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GMEG - Geology, Minerals, Energy, & Geophysics Science Center

Geologic and Geomorphic Evolution of the lower Colorado River

 

 

 

Late Holocene channel and floodplain dynamics

 

The lower Colorado River floodplain hosted a dynamic and wandering river prior to the completion of Hoover Dam (1936), Parker Dam (1938), and Davis Dam (1950). Concurrent and subsequent channel stabilization efforts have further constrained the river and allowed for extensive agricultural utilization of the floodplain. Both the NoLOCO and SoLOCO map areas contain long reaches that transect broad alluvial valleys across which the unregulated river would actively migrate. Small patches of relict, unaltered floodplain are present in each valley. These small swaths show highly complex patterns of overprinted and cross-cut meander complexes that attest to pre-regulation channel dynamics. We plan to develop a map-based characterization of channel changes along the river floodplain using historical imagery and surveys of the channel in combination with geologic mapping of unaltered floodplain swaths to illustrate and quantify the river’s dynamic behavior in the relatively recent past. Characterization of fluvial deposits, landforms, and patterns in the unaltered swaths will help inform interpretation of similar features seen in historical photos, surveys, and as palimpsests features locally apparent through the veil of overlying agricultural development. Preliminary observations suggest that the entire floodplain is very young and rapidly reworked such that the floodplain surface may only include Late Holocene and younger deposits.

Our objectives are to

  • Create maps at appropriate scale that illustrate time series of channel changes in the principal alluvial valleys of the lower Colorado River corridor
  • Sample key locations for Late Holocene age control, and define discrete mappable chronostratigraphic units.
  • Acquire all relevant imagery products that span the main floodplain areas of the lower Colorado River. The earliest available imagery is 1938 aerial black and white USDA photographs. These photographs have been ortho rectified (Norman et al., 2006) but some require improved processing and rectification for accurate mapping purposes in GI S. Develop mapping and nomenclature protocol specific to the floodplain – channel system.
  • Integrate linework and nomenclature into ‘local’ enterprise GIS system, which will require a scaling process for integration of linework into the products of Task 1 and Task 2 as well as nomenclature standardization across the entire map area.

 

 

   

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