Floodplain Development Along the Lower Guadalupe River: Case Study at Gonzales, Texas

1
Floodplain Development Along the Lower Guadalupe
River Case Study at Gonzales, Texas
Jillian Aldrin CE 394K Fall 2003
Guadalupe River at New Braunfels Looking North
at 945 AM CDT Friday July 5th, 2002 From NWS
website
2
The Guadalupe River Basin
The basin originates in the Hill Country on the
Edwards Plateau, flows over the Balconies Fault
zone and into the Gulf Coastal Plains before
emptying into the Gulf of Mexico
3
Formation of a Floodplain

• Lateral Migration of the river channel
• -Scour and deposition of sediment due to the
  pool and point bar formations along a meandering
  channel
• -Get features such as meander scrolls, abandoned
  channels and oxbow lakes
• Overbank deposition due to flooding
• -Flooding occurs when flows exceed the confines
  of a channel
• -Overbank flows carry sediment in a variety of
  sizes to the floodplain region
• -Features such as levees, crevase splays and
  distributary channels are formed

4
Now onto a floodplain altering event
5
Central Texas Flood of 2002

• Heavy rains fells across the Hill Country
  beginning June 29, 2002 and continued to fall on
  and off until July 10, 2002.
• Rainfall totals throughout central Texas were
  estimated from 14 inches up to 33 inches of rain
  in 12 days.
• The effects of the rainfall were seen on the
  Guadalupe River through the end of July 2002.
• This flood was approximately a 10 year flood
  according to the USGS historical data.

6
The length of inundation at the Gonzales Gauging
Station
7
The Gonzales Study Site
San Marcos R.
Guadalupe R.

• Sampling locations indicated by red dots

Maps downloaded from TNRIS, 2.5 m DOQQ
8
Sediment Deposition Near Gonzales, Texas

• Flows exceeded the banks at Gonzales for 9 days
• GPS coordinates and sediment samples were
  collected at the end of June 2002
• Range of sediment deposited 0.15cm-12.35 cm

9
Methods Used to Correlate Data

• The sampling points were collected using a GPS to
  map the location of the sample
• The data was entered into Excel and subsequently
  plotted in Arc Map
• To spatially analyze the data, the Kriging method
  was employed in the Geostatistical Analyst Tool
• The results were used to visually asses the depth
  of sedimentation throughout the floodplain

10
Results The patterns of deposition correlate with
the elevations and floodplain features observed
at the site. Dark brown little deposition
occurred, areas of higher elevation, flood waters
were not as prevalent in these areas Lt brown Lt
blue moderate deposition, waters flowed over
these areas, but flows were not concentrated at
these locations Dark blue high deposition
occurred here, indication of levees, abandoned
channel from the cut off oxbow lake
11
Guadalupe Valley at Gonzales
12
Sediment deposited along the floodplain at
Gonzales
13
The elevation change along the oxbow lake in the
Gonzales Floodplain
14
Flooding in the backswamp regions near Gonzales,
Tx
15
July 3rd July 7th
Guadalupe River floodplain _at_ Cuero
16
Future Work

• Further analysis of kriging to determine the
  validity of the methods used.
• If or where there are errors in the data produced
  by the kriging

17
Acknowledgements

• Thanks to Dr. Hudson and his students for
  collecting the data
• Dr. Maidment for the use of the data sets for the
  Guadalupe River

18
???QUESTIONS???