Rivers Systems of the Southwest

Native Species

Natural Dynamics

Impacts

Riparian Systems of the Southwest

• Native Tree & Shrub Species

Native Cottonwood-Willow Riparian Forest

Native Species of western riparian habitats

Broad-leaf Cottonwood (lower elevations)

Populus deltoides or P. fremontii

Narrow-leaf Cottonwood (higher elevations)

Populus angusitifolia

Hybrid: Lance-leaf Cottonwood (intermediate elevations)

Populus X acuminata

Native Species of western riparian habitats

© Br. Alfred Brousseau, Saint Mary's College. Permission to use is granted freely to not-for-profit organizations

Native shrubby willow species – e.g. Coyote or Sandbar Willow, Salix exigua

Silverleaf BuffaloberryShepherdia argentea

River & Stream Dynamics

Naturally Occurring Disturbance

Animas River Valley – Fall 2004

Animas River north of Durango (1994 air photo)

River meanders

Animas River north of Trimble Lane (air photo 1994)

Braided stream

Animas River, 23 May 2005(8,700 cfs)

Animas River, 23 May 2005

Dolores River (Slickrock Canyon)

Dolores River, Slickrock Canyon – May 2005 (4000 cfs)

Sliderock State Park – Sedona AZ (normal summer flows)

Sliderock State Park, Sedona AZ – winter/spring 2005

SW Flash Floods:

• http://www.youtube.com/watch?v=TDtBby7lJX0

Flood Dynamics

• What is the timing of high flows on southwestern rivers?

• Seasonality – 2 main seasons

• Storm types – 2 main types of precipitation

• Flood types/events – 3 types of floods

Reliance of native species on flood regimes

• Cottonwood seed dispersal:– Timing– Requirements for germination– Location for seedling establishment– Nature of cottonwood forest stands

Meandering river, showing floodplain development & location of older & younger riparian woodland.

From: http://www.uwsp.edu/geo/faculty/lemke/geog101/images/23e_river_meanders_ia_maher_156-18.jpg

From:http://pubs.usgs.gov/fs/2004/3121/images/river.jpg

Impacts on Western River Dynamics

Human-induced changes to river systems

Exotic Species Invasions:

Non-native TamariskTamarix spp.

Dense tamarisk stand on Little Colorado River, Cameron AZ

Russian Olive

Eleagnus angustifolia

Results of these invasions?

• Native species choked out

• ↓ wildlife habitat

• ? ↑↑ water use…

• ↑ salt concentrations in soil (how?)

• ↑ litter accumulation & so…

• ↑ FIRE!! (new to riparian systems)

What conditions favor exotics?

• Constant, low volume flows

• Limited bank scouring

• Limited input of new sediments

• Stable, “armored” banks

• HOW DO YOU GET THESE STABLE CONDITIONS ON RIVERS??

You Build DAMS:

http://www.usbr.gov/power/data/site_map.html

US Bureau of Reclamation Hydroelectric Dams

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Glen Canyon Dam, Colorado River May 2005

What happens to a river below a dam?

• Constant, regular flow

• Low-volume discharge

• Reservoirs trap sediment

• Stops erosion of older deposits & deposition of new

• Banks no longer scoured… become “armored”

Colorado River below Glen Canyon Dam

Who likes such conditions?

Other effects of dams:

Lake Powell Pool Elevations (feet)

Low water in Lake Powell – what does it look like?

Boat ramp at Hite Marina – ca. 2004

Hite Marina - Lake Powell, Utah 2006

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Lake Powell Surface Elevation (2005 Predictions: up 50’ then down 40’)

“This is the mighty Colorado River trickling into Lake Powell.  …The banks on the far side are 15 feet high.”

page: clydesisler.com/.../Utah/UT-GlenCanyon.htm

“This is what the northern part of Lake Powell looked like in May/2005.  That is the Hite Marina boat ramp in the upper left corner.” page: clydesisler.com/.../Utah/UT-GlenCanyon.htm

How can we fight such invasions?

• Biocontrol

The tamarisk leaf beetle - Diorhabda elongata