Embed Size (px)
DESCRIPTION
Water Canyon/Canyon de Valle investigation was conducted by Glorieta Geoscience, Inc., in collaboration with Los Alamos National Laboratory during 2010-2011 to assess contaminant inventory in post-1942 sediments. Characterization of post-1942 sediments using hand-dug pot holes, dendrochronology and measurement of cross sections following post-fire floods.
Citation preview
Post-Fire Sediment Transport and Erosion in the Water Canyon and Cañon de Valle
Watershed, Jemez Mountains, NM DRAKOS, Paul, RENEAU, Steven, SCHULTZ-FELLENZ, Emily, RIESTERER, Jim, KELLEY, Rick, MILLER, Elizabeth, GOETZE, Phillip, and CHAMBERLAIN, Paul
GLORIETA GEOSCIENCE INC
Pajarito Plateau watersheds
Water Canyon/Cañon de Valle investigation conducted 2010-2011 to assess contaminant
inventory in post-1942 sediments • 1:200 scale mapping in 25+ reaches
• Characterization of post-1942 sediments using hand-dug pot holes (identified based on presence of exotic clasts, buried soils, bedrock, etc.)
• Dendrochronology utilized to provided supplemental information to constrain the age of flood deposits
• Reworked ash from 1977 La Mesa fire and 2000 Cerro Grande fire preserved in situ within sediment deposits provides additional age control
• Measurement of cross sections following post-fire floods on 8/3/11 and 8/21/11
• 8/21/11 flood est. ~3000 cfs in CDV, larger than 8/3/11 flood
GLORIETA GEOSCIENCE INC
Extent of 1977 La Mesa fire within Water Canyon/ Cañon de Valle Watershed
Extent of 2000 Cerro Grande fire within Water Canyon/Cañon de Valle Watershed and maximum post-fire discharge (6/2000)
840 cfs
274 cfs
740 cfs
Extent of 2011 Las Conchas fire within Water Canyon/Cañon de Valle Watershed, and estimated discharge from 8/21/2011 flood
~3000 cfs (estimated)
1600+ cfs (estimated)
3500 cfs (est.)
Sediment delivery after Cerro Grande wildfire (Reneau et al., 2007)
• Over 90% of ash delivered to LA Canyon reservoir in the first year after the fire
• Slurries dominated by ash flow (suspended sediment) follow first convective storm after the wildfire
• Sediment transport rates declined after first year, but remained above pre-fire levels five years after the fire
• Significant increase in erosion rates in the first year following the fire
• Rapid decline in fine-grained sediment transport, whereas coarse-grained sediment transport is prolonged (bedload transport during snowmelt runoff)
• Post-fire sediment is primarily deposited within first two years after the fire
Preservation of in situ ash in post-1942 sediment deposits
Cerro Grande muck deposit (June 2000)
Methods – 1:200 Scale Mapping
Methods – Characterization of post-1942 sediment deposits
Methods – Characterization of post-1942 sediment deposits
GLORIETA GEOSCIENCE INC
Methods – Measure geomorphic cross sections Location selection based on contaminant concentrations and
dendrochronology, prior to Las Conchas fire
Water Canyon/Cañon de Valle watershed showing reaches
Reach WA-2 Geomorphology, cross section location
c1
f1
c3
Qbt
c2
Reach WA-3 Geomorphology, cross section location
c1
f1
c3
Qc
c2 Qt
c1
f2
Cross sections in Reaches WA-2 and WA-3 showing post-1942 sediment deposition and post-Las Conchas fire muck deposits
CG ashy si
CG ashy si at base
LM deposit at base
CG ashy si
LM(?) ashy vfs
17 of 127 cm post-fire sed (c3)
~58 of 123 cm post-fire sed (c2)
~58 of 123 cm post-fire sed (f1)
10 of 10 cm post-fire sed (f2)
CG ashy si-fs
23 of 58 cm post-fire sed (f1s)
Water Canyon/Cañon de Valle watershed showing reaches
Cross sections in Reach CDV-1E showing post-1942 sediment deposition and post-Las Conchas fire muck deposits and erosion
measured after floods on 8/3/11 (left) and 8/21/11 (right) > 50% (+/-75%) of post 1942 sediment deposits are post-fire seds
CG ashy si
CG muck at base
Cross sections in Reach CDV-2W showing post-
1942 sediment deposition and post-Las
Conchas fire muck deposits and erosion measured after flood
on 8/21/11
GLORIETA GEOSCIENCE INC
CG muck
CG ashy si+vfs
Note in lower cross section Some channel incision but most post-1942 sediments remain in place.
Cross sections in Reach CDV-2W showing post-1942 sediment deposition and post-Las Conchas fire muck
deposits and erosion measured after flood on 8/21/11
Note erosion of c2 sediments next to channel, preservation of c3/f1 deposits on higher surface, deposition of muck from 8/3/11 and coarse sediment from 8/21/11 flood.
Sampling location CV-613603 in reach CDV-2W where c2 unit was completely eroded during 8/21/2011, flood.
Reach CDV-3 Geomorphology, cross
section locations
f1
c3
c2
Qbt
c1
Qc
Cross sections in Reach CDV-3 showing post-1942 sediment deposition and post-Las Conchas fire muck deposits measured after flood on
8/3/11; upstream (left) and downstream (right); post-fire sediment <20% of total post-1942 deposition
Water Canyon/Cañon de Valle watershed showing reaches
Cross sections in Reach WA-4 showing post-1942 sediment deposition and post-Las Conchas fire muck deposits; < 20% are post-fire deposits
CG dk vfs+si
Reach WA-5 Geomorphology, cross section location
c1
f1
Qc
c2
Tb
c1
GLORIETA GEOSCIENCE INC
Cross sections in Reach WA-5 showing post-1942 sediment deposition and post-Las Conchas fire muck deposits and erosion
measured after floods on 8/3/11 (left) and 8/21/11 (right)
GLORIETA GEOSCIENCE INC
8/23/11 Flood coarse sediment deposits and scouring
Coarse sediment deposits in Cañon de Valle from August 21, 2011, flood. Gravel bar adjacent to channel in reach CDV-1E.
Coarse sediment deposits in Cañon de Valle from 8/21/2011 flood. ~2 to 4 m wide gravel deposit buries 0.5m wide
channel in Reach CDV-2W
Scour hole in reach CDV-1E demonstrating channel erosion in Cañon de Valle from August 21, 2011, flood.
Water Canyon fan deposit at Rio Grande (left) and detail showing ~10 cm thick L.C. muck deposit (right)
Photos taken 11/30/11
Muck from 8/3/11 flood?
Coarse (ms-cs) sediment from 8/21/11 flood?
Water Canyon Fan
Post-Las Conchas sediment deposits along Rio Grande
Conclusions • First post-Las Conchas fire flood on 8/3/11 deposited muck layer
(ashy silt) with a maximum thickness of 22 cm at cross section locations
• Some erosion also occurred
• Second post-Las Conchas fire flood on 8/21/11 was larger discharge event. Coarser-grained sediment deposits up to 50 cm thick at cross section locations were observed in both overbank and channel settings.
• Considerable scour and bank widening also observed during second flood event.
• Total post-fire related sediment deposits from LM, CG, and LC fires at randomly selected cross sections ranges from up < 20% to 75%, shows a general down-stream attenuation trend
• Post-LC muck and coarser-grained sediment deposits observed at mouth of Water Canyon at Rio Grande.
GLORIETA GEOSCIENCE INC
Pending Investigation (2012)
• Systematic assessment of post-Las Conchas erosion and deposition in reaches investigated in 2010/2011
• Reoccupy and resurvey cross sections to quantify post-Las Conchas fire erosion and deposition at specific locations
GLORIETA GEOSCIENCE INC
Acknowledgements Steve Veenis
LANL Environmental Programs TerranearPMC.com
GLORIETA GEOSCIENCE INC
