U.S. Department of the Interior

U.S. Geological Survey

Analysis of Virtual ShoreRelation to Archaeologicin the Colorado River EcoHelen Fairley, Socio-cultural Program ManagerHoda Sondossi, Socio-cultural Program Geomorp

Technical Work Group Meeting, PhoenixMarch 16-17, 2009
Background: AMWG M

To review the flow levels (as indicated b

available shorelines of the HEC-RAS massociated with each of the 158 archaethat have been identified for monitoring mitigation of impacts, and to report this and any recommendations with regard data would fit into the process of makinsites to be monitored and/or impacts mAMWG at its next meeting, with the prorecommendation will not alter the choiselected for impacts mitigation in FY09
TWG Motion

The CRAHG will review the reviseshoreline analysis, in relation to archaeological sites, and bring recommendations to the TWG at meeting focusing its review on thof the AMWG motion assessing thflow lines as simulated (with uncethe HECRAS model and other err
Water Surface Model (Magirl and ot

USGS Scientific Investigation Report 2

 1D model built in HEC-RAS (Hydrologic Engineering 

Analysis System) -- a “standard step” model

 Uses 1D equations of energy and continuity to pred

surface elevation) for known discharges at specific 

 2,680 cross-sections generated between Lees Ferry  Uses high-resolution topography for stage above 22

and synthetic bathymetry below

 Model for prediction of stage ONLY—other paramet

roughness, velocity) adjusted for each cross-sectio

 Stage predicted to within:

 ± 0.4 m (1.31 ft) for discharge less than 1,300 m3/s (<46,000 cfs ± 1.0 m (3.28 ft) for discharge ranging 1,300

−2,500 m3/s (46,000

 ± 1.5 m (4.92 ft) for discharge ranging 2,500

−5,900 m3/s (88,000
Basic Diagram of Model Co

Accurate topographyabove 8,000 cfs stage

Synthetic bathymetry below 8,000 cfs

Mod

Modeling Virtual Shore

 Uses topography generated from 2002 

sensed aerial imagery (photogrammetr

 Assigns elevation values from 1D mod

cross-sections, then interpolates betwesections to generated a 3D surface

 Generates “areas of inundation” by co

elevation of the water surface layer wittopographic layer



Profile view showing interse

modeled water surfaces with 

125k

170k

210K

Archeological site
Virtual shoreline mapview
Analysis incorporates erro

Limitations of Analy

 Only ground surface at archaeological sites wa

how each flow level could affect 3D sites was n

 Analysis depends on accurate outline of archa

area – small boundary changes may produce d

 Error range may exceed preceding or subsequ

upper error range of 170K exceeds lower & mid 

 Modeled water-surface elevations are based on 

topography—changes in local topography (e.gfrom side canyon) may change local stage-discrelationships

 Synthetic bathymetry suboptimal— future mea

from channel mapping project may be used to 
Virtual shorelines at excava

SITE Project Lowe

partia

C:13:291 MNA-GRCA 25kC:13:010 MNA-GRCA 45KC:13:371 MNA-GRCA 45KC:02:096 MNA-GRCA 97KC:13:099 MNA-GRCA 97KC:13:070 MNA-GRCA 97KC:13:347 MNA-GRCA 97KB:15:138 MNA-GRCA 97K+G:03:020 MNA-GRCA 125K
Virtual shorelines at excava

SITE Project Lowe

partia

C:02:032 BOR TP 2008 N/A (A:15:039 BOR TP 2008 125KC:13:323 BOR TP 2008 >210C:13:327 BOR TP 2008 >210C:02:098 BOR TP 2009 45K+C:13:069 BOR TP 2009 97k+C:13:385 BOR TP 2009 >210C:13:387 BOR TP 2009 170KG:03:064 BOR TP 2009 97K+
False negative: Archaeologica

affected but GIS analysis says 

Archaeological deposits below ground surface

Mapped Surface Area of Site

210K Modeled wa

170K

125K

97K
False positive: GIS analysis in

site is inundated when it is not

Virtual sho

Cultural site on top of a terrace with surface artifacts and a deep gully cut

GIS analysis would indicate that a portion of this site was inundated, whe

materials are affected. 

Cultura

artifacts

Terrace 

artifacts

gully


QUESTIONS?