USGS gauging station

Wyoming

Colorado

Utah

Arizona.New Mex

0 50 100 Miles 150

N

Glen Canyon Dam

San Juan River

Lake

Pow

ell

Moab

PageLees Ferry

Cisco

Gre

en R

iver

Upper Colorado River

Gunnison River

Dolores River

Grand JunctionStudyArea

Colo

rado

Rive

r

Annu

al pe

ak d

ischa

rge,

m3

s-1

0

500

1000

1500

2000

2500

3000

3500

400018

84

1915

1920

1925

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

Years

nodata

average1,012 m3 s-1

Arc

hes N

atio

nal P

ark

MOAB

Atlas MillTailings

Study Area StudySite

Salt Wash

Sandy Beach

1514

1312111098

76

BLM - Take Out

54

321

0 0.5 1 km

Big Bend

Salt Wash

109o30’

Arc

hes

Natio

nal

Park

Cross sectionpaleoflood slackwater depositsBoat put-in/take-out site

38o40’

N

COL-1

COL-3

2423

2221

201918

1716

BLM-TO

1413

12 1110

987

65

43

21

High water marks 25-26/5/2005

0

20

40

60

80

Pit 10

20

40

60

80

100

120

Pit 3

R

R

R

0

20

Pit 6Pit 70

20

40

60

0

20

40

60

80

Pit 8Pit 20

20

40

60

1,410±110 BP

1650-1950 AD

0

20

40

60

80

100

120

140

Pit 4

2,140±220 BP

0

20

40

60

80

100

Pit 5

R

1,460±80 BP

1,300±90 BP1

2

2

1

3

4

2

1

3

4

5

2

1

3

4

2

1

3

2

1

2

1

1

siltfine sand - siltfine sandmedium - fine sandmedium sandcoarse - fine sandcoarse - medium sandreddish, fine angular clasts - debris flowscoarse angular slope clasts - debris flowcobbles and boulders - alluvial terrace

cross beddinghorizontal beddingripplesOSL sampleC14 sample - organic materialsoilreddish, cemented fine unittop of floodflood No.

s sR

1

Pit 90

20

40

60

80

100

120

140

160

180

200

RR

390±100 BP

0

20

40

60

80

100

120

140

Pit 11

RR

230±60 BP

0

20

40

60

80

100

Pit 12

490±150 BP

1950-present

0

20

40

60

80

100

120

Pit 13

220±70 BP

7413-6994 BP

Pit 140

20

40

60

80

100

120

140

160

180

200

s s s sR

460±110 BP

200±60 BP

Pit 100

20

40

60

80

100

120

140

160

180

R

170±40 BP(1884 AD?)

410±70 BP483-309 BP

2

1

3

4

5

6

2

1

34

5

6

7

8

2

1

3

4

2

1

3

2

1

3

2

1

3

4

5

6

7

siltfine sand - siltfine sandmedium - fine sandmedium sandcoarse - fine sandcoarse - medium sandreddish, fine angular clasts - debris flowscoarse angular slope clasts - debris flowcobbles and boulders - alluvial terrace

cross beddinghorizontal beddingripplesOSL sampleC14 sample - organic materialsoilreddish, cemented fine unittop of floodflood No.

s sR

1

0 2000 4000 6000 8000 10000 1200095

100

105

110

115

120

Elev

atio

n, m

W.S. Elev - Plan 05W.S. Elev - Plan 14W.S. Elev - Plan 15

pit 14

OWS

pit 11pit 9

pit 6pit 4

pit 2pit 1

Discharge, m3s-1

90

95

100

105

110

115

120

0 50 100 150 200 250

Elev

atio

n, m

Distance, m

Road

OWS - 1140 m3s-1 25-26/5/05

W E

OWS - 425 m3s-1 13-14/6/05

Pit 1

Pit 2

Pit 4

Pit 6

Pit 11

Pit 9

Pit 14

8,150-9,880 m3s-1

6,840-7,330 m3s-1

5,550-6,800 m3s-1

4,000-5,100 m3s-1

2,800-3,500 m3s-1

1,900-2,300 m3s-1

channel bedreconstructed

channel bedmeasured

Slackwater Deposits

0 1000 2000 3000 4000

80

90

100

110

120

Channel Distance (m)

Elev

atio

n (m

)

10,000 - Plan 1410,000 - Plan 158,000 - Plan 148,000 - Plan 156,000 - Plan 146,000 - Plan 154,000 - Plan 144,000 - Plan 152,000 - Plan 142,000 - Plan 151,140 - Plan 141,140 - Plan 15

Channel

0.0(

1)

271.

4(2)

543.

4(3)

762.

2(4)

935.

0(5)

1170

.0(6

)

1349

.1(7

)

1669

.1(8

)17

60.0

(9)

1830

.4(1

0)

1953

.2(1

1)

2135

.1(1

2)

2359

.0(1

3)

2527

.3(1

4)

2833

.6(1

5)

3033

.1(1

6)

3182

.2(1

7)

3397

.4(1

8)

3558

.4(1

9)

3811

.8(2

0)

3938

.0(2

1)

4067

.9(2

2)

4319

.0(2

3)

4511

.3(2

4)

Pit 1

0 1000 2000 3000 4000

90

100

110

Channel Distance (m)

Elev

atio

n (m

)

OWS

271.

4 27

1.4(

2)

543.

4 54

3.4(

3)

762.

2 76

2.2(

4)

935.

935.

0(5)

1170

.117

0.0(

6)

1349

.1 1

349.

1(7)

1669

.1 1

669.

1(8)

1760

176

0.0(

9)18

30.4

183

0.4(

10)

1953

.2 1

953.

2(11

)

2135

.1 2

135.

..

2359

235

9.0(

13)

2527

.3 2

527.

3(14

)

2833

.6 2

833.

6(15

)

3033

.1 3

033.

1(16

)

3182

.2 3

182.

2(17

)

3397

.4 3

397.

4(18

)

3558

.4 3

558.

4(19

)

3811

.8 3

811.

8(20

)

3938

.393

8.0(

21)

4067

.9 4

067.

9(22

)

4319

.431

9.0(

23)

4511

.3 4

511.

3(24

)

10,000 - Plan 1410,000 - Plan 058,000 - Plan 148,000 - Plan 056,000 - Plan 146,000 - Plan 054,000 - Plan 144,000 - Plan 052,000 - Plan 142,000 - Plan 051,140 - Plan 141,140 - Plan 05

Measured Channel

Reconstracted channel

Pit 1

The Paleoflood Record of the Upper Colorado River near Moab, UtahNoam Greenbaum1, Tess Harden2, Victor R. Baker3, John Weisheit4, Michael L. Cline5, Rafi Halevi6, John C. Dohrenwend7 and Naomi Porat8

1. Department of Geography and Environmental Studies, University of Haifa, Mt. Carmel, Haifa 31905, Israel noamgr@geo.haifa.ac.il; 2. Seismotectonics and Geophysics Group, Bureau of Reclamation, P.O. Box 25007, Denver, CO 80225, tharden@usbr.gov;3. Department of Hydrology and Water Resources, The University of Arizona, Tucson, Arizona 85721-0011 USA, baker@email.arizona.edu; 4. Living Rivers, P.O. Box 466, Moab, Utah 84532, john@livingrivers.org;

5. School of Earth Sciences & Environmental Sustainability, Northern Arizona University Flagstaff, AZ 86011; 6. Nehara, Moshav Yaad, Misgav 20155, Israel, ra.halevi@gmail.com; 7. Southwest Satellite Imaging, P.O. Box 1467, Moab, Utah 84532, dohrenwend@rkymtnhi.com; 8. Luminescence Dating Lab., Geological Survey of Israel, 30 Malkhe Israel St., Jerusalem 95501, ISRAEL, Naomi.Porat@gsi.gov.il.

The paleoood record of the Upper Colorado River was reconstructed 17 km upstream of the town of Moab, Utah (drainage area about 62,470 km2; gs. 1,3) using paleostage indicaters. The data was collected for an updated risk analysis of the uranium Mill Tailings located on the right bank of the Colorado River in the Moab Valley (gs. 3,6,8).

The 4.5 km long study reach (g. 4) is a bedrock canyon incised some 300-350 m into the sandstone of the Colorado Plateau (g. 5) with a general gradient of 0.0004. The largest oods documented at the Cisco gauging station (1914-2011) (g. 2) �– 30 km upstream, is the historical 1884 ood �– 3,540 m3s-1, the 1917 ood �– 2,175 m3s-1 and the 1984 ood �– 1990 m3s-1.

The paleostage indicators in the form of slackwater deposits and driftwood lines at this site are up to 15 m above the summer water discharge of July 2005 (425 m3 s-1) (gs. 9, 10). The detailed paleoood stratigraphy was performed using a series of 14 pits across the SWD relict with a depth of up to 2 m (gs. 10, 11, 12). Dating of the paleoood deposits include 14 OSL ages and 4 radiocarbon ages of wooden debris and charcoal (gs. 11, 12; table 2).

The canyon and channel geometry was reconstructed using a eld survey of 24 cross sections (g. 4) during 2005. The underwater channel topography was estimated based on documented peak discharge. In 2010 a complementary survey of the underwater channel geometry using sonar, was conducted. The measured underwater channel topography show high similarity to the assumed topography (gs. 14, 16). Water surface proles, peak discharges and hydraulic analyses where preformed using HECRAS hydraulic program (gs. 13, 14). The water surface proles were calibrated using the observed water levels of the oods of 25-26.5.2005 �– 1,140 m3s-1 and the 25-26 June 2011 �– 260 m3s-1.

The results indicate evidence of about 40 oods that occurred during the last 2,140 +/- 220 years. The ow regime for the high-magnitude oods is subcritical and the canyon is relatively narrow, therefore the peak discharges are very sensitive to Manning`s n roughness coefcient (g.13). Due to the very low gradient the discharge results are also sensitive to the initial boundary conditions downstream. The peak discharges range from about 1,500 m3s-1 and up to between 8,200 and 10,000 m3s-1 depending on the Manning n (gs. 13, 15).

At least 2 oods in this record probably exceeded the conservative value (8,200 m3s-1) which is close to the almost as high as the USGS probable maximum ood (PMF; 8,500 m3 s-1) (gs. 13, 15, 16) and 24 oods exceeded 3,400 m3s-1 (the 500-year ood) calculated for the Moab Valley.

Preliminary ood frequency analysis using the Bureau of Reclamation�’s FLDFRQ3 ood frequency model which combines the paleoood and systematic data shows that the 100-year ood using both systematic and paleoood records is 5,490 m3 s-1, the 500-year and the 1,000-year oods are 8,730 and 10,500 m3 s-1, respectively (g.17; table 1).

1. The Upper Colorado River Basin including the larger tributaries, USGS gauging stations and the study area near Moab Utah.

2. Annual maximum peak discharges in the Colorado River at Cisco gauging station (Utah), 1914-2009 (drainage area �– 62,470 km2). The largest ood on record is the historical 1884 ood (3,540 m3s-1)

3. Satellite-photo of the region including Moab town and valley, the Colorado River, the Atlas Mill Tailings and the study area

4. The present study reach of the Colorado River including the main slackwater deposits (SWD) accumulations, the location of the cross sections and the paleoood BLM-TO study site

9. The paleoood slackwater relict at the study site. The numbers represent stratigraphy pits. Pit 1 includes the 2 highest ood deposits at the site �– elevation of about 15 m above water surface. Note the high water marks of the observed 25-26/5/2005 ood �– peak discharge of 1,140 m3 s-1. Encircled person for scale near pit 1

11. Stratigraphic sections of the pits at the upper depression of the BLM-TO site (pits 1-8) including texture, structure radiocarbon and OSL ages. The sections include a separation of the sedimentary units into ood-related deposits. Reddish deposits of ne angular clasts represent local slope ows deposited over Colorado River ood deposits

12. Stratigraphic sections of the pits at the lower depression of the BLM-TO site (pits 9-14) including texture, structure and radiocarbon and OSL ages. The lowest pit �– pit 14 is probably composed of the oldest deposits. The young OSL ages below the much older radiocarbon age were not considered

16. Cross section no. 9 through the Colorado River at the BLM-TO site including the reconstructed and measured underwater segment of the XS, elevations of pits and associated peak discharges. Note the minor differences between the measured and the assumed and the measured cross sections

14. Comparison between assumed channel topography (blue �– plan 5) and measured channel topography (orange �– plan 14) including channel-beds (plan 5 and plan 14 - Manning n=0.035) for water surface proles of 1,140 m3 s-1 (the observed ood of the 25-26.5.2005), 2,000 m3 s-1, 4,000 m3 s-1, 6,000 m3 s-1, 8,000 m3 s-1 and 10,000 m3 s-1. Note the elevation of the highest ood deposit at the site in pit 1 - about 22 m above channel bed

13. Comparison between water surface proles of plan 14 �– Manning n=0.035 for the channel and banks (red) and plan 15 - Manning n=0.028 for the channel and 0.045 for the banks (green) for water surface proles of 1140 m3 s-1 (the observed ood of the 25-26.5.2005), 2,000 m3 s-1, 4,000 m3 s-1, 6,000 m3 s-1, 8,000 m3 s-1 and 10,000 m3 s-1. Note the elevation of the highest ood deposit at the site in pit 1 - about 22 m above channel bed

15. Comparison between rating curves for the BLM-TO site (XS 9, 1,760 m) for plan 5 (assumed channel topography, Manning n=0.035), plan 14 (measured channel topography, Manning n=0.035) and plan 15 measured channel topography, Manning n=0.028 for the channel and 0.045 for the banks). Note the minor differences between the rating curves of plan 5 and plan 14

8. Inundation maps of Moab valley during the observed May 26, 1984 ood �– 1,880 m3 s-1 and for the USGS calculated PMF of 8,500 m3 s-1 (John C. Dohrenwend, 2006)

6. The Colorado River inlet into the Moab Valley and the uranium mill tailings (John C. Dohrenwend, 2006)

7. Comparative photos of the study reach in (a) 1905 (Whitman Cross, USGS, Denver) and (b) 2005

Table 2. Results of OSL dating of paleoood deposits at the BLM-TO site (N. Porat, 2006) Sample Depth

(m)

K

(%)

U

(ppm)

Th

(ppm)

Ext.

( Gy/a)

Ext.

( Gy/a)

Ext.

( Gy/a)

Cosmic

( Gy/a)

Total dose

( Gy/a)

Aliquots

used

De

(Gy)

Age

(years)P2U5 40-50 1.66 2.05 6.7 8 1492 903 214 2617±47 12/12 3.68±0.27 1410±110P4U4 110-120 1.99 2.90 9.2 11 1870 1182 182 3245±56 11/12 6.95±0.71 2140±220P5U1 40-50 1.74 2.50 8.4 10 1639 1046 214 2909±51 11/12 3.79±0.26 1300±90P5U2 70-80 1.74 2.50 8.6 10 1643 1055 193 2901±51 10/12 4.24±0.22 1460±80P9U5 90-100 1.58 1.97 5.8 7 1388 816 186 2397±64 12/12 0.92±0.24 390±100P10U3 50-60 1.58 2.30 7.4 9 1487 942 207 2645±46 11/12 0.45±0.12 170±40P10U7 100-110 1.66 1.80 5.5 7 1434 822 184 2447±45 9/12 1.01±0.18 410±70P11U5 90-100 1.58 2.15 7.2 9 1464 917 186 2576±46 10/12 0.58±0.15 230±60P12U5 90-100 1.74 2.58 8.3 10 1646 1050 186 2892±51 11/12 1.40±0.45 490±150P13U6 70-80 1.49 2.53 7.5 10 1458 951 193 2611±47 11/12 0.57±0.19 220±70P14U7 60-70 1.66 4.20 7.7 13 1779 1177 199 3168±55 12/12 1.46±0.34 460±110P14U13 170-180 1.83 4.50 10.8 16 1998 1388 169 3570±61 11/12 0.73±0.22 200±60FPU3 40-50 1.66 2.80 6.4 9 1490 920 169 2587±62 10/12 1.68±0.59 650±230FPU15 170-180 1.58 3.80 5.4 10 1534 961 214 2720±78 8/12 1.80±0.34 660±130Aliquots used �– the number of aliquots used for the average De out of the aliquots measured (distinct outliers were removed)

a

b

s sR

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

HWM 25-26/5/05 flood 1,140 m3s-1

Colorado River Channel water level 14/6/05

425 m3s-1

0 2 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48

m 12.5

P-1

P-2

P-4

P-5

P-8 P-6

P-9

P-10

P-11

P-12

P-13

P-14

RR

|| |||

|||||

||

xxxx

xxxx

Elev

atio

n ab

ove

Sum

mer

Wat

er L

evel

(m)

Distance from Rt. Canyon wall (m)

Upper depression

Lower depression

W E

xxxx

xxxx

Floodplain

xxxx Driftwood line

Pit no. 6

Alluvial cobbles and boulders

Large slope clasts

High Water Marks

Surface of SWD

Base of SWD

P-6

HWM

10. Cross section perpendicular to the slackwater deposit relict at the BLM-TO study site including the vertical and horizontal locations of the pits in relation to the summer water level of the Colorado River in June 2005. Note that the SWD trap is composed of 2 separate depressions �– an upper depression (pits-1-8) and a lower depression (pits 9-14). Pit 1 is separated and located at the base of a rocky bench of the canyon wall

U d i

m 12.5

P-1

P-2

P-4

P-5

P-8 P-6

s ssRR

P-9

P-10

P-11

P-12

P-13

P-14P

RRRR

xxxx

xxxxx

xxxxx

American Geophysical Union (AGU) annual meeting, San Francisco USA 2011

Dis

char

ge, i

n cu

bic

met

ers

per

seco

nd

100

1000

10000

Annual Exceedance Probability

0.0050.010.050.10.20.51

Dis

char

ge, i

n cu

bic

met

ers

per

seco

nd

100

1000

10000

Hirsch Stedinger plotting postion Modeled flood frequency (Log-Pearson Type 3), EMA95th percentile confidence limits, EMA

Hazen plotting position Modeled flood frequency (Log-Pearson Type 3), fldfrq3 95th percentile confidence limits, fldfrq3

Gaged record only

Gaged record plus paleoflood data

A

B

5. The study reach of the Colorado River canyon, 17 km upstream of Moab, Utah

17. Preliminary results of ood frequency analysis at the Colorado River using (a) the gaged record only (b) gaged record plus paleoood data. The analysis is based on the fldfrq3 model from the Bureau of Reclamation that uses Bayesian statistics and the PeakfqSA from the USGS that uses EMA analysis. The results of both models are similar!. Note that the USGS model stops at the 500-year ood. The top �“gaged�” line of results are just the gaged oods and don�’t include any paleooods

Table 1: A comparison between results of ood frequency analyses of the present study and previous study

Recurrence Interval(years)

Gaged Record (USGS)(m3s-1)

Gaged +paleooods(m3s-1)

100 2,765 5,490

500 3,400 8,730

1,000 ------- 10,500

PMF(10,000?) 8,500 -------