Smith AGU

Greenland supraglacial rivers during the extreme 2012 melt seasonLaurence C. Smith1, Asa K. Rennermalm2, Carl J. Legleiter3, Alberto E. Behar4, Vena W. Chu1, Richard R. Forster5, Colin J. Gleason1, Adam LeWinter6, Samiah E. Moustafa2, Brandon T. Overstreet3, Lincoln H. Pitcher1, Marco Tedesco7, Kang Yang1

1 UCLA, 2Rutgers, 3U. Wyoming, 4NASA JPL, 5U. Utah, 6CRREL, 7CUNY

American Geophysical Union, 6 December 2012, San Francisco

Ice margin melt insufficient to explain Watson River flooding

[C43C-0616 Asa Rennermalm]

Simultaneious flooding in the Isortoq River

[H31E-1162 Colin Gleason]

6/13/11

7/13/12


Acoustic Doppler Current Profile (ADCP) measurements for velocity, bathymetry, water surface slope, roughness coefficient


Manual radar and field surveysof flow velocity, width, depth,slope, roughness coefficient


EMPIRICAL HYDRAULICS

[C43C-0618 Vena Chu]

Parameter Units Min Mean Max

Discharge (Q) m3s-1 0.01 3.75 28.78

Width (w) m 0.20 4.62 19.06

Avg depth (d) m 0.03 0.48 1.950

Avg surface velocity (v) ms-1 0.24 1.09 2.59

Cross-sectional area (A) m2 0.01 5.76 29.00

Wetted perimeter (P) m 0.21 6.01 31.14

Width/Depth Ratio (F) 1.27 11.23 42.17

Hydraulic radius (R) m 0.02 0.36 1.63

Froude number (Fr) 0.06 0.89 3.12

Manning's resistance coefficient (n) 0.01 0.14 1.28

Water surface slope (S) 0.001 0.032 0.088

Manual radar and field surveysof flow velocity, width, depth,slope, roughness coefficient


“Drone-boat” measurements of water column spectra and attenuation (ASD), and depth (echo sounder)


Sacrificial GPS drifters(3 velocity, 1 depth sounder)


Sacrificial GPS drifters(3 velocity, 1 depth sounder)

Typical flow velocities ~ 0.5-2 m/s

Max 6.6 m/s with supercritical flow (Fr = 3.6)d super


32 WorldView-2 scenes acquired simultaneously with field campaigns (July 18-23)


(Yang and Smith, in press)


[C43C-0619 Kang Yang]

(Yang and Smith, in press)


For this July 18-23 WV2 mosaic:-5,514 km2 mapped with WV2 (~1100m to 1600m a.s.l.)

-5,928 km total length “blue-water” rivers

-Typical survival length scale ~10-20 km

-596 actively flowing moulins

-100% of mapped rivers terminate in moulins, including lateral breaches from all remaining lakes


Modeled potentiometric depressions- GIMP DEM(Howat et al, 2012)- basal topography(Bamber et al, 2012)

C43C-0614 (Lincoln Pitcher)

C43C-0623 (Samiah Moustafa)


Can supraglacial water fluxes be estimated from space?

- “Universal” supraglacial river hydraulic geometry relationships holds promise using an empirical approach


Can supraglacial river bathymetry be estimated from space?


Conclusions & future work

Greenland’s supraglacial rivers are large, extensive, and hydraulically efficient.

During July 18-23, 2012, these rivers were transporting large fluxes of meltwater over and into the ice sheet, with virtually no depression storage and 100% termination into moulins.

This observation, combined with proglacial discharge measurements at the ice edge, suggests that record terrestrial floods downstream received significant meltwater inputs from the ice sheet interior.

Field spectral and hydraulic measurements hold promise for calibrating remote sensing WorldView-2 data for estimating supraglacial river fluxes. This goal, together with “closing” the water balance (from ADCP discharge measurements in the Isortoq and Watson rivers) are key future objectives.


Logistics support:CH2MHill Polar Field ServicesKISSAir Greenland

Special thanks to:Paul Morin (Polar Geospatial Center)Claire Porter (Polar Geospatial Center)Ian Howat (OSU)Jonathan Bamber (U. Bristol)Ian Joughin (U. Washington)

Supported by the NASA Cryosphere Program Program Manager Thomas Wagner (grant NNX11AQ38G)

Poster session this afternoon:

C43C-0614 Lincoln PitcherC43C-0616 Asa RennermalmC43C-0618 Vena ChuC43C-0619 Kang YangC43C-0623 Samiah Moustafa


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