217 217 217

200 200 200

255 255 255

0 0 0

163 163 163

131 132 122

239 65 53

110 135 120

112 92 56

62 102 130

102 56 48

130 120 111

237 237 237

80 119 27

252 174 .59

Suzanne Hess-Brittelle P.G., USACE, Risk Management Center Amy Ebnet, P.G., USACE, Seattle District, NWD-W Risk Cadre 14 September 2017

ASSESSMENT OF HISTORIC PIEZOMETER DATA, ABIQUIU DAM AND RESERVOIR, RIO CHAMA, NEW MEXICO

“ The views, opinions and findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other official documentation.”

PRESENTATION OVERVIEW

• Project Overview • Construction History • Sources of Data • Geology • Post Construction Seepage • Post Construction Seepage Reduction Measures • Project Instrumentation & Piezometers • P-13 example • Conclusions

Abiquiu Dam & Reservoir

• Rio Chama; tributary of the Rio Grande • 35 river miles upstream Española, New Mexico • Construction from 1958-1963

ABIQUIU DAM - PROJECT OVERVIEW

• 340 ft high rolled earthfill dam with impermeable core, chimney drain, and blanket drain • Controlled outlet works • Uncontrolled rock-cut spillway • Hydropower facility (County of Los Alamos) • Authorized for flood control and sediment retention

Designed as a ‘dry dam’

ABIQUIU DAM - PROJECT OVERVIEW

EMBANKMENT

• Dam raised 13 ft and spillway widened 28 ft due to revised PMF in 1985

SOURCES OF DATA • District Files, ERDC Library, National Archives • Instrumentation Data

• Periodic Inspection Reports • WinIDP Database (back to 1980 only…)

GEOLOGY

Trinidad Dam & Lake

• Abiquiu Dam located SE-corner of Chama Basin

• Chama Basin transition from Rio Grande Rift to Colorado Plateau

• Thick sequences of Permian and Triassic age sedimentary rock

• sandstones, conglomerates, and mudstones; interbedded and moderately fractured

Abiquiu Dam

(After Kelly and others, 2013)

Set 1 Set 2 Set 3

REGIONAL TECTONIC SETTING

9

• Note undulose nature of contact between Arroyo del Agua and Shinarump as well as interbeds within the Poleo • Note moderately fractured nature of rock; fractures are near vertical • Salitral (upper mudstone) essentially acts as an aquiclude between the Poleo (upper sandstone) and the Shinarump/Arroyo del Agua interbedded sandstone and mudstones

Poleo

Salitral Shinarump

Arroyo del Agua

Upper Sandstone

Upper Mudstone Middle Sandstone

Middle Mudstone Lower Sandstone

Lower Mudstone

TYPICAL STRATIGRAPHY AT

ABIQUIU DAM

Photo of downstream left abutment; taken during the 2008-2009 Bank Stabilization

Upper Aquifer

Lower Aquifer

Significant Scour &

Fill Contacts

(paleochannels)

ORIGINAL FOUNDATION GROUTING Exceptional losses of drilling fluids noted during initial drilling and testing along both abutments

Designers acknowledged highly permeable zones in rock and recommended a single-row grout curtain

• Single line grout curtain • Primary holes spaced 40 ft in stream bed and 20 ft in abutments • Grout mix varied from 0.6:1 to 4:1 by volume

POST CONSTRUCTION SEEPAGE

Abiquiu Historic Pool Elevations Top of Dam

Conduit Invert

Sediment trap pools

Began storing SJC pool as temp deviation

Began storing authorized SJC pool

Pool of Record

HISTORIC SEEPAGE

Seepage has been a problem since water first

impounded

6200

1970 – Pool El. 6105 ft

2 cfs

HISTORIC SEEPAGE 1987 RECORD POOL

1987; Hydropower Construction; after slope repairs

HISTORIC & CURRENT OBSERVED SEEPAGE

Seepage Observed During 1987 Record Pool

Seepage Currently Observed at Left Abutment Groin

POST CONSTRUCTION SEEPAGE REDUCTION MEASURES

ADDITIONAL GROUTING – 1966 GROUT CURTAIN

• Grouted left abutment from Sta. 0+00G to 5+00G • Re-grouted Sta. 4+30A to 9+50A through embankment,

on left abutment • Report of fluid losses in the impervious core

Reported fluid losses from drilling and grouting

ADDITIONAL GROUTING – 1978-80 GROUT CURTAIN

Reported fluid losses during drilling

• Extended grout curtain on left abutment (5+00G to 10+00G) • Extended grout curtain on right abutment (0+00S to 10+00S) • Re-grouted Sta. 14+70 to 19+79 through embankment, on right abutment

-Fluid losses were recorded in the core

OTHER HISTORIC SEEPAGE REDUCTION MEASURES • 1966: 12 horizontal drains installed 110 ft into fractured conglomeratic

sandstone on downstream left abutment • 1977: 12 horizontal drains installed 110 ft into fractured conglomeratic sandstone

(elev. 6075 ft) on downstream right abutment • 1978: Toe Drain Construction; modified in 1990

PROJECT INSTRUMENTATION & PIEZOMETERS

INSTRUMENTATION

• Piezometers • No PZs installed during original construction • Foundation & Embankment Drain

• Flumes • Along Right and Left Abutment

• Surface Settlement & Horizontal Movement Points

PIEZOMETERS

• Piezometers installed throughout history of project • 14 installed in 1966 (P-1 through P-14) • 21 installed in 1977 (P-15 through P-35) • 10 installed in 1986 (P-35 through P-40; P-43, P-45, P-48) • 8 installed in 1987 (AB-C-1 through AB-C-8) • 2 replaced in 2008 (P-14a and P-39a) • 3 installed in 2013 (P-49 through P-51)

• Downhole camera survey in 2007

• Piezometers automated in 2010

PIEZOMETER RECORDS OVER TIME

Plot taken from the 1976 PI Report Plot taken from the 1970 PI Report

• Records span 50 years and in most cases, tabulated historic records (pre-1980) were not located after exhaustive records searches

• They are shown in time history plots in Periodic Inspection (PI) reports

P-13 P-13

PIEZOMETER RECORDS OVER TIME (CONT.) • PZs read manually on a monthly

basis; and for every 5-ft increase/decrease of pool • PZs read weekly during record pool

and as pool receded

PREPARATIONS FOR 2013 PERIODIC ASSESSMENT

• Requirement to assess all historic performance data • WinIDP database was only complete to 1980

• Could not locate tabulated instrument reports • Covered 36 years of performance for a 54 year old project

• Wanted to go back as far as possible…

• Had enthusiastic intern estimate piezometer elevations from old

time history plots • Estimated water surface elevations were within +/- 2 ft

TIME HISTORY PLOT 1976-2013 Missing automated data

TIME HISTORY PLOT 1976-2013 Added automated data and seepage reduction modifications

2014-2016: IES – TAKING PIEZOMETER DATA FURTHER TO ASSESS PERFORMANCE

• Updated the overall database to include more recent automated data

• Searched for PZ boring log and construction details • Drafted new sections to help assess performance of abutments

and structure • In some cases, it was obvious that the seepage reduction

measures (grouting, adits) lowered the phreatic surface • In some cases, interpretation was problematic…

• Multiple instruments has suspect readings

LT ABUTMENT LOWER AQUIFER & DRAINAGE BLANKET PERFORMANCE

6000

6050

6100

6150

6200

6250

6300

Jan-

76

Jan-

77

Jan-

78

Jan-

79

Jan-

80

Jan-

81

Jan-

82

Jan-

83

Jan-

84

Jan-

85

Jan-

86

Jan-

87

Jan-

88

Jan-

89

Jan-

90

Jan-

91

Jan-

92

Jan-

93

Jan-

94

Jan-

95

Jan-

96

Jan-

97

Jan-

98

Jan-

99

Jan-

00

Jan-

01

Jan-

02

Jan-

03

Jan-

04

Jan-

05

Jan-

06

Jan-

07

Jan-

08

Jan-

09

Jan-

10

Jan-

11

Jan-

12

Jan-

13

Wat

er S

urfa

ce E

lev.

(FT

-NGV

D29)

Date

Abiquiu DamHorizontal Drainage Blanket and Lower Sandstone

Piezometers Left Abutment

P-10

P-11

P-12

P-13

AB-C-3POOL

P-7

P-28

P-29

P-30

P-31

Low

erSa

ndst

one

Drai

nage

Bl

anke

t1977 right abutment horiz. drains added

1978 Supplemental alignment grouting; possible core damage

1979 grouting in both abutments September 2010 instrument

automation goes online

1989-1990 right and left aditconstruction

1980 right and left abutment horiz. drains added

1986 embankment raised 14.8ft and spillway widened 28ft

2008 instruments cleaned

1987-1990 hydropowerplant construction

2009-2011 low flow turbine construction

• Less responsive to pool fluctuations after construction of adits • Abutment piezometers have higher water levels than the drain

• Water flow pattern is not moving into abutment, but is moving from abutments into the drain

• Significant drop across grout curtain 88 ft between P-15 and P-13 in 1987.

• P-13 and P-AB-C-1 erratic readings

1995 Pool Groundwater Contours - Lower Aquifer, Blanket Drain & Alluvium

1987 POR Water Levels

1995 High Pool Water Levels

HOW CAN WE LOOK AT SOME KEY INSTRUMENTS MORE CLOSELY?

• Check construction details and any modifications • Sound depth of instrument • Conduct downhole camera survey to get a visual

on instrument (scale, debris, sediment) • Conduct insitu testing (slug test, falling head

test)

• PZs sounded in Feb 2006

• Downhole camera survey conducted in Aug-Sep 2007 • Could not image PZs

completed with ¾-inch ID PVC

HOW CAN WE LOOK AT SOME KEY INSTRUMENTS MORE CLOSELY?

• P-13 has historically been difficult to interpret • Degradation of grout curtain over time? • Something else? • Can data collected even be trusted/used?

• Began taking historic data for all PZs and created correlation plots

• Intention was to use these to create PZ threshold plots too

• Time-History Plots • Typically how data is presented and can be useful

• Pool vs. Piezometer Correlation Plots • Can be used to predict future performance at higher pools

P-13

• In order to better understand plot, tried to bracket time between seepage reduction measures • 1979 left abutment

grouting • 1988-1990 adit

construction • And bracketed

estimated, manual, and automated readings

P-13

• Since 1986 • Water levels in P-13 rise to ~6200 ft

when pool is above 6210 – 6225 ft. • Drop to ~6100 when pool is below

6210 - 6225 ft. • Started before the POR.

• Possible Causes • Damaged riser in Piezometer allowing

water from upper aquifer to enter piezometer?

• Degradation of grout curtain? • Leak through Aquiclude

P-13

Manual readings

Automated readings

~Elev. 6130 ft

Conducted basic falling head test for P-13 • 5 gallon bucket, funnel and hose

• Water dropped fairly consistently • And then started coming back up

6130

Interpreted to be a break in riser pipe at approximate elevation 6130 ft

HOW EFFECTIVE WERE THE SEEPAGE REDUCTION MEASURES?

Right abutment, downstream grout curtain Left abutment,

downstream grout curtain

P-13 CONCLUSIONS • Initial construction of P-13 (1966), where the lower portion of the

instrument was left open to the fractured foundation rock, resulted in collapse of the lower 24 ft • Instrument was sleeved with ¾-inch ID PVC in 1977

• The instrument appeared to be functioning until the pool of record in 1987, at which time it was likely damaged

• Correlation plot was helpful in confirming that instrument behavior was indicative of a damaged instrument

• Insitu permeability testing was useful in gaining understanding that riser pipe is likely broken and open to the formation

• P-13 is slated for replacement per the results of the study

CONCLUSIONS 38

• For projects with challenging site conditions and variable instrument datasets, interpretation of data can be challenging • Fractured bedrock with impermeable layers that control seepage flow • Poor instrument construction practices • Multiple phases of seepage reduction measures over long project

history • Encourage the assembly of all performance data and integration

of this data with respect to the site characterization • Encourage teams to conduct comprehensive instrument

evaluations to understand what your instruments are telling you and where you may need to upgrade your monitoring system

ACKNOWLEDGEMENTS Albuquerque District: Dwayne Lillard, P.E., Geotechnical Engineer (SPD DSPM, retired) Jim McAdoo, P.G., Engineering Geologist (retired) Art Maestas, P.E., Geotechnical Engineer (now DSO) Carlos Aragon, P.E., Geotechnical Engineer Tracy Baker Aragon, P.E., Geotechnical Engineer NWD-W Cadre: Sharon Schulz, Hydraulic Engineer (Portland), Cadre Lead Lisa Scott, P.G, Geologist, Cadre PM (Seattle) Amy Ebnet, P.G., Geologist, (Seattle) Michael Gonia, P.E., Geotechnical Engineer (Seattle) Risk Management Center Gregg Batchelder Adams, P.E., Senior Advisor Andy Hill, P.E., Technical Advisor Troy O’Neal, P.E., Former Senior Advisor

QUESTIONS??