Geomorphic Summary San Acacia to Elephant Butte Reservoir

1
Geomorphic Summary San Acacia to Elephant Butte
Reservoir

• Prepared by
• Tamara Massong
• USACE-Albuquerque District
• Hydrology and Hydraulics Section

2
General Characterizations

• Sediment Supply from upstream to downstream
• Incision/Aggradation Trends
• Planform Changes/Trends

3
Sediment Supply
4
Sediment Supply

• Quantity and Size of sediment controls
• how it moves (transport processes)
• when it moves (timing of transport)
• if any is stored (relative volume moved)
• Influences
• incision/aggradation
• planform and habitat features

5
Sediment Sources (this section has a high
supply of local sediment)

• Rio Puerco to Arroyo de las Cañas
• many additional sources of
• sediment, relatively low
• storage, mix of particle sizes.

• Arroyo de las Cañas to Mid-BDANWR
• few additional sources of sediment, moderate
  storage, mostly sand particle sizes.

• South of Mid-BDANWR
• no additional sediment sources, but high storage
  in channel-floodplain, sand-silt sizes.

6
Sediment Supply
Rio Salado
Arroyo de las Cañas
Rio Grande
Arroyo de la Parida
7
Bi-Modal Sizes of Sediment Rio Puerco to Arroyo
de las Cañas with sand overlaying gravel
sand dunes
gravel layer
8
Sand to Silt-Bedded River Downstream from Arroyo
de las Cañas
sand dunes and macro dunes
9
Incision/Aggradation
10
Incision
11
Incision- Two Type of Terraces

• Terraces older than 1949
• layers of strata/soils within terraces
• higher terraces
• Terraces younger than 1949
• single layer of sediments consisting of
  sugar-sand

Post-1949 terrace
Pre-1949 terrace
7/2001
12
Incision
13
Incision
14
Incision Boundaries High Incision
15
Incision Boundaries Aggrading
16
Aggrading Section (cont)

• long term aggradation pattern
• active floodplain surfaces
• Generally low banks
• process/es governing this aggradation is not well
  understood.

2005
17
Planform
18
Planform u/s of Cañas
Dominant channel with planform change.
2001
flow
A
A
A
A
-Slightly sinuous single thread channel with
limited alternating bar development. -Bank
heights continue to increase, some floodplain
surfaces become abandoned. -Water flow and
sediment transport is efficient. -Gravel patches
are abundant, and fully spanning the channel.
The channel may be fully converted to a gravel
bed.
19
Planform u/s of Cañas
Migration.
flow
A
A
RM 110, east bank
-Alternating thalweg erodes banklines at the
outside of bends, while deposits bed load on the
inside of bends. -Channel dimension (i.e.,
width) stabilizes. -New floodplain surfaces
form. -Water flow and sediment transport are
efficient, such that gravel is easily transported.
A
2000
A
2002
May 2005
main channel
Bends at RM 117, 2006
Oct 2006
20
Planform d/s of Cañas
Bar braided or split flow channel.
flow
A
A
A
A
-Convoluted flow pattern around bars/macro dunes.
-Several, relatively deeper channels. -Classified
as a bar-braided morphology (a.k.a,
anastomosing). -An indication of reduced
transport capacity due to lowered river
flows/lowered peak flows
Dominant channel with filled side channels.
flow
gravel drape
A
A
A
A
-Convoluted flow pattern around
islands. -Several, relatively deeper channel
form. -Classified as a bar-braided morphology
(a.k.a, anastomosing). -An indication of reduced
transport capacity due to lowered river
flows/lowered peak flows. -clay sediments
stabilize some of the island and side channel
edges.
gravel
21
Near San Marcial
22
Rapidly Aggrading
23
2003 Headcut
5/2004
24
2003 Headcut
09/2004
09/2004
25
Elephant Butte Reservoir Headcut

• Nov. 2003 headcut forms at
• approximately RM 54.5
• (2002 lake level)

2002 lake level

• April 2004, RM 58

• May 2005, RM 60

• July 2005, field observations indicated that
  the headcut had split into several smaller
  headcuts
• Sept 2005 survey data confirms the July
  observations, showing the headcut zone extends
  from RM 62 up to RM 70

26
Floodplain Evolution (RM 60)
5/2005
7/2005
3/2006
27
Summary

• Three geomorphic provinces based on current
  conditions/processes
• Rio Puerco to Arroyo de las Cañas
• Relatively high supply of sediment with mixed bed
  of coarse and fine grained sediments
• High incision
• Active meandering channel planform.
• Arroyo de las Cañas to Mid-BDANWR
• Fewer supplies of sediment
• Slightly aggading with sand bed
• Rapidly changing planform.
• Mid-BDANWR to near San Marcial
• No new supplies of sediment
• Rapidly aggrading but with recent incision
• Sand-silt bed
• Few recent planform changes.