How have hydrologic controls on the Rio Grande effected the morphology of the river downstream of Brownsville?

1
How have hydrologic controls on the Rio Grande
effected the morphology of the river downstream
of Brownsville?
Chris Braun
2
(No Transcript)
3
(No Transcript)
4
Controls of River Morphology

• Natural controls
• velocity of flow geology
• sediment load gradient
• climate time
• (sources Costa and OConner 1995, Eschner, et
  al. 1983, Leopold and Wolam 1957,
• Pickup 1976, Shumm 1977)
• Anthropogenic controls
• water diversions dams
• land use in the flood plain channel
  rectification
• (sources Church 1992, Collier, et al. 1996,
  Hirsch et al. 1990, Huang and Pogge 1978,
• Lagasse 1981, Milhous 1997, Petts 1979, Sing 1987)

5
Hydrograph showing the Effect of Elephant Butte
Dam on Rio Grande Discharge
(Modified from Everitt, 1993)
6
Methodology Aerial Photos / Topographic Surveys

• 1911 Topographic Survey 1950s aerial
  photos 1995/96 DOQQS
• N/A ASCS NAPP
• Scale 110,000 scale 120,000 scale
  140,000
• W.W. Follett TNRIS USGS

7
Registered 1950s Aerials and 1911 Topographic
Survey to 1995 DOQQs in ARC/INFO using the
Transform command
Common features, such as major intersections,
were used as match points.
8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
Measuring River Features Using Arc/Info
Digitized thalweg (deepest part of the river
where water tends to move the fastest) Digitized
100 transects to compute an average value of
wetted channel width
12
Results and Conclusions
The decrease in discharge caused by hydrologic
controls on the Rio Grande has resulted in

• narrowing of channel width (average width of 100
  digitized transects in meters)
• 1911 87.9
• 1950 52.8
• 1995 34.4
• channel migration / increased sinuosity (length
  of digitized thalweg in meters)
• 1911 46766
• 1950 49917
• 1995 51472