spread.
We used seed money in the FY2018-20 TWP in combination with funding from the USBR and
USFWS to commence a project to collect eDNA samples at 300 spatially distributed sites
throughout the Colorado River, at tributary junctions, and in Lakes Mead and Powell. This trip
was scheduled to launch in May 2020 but was postponed due to the COVID-19 pandemic and
closure of the Colorado River in Grand Canyon in spring 2020. This sampling may be postponed
to June 2020 or rescheduled entirely to May 2021.
In the FY2021-23 TWP, we propose to use data on any nonnative species detections from the
2020 eDNA sampling trip to target reaches where problematic nonnative species detections
occur. The objective of this second sampling trip is twofold: 1) determine whether invasive
species of interest have geographically expanded; and 2) determine whether relative abundance
has increased (or decreased) in the interim time period. This information will be used to help the
NPS implement strategies that respond to new or expanded invasions, should they occur.
Project J: Socioeconomic Research
Project J contains research elements that collect and integrate socioeconomic information with
data and predictive models from ongoing long-term physical and biological monitoring and
research led by the USGS GCMRC. The project elements improve the ability of GCDAMP
resource managers and stakeholders to evaluate management actions and prioritize monitoring
and research. This project involves three interrelated socioeconomic research elements that
address novel resource management challenges and build on research in the FY2018-20 TWP
(Bureau of Reclamation, and U.S. Geological Survey, 2017):
- The development and integration of predictive biological and physical models with economic metrics to evaluate and prioritize monitoring of, and research on, resources downstream of Glen Canyon Dam (GCD), including the anticipated success (or lack thereof) of proposed flow experiments in the LTEMP EIS (U.S. Department of Interior, 2016a) (Element 1);
- The design, implementation, and monitoring of the impacts of an incentivized harvest program to reduce brown trout abundance in Lees Ferry (Element 2); and
- The survey of recreational angler and whitewater boater’s preferences for flow attributes, in accordance with GCD maintenance and LTEMP EIS experimental flows (Element 3).
The proposed project elements address the LTEMP Record of Decision (ROD) (U.S. Department
of Interior, 2016b) resource goals related to humpback chub, sediment, invasive fish, and
hydropower, as specified in Section 4.
Project K: Geospatial Science, Data Management and Technology
A crucial component of any long-term adaptive management program is the proper management
and accessibility of its data resources necessary for measuring the status, trends, and
experimental results related to the program’s objectives. The data collected through the USGS
GCMRC are a vital resource used to determine the status of the natural resources identified
through the GCDAMP and to make timely decisions on dam operations. The primary purpose of
this project is to provide high-level support to GCDAMP-funded science efforts in the
disciplines of geospatial science, data management, database administration, and emerging
information technologies.
Shifts in the geospatial and information technology industries are pushing the boundaries on how
data can be managed and made accessible to outside entities. Much of this change is driven by
advances in technology—from improved sensors for monitoring the Earth, to increased digital
data storage capacity, to newer computer systems designed for processing large data sets more
efficiently, and to the greater emphasis of the “Internet of Things” where the reliance of webbased technologies have revolutionized our world.
A common thread for the different aspects of this project is to continue to advance GCMRC’s
ability to leverage many of these new technologies for the benefit of the GCMRC, the science
projects described within this work plan, and the larger GCDAMP. While some of the work
elements described within this project discuss the use of newer technologies and methods for
managing, analyzing and providing access to the Center’s data resources, the concepts that this
work serves are not new and have been part of the GCDAMP since the beginning. By
standardizing our data resources, streamlining workflows and leveraging new technologies, we
can fulfill these important needs of the program more efficiently, and ultimately, for much lower
costs than would occur if each project were instead left to develop their own closed systems.
Work performed within this project makes it possible to share important information about
trends in resources of the CRe to the GCDAMP through web-based, interactive tools and
mapping products, allowing the GCDAMP to make better informed, time-sensitive decisions on
experimental and management actions under the 2016 LTEMP and the (ROD (U.S. Department
of Interior, 2016a, b).
Project L: Overflight Remote Sensing in Support of GCDAMP and LTEMP
This project seeks to acquire high-resolution multispectral imagery and a digital surface model
(DSM) of the Colorado River and riparian area from the forebay of Glen Canyon Dam
downstream to Lake Mead, and along the major tributaries to the Colorado River. The proposed
schedule for this data collection mission is in May 2021, during the first year of the FY2021-23
TWP. The data sets derived from remote sensing overflights (Table 1 and Figure 1) have proven
to be extremely valuable to most of the research projects conducted by GCMRC over the past
two decades. Importantly, scientific research which relied heavily on these data were the basis
for the 2016 LTEMP (U.S. Department of Interior, 2016a). Data derived from the 2021
overflights will be used in the LTEMP ROD implementation process (U.S. Department of
Interior, 2016b).
GCMRC’s Scientific Monitoring Plan in support of LTEMP, notes that the ROD “calls for a
comprehensive, decadal-scale assessment of the impact of dam operations on sandbar resources
and on the status of humpback chub” (VanderKooi and others, 2017). Given that the most recent
overflight was previously conducted in 2013, and given the physical, geographic and logistical
constraints of the Colorado River in Grand Canyon, system-wide remotely-sensed data are
necessary to complement ground-based data collection and assist with the GCMRC’s efforts to
effectively assess these impacts for the entire river ecosystem over decadal time frames. The
imagery and derivative data products from overflight remote sensing are used either directly or
indirectly by every science project proposed in this TWP to address every resource goal of the
LTEMP.
While this proposed work is discussed within the context of the FY2021-23 TWP, the nature and
justifications for conducting the overflight are directed at the GCMRC’s ability to respond to and
deliver information for the LTEMP implementation process that tracks decadal-scale changes to
resources system-wide. As such, the overflight is a scientific effort that has both an immediate
and a longer-term payoff; future LTEMP studies will require similar information that can be
effectively derived from remotely-sensed data acquired over coming decades. For these reasons,
this project is mission critical to successfully inform the GCDAMP on performance of the
LTEMP ROD.
Project M: Leadership, Management, and Support
The Leadership, Management, and Support budget covers salaries for a budget analyst, librarian,
a part-time library assistant, three members of the logistics support staff, as well as leadership
and management personnel for GCMRC. Leadership and management personnel salaries include
those for the GCMRC Chief and Deputy Chief as well as half the salary for one Principal
Investigator and half the salary for one data specialist. Most of the travel and training costs for
administrative personnel are included in this project as well as the cost of GCMRC staff to travel
to AMWG and TWG meetings. Cooperator funding is for support of the Partners in Science
Program with Grand Canyon Youth. Operating expenses include:
- GSA vehicle costs including monthly lease fees, mileage costs, and any costs for accidents and damage;
- DOI vehicle costs including gas, maintenance, and replacements costs;
- GCMRC’s Information Technology equipment costs; and
- A $20,000 annual contribution to the equipment and vehicles working capital fund.
Project N: Hydropower Monitoring and Research
The LTEMP (U.S. Department of the Interior, 2016a) states that the objective of the hydropower
and energy resource goal is to, “maintain or increase Glen Canyon Dam (GCD) electric energy
generation, load following capability, and ramp rate capability, and minimize emissions and
costs to the greatest extent practicable, consistent with improvement and long-term sustainability
of downstream resources.” Project N will identify, coordinate, and collaborate with external
partners on monitoring and research opportunities associated with operational experiments at
GCD designed to meet hydropower and energy resource objectives, as stated in the LTEMP EIS
and its ROD (U.S. Department of the interior, 2016a, b), and guided by the memorandum
(Guidance Memo) from the Secretary's Designee, dated August 14, 2019 (Petty, 2019).
Operational experiments include proposed experiments in the LTEMP EIS (U.S. Department of
Interior, 2016b), and other identified operational scenarios at GCD to improve hydropower and
energy resources, while consistent with improvement and long-term sustainability of other
downstream resources. Project N will prioritize research associated with operational experiments
at GCD designed to meet hydropower and energy resource objectives. Project N will also
conduct monitoring and research of proposed experiments in the LTEMP EIS and consider
impacts on hydropower and energy as part of the experimental design. Coordinated project
implementation and development will occur between Reclamation, Western Area Power
Administration (WAPA), and other collaborators to utilize and build on existing hydropower and
energy models and data, specifically those from Appendix K in the LTEMP EIS (U.S.
Department of Interior, 2016b).
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