Hydrologic Change, and the Geomorphic Transformation 

of the Little Colorado River: Implications for Sediment 

Delivery to the Grand Canyon

David J. Dean, David J. Topping
The LCR Basin
1914

2016

The Little Colorado River:

100 Years of Change

A formerly braided river – now 

single-threaded

The former channel devoid of 

riparian vegetation – now 

dense floodplain forests
Previous Work on the LCR:

Between the early 1900s and the 1980s:

• Three alternating periods of erosion and deposition

• 1900-1940s – frequent large floods, high annual 

discharge – the channel was wide and sandy

• 1940s-1950s – precipitation and discharge 

decreased – the channel narrowed and 

floodplains developed – salt cedar (Tamarisk spp.) 

became widely established on these floodplains

• 1950/60s-1980s – precipitation and discharge 

increased – the largest floods during this period 

caused continued overbank deposition and 

vertical accretion. 

Hereford, 1984

Conclusion: hydrologic and geomorphic 

changes were driven by changes in 

climate.
Historical Land Use and Human 

Development within the LCR Basin

• In the 1870s, Mormon settlers began building diversion dams and irrigation 

networks.

• Completion of the railroad in the 1880s brought ranchers and their large herds 

of sheep and cattle (150,000 head of cattle, 120,000 head of sheep).

• Widespread denudation of the LCR ranges had occurred by the 1890s = 

gullying and erosion occurred throughout the LCR drainage network. 

• Although grazing likely had some impact on erosion, the primary cause of 

erosion is believed to be above average rainfall.

• Prior to the start of stream gaging in 1926, substantial changes to LCR 

hydrology/geomorphology had already occurred

• Today, there are nearly 100 reservoirs within the basin, and over 3,700 stock 

ponds
Hydrology – Winter/Spring
Hydrology – Winter/Spring
Hydrology – Winter/Spring

• Long-duration winter/spring runoff driven by large frontal 

storms.

• Floods can be large, but sediment loads are generally small

Preliminary, do 

not cite

Preliminary, do 

not cite
Hydrology – Summer/Fall
Hydrology – Summer/Fall Preliminary, do 

not cite
Hydrology – Summer/Fall

• Short-duration, high-intensity, summer/fall floods driven by 

convective thunderstorms

• Floods can be large, and sediment loads can be huge. Sediment 

can be deposited within/on LCR channel and floodplain, or 

delivered to the Colorado River. 

Preliminary, do 

not cite
Determining the Timing of Historical Hydrologic Changes

• We created a cumulative discharge curve of LCR stream flow data

• We fit a line to the data, and detrended the data to determine periods 

of high and low stream flow. 

1926-1943

high

1944-1964

low

1965-1995

high

1996-2014

low

Preliminary, do 

not cite
Determining the Timing 

of Historical Hydrologic 

Changes

1926-1943

high

1944-1964

low

1965-1995

high

1996-2014

low

• Our findings concerning timing of 

change are consistent with Hereford’s 

(1984)

• The most recent low-flow period has 

had the lowest flow over the entire 

period of record. 

1972/73

1993

1941

Preliminary, do 

not cite
Temporal Changes in Annual Flow Volume

The years with the largest flow volumes are also years dominated by winter/spring flow
Temporal Changes in Annual Flow Volume

Calendar Year Winter/Spring

Summer/Fall

Winter/Spring flow volume mirrors 

trends in flow volume for calendar year 

Summer/fall trends are similar, but 

much more muted than winter/spring

Preliminary, do 

not cite
Temporal Changes in Peak Flow

Calendar Year Winter/Spring

Summer/Fall Regardless of increases and decreases 

in total flow, peak flows have 

continuously declined over the period 

of record. 

Preliminary, do 

not cite
Reasons for Hydrologic Change

Why have peak flows declined even though total flow

has not? 

Hypothesis 1: Water development and reservoir construction/management have

captured floodwater, and have contributed to reduction in flood magnitude

East Clear Creak - 1929

Preliminary, do 

not cite
Reasons for Hydrologic 

Change

Why have peak flows declined even though there 

has not been a progressive decline in total flow? 

Hypothesis 2: Geomorphic change (channel narrowing, 

floodplain development) has affected floodwave

propagation, and causes flood attenuation. 

1933/34 1979 2013 1992 1954

• Large floods inundate floodplains

• Floodplains vegetation provides drag 

which slows flow velocities and 

disrupts conveyance. 
Continued Geomorphic Change and 

Changes in Sediment Transport

1999

2016

1999

2016

1929

2016

Hereford,

1984

>200,000 mg/L

The channel continues to fill with 

sediment! Change is ongoing. 

Sediment transport concentrations 

over last 23 years have only been 1⁄4 of 

historic measurements. Partly 

controlled by Moenkopi Wash. 

Preliminary, do 

not cite
Conclusions

• Fluctuations in total flow have occurred 

• Peak flows have progressively declined, mostly in 

winter/spring. 

• Declines in peak flow = sediment accumulation within LCR 

channel

• Peak flow declines driven by: 1) human water use and 

development, 2) geomorphic changes of the river. 
Next Steps

• Manuscript on hydrologic change (LCR and Moenkopi Wash) –

to be submitted within a month 

• Analyses of geomorphic changes (LCR and Moenkopi Wash) to 

be submitted by the end of year. 

• Future manuscript linking hydrology/geomorphic change with 

sediment transport modeling = determine historic changes to 

sediment contributed to Colorado River. Implications for 

endangered fish habitat. 
Questions.