U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2007–1314

Prepared in cooperation with the North Carolina Division of Water Resources

Review of Selected Documents Related to Flooding at City of 

Salisbury Facilities on the Yadkin River Upstream from High 

Rock Dam, North Carolina, September 2007

Review of Selected Documents Related to 

Flooding at City of Salisbury Facilities on 

the Yadkin River Upstream from High Rock 

Dam, North Carolina, September 2007

By Jerad D. Bales

Prepared in cooperation with the North Carolina Division of Water Resources

Open-File Report 2007–1314

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Bales, J.D., 2007, Review of selected documents related to flooding at City of Salisbury facilities on the Yadkin River 

upstream from High Rock Dam, North Carolina, September 2007: U.S. Geological Survey Open-File Report 2007–1314, 

9 p. (available online at http://pubs.water.usgs.gov/ofr2007-1314)
iii

Contents

Abstract ..........................................................................................................................................................1

Introduction ....................................................................................................................................................1

Purpose and Scope .............................................................................................................................2

Materials Reviewed .............................................................................................................................2

One-Dimensional Hydraulic Modeling ......................................................................................................3

Stone & Webster Modeling ................................................................................................................3

Federal Energy Regulatory Commission Modeling ........................................................................5

Hazen and Sawyer Modeling .............................................................................................................5

One-Dimensional Sediment-Transport Modeling ....................................................................................7

Other Studies .................................................................................................................................................8

Summary and Further Analyses .................................................................................................................8

References .....................................................................................................................................................9

Figures

1. Map showing Yadkin River, South Yadkin River, Grants Creek, and upstream 

end of High Rock Lake, North Carolina ....................................................................................2

Tables

1. Characteristics of one-dimensional steady-flow modeling applied to 

High Rock Lake and the Yadkin River, North Carolina, by Stone & Webster, 

the Federal Energy Regulatory Commission, and Hazen and Sawyer ................................4
iv

Conversion Factors and Datums

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Volume

cubic foot (ft3) 0.02832 cubic meter (m3) 

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Specific capacity

gallon per minute per foot [(gal/min)/ft)] 0.207 liter per second per meter [(L/s)/m]

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information (latitude/longitude) is referenced to the North American 

Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.
Abstract

This report documents a review of the hydraulic and 

sediment-transport models developed by the City of Salisbury, 

Alcoa Power Generating, Inc., and the Federal Energy 

Regulatory Commission to address issues of flooding and 

sedimentation in the vicinity of Salisbury’s water-supply 

intake 19.4 miles upstream from High Rock Dam. The 

objective of the review was to determine if the modeling 

results submitted by Salisbury clearly demonstrate that the 

presence of High Rock Dam has led to an increase in water 

levels at Salisbury facilities or, conversely, if the documents 

of Alcoa Power Generating, Inc., demonstrate that High 

Rock Dam has not had an effect on water levels at Salisbury 

facilities. No new data were collected as a part of the review, 

and the models developed by involved parties were not tested 

during the review. Some historical discharge-measurement 

notes and previously published reports were checked as part of 

the review.

The one-dimensional hydraulic modeling results 

submitted by Alcoa Power Generating, Inc., did not assess the 

effects of changes in bathymetry on changes in flood levels 

at Salisbury’s facilities because pre-impoundment conditions 

were not simulated. Hydraulic modeling performed by consultants for the City of Salisbury seems to indicate that both the 

presence of the dam in the absence of any post-impoundment 

sedimentation and changes in bathymetry between preimpoundment and 1997 conditions have resulted in increased 

water levels relative to pre-impoundment conditions at 

Salisbury facilities on the Yadkin River for a fairly wide range 

of flows. The degree to which the dam and the changes in 

bathymetry have affected flood levels at the Salisbury facilities 

relative to pre-impoundment conditions is open to discussion 

because of uncertainty in topographic/bathymetric data and the 

absence of calibration and sensitivity testing of the hydraulic 

models. None of the three hydraulic models appears to have 

been calibrated to or tested against measurements, and no 

sensitivity testing was reported. Sediment-transport modeling 

results submitted by the City of Salisbury were calibrated, 

well documented, and provide a good understanding of the 

expected growth of the sediment delta in the upper end of 

High Rock Lake. Simulations made using this model seem 

to have demonstrated that the presence of the dam and the 

growth of the delta have resulted in increases in water-surface 

elevations at Salisbury’s facilities over a range of flows and 

that these increases are expected to increase through time if 

current conditions remain unchanged.

Introduction

The City of Salisbury has operated a water-supply intake 

at the confluence of the Yadkin and South Yadkin Rivers since 

1917 (fig. 1). The City maintains that the operation of High 

Rock Dam, completed in 1927 and currently operated by 

Alcoa Power Generating Inc. (APGI), has created a sediment 

delta in the headwaters of High Rock Reservoir and that this 

delta has caused (1) increased flooding of the water-supply 

pump station, (2) sediment deposition around the pump intake, 

and (3) increased flooding at a wastewater-treatment plant 

pump station located near the mouth of Grants Creek (fig. 1).

The APGI currently (2007) is seeking to relicense four 

hydroelectric stations, including High Rock Dam, on the 

Yadkin-Pee Dee River. The license for the hydroelectric 

stations and the reservoirs that support them is granted by the 

Federal Energy Regulatory Commission (FERC). The North 

Carolina Department of Environment and Natural Resources 

(NCDENR) is participating in the relicensing process. 

NCDENR has signed a Relicensing Settlement Agreement 

with APGI and subsequently must respond to an application 

by APGI for a section 401 water-quality certification for the 

stations. 

The City of Salisbury has requested that APGI address 

the issue of flooding and sedimentation at the City’s facilities 

on the Yadkin River during the FERC relicensing process 

settlement agreement. APGI maintains that (1) their operation 

is too far downstream to affect the City’s pump stations, 

(2) the Yadkin River has a naturally high sediment load, and 

(3) the pump station is in the floodplain. Because of APGI’s 

position, Salisbury retained consultants to develop hydraulic 

Review of Selected Documents Related to Flooding at City 

of Salisbury Facilities on the Yadkin River Upstream from 

High Rock Dam, North Carolina, September 2007

By Jerad D. Bales
and sediment-transport models for the reach in question. The 

final report was submitted to FERC on February 26, 2007, 

as part of Salisbury’s relicensing scoping comments. APGI 

also has funded studies of their own, including a review of the 

City’s documents.

Because of the complexity of the issues, NCDENR 

enlisted the U.S. Geological Survey (USGS) to review 

documents from both APGI and the City of Salisbury related 

to flooding at the City’s facilities. The independent review 

is needed in order to assist NCDENR in their review of the 

application of APGI for a section 401 water-quality certification and subsequent renewal of the FERC license for High 

Rock Dam.

Purpose and Scope

The purpose of this report is to summarize a review of 

the hydraulic and sediment-transport models developed by the 

City of Salisbury, APGI, and FERC, 

as well as related data and information. The objective of the review 

was to determine if the documents 

submitted by Salisbury clearly 

demonstrate that the presence of High 

Rock Dam has led to an increase in 

water levels at Salisbury facilities, 

or conversely if APGI documents 

demonstrate that High Rock Dam has 

not had an effect on water levels at 

Salisbury facilities. Documents that 

were included in the review are listed 

in the following section. The review 

included a site visit to the Yadkin and 

South Yadkin Rivers and downstream 

to High Rock Lake. No new data were 

collected as a part of the review, and 

the models developed by the parties 

involved were not tested during the 

review. Some historical dischargemeasurement notes and previously 

published reports were checked as part 

of the review. 

This report is structured in 

the following manner—first, the 

documents that were reviewed are 

listed, next are the reviews of the 

hydraulic modeling and related 

documents, followed by reviews of 

the sediment-transport modeling 

conducted by the City’s consultant 

and comments provided by APGI’s 

consultant. A brief review of other 

documents provided by the City and 

APGI is followed by a summary and 

recommendations.

Materials Reviewed

The documents reviewed during this study are as follows:

Documents from the City of Salisbury

Technical Report—“High Rock Dam and High Rock 

Lake sedimentation flooding effects as estimated using 

HEC–RAS modeling, January 2006,” prepared by Hazen 

and Sawyer for Salisbury-Rowan Utilities (hereafter 

referred to as SAL–1)

Correspondence—Letter from V. Randall Tinsley to 

Secretary Magalie Salas, Federal Regulatory Commission, dated February 23, 2006 (SAL–2)

Report—“Numerical sedimentation investigation, Yadkin 

River, North Carolina, February 20, 2007,” prepared by 

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   Review of Documents Related to Flooding on the Yadkin River Upstream from High Rock Dam, NC, September 2007

Figure 1. Yadkin River, South Yadkin River, Grants Creek, and upstream end of High Rock 

Lake, North Carolina.

0 2 4 MILES

0 2 4 KILOMETERS

South Yadkin River

Yadkin River

Grants Creek

High Rock Lake

I - 85

US Hwy. 70

State Hwy. 150

N
R.R. Copeland, Mobile Boundary Hydraulics for the City 

of Salisbury (SAL–3)

Report—“High Rock Dam and sediment delta flooding 

and sedimentation effects (1927–2058) on City of Salisbury critical infrastructure, February 2007,” prepared by 

Martin Doyle for the City of Salisbury (SAL–4)

Correspondence—Letter from R.R. Copeland and W.A. 

Thomas to Matt Bernhardt, Salisbury-Rowan Utilities, 

May 8, 2007, in response to Williams’ affidavit (SAL–5)

Correspondence—Letter from Martin Doyle to Matt 

Bernhardt, Salisbury-Rowan Utilities, May 9, 2007, in 

response to Shiers’ affidavit (SAL–6)

Documents from Yadkin / Alcoa Power Generating, Inc.

Report—“Review of January 1998 flood of Yadkin 

River, February 1998,” prepared by Stone & Webster for 

Yadkin, Inc. (hereafter referred to as APGI–1)

Report—“Yadkin Hydroelectric Project—FERC 

No. P–2197–073, Alcoa Power Generating, Inc., 

responses to Federal Energy Regulatory Commission’s 

September 14, 2006, and November 22, 2006, additional 

information requests, April 6, 1998,” prepared by Julian 

Polk, Yadkin, Inc. (APGI–2)

Correspondence—Letter from Gene Ellis, Licensing and 

Property Manager, APGI, to Secretary Magalie Salas, 

FERC, December 13, 2006, in response to the additional 

information request for Yadkin Hydroelectric Project 

(APGI–3)

Affidavit of David Williams, Ph.D., P.E., March 26, 2007 

(APGI–4)

Affidavit of Paul F. Shiers, P.E., March 27, 2007 

(APGI–5)

“Consolidated answer of Alcoa Power Generating, Inc., 

to petitions to intervene and comments in response to 

scoping document 1,” prepared by LeBoeuf, Lamb, 

Greene, and MacRae, LLP, Counsel to Alcoa Power 

Generating, Inc., [undated] (APGI–6)

Report—“Sediment fate and transport report, final report, 

November 2005,” prepared by Normandeau and Associates, Inc., and PB Power (APGI–7)

Documents from FERC

Correspondence—Letter from Jerrold Gotzmer, 

Director, FERC, to Julian Polk, Yadkin, Inc., dated 

March 11, 1998 (hereafter referred to as FERC–1)

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Correspondence—Letters from Jerrold Gotzmer, 

Director, FERC, to Ron Qualkenbush, dated May 6, 

1998, and May 21, 1998 (FERC–2)

Report—“Hydraulic modeling report for Yadkin 

Project—North Carolina, Alcoa Power Generating, 

Inc. (APGI), June 2003,” prepared by Federal Energy 

Regulatory Commission (FERC), and transmittal letter 

from FERC to David Treme, Ron Qualkenbush, and 

Milton Crowther (FERC–3)

One-Dimensional Hydraulic Modeling

One-dimensional hydraulic models were developed by 

Stone & Webster for APGI (APGI–1), FERC (FERC–2), and 

Hazen and Sawyer for Salisbury-Rowan Utilities (SAL–1). 

Important aspects of these models are summarized in table 1.

Stone & Webster Modeling

In January 1998, a campground approximately 20 miles 

(mi) upstream from High Rock Dam was flooded during high 

flows. The Stone & Webster model was created to evaluate 

“the effect that the operation of High Rock Dam may have had 

on this flooding” (APGI–1). The model extent is from High 

Rock Dam to the confluence of the Yadkin and South Yadkin 

Rivers, 19.4 mi upstream from High Rock Dam (or river mile 

(RM) 19.4). An estimated inflow hydrograph at the upstream 

boundary and a range of downstream water-surface elevations 

at the dam were used for this model. 

Cross sections were scaled from topographic maps and 

were assumed to be trapezoidal in shape. The report does not 

specify how the bottom and(or) top width of the cross sections 

were determined nor how the side slopes were determined. 

Apparently, more detailed cross sectional data were available 

(APGI–7) from 1997 surveys, but these data were not used. 

The channel bed slope was based on the assumption of a linear 

slope between the dam and RM 18.1; the slope was assumed 

to be zero between RM 18.1 and RM 19.4. It does not appear 

that the model was calibrated.

The report concluded that, for existing conditions, the 

water level at RM 19.4 was independent of the lake level at 

High Rock Dam. The report also concluded that water levels 

at RM 19.4 were affected by a channel constriction at the 

railroad bridge near the NC–150 bridge and by a narrow bend 

in the river at about RM 18.4. 

The conclusion regarding the relation of water levels 

at High Rock Dam and water levels at RM 19.4 for current 

conditions is reasonably supported by the modeling for current 

conditions. The conclusions could be strengthened by conducting a sensitivity analysis of the effects of the assumed channel 

geometry and bed slope on simulated water levels at RM 19.4. 

No evidence is given in the report for the conclusion that the 

channel constriction and narrow bend in the river control water 

•

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One-Dimensional Hydraulic Modeling 
Table 1. Characteristics of one-dimensional steady-flow modeling applied to High Rock Lake and the Yadkin River, North Carolina, by 

Stone & Webster, the Federal Energy Regulatory Commission, and Hazen and Sawyer. — Continued

[FERC, Federal Energy Regulatory Commission; mi, mile; ft, foot; NGVD 29, National Geodetic Vertical Datum of 1929; ft3/s, cubic foot per second]

Stone & Webster FERC Hazen and Sawyer

Purpose

Evaluate effects of High Rock Dam operation on upstream flooding; at request of 

FERC, additional analysis was conducted 

to evaluate upstream flooding with no 

dam present.

“Determine the influence of the High Rock 

Reservoir elevation on the water-surface 

elevation at the confluence of the Yadkin 

and South Yadkin Rivers” (FERC–3).

“...evaluate the effects of High Rock Dam 

and dam-induced sediment accumulation on 

the frequency and magnitude of flooding...at 

the Yadkin-South Yadkin confluence.”

Cross-section locations

At bends, constrictions, and contractions; 

although the number was not specified, 

based on the Hazen and Sawyer report 

(SAL–1), the number was probably 24 

over a 19.4-mi reach.

Started with Stone & Webster model; added 

cross sections in reaches where needed; 

extended model reach upstream from 

confluence.

24 cross sections over the 19.4-mi reach; same 

locations as Stone & Webster model.

Source of geometry data

Scaled from 1:24,000 topographic maps 

with 10-ft contour intervals.

10-ft contours developed from 100-ft digital 

elevation model. Centerline of channel and 

bank elevations from 1:24,000 topographic 

maps.

Pre-impoundment conditions—1917 topographic map (1:4,800) with 5-ft contours 

above 630-ft elevation and 10-ft contours 

below 630-ft elevation. Post-impoundment 

conditions—1997 surveys.

Channel cross sectional geometry

Assumed to be trapezoidal; assumptions 

regarding top width, bottom width, and 

side slope were not given.

Assumed to be trapezoidal with 4:1 side slope 

from channel banks to the bed.

Trapezoidal cross section assumed below 

1997 water surface.

Reach length

High Rock Dam to confluence of YadkinSouth Yadkin, or about 19.4 mi.High Rock Dam to 10,000 ft upstream from 

Yadkin-South Yadkin confluence, or about 

21.3 mi.

High Rock Dam to confluence of YadkinSouth Yadkin, or about 19.4 mi.

Calibration

No mention of calibration. No mention of calibration. No mention of calibration.

Bed configuration

Assumed that channel bottom was at 

613.6-ft elevation at 7,000 ft downstream 

from Yadkin-South Yadkin confluence; 

flat upstream to confluence; linear slope 

to dam.

Same as Stone & Webster model from point 

7,000 ft downstream from confluence to dam 

(linear bed with slope = 0.00062); upstream 

from confluence, slope was 0.0002 based on 

topographic maps.

Linearly interpolated between the dam and 

Salisbury’s water-supply intake.

Bed slope

0.00062 0.00062 and 0.0002 (see above). Pre-impoundment slope = 0.0005.

Manning’s n

0.035 in channel; 0.05 in overbank. Not reported; assumed to be the same as Stone & 

Webster.

Not reported; assumed to be the same as 

Stone & Webster.

Expansion and contraction coefficients

0.1 and 0.3, respectively, except at NC-150 

bridge, where the values were 0.3 and 

0.5, respectively.

Not reported; assumed to be the same as Stone & 

Webster.

Not reported; assumed to be the same as 

Stone & Webster.

Conditions simulated

1998 flood and current conditions. 2003 flood, a range of flows, and current conditions.No dam, current conditions, and possible 

future conditions for a range of flows at 

confluence.

Vertical datum

Not clear whether it was NGVD 29 or 

other.

“...local vertical datum” (FERC–3). NGVD 29

 Review of Documents Related to Flooding on the Yadkin River Upstream from High Rock Dam, NC, September 2007
levels at RM 19.4 during high flows. A sensitivity analysis 

of the effects of the expansion and contraction coefficients 

and simulations without the bridges in place is needed to give 

credibility to the conclusion regarding the effects of bridge 

constrictions. It is not clear how results from the onedimensional model were used to make conclusions regarding 

the effects of the bend. 

Doyle (SAL–4) briefly described the HEC–RAS modeling that was conducted to evaluate the effects of the bridges on 

water levels at the Salisbury facilities. His analysis indicated 

that the upstream effects of the bridges are minimal, even 

under high flows. Essentially no details are given in Doyle’s 

report regarding the model, so it is impossible to assess these 

conclusions.

The results of the Stone & Webster modeling are not 

directly relevant to the issue of the effects of the presence of 

High Rock Dam or the delta on flooding at RM 19.4. This 

is because no simulations for pre-impoundment or pre-delta 

conditions were performed for comparison with 1998 conditions. Moreover, simulations for conditions with and without 

the bridges were not conducted, making it impossible to assess 

the effects of the bridges on water levels at the Salisbury 

facilities.

Federal Energy Regulatory Commission 

Modeling

 The Federal Energy Regulatory Commission (FERC) 

obtained the HEC–RAS model used by Stone & Webster 

(APGI–1) to conduct additional one-dimensional hydraulic 

modeling investigations (FERC–3), and particularly to 

“determine the influence of the High Rock Reservoir elevation on the water surface elevation at the confluence of the 

Yadkin and South Yadkin Rivers” during a 2003 flood. The 

model domain was extended upstream to about RM 21.3, and 

additional cross sections were added to the model to provide 

greater resolution at locations where FERC concluded that 

the Stone & Webster cross sections were too widely spaced. 

The model was used to simulate water-surface profiles for 

the March 2003 flood for a range of water levels at High 

Rock Dam. FERC used a digital elevation model to develop 

a topographic map that perhaps provided more detailed cross 

sectional information than was in the Stone & Webster model, 

but the detailed data from the 1997 survey were not used in 

the model. The approach used by FERC was much the same 

as the approach used in the Stone & Webster study other than 

the source of the topography data and the flood to which the 

model was applied. As a result, the conclusions from this 

study were essentially the same as those from the Stone & 

Webster study—water level at RM 19.4 is essentially independent of water level at High Rock Dam for flows between 

40,000 and 70,000 cubic feet per second (ft3/s) under current 

conditions. As with the Stone & Webster study, no simulations 

were produced for pre-impoundment or for 1917 bathymetric 

conditions for comparison to current conditions.

Hazen and Sawyer Modeling 

Hazen and Sawyer (SAL–1) constructed a HEC–RAS 

model for High Rock Lake and a portion of the Yadkin River 

to “evaluate the effects of High Rock Dam and dam-induced 

sediment accumulation on the frequency and magnitude of 

flooding . . . at the Yadkin-South Yadkin confluence.” This 

statement presumes the conclusion that all of the sediment 

accumulation in the reservoir is “dam-induced.” The modeling 

effort was unique in two ways—(1) 1997 topography was 

Table 1. Characteristics of one-dimensional steady-flow modeling applied to High Rock Lake and the Yadkin River, North Carolina, by 

Stone & Webster, the Federal Energy Regulatory Commission, and Hazen and Sawyer. — Continued

[FERC, Federal Energy Regulatory Commission; mi, mile; ft, foot; NGVD 29, National Geodetic Vertical Datum of 1929; ft3/s, cubic foot per second]

Stone & Webster FERC Hazen and Sawyer

Important conclusions

At flow rates greater than 30,000 ft3/s, 

water level near Yadkin-South Yadkin 

confluence is independent of High Rock 

Dam operations. Reason: downstream 

constrictions at railway bridge and 

NC-150, and sharp bend in river.

Operation of High Rock Reservoir did not have 

a significant effect on water levels at YadkinSouth Yadkin confluence for March 2003 flood.

Pre-impoundment and current conditions 

were simulated, showing increases in watersurface elevations over a range of flows at 

Salisbury’s intake as a result of changes in 

reservoir bathymetry.

Limitations

No analysis of pre-dam or pre-bridge conditions; therefore, not directly relevant to 

evaluation of effects of delta on flooding 

at Salisbury’s facilities. No sensitivity 

tests. 1997 topography was not used.

No analysis of pre-dam or pre-bridge conditions; 

therefore, not directly relevant to evaluation of 

effects of delta on flooding at Salisbury’s facilities. No sensitivity tests. 1997 topography was 

not used.

No mention of pre-impoundment bridges. No 

sensitivity tests. All aspects of model not 

well documented.

One-Dimensional Hydraulic Modeling 
used to construct cross sections for current-conditions model 

input, and (2) pre-impoundment conditions were simulated. 

The 1997 topographic survey was conducted by APGI 

contractors when the lake level was at 12 feet (ft) below full 

pool. The survey extended out from the full-pool elevation 

about 0.25 mi. A topographic map with 2-ft contour intervals 

was prepared (APGI–7). Hazen and Sawyer also simulated 

pre-impoundment conditions by using 1917 topographic data 

obtained from maps provided by APGI and estimating channel 

cross sectional shape below the 1917 water surface. Simulations were made assuming the dam was not in place and using 

1917 topography. 

Results indicated that the presence of the dam alone, with 

no sediment accumulation (that is, 1917 bathymetry), may 

have led to an increase in water levels at RM 19.4 for flows 

less than about 80,000 ft3/s. At a flow of about 20,000 ft3/s, 

the increase may be about 6 ft relative to pre-impoundment 

conditions. The increases relative to pre-impoundment 

conditions were greater when simulations were made using 

1997 topography/bathymetry, with an increase of about 10 ft 

at a flow of about 20,000 ft3/s. Water levels for estimated 2038 

conditions were linearly extrapolated by assuming that the 

average annual increase in water-surface elevation for each 

flow rate during 1927–97 continues through 2038. 

Various aspects of the Hazen and Sawyer model are 

poorly documented, including the Manning’s n, expansion and 

contraction coefficients, and treatment of bridges for historic 

conditions (that is, did the simulations for 1917 include the 

bridges from 2005, the bridges from 1917, or no bridges?). In 

addition, as in the Stone & Webster and the FERC models, the 

Hazen and Sawyer model does not appear to have been calibrated or compared to observed conditions. Nevertheless, this 

model seems to clearly demonstrate that the presence of the 

dam and the changes in bathymetry likely have had an effect 

on water levels at the Salisbury intakes relative to the preimpoundment conditions. The exact magnitude of the change 

is less certain, primarily because of uncertainties in current 

and historic bathymetry, because model performance has not 

been tested through comparison to measured conditions, and 

because all aspects of the model were not documented.

Doyle (SAL–4) summarized the work of Hazen and 

Sawyer (SAL–1) in his report. The hydraulic modeling aspects 

of Doyle’s report were subsequently reviewed by APGI’s 

consultant, Parsons Brinkerhoff (PB; APGI–5). The PB review 

identified four major areas of concern, which are listed below, 

along with observations regarding the concerns. It should be 

noted, however, that none of these criticisms by PB relates 

directly to the issue of the effects of High Rock Lake on 

possible increased water levels at Salisbury’s facilities but 

rather to peripheral issues related to the details of the analysis 

by Salisbury’s consultants. Doyle (SAL–6) subsequently 

responded to PB’s criticisms (APGI–5). 

The resolution of the topographic data used in Hazen 

and Sawyer’s modeling, in particular the pre-dam 

conditions, does not justify Doyle’s conclusions. 

▪

In fact, Doyle reported water-surface elevations to the 

nearest 0.1 ft for future conditions. These numbers should be 

used with caution. Copeland (SAL–3), however, addressed the 

issue of uncertainty with regard to topography in the sedimenttransport modeling, although the sediment-transport model 

did not address the effects of High Rock Dam on water levels 

at Salisbury’s intake. Doyle (SAL–6) also noted that Stone & 

Webster’s modeling (APGI–1) did not include an analysis of 

the sensitivity of model results to topographic elevations.

Doyle calculated the “design flow” of 121,000 ft 3/s 

at RM 15.2 rather than at the water-supply intake at 

RM 19.4. 

Doyle apparently used records collected at RM 15.2 to 

represent conditions at RM 19.4. The increase in drainage area 

between the two sites is about 90 mi2, or less than 3 percent 

of the total drainage area. The at-station 100-year recurrence 

interval flow at RM 15.2 is 166,000 ft3/s based on records 

collected during 1896–1927 (Pope and others, 2001), which 

is less than Doyle’s “design flow.” These issues, however, do 

not directly relate to the question of the effect of High Rock 

Lake on water levels at Salisbury’s intake but rather to the 

magnitude of the effect of selected conditions (100-year flow, 

“design flow,” etc.). 

As an aside, the methods used by Doyle (SAL–4) and 

Copeland (SAL–3) may underestimate the 100-year flood at 

the confluence of the Yadkin and South Yadkin Rivers. Pope 

and others (2001) provide methods for estimating flood flows 

at ungaged sites. Greater use of at-station flood-frequency 

information for the Yadkin River at Salisbury and South 

Yadkin River at Cooleemee also may be helpful. 

Doyle (SAL–6) asserts that inflows from Grants Creek 

would not affect peak flows measured at RM 15.2, because 

Grants Creek likely would peak before the Yadkin River. This 

argument is reasonable, although no data were provided to 

support this assertion for the particular case of the 1916 flood.

PB asserted that Doyle mischaracterized APGI’s statements regarding causes for sediment accumulation in 

the reservoir. 

This criticism may be valid but is not relevant to the issue 

of effects of High Rock Dam on water levels at Salisbury’s 

intake. APGI argued that sediment accumulation is caused, in 

part, by natural bends in the river and that channel constrictions from bridges contribute to flooding at Salisbury’s 

facilities. As noted above (and by Doyle, SAL–6), however, 

the evidence presented by APGI to substantiate these claims 

is weak to nonexistent, at least in the documents available for 

review. 

PB also indicated that Doyle did not present evidence that the 

river was in geomorphic equilibrium prior to 1927. 

Indeed, Doyle did not present quantitative evidence 

for this assertion, although Copeland (SAL–3) apparently 

examined the stage-discharge relation for Yadkin River at 

Yadkin College and found the rating to be stable.

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 Review of Documents Related to Flooding on the Yadkin River Upstream from High Rock Dam, NC, September 2007
There is an issue related to Doyle’s characterization of 

flooding at the Grants Creek wastewater pump station 

and the design of the pump station to account for possible flooding. 

This issue is unrelated to the effects of High Rock Lake 

on increased flooding at Salisbury’s facilities.

One-Dimensional Sediment-Transport 

Modeling

A one-dimensional unsteady sediment-transport model 

was constructed “to evaluate the potential impact of continuing 

delta aggradation in the Yadkin River at the upstream end 

of High Rock Lake” (SAL–3). The objective of this study 

seems to presume that all of the sediment accumulation is 

directly attributable to the presence of High Rock Dam. The 

model was applied to evaluate four alternatives for reducing 

sedimentation at the City of Salisbury facilities near RM 19.4. 

The HEC–6T model, which is a proprietary version of the U.S. 

Army Corps of Engineers HEC–6 model, was used for the 

simulations. 

Cross sections for the sediment-transport model were 

obtained from the Hazen and Sawyer HEC–RAS model, 

from light-detection and ranging (LiDAR) data, and from 

bathymetric survey data. Additional cross sections were 

surveyed between RMs 21.3 and 31.3, and these cross sections 

were assumed to be stable over the simulation period. The 

pre-impoundment river-bottom elevations used in the HEC–6T 

model were, however, adjusted upward from those used in 

the Hazen and Sawyer HEC–RAS model. Fairly extensive 

sediment inflow records were available for the inflow sediment model-boundary conditions. Sediment inflow rates for 

future conditions were assumed to be the same as those for 

historical conditions, but the sensitivity of model results to 

this assumption was evaluated. Assumptions regarding inflow 

hydrographs were required, and these assumptions seem 

reasonable, although a number of other approaches could have 

been used for estimating inflow scenarios.

The model was calibrated such that measured and 

simulated bed profiles for 1917 and 1997 were in general 

agreement. The model also was calibrated to water levels 

measured at RM 19.4 for selected events. The sensitivity of 

model results to changes in sediment inflows, the sedimenttransport equation used in the model, and to variability in 

bottom elevation was evaluated. The model does not simulate 

natural adjustments in channel width; it has been noted 

elsewhere (APGI–7, SAL–3) that channel widths in the region 

of concern have changed over the last 70 years.

The model was applied to simulate the growth of the 

delta in the headwaters of High Rock Lake during 1928–97. 

Changes in water-surface elevations at the Salisbury facilities 

for three flow conditions as a function of changes in bed 

elevation are presented for the period 1920–2057.

▪ Copeland’s report (SAL–3) provides good documentation 

of the data and assumptions used to construct the model and 

provides a reasonable assessment of uncertainty in model 

results. The data, analyses, and simulations presented in the 

report add to current understanding of sediment transport and 

accumulation in High Rock Lake and the Yadkin River. 

The report does not, however, address the issue of the 

relative effects of High Rock Dam on sediment accumulation, 

because the model was not applied to simulate conditions 

without the dam in place. The study also does not address the 

relative effects of the bridges on sediment accumulation in the 

upper reach of High Rock Lake. As a result, it provides much 

improved understanding of sediment transport and accumulation but no new information on the effects of High Rock Dam 

or bridges on sediment accumulation relative to what may 

have occurred naturally.

Copeland’s report (SAL–3) was reviewed by David 

Williams (APGI–4). The review identified three major areas 

of concern regarding Copeland’s sediment-transport modeling. 

Copeland and Thomas (SAL–5) subsequently responded to 

Williams’ affidavit. 

The base condition (or pre-impoundment condition) was 

not modeled, so the effect of High Rock Dam on sediment accumulation is not known. 

This is a valid criticism of Copeland’s work, just as it 

is for the Stone & Webster (APGI–1) and FERC (FERC–3) 

hydraulic modeling. The actual increase in sediment deposition in the reach of the Yadkin River between High Rock Dam 

and RM 19.4 attributable to the presence of the dam cannot be 

determined from Copeland’s original results.

As noted above, the objective of Copeland’s work 

(SAL–3) was “to evaluate the potential impact of continuing 

delta aggradation in the Yadkin River at the upstream end of 

High Rock Lake.” As a result of Williams’ criticism, Copeland 

and Thomas (SAL–5) used their sediment-transport model 

to simulate sediment thalweg and water-surface elevations in 

the study reach for the pre-impoundment condition. Widths 

of the channel cross sections were set equal to original river 

bank widths, presumably determined from 1917 maps, and no 

erosion of bed or bank material was simulated in the model. 

Comparison of the simulations for pre-impoundment 

and current (or base) conditions indicates that water-surface 

elevations for the 10-year flood are about 8 ft higher currently 

than would be expected if the dam were never constructed. 

Similar results are shown for other flood flows. Results also 

demonstrate temporal increases in water-surface elevation at 

RM 19.4 relative to the pre-impoundment condition as a result 

of the growth of the delta. Copeland and Thomas did not state 

whether their pre-impoundment model included bridges.

The sediment-transport model appears to have numerical instabilities when results are displayed for each 

computational time step. 

The computational time step used by Copeland was one 

day, except during high-flow events (SAL–3). Figures 1, 3, 

and 4 of Williams’ report (APGI–4) show oscillations of about 

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One-Dimensional Sediment-Transport Modeling   
6 ft in the bed elevation at RM 19.4. Similar oscillations are 

not evident upstream from RM 19.4. The largest oscillations 

(Williams’ figs. 3 and 4) begin at about day 22,000 from the 

beginning of the simulations, which seems to correspond to 

sometime in the mid-1980s (although this is an estimate based 

on material presented in the reports). Oscillations appear to 

have an approximately annual frequency. 

Copeland noted that his model simulated sand extraction 

at locations near RM 19.4 during 1965–84 and from 1988 

to the end of simulation; sand was extracted in the model 

simulations at the end of each water year.1 It seems likely that 

the oscillations in bed elevation presented by Williams are the 

result of the annual sand extraction in the model, particularly 

because the oscillations seem to be present at RM 19.4, where 

extraction occurred, but not at other nearby cross sections. 

Copeland and Thomas (SAL–5) confirmed that the oscillations were indeed a result of dredging operations on thalweg 

elevation. Copeland and Thomas presented additional results 

to demonstrate that the model is not numerically unstable, citing guidelines from a U.S. Army Corps of Engineers training 

document containing guidelines for application of HEC–6.

Williams also pointed out that model results seemed unusual 

during the first 2 years of the simulation (Williams’ fig. 2), 

in that there were large changes in bed elevation during this 

period. 

Some numerical models require a “warm-up” period, 

because initial conditions cannot be known throughout the 

model domain. Therefore, this warm-up period is used to 

transport the estimated initial conditions out of the model 

domain before boundary conditions begin to affect model 

simulations throughout the model domain. Simulation results 

normally are not considered useful during this warm-up 

period. 

Copeland did not address the issue of initial conditions, a 

warm-up period, or the bed-elevation changes during the first 

2 years of simulation in his original report (SAL–3). Copeland 

and Thomas, however, confirmed in their response to Williams’ affidavit that these changes were a result of model 

“warm-up” (SAL–5). 

Other Studies

Normendeau Associates, Inc., and PB Power prepared a 

report on sediment fate and transport in the Yadkin-Pee Dee 

River basin (APGI–7). The report provides a comprehensive 

review of literature on sediment transport in the Yadkin River 

basin. Although the material in the report is quite interesting 

and well documented, most of the information is not directly 

relevant to the question of the effects of High Rock Dam on 

water levels at RM 19.4. The study presents a comparison 

of the 1917 bathymetry with 1997 topography in the upper 

1

Water year is the period October 1 through September 30 and is identified 

by the year in which the period ends.

12 ft of the reservoir, although a full bathymetric survey of 

current conditions has not been completed. Sedimentation 

patterns also were analyzed by comparing the 1917 and 1997 

topographic maps. The report notes “the deepest portion of 

the river has narrowed” from the I–85 bridge upstream to the 

confluence of the Yadkin and South Yadkin Rivers.

Doyle (SAL–4) presented an overview of reservoir 

sedimentation processes. A time series of aerial photographs 

of High Rock Lake also was provided, and Doyle discussed 

sedimentation patterns and the growth of the delta in the 

upstream end of the reservoir. The riverbed profile also was 

reconstructed for pre-impoundment and 2000 conditions. This 

discussion provides a useful documentation of sedimentation 

in High Rock Lake. The discussion by itself, however, does 

not unequivocally demonstrate that High Rock Dam is responsible for all or part of the sedimentation. Doyle’s arguments, 

the aerial photographs, and a general understanding of river 

morphology could lead one to conclude that sedimentation 

in the portion of the Yadkin River that is now the upper end 

of High Rock Lake has increased as a result of High Rock 

Dam. The amount of increase attributable to the presence of 

High Rock Dam and to the bridge abutments in the reach, 

respectively, has not been quantified through either Doyle’s 

presentation or Copeland’s modeling.

Doyle asserted that the Yadkin River was in morphological equilibrium prior to 1917 and continues to be in equilibrium, meaning that the overall sediment deposition and erosion 

in the river is in general balance with the sediment supply. 

Doyle offered no quantitative evidence of this assertion. Cross 

sections measured at USGS gaging stations (Yadkin River 

at Salisbury at about RM 15.2 and Yadkin River at Yadkin 

College) could be examined to document changes in the river 

geometry at measurement sections for both pre-impoundment 

and post-impoundment periods, although the channel width 

at these cross sections may be constrained by bridge abutments. Given the known sediment-legacy issues in the basin 

(extremely high sediment loads in the past; somewhat lower 

loads currently), the assumption of morphological equilibrium 

seems to require greater support than what was offered in 

SAL–4.

Summary and Further Analyses

The following primary conclusions resulted from this 

review:

The hydraulic models of Stone & Webster and FERC 

did not assess the effects of changes in bathymetry on 

changes in flood levels at the confluence of the Yadkin 

and South Yadkin Rivers. In other words, pre-impoundment conditions were not simulated, so the effect of High 

Rock Dam and post-impoundment sedimentation on 

water levels at RM 19.4 cannot be evaluated from these 

studies.

•

 Review of Documents Related to Flooding on the Yadkin River Upstream from High Rock Dam, NC, September 2007
The hydraulic modeling performed by Hazen and Sawyer 

seems to indicate that both the presence of the dam in 

the absence of any post-impoundment sedimentation and 

changes in bathymetry between pre-impoundment and 

1997 conditions have resulted in increased water levels 

relative to pre-impoundment conditions at Salisbury 

facilities on the Yadkin River for a fairly wide range of 

flows.

The degree to which the dam and the changes in bathymetry have affected flood levels at the Salisbury facilities 

relative to pre-impoundment conditions is open to 

discussion because of uncertainty in topographic/bathymetric data and the absence of calibration and sensitivity 

testing of the hydraulic models.

None of the three hydraulic models appears to have been 

calibrated to or tested against measurements, and no 

sensitivity testing was reported.

Copeland’s sediment-transport model was calibrated to 

estimated bed elevations and to water levels at RM 19.4. 

The model is well documented (except for issues related 

to initial conditions and possible numerical instabilities) 

and provides a good understanding of the expected 

growth of the sediment delta in the upper end of High 

Rock Lake.

In a response to criticism from APGI, Copeland and 

Thomas simulated thalweg and water-surface elevations 

for the pre-impoundment condition and seemingly 

demonstrated that the presence of the dam and the 

growth of the delta have resulted in increases in watersurface elevations at RM 19.4 over a range of flows, and 

that these increases are expected to increase through time 

if current conditions remain unchanged.

Further analyses and studies to improve understanding 

of the relation of High Rock Lake to sedimentation in the lake 

and changes in the flood regime in the upper part of High 

Rock Lake include the following:

Several elevation datums are used in the various documents, including the Yadkin datum, “USGS datum,” 

NGVD 29 datum, and some datums that are unspecified. 

This leads to a good bit of confusion in interpreting 

results from the reports. All parties should agree that 

elevations will be referenced to the current standard 

North American Vertical Datum of 1988 (NAVD 88).

A detailed bathymetric survey of High Rock Lake 

and the Yadkin River from High Rock Dam to 20 mi 

upstream from the dam would provide the correct 

information needed for hydraulic (and sedimenttransport) modeling of the reach for current conditions. 

Detailed topographic data of the region are available 

from the North Carolina Floodplain Mapping Program at 

http://www.ncfloodmaps.com/default_swf.asp . 

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The current bathymetry and topography could be 

combined to generate realistic channel cross sections for 

hydraulic modeling of current conditions. Pre-impoundment conditions have been simulated by Hazen and 

Sawyer, although some clarification and documentation 

of their approach is needed.

Copeland’s model could be used to simulate sediment 

accumulation as a result of the presence of bridges. 

Sediment accumulation attributable to the dam and to 

bridges then could be distinguished from what may have 

occurred for a natural condition. 

In the absence of realistic bathymetry for current 

conditions, a sensitivity analysis could be performed 

to determine the effects of changes in channel cross 

sections and slope on final results. A sensitivity analysis 

for pre-impoundment conditions, for which it is not 

possible to know channel cross sectional geometry, 

could be conducted. Likewise effects of bridges could be 

evaluated for current and pre-impoundment conditions.

Cross sections measured at USGS gaging stations 

(Yadkin River at Salisbury at about RM 15.2, South 

Yadkin River at Cooleemee, and Yadkin River at Yadkin 

College) could be examined to document changes in 

the river channel for both pre-impoundment and postimpoundment periods.

Sediment-coring and age-dating methods on both the bed 

and the floodplain could be investigated as a means to 

evaluate sediment throughout the reaches of interest for 

both the post- and pre-impoundment periods. It may be 

possible to estimate accumulation rates for both pre- and 

post-impoundment conditions. It also may be possible 

to estimate geomorphic equilibrium conditions prior to 

and following dam operations and the effect of the legacy 

sediment on current morphological conditions.

Flood data from current and discontinued gages could 

be examined to determine if a change in the flood-flow 

regime has occurred. Improved estimates of flood-recurrence intervals could be obtained by using the methods 

of Pope and others (2001) and historical at-gage flood 

frequencies.

References

Pope, B.F., Tasker, G.D., and Robbins, J.C., 2001, Estimating 

the magnitude and frequency of floods in rural basins of 

North Carolina—Revised: U.S. Geological Survey WaterResources Investigations Report 01–4027, 44 p.

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References 

Prepared by:

USGS Enterprise Publishing Network

Raleigh Publishing Service Center

3916 Sunset Ridge Road

Raleigh, NC 27607

For additional infomration regarding this publication, contact:

Jerad D. Bales, Director

USGS North Carolina Water Science Center

3916 Sunset Ridge Road

Raleigh, NC 27607

phone: 1-919-571-4000

email: dc_nc@usgs.gov

Or visit the North Carolina Water Science Center website at:

http://nc.water.usgs.gov
Bales—Review of Documents Related to Flooding on the Yadkin River Upstream from High Rock Dam, NC, September 2007—Open-File Report 2007–1314