U.S. Department of the Interior

U.S. Geological Survey

What’s Next?

Key Uncertainties and Future HFE 

Design

Michael Moran

Grand Canyon Monitoring and Research Center

Southwest Biological Science Center

Annual Reporting Meeting

March 13, 2019
Project A

Sediment and Water Quality – Slide 1 of 2

Results

 HFEs must be conducted when the most fine sand is

available

 Sediment-triggered spring HFEs are not likely to occur

because inputs of sand in spring are generally low

 Sand mass balance should be

positive after HFE; RR>0

March 13, 2019
Project A

Sediment and Water Quality – Slide 2 of 2

What’s Next?

 No monitoring changes recommended

 Improve sediment model

 Improve spatial resolution

 Expand particle size to include the silt and clay fraction

 Add sandbar evolution component

March 13, 2019
Project B

Sandbar Monitoring – Slide 1 of 2

Results

 Each HFE since 2012 has

resulted in sandbar deposition

 Although bars erode, they are

larger than they would be

without HFEs

 There is evidence for

cumulative increases in bar

size at some sites

RM 9 L

pre-HFE 2012

Post-HFE 2018

March 13, 2019
Project B

Sandbar Monitoring – Slide 2 of 2

What’s Next?

 Results indicate future HFEs

should continue to be

successful in building some

sandbars through time

 Could experiment with

hydrograph shape to affect

sandbar shape (e.g. slope of

bar front)

RM 194 L

4/20/1996

11/20/2016

March 13, 2019
Project C

Riparian Vegetation Monitoring – Slide 1 of 2

Results

 Current fall HFEs are probably not speeding up or slowing

down vegetation expansion

 HFEs are primarily impacting vegetation by maintaining

habitat in the active floodplain

 Fall HFEs are not likely

“watering the garden” and

may be removing

seedlings of some species

March 13, 2019
Project C

Riparian Vegetation Monitoring – Slide 2 of 2

What’s Next?

 Physiological measurements immediately before and after

HFEs could help to identify effects on established plants

 Controlled experiments outside the river corridor can help

to develop mechanistic models of vegetation

establishment and mortality

March 13, 2019
Project D

High Elevation Sand – Slide 1 of 2

Results

 The past, present, and likely future expansion of riparian

vegetation onto sandbars reduces the supply of HFE sand

for dunefields

 NPS will begin implementing experimental vegetation

removal treatments in Grand Canyon to increase aeolian

sediment supply to several dunefields that host

archaeological sites

March 13, 2019
Project D

High Elevation Sand – Slide 2 of 2

What’s Next?

 GCMRC will monitor the outcome of the treatments

relative to future HFEs

 To be effective, vegetation treatments need to be done in

conjunction with consecutive annual HFEs

March 13, 2019
Project F

Aquatic Ecology – Slide 1 of 2

Results

 2008 Spring HFE appeared to improve food base

 However, it is hard make inferences:

 Spring HFEs have been relatively infrequent compared to Fall HFEs

 Most recent Spring HFE was >10 years ago predating foodbase data

sets

March 13, 2019
Project F

Aquatic Ecology – Slide 2 of 2

What’s Next?

 Fall disturbances don’t help food base

 Will Spring disturbances improve food base?

 Test benefits of Spring

disturbance

 Spring HFE

 Powerplant flow

March 13, 2019
Project H

Salmonid Research – Slide 1 of 3

Results

 Rainbow trout response (in Glen Canyon) to:

 Fall HFE – small positive recruitment response, moderately negative

growth response

 Spring HFE - Highly

uncertain

March 13, 2019
Project H

Salmonid Research Slide 2 of 3

Results

 Large brown trout are increasing

 Not sure what is driving variation in brown trout

reproduction, however a simple relationship with fall HFEs

doesn’t seem likely

March 13, 2019
Project H

Salmonid Research – Slide 3 of 3

What’s Next?

 Understanding of brown trout abundance and vital rates

should improve with continued mark-recapture study

 We need to think more about the aquatic vegetation in

Lees Ferry

 BNT abundances are uncertain but likely to be increasing

 Evidence from other systems suggests spring HFEs could be a way

to lower their reproduction

March 13, 2019
Project I

Native and Nonnative Fish – Slide 1 of 2

Results

 HFE effects depend on a variety of factors such as turbidity

and geomorphology

 Native and nonnative fish

thrive in the environment

of post-dam CO River

March 13, 2019
Project I

Native and Nonnative Fish – Slide 2 of 2

What’s Next?

 Probably no adverse effect on native fish from fall HFEs

March 13, 2019
Project J/N

Socioeconomic Research

Results

 HFEs have created substantial sandbar benefits to whitewater rafters

 Economic benefits of spring HFEs are greater than equivalent fall

HFEs due to seasonal visitation and recreation specific preferences

Southwest Fly Fishing Grand Canyon West

March 13, 2019
Project J/N

Hydropower Research

Results

 Fall and Spring HFE hydropower generation costs

range from $1-3 million per experiment

 HFEs are not anticipated to incur hydropower capacity

costs

March 13, 2019
Project N

Hydropower Research

What’s Next?

 Would an assessment of power system emissions

inform timing and design of HFEs in order to minimize

total power system costs?

March 13, 2019
Questions