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Use of airborne digital imagery to examine floodplain complexity at varying discharges

Date: August 16, 2016

How hydrology and geomorphology interact to create ecological complexity throughout the course of a flood event.


Aerial view of island braided study reach of the Clark Fork River as it flows through the Missoula valley in western Montana.
Aerial view of island braided study reach of the Clark Fork River as it flows through the Missoula valley in western Montana.
The typical way water moves through a floodplain is considered a river’s natural flow regime and it includes the size, timing, and duration of flooding events. The normal pattern of a river’s discharge is linked to the construction and destruction of its floodplain, which then affects biodiversity, plant and animal life cycles, and ecological integrity. Understanding the link between discharge and floodplain structure is critical as natural flow regimes are increasingly threatened by irrigation, dams, and climate change.

This study used aerial photographs collected at varying discharges throughout a flood to examine how the amount of water moving through a floodplain is related to the abundance and diversity of different habitats. The floodplain was divided into three zones, the main channel, the parafluvial (active channel), and the orthofluvial (seasonally flooded), and researchers tracked changes within each.

The results demonstrated that diverse habitats were created and destroyed throughout the flood, which directly affected habitat heterogeneity at different flows. The three zones evolved and provided different habitat types at each discharge and the complexity of the floodplain as a whole was driven by the parafluvial zone. Furthermore, habitats that occupy a small proportion of the landscape were very important to habitat diversity and therefore ecological integrity. The area of some habitat types, but not all, changed throughout the flood, indicating that discharge was only a partial driver of the abundance of aquatic habitats.

While researchers concluded there was a relationship between discharge and floodplain complexity, the association is influenced by location on the landscape. The study underscores the importance of natural flow patterns and how the timing, size, and frequency of flooding impacts complexity.

Key Findings

  • Observed a relationship between discharge and floodplain complexity through a flood pulse.

  • Diverse habitats were created and destroyed throughout the snowmelt event, directly affecting habitat heterogeneity at different flows.

  • Maximized complexity during intermediate discharges is manifested in the parafluvial zone

  • Understanding the link between discharge and floodplain structure is critical as natural flow regimes are increasingly threatened by diversions, regulation, and climate change.

Related Publication

Driscoll, Katelyn P. 2015. Use of airborne digital imagery to examine floodplain complexity at varying discharges. Thesis, University of Montana, Missoula, MT.

Example of habitat classification scheme, with main channel, parafluvial, and orthofluvial plots. Each color describes a different habitat cover type.
Example of habitat classification scheme, with main channel, parafluvial, and orthofluvial plots. Each color describes a different habitat cover type.

Alluvial diagram showing the habitat cover transitions and complexity throughout the study period in the parafluvial zone (light blue = main channel habitat cover types; dark blue = off channel aquatic habitats).
Alluvial diagram showing the habitat cover transitions and complexity throughout the study period in the parafluvial zone (light blue = main channel habitat cover types; dark blue = off channel aquatic habitats).

Complexity as represented by evenness for the three floodplain zones at six discharges (CMS=cubic meters per second) on the samples dates of the study.
Complexity as represented by evenness for the three floodplain zones at six discharges (CMS=cubic meters per second) on the samples dates of the study.



Principal Investigators: 
External Partners: 
Dr. Ric Hauer, PI, University of Montana