U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2020–5082

Prepared in cooperation with the National Park Service

Delineation of Flood-Inundation Areas in Grapevine Canyon 

Near Scotty’s Castle, Death Valley National Park, California
Cover photo: Looking upstream from Tie and Grapevine Canyon confluence at Scotty’s Castle, Death 

Valley National Park. Photograph taken by Neal Nurmi, National Park Service, on November 27, 2015.
Delineation of Flood-Inundation Areas in 

Grapevine Canyon Near Scotty’s Castle, 

Death Valley National Park, California

By Christopher M. Morris, Toby L. Welborn, and J. Toby Minear

Prepared in cooperation with the National Park Service

Scientific Investigations Report 2020–5082

U.S. Department of the Interior

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

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

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Suggested citation:

Morris, C.M., Welborn, T.L., and Minear, J.T., 2020, Delineation of flood-inundation areas in Grapevine Canyon 

near Scotty’s Castle, Death Valley National Park, California: U.S. Geological Survey Scientific Investigations 

Report 2020–5082, 27 p., https://doi.org/10.3133/sir20205082.

Associated data for this publication:

Morris, C.M., Welborn, T.L., and Minear, J.T., 2020, Geospatial Data: California, Tabular Data, and Surface-Water 

Model Archive for Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley 

National Park, https://doi.org/10.5066/P9IPKW55.

ISSN 2328-0328 (online)
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................6

Previous Work .......................................................................................................................................6

Data Acquisition and Processing ................................................................................................................6

Hydrological Data .................................................................................................................................6

Channel Bed Particle Size ...................................................................................................................7

Topographic Data..................................................................................................................................7

Surface Generation ............................................................................................................................10

Hydraulic Modeling .....................................................................................................................................14

Model Geometry..................................................................................................................................15

Model Hydrology .................................................................................................................................15

Roughness Coefficients .....................................................................................................................15

Model Calibration................................................................................................................................16

Sensitivity Analysis .............................................................................................................................17

Results ...........................................................................................................................................................17

Grapevine Canyon...............................................................................................................................17

Tie Canyon............................................................................................................................................18

Channel Bed Particle Size and Roughness ....................................................................................22

Discussion.....................................................................................................................................................23

Grapevine Canyon...............................................................................................................................23

Tie Canyon............................................................................................................................................23

Uncertainties and Limitations ...........................................................................................................24

Physical Limitations ...................................................................................................................24

Model Limitations.......................................................................................................................24

Suggestions for Future Research ....................................................................................................24

Summary and Conclusions .........................................................................................................................25

References Cited..........................................................................................................................................25

Figures

1. Map showing location of Scotty’s Castle in Grapevine Canyon, Death Valley 

National Park, California and Nevada .......................................................................................2

2. Map showing study area extent and model reaches of Scotty’s Castle in 

Grapevine Canyon, Death Valley National Park, California ...................................................3

3. Aerial photographs from before and after the October 18, 2015, flood of Scotty’s 

Castle in Grapevine Canyon, Death Valley National Park, California ..................................4

4. Images of flood damage from the October 18, 2015, flood of Scotty’s Castle in 

Grapevine Canyon, Death Valley National Park, California ...................................................5

5. Map showing pebble count, terrestrial laser scanner, single-baseline static 

survey observation locations for Scotty’s Castle in Grapevine Canyon, Death 

Valley National Park, California ..................................................................................................8
iv

6. Map showing terrestrial laser scanner minimum elevation filtering areas used 

to create the digital terrain model for Scotty’s Castle in Grapevine Canyon, 

Death Valley National Park, California ....................................................................................11

7. Map showing digital terrain model for Scotty’s Castle in Grapevine Canyon, 

Death Valley National Park, California ....................................................................................12

8. Map showing spatial distribution of measured residual error between ground 

control points and the digital terrain model for Scotty’s Castle in Grapevine 

Canyon, Death Valley National Park, California.....................................................................13

9. Histogram and cumulative percentage of residual error between ground 

control points and the digital terrain model for Scotty’s Castle in Grapevine 

Canyon, Death Valley National Park, California.....................................................................14

10. Graph showing surveyed versus modeled water surface for October 18, 2015, 

flood at Scotty’s Castle in Grapevine Canyon, Death Valley National Park, 

California ......................................................................................................................................16

11. Map showing flood-inundation areas for the 4-percent annual exceedance 

probability flood streamflow for Scotty’s Castle in Grapevine Canyon, Death 

Valley National Park, California ................................................................................................18

12. Map showing flood-inundation areas for the 2-percent annual exceedance 

probability flood streamflow for Scotty’s Castle in Grapevine Canyon, Death 

Valley National Park, California ................................................................................................19

13. Map showing flood-inundation areas for the 1-percent annual exceedance 

probability flood streamflow for Scotty’s Castle in Grapevine Canyon, Death 

Valley National Park, California ................................................................................................20

14. Map showing flood-inundation areas for the 0.5-percent annual exceedance 

probability flood streamflow for Scotty’s Castle in Grapevine Canyon, Death 

Valley National Park, California ................................................................................................21

15. Map showing flood-inundation areas for the 0.2-percent annual exceedance 

probability flood streamflow for Scotty’s Castle in Grapevine Canyon, Death 

Valley National Park, California ................................................................................................22

Tables

1. Historic flood streamflow measurements made in Grapevine Canyon, Death 

Valley National Park, California ..................................................................................................7

2. Drainage areas and percent annual exceedance probability streamflows for 

select locations in Grapevine Canyon, Death Valley National Park, California .................7

3. Results of single-baseline static surveys for Scotty’s Castle in Grapevine 

Canyon, Death Valley National Park, California.......................................................................8

4. Error assessment for maximum errors in terrestrial laser scanning data for 

Scotty’s Castle in Grapevine Canyon, Death Valley National Park, California ...................9

5. Results of pebble counts and computed n-values for Scotty’s Castle in 

Grapevine and Tie Canyons, Death Valley National Park, California .................................23
v

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2)

Volume

cubic foot (ft3) 0.02832 cubic meter (m3)

Flow rate

foot per second (ft/s) 0.3048 meter per second (m/s)

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

International System of Units to U.S. customary units

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

Area

square meter (m2) 0.0002471 acre

Datum

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

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

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

Abbreviations

AEP annual exceedance probability

DTM digital terrain model

FHWA Federal Highway Administration

GCP ground control points

GNSS Global Navigation Satellite System

HEC–RAS Hydrologic Engineering Center–River Analysis System

lidar light imaging, detection, and ranging

NPS National Park Service

OPUS–S Online Positioning User Service–Static

RMS root mean square error

RTK real-time kinematic

TIN triangulated irregular network

TLS terrestrial laser scanner

USGS U.S. Geological Survey
Delineation of Flood-Inundation Areas in Grapevine 

Canyon Near Scotty’s Castle, Death Valley National 

Park, California

By Christopher M. Morris, Toby L. Welborn, and J. Toby Minear

Abstract

On October 18, 2015, a large flood caused considerable 

damage in Grapevine Canyon near Death Valley Scotty 

Historic District, in Death Valley National Park, California. 

Significant channel changes had limited the applicability 

of previously created flood-inundation maps to current 

conditions. Predicted flood-inundation maps for Scotty’s 

Castle were updated using one-dimensional hydraulic models. 

A digital terrain model was created for the study area using 

a terrestrial laser scanner for use in the hydraulic models. 

Estimations of the 4, 2, 1, 0.5, and 0.2-percent annual 

exceedance probability flood streamflows (previously known 

as the 25, 50, 100, 250, and 500-year floods) were computed 

from regional flood regression equations. The estimated 

flood streamflows were used with the hydraulic models to 

compute water surface elevations that were mapped on the 

digital terrain model. The results indicate inundation of the 

visitor center and park offices occurs by the 4-percent annual 

exceedance probability flood. Bridge and embankment 

overtopping occurs by the 2-percent annual exceedance 

probability flood. Sections of Grapevine Canyon Road and the 

parking lot are inundated by the 4-percent annual exceedance 

probability flood and above streamflows. None of the 

computed streamflows reach Scotty’s Castle main building.

Introduction

Death Valley Scotty Historic District (hereafter referred 

to as Scotty’s Castle) is in the northeast part of Death 

Valley National Park, in Grapevine Canyon, adjacent to the 

confluence with Tie Canyon. Grapevine Canyon drains the 

steep western slopes of the Grapevine Mountains near the 

Nevada and California State line (fig. 1) with a drainage area 

of approximately 47.9 square miles (mi2). Tie Canyon makes 

up the northwestern part of the Grapevine Canyon Basin and 

has a drainage area of approximately 20.5 mi2. Elevations 

in the Grapevine Canyon Basin range from 7,008 feet (ft) in 

the Grapevine Mountains to 2,300 ft at the canyon mouth, 

with an average slope of 17.6 percent. Both Grapevine 

and Tie Canyons have very steep channels (0.04 and 0.06, 

respectively). At its confluence with Grapevine Canyon, the 

Tie Canyon channel becomes a narrow alluvial fan with two 

main and several smaller distributary channels (fig. 2).

Several small springs provide perennial streamflow 

over short distances, but otherwise both Grapevine and Tie 

Canyons are dry, with streamflow only occurring for short 

durations as a result of heavy rainfall. Such rainfall induced 

streamflows are flashy, with drastic changes in streamflow 

over short periods of time. Both Grapevine and Tie Canyon 

have been gaged since December 2016. In areas with perennial 

streamflow, or shallow groundwater, very dense thickets of 

willow (Salix sp.), Fremont cottonwood (Populus fremontii), 

three-square bulrush (Schoenoplectus americanus), mesquite 

(Prosopis sp.), saltgrass (Distichlis spicata), desert wild 

grapevine (Vitis girdiana), and other riparian vegetation grow. 

Elsewhere, the active channel is mostly bare, with a gravel 

and cobble channel bed. In wider sections of the canyon, 

moderately dense saltbush (Atriplex sp.) and rabbitbrush 

(Ericameria sp.) grow on small alluvial terraces with vertical 

cut banks at the active channel. Elsewhere, colluvium slopes, 

alluvial fans, or bedrock directly border the active channel. 

Canyon slopes are either bedrock or have thin soils of 

gravel with sparse creosote (Larrea tridentata) and bursage 

(Ambrosia dumosa) shrubs.

Scotty’s Castle is a popular tourist attraction on 

the National Register of Historic Places (National Park 

Service, 2016). The area includes several historically and 

architecturally significant buildings, park administration 

facilities, parking lots, and public water supply and utility 

infrastructure (fig. 2). Access to Scotty’s Castle is limited to 

the paved Grapevine Canyon Road that passes along the entire 

length of Grapevine Canyon and, in some locations, takes up 

the entire width of the canyon floor.
2 Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP

Shaded Relief from the 3D Elevation Program

(3DEP), 2017, 1:225,000 scale. Grapevine

Canyon basin boundary from Watershed

Boundary Dataset HUC12, 2017. Universal

Transverse Mercator, zone 11, World

Geodetic System of 1984

D E AT H VA L L E Y N AT I O N A L PA R K

Study Area

Grapevine

Canyon

Basin

GRAPEVINE

MOUNTAINS

Tie Canyon

Basin boundary

NEVADA

CALIFORNIA

Grapevine Canyon

0 1.5 3 MILES

0 1.5 3 KILOMETERS

117°21' 117°18' 117°15' 117°12'

37°09'

37°06'

37°03'

37°

CALIFORNIA

DEATH VALLEY

NATIONAL PARK

NEVADA

Map area

Figure 1. Location of Scotty’s Castle in Grapevine Canyon, Death Valley National Park, California and Nevada.
Introduction 3

Base modified from National Agricultural Imagery

Program, 2016, 1:8,000 scale. Universal

Transverse Mercator, zone 11,

World Geodetic System of 1984

GRAPEVINE CANYON R O AD

117°20'40" 117°20'30" 117°20'20" 117°20'10" 117°20' 117°19'50"

37°02'

37°01'50"

37°01'40"

G

F

H

E

C

B A

D

I

J

GRAPEVINE CANYON ROAD

EXPLANATION

0 400 800 FEET

0 100 200 METERS

Model reaches

Buildings and structures

Upper Grapevine Canyon 

Cross sections from October 18, 2015, indirect

Middle Grapevine Canyon 

Lower Grapevine Canyon

Upper Tie Canyon

Lower Tie Canyon

Side Channel

A Gravel separator Hacienda F

B Overflow parking lot Stable G

C Castle Gate Bridge Pools H

D Chimes Tower Visitors center and park offices I

E Scotty's Castle Main parking lot J

Figure 2. Study area extent and model reaches of Scotty’s Castle in Grapevine Canyon, Death Valley National Park, California.

On October 18, 2015, an intense, nearly stationary 

thunderstorm triggered flooding in Grapevine and Tie 

Canyons (National Weather Service, 2015). A rain gage at 

Scotty’s Castle recorded 2.72 inches of precipitation over a 

5-hour period, and information from weather radar suggested 

3–4 inches of precipitation in the lower part of the drainage 

basin during the same event (National Weather Service, 2015). 

Grapevine Canyon Road, power and water infrastructure, 

and several buildings at Scotty’s Castle were damaged by the 

flood water and debris, necessitating closure of the area to 

the public. As a result of the flood, mud, gravel, cobble, and 

boulders were deposited inside and outside of several historic 

and park administration buildings, damaging walls and 

breaking windows and doors. The visitor center parking lot, 

within the active channel, had sediment deposits several feet 

deep (fig. 3). The spring house and water pipeline transporting 

water to Scotty’s Castle from a spring upstream were heavily 

damaged. Twenty power poles and over 1 mile of fencing 

were destroyed (fig. 4). Five to ten feet of channel incision 

occurred in Grapevine Canyon from near the confluence with 

Tie Canyon through Castle Gate Bridge (hereafter referred to 

as the bridge) to the picnic area next to the parking lot (fig. 2). 
Figure 3. Aerial photographs from before and after the October 18, 2015, flood of Scotty’s Castle in Grapevine Canyon, Death Valley National Park, Cataken on March 21, 2015, looking upstream from downstream end of the modeled reach. Photographs by Birgitta Jansen, National Park Service. PhotoNovember 27, 2015, looking upstream from Tie and Grapevine Canyon confluence. Photographs by Neal Nurmi, National Park Service.
Figure 4. Images of flood damage from the October 18, 2015, flood of Scotty’s Castle in Grapevine Canyon, Death Valley National Park, California. Froupper left clockwise: visitor center and park offices, road damage downstream of modeled reach, visitor center and park offices, damaged power polPhotographs by National Park Service.
6 Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP

A large percentage of vegetation in Grapevine Canyon was 

removed, leaving bare channels in areas that had previously 

been dense shrubs. Finally, sections of the Grapevine Canyon 

Road were either completely removed by the flood waters or 

heavily damaged (fig. 4; Josh Hoines, National Park Service, 

oral commun., 2017).

In additional to the main channel streamflow in 

Grapevine and Tie Canyons, streamflow also occurred in 

gullies and on hillslopes. At Scotty’s Castle, many natural 

gullies end at pavement or at the walls of buildings, resulting 

in additional damage and debris deposits.

The area is expected to be closed to the public until 

at least 2020 and cost $50 million to repair (National Park 

Service, 2016).

At Scotty’s Castle, flood waters from the October 18 

flood rose to the 1-percent annual exceedance probability 

(AEP) flood water level delineated from a flood-inundation 

map for the area (Bowers, 1989), with an estimated streamflow 

of 12,000 cubic feet per second (cfs). However, a post-flood 

streamflow measurement using surveyed high-water marks, 

cross sections, roughness, and other channel characteristics 

(hereafter referred to as an indirect measurement) made 

approximately 2,000 ft upstream of Scotty’s Castle computed 

a streamflow of only 3,200 cfs.

The difference in streamflow between the indirect 

measurement and the estimated streamflow from Bowers 

(1989) suggests that the previous flood-inundation mapping 

is no longer applicable, and a new analysis, based on current 

(2016) conditions, is needed to document current channel 

conditions.

Purpose and Scope

This report describes and documents the field data 

collection and development of a one-dimensional model to 

map the 4, 2, 1, 0.5, and 0.2-percent AEP flood-inundation 

areas near Scotty’s Castle. The model extent is from about 

1,300 ft downstream from the confluence of Grapevine and Tie 

Canyons to about 3,500 ft upstream in Grapevine Canyon, and 

to about 2,200 ft upstream in Tie Canyon (fig. 2). All spatial 

data and models are published in Morris and others (2020).

Previous Work

Steep slopes, shallow soils, limited vegetation, and 

potential for intense rainfall make flash floods a common 

occurrence in Death Valley. Peak streamflows were monitored 

at seven sites in the current Death Valley National Park 

boundaries by the U.S. Geological Survey (USGS) from the 

late 1950s to the mid-1970s in association with a California 

statewide monitoring program of floods in small drainages 

(Waananen, 1971). Only two of these sites continued to be 

monitored past 1974, and peak streamflow monitoring at 

both of those ended by 1989 (US. Geological Survey, 2018a, 

2018b). Miller (1977) provided some additional discrete 

measurements and descriptions of several flood events, 

including an indirect measurement of a 727 cfs flood from 

July 1968 at the mouth of Grapevine Canyon.

Several USGS studies have examined and mapped 

flood-inundation areas at Furnace Creek (Crippen, 1979), 

Wildrose Canyon (Crippen, 1981), and Grapevine Canyon 

(Bowers, 1989) in Death Valley National Park. In 1983, 

the National Park Service (NPS) completed a more 

geographically diverse analysis of flooding using single 

channel cross-sections near major infrastructure (Overzet 

and others, 1983). These studies computed supercritical, high 

velocity streamflow with the possibility of dramatic changes 

in hydraulics during floods because of possible erosion, 

transportation, and deposition of large amounts of debris and 

sediment. The lack of long-term data for flood frequency 

analyses has also been noted as an additional uncertainty.

Flood-inundation areas in Grapevine and Tie Canyons 

(including Scotty’s Castle) were mapped after the July 1976 

flood by Bowers (1989). Eighteen cross sections were 

surveyed along the entire length of Grapevine Canyon and 

the downstream end of Tie Canyon. Step-backwater (Chow, 

1959) and slope-conveyance methods were used to compute 

the water surface elevations for the 4, 2, and 1-percent AEP 

floods as computed from regional regression equations. The 

computed AEP water surfaces were delineated using an 

existing 1972 topographic map. Since Grapevine Canyon and 

Tie Canyon were ungaged, no model calibration or verification 

was completed. However, the area delineated for the 4-percent 

AEP flood (3,500 cfs) was generally verified by an estimated 

streamflow of 2,900 cfs from the July 1976 flood, which was 

calculated based on depth and width observations made by the 

NPS. The July 1976 flood reportedly incised a channel into the 

parking lot (Bowers, 1989).

Data Acquisition and Processing

The hydraulic model used required topographic and 

streamflow data. Topographic data were surveyed using a 

terrestrial laser scanner. In the absence of streamflow data, 

regional regression models were used to estimate streamflow 

for 4, 2, 1, 0.5, and 0.2-percent AEP floods.

Hydrological Data

Floods can be described based their frequency of 

occurrence. The AEP of a flood is the likelihood of a given 

streamflow occurring or being exceeded in any given year. The 

1-percent AEP has a 1 in 100 chance to occur or be exceeded 

in any given year. Although a 1-percent AEP is colloquially 

known as the “100-year flood,” this terminology is misleading 

because the flood may not occur every 100 years (Holmes and 

Dinicola, 2010).
Data Acquisition and Processing 7

With only three flood streamflow measurements made 

in Grapevine Canyon (table 1), the data requirements for 

a flood frequency analysis as described in Bulletin 17C 

(England and others, 2018) are not met. Therefore, regional 

regression equations from Gotvald and others (2012)

were used to estimate the streamflow for 4, 2, 1, 0.5, and 

0.2-percent AEP floods at three ungaged locations using the 

following equations:

Q4 = 403 A0.506 (1)

Q2 = 760 A0.506 (2)

Q1 = 1350 A0.506 (3)

Q0.5 = 2270 A0.506 (4)

Q0.2 = 4280 A0.506 (5)

where Qn is the AEP streamflow in cfs and A is the drainage 

basin area in square miles.

The regional regression equation estimates for Grapevine 

Canyon Bridge, Tie Canyon, and Lower Grapevine Canyon 

are presented in table 2.

Channel Bed Particle Size

The composition of the streambed and banks influences 

channel form and hydraulics. To gain a better understanding of 

the composition of the study area, a total of five Wolman-style 

pebble counts were performed in the channel to determine 

the size of the channel bed particles (Wolman, 1954) and help 

evaluate channel roughness used in the models. A 30 ft by 

30 ft square was established, and 100 particles were selected 

randomly every 3 ft by 3 ft in a grid pattern. The intermediate 

axis was measured using a gravelometer and tallied. Pebble 

counts were made at an overbank location and active channel 

location in Grapevine and Tie Canyons and an active channel 

location at their confluence (fig. 5). The pebble count locations 

were selected to be representative of the channels.

Topographic Data

Terrestrial laser scanner (TLS) and Global Navigation 

Satellite System (GNSS) surveys were completed at Scotty’s 

Castle from July 12–14, 2016, to collect present-day, 

high-resolution topography data for the one-dimensional 

modeling. The GNSS surveys consisted of single-baseline 

Online Positioning User Service–Static (OPUS–S) surveys 

at four locations for survey control and single-base, real-time 

kinematic (RTK) GNSS surveys. The RTK surveys collected 

observations at TLS scan origins, survey control, back-sights, 

and ground control points (GCP). The GCP were used for an 

independent quality check of the TLS-derived digital terrain 

model (DTM).

No published benchmark data were found for the study 

area. Because of this, single-baseline OPUS–S surveys were 

completed at three Federal Highway Administration (FHWA) 

benchmarks and one temporary reference point, Rebar1, in 

the Scotty’s Castle area (fig. 5). Static observations were 

collected using Topcon GR-3 and Leica Viva GS14 GNSS 

receivers on 2-meter fixed height tripods. Processing of static 

observations was done using the National Geodetic Survey 

Online Positioning User System (OPUS). Single-baseline 

static survey level quality, occupation times, observations 

used, ambiguities, solution root mean square error (RMS), 

and vertical peak-to-peak are presented in table 3. Known 

errors affecting the single-baseline OPUS–S surveys included 

a battery failure at FHWA-3511 on July 12, 2016, and a failed 

data collection at Rebar1 on July 13, 2016, resulting in a 

single observation on the benchmark.

Table 1. Historic flood streamflow measurements made in 

Grapevine Canyon, Death Valley National Park, California.

[cfs, cubic foot per second; ft, foot]

Date Location Streamflow 

(cfs) Type

July 28, 1968 15,000 ft downstream 

of Scotty’s Castle

727 Slope area

July 1976 Scotty’s Castle 2,900 Estimate

October 18, 2015 2,000 ft upstream of 

Scotty’s Castle

3,200 Slope area

Table 2. Drainage areas and percent annual exceedance 

probability streamflows for select locations in Grapevine Canyon, 

Death Valley National Park, California.

[Based on regional regression equations from Gotvald and others, 2012]

Location

Area 

(square 

miles)

Percent AEP streamflow

(cubic feet per second)

4 2 1 0.5 0.2

Tie Canyon 20.5 1,860 3,510 6,230 10,500 19,700

Grapevine 

Canyon Bridge

24.4 2,030 3,830 6,800 11,400 21,600

Lower Grapevine 

Canyon

44.9 3,890 7,340 13,030 21,900 41,300
8 Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP

Base modified from National Agricultural Imagery

Program, 2016, 1:7,000 scale. Universal

Transverse Mercator, zone 11,

World Geodetic System of 1984

GRAPEVINE CANYO N ROAD

117°20'40" 117°20'30" 117°20'20" 117°20'10" 117°20'

37°02'

37°01'50"

37°01'40"

0 400 800 FEET

0 100 200 METERS

Pebble count locations

Terrestrial laser scanner scan origins

Single-baseline static survey observation locations

EXPLANATION

Figure 5. Pebble count, terrestrial laser scanner, single-baseline static survey observation locations for Scotty’s Castle in Grapevine 

Canyon, Death Valley National Park, California.

Table 3. Results of single-baseline static surveys for Scotty’s Castle in Grapevine Canyon, Death Valley National Park, California.

[hh:mm, hour:minute; mm/dd/yyyy, month/day/year; RMS, root mean square error]

Benchmark Date

(mm/dd/yyyy)

Level 

quality

Occupation time

(hh:mm)

Observations used

(percent)

Fixed ambiguities

(percent)

RMS error

(meters)

Vertical peak to peak

(meters)

FHWA3510 07/12/2016 Level II 03:54 96 94 0.011 0.038

07/13/2016 06:25 94 100 0.013 0.024

FHWA3511 07/12/2016 Level III 04:20 61 71 0.016 0.044

07/14/2016 10:01 97 94 0.014 0.037

FHWA3512 07/13/2016 Level I 04:01 95 96 0.016 0.025

07/14/2016 06:45 97 95 0.012 0.024

Rebar1 07/12/2016 Level II 08:56 98 99 0.01 0.028
Data Acquisition and Processing 9

Single-base RTK GNSS surveys were completed on 

July 12–14, 2016, using Topcon GR-3 GNSS receivers. The 

base station was set on a 2-meter fixed height tripod at Rebar1 

on July 12, 2016, and at FHWA-3511 on July 13–14, 2016. 

The single-base RTK GNSS surveys followed techniques 

and methods for a level II survey as outlined in Rydlund and 

Densmore (2012). However, owing to the lack of known 

benchmarks, the unknown quality of the benchmarks used, 

and the use of single-base static observations to establish 

survey control, level IV results were the highest single-base 

RTK GNSS survey level-quality achieved. Observations at 

TLS scan origins, survey control, back-sight locations, blunder 

checks, and repeat measurements on observation points 

were collected at 1-second intervals for 3 minutes. Seven 

hundred seventy ground control points also were collected 

on representative hard and soft surfaces and slopes at various 

locations throughout the study area for vertical precision 

verification of the derived DTM. These observation points 

were collected at 3-second intervals.

High-resolution topographic data were collected in 

Grapevine and Tie Canyons within the Scotty’s Castle vicinity 

(fig. 5). A Maptek I-Site 8820 XR TLS, mounted on a standard 

tripod, was set up at 38 fixed locations with an open field of 

view to collect 360-degree scans and targeted scans of the 

topography within the study area. Each scan produces a point 

cloud of X, Y, and Z data referenced to the scan origin. The 

self-leveling procedure within the Maptek unit was used for 

every scan. Over 83 million topographic data points were 

collected during the TLS survey.

The TLS data were processed through an integrated 

suite of registration, georeferencing, and filtering generally 

following the framework reported in Collins and others 

(2014). Each scan contains data for a portion of the study 

area and must be combined (registered) and spatially located 

(georeferenced) to a coordinate system. Scan origins (fig. 5) 

collected from the single-base RTK GNSS survey were input 

into I-Site Studio software to georeference each scan. Because 

of an error in the compassing system, individual scans were 

registered manually using a best fit approach where scans 1, 2, 

and 3 were rotated about the fixed, georeferenced scan origin, 

matching overlapping surface features visible in all three 

scans. The registered and georeferenced group of point clouds 

were then used as control for an automated alignment of the 

reaming scans to create a single, point cloud dataset for the 

entire study area. Ground points were then defined using an 

iterative, minimum elevation block filtering process.

Overall error position (Etotal) in the TLS data was 

calculated by treating each component of the survey 

independently. Potential errors in the TLS data are expected 

to originate during both data collection and point cloud 

processing. Error is additive from each component of the TLS 

data collection: laser error, registration error, georeferencing 

error, survey error, and control error (Collins and others, 

2014). Laser error (Elaser) can be from either range or angular 

inaccuracies and is reported by the instrument manufacturer. 

Registration errors (Egeoreference) are a product of combining 

data from different scan locations into a single coordinate 

system. Georeferencing errors (Egeoreference) originate from 

the conversion of the locally registered data into surveyed 

horizontal projection and vertical datum (for example, North 

American Datum of 1983 [NAD 83], National Adjustment 

of 2011 [NA 2011], and North American Vertical Datum 

of 1988 [NAVD 88] derived from GEOID 12B). Because 

the registration and georeferencing of the scan data was 

done through an integrated suite in I-Site, registration and 

georeferencing error is combined into one component 

as Egeoreference. Surveying errors (Esurvey) originate from 

the uncertainty in reported X, Y, and Z coordinates from 

comparisons between survey observations and known control 

locations. Control network errors (Econtrol) originate from 

the known absolute accuracy of the benchmarks used to 

conduct the GNSS surveys in this study. Control error for this 

study was estimated as the RMS of peak-to-peak errors of 

single-baseline static observations as reported by OPUS. Error 

from each component is additive, producing a conservative, 

worst case RMS estimate:

Etotal = √

___________________________________

Elaser 

2+ Egeoreference 2+ Elasesurvey 2+ Econtrol 2 (6)

Error for each component and total error are presented in 

table 4.

Table 4. Error assessment for maximum errors in terrestrial laser 

scanning data for Scotty’s Castle in Grapevine Canyon, Death 

Valley National Park, California.

Laser Survey Georeference Control Total

Horizontal (feet) 0.02 0.10 1.56 0.29 1.56

Vertical (feet) 0.02 0.04 0.57 0.21 0.60
10 Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP

Surface Generation

To obtain a continuous DTM of the Scotty’s Castle study 

area, the point cloud data must be filtered of extraneous data 

such as vegetation, fences, power lines, and atmospheric 

interference (birds, dust, and others), and then a surface is 

built from the remaining data. Ground points were defined 

using an iterative process in I-Site Studio that filtered the 

minimum elevation observations in a defined search area 

window. Because of the large area scanned and the heavy 

vegetation, three individual box filters were used to identify 

ground points (fig. 6). A 5-square-meter (m2) box filter size 

was used for areas of heavy vegetation; a 3-m2 box filter was 

used upstream of the Scotty’s Castle area, Tie Canyon, and 

from the confluence of Grapevine and Tie Canyons to the 

downstream end of the study area; and a 1-m2 box filter was 

used for the immediate Scotty’s Castle vicinity. A total of 

122,104 points were identified as minimum ground points. The 

bridge at Scotty’s Castle was manually removed from the final 

surface while the buildings were left as mounds in the final 

surface. A large amount of flood debris in the main channel 

near the visitor center and park offices was removed from the 

DTM because it was a temporary feature that the NPS planned 

to remove from the channel (Josh Hoines, National Park 

Service, oral commun., 2017). For this study, the final surface 

model was created using a triangulated irregular network 

(TIN) of only the minimum points identified in the filtering 

process. The extent and spatial distribution of elevations is 

shown in figure 7.

Vertical accuracy was assessed from the 769 GCPs and 

reported at the 95th confidence level following the standards 

for reporting the accuracy of digital geospatial data (American 

Society for Photogrammetry and Remote Sensing, 2014). 

Vertical accuracy of the DTM at the 95-confidence level is 

2 ft, which is within the accuracy guidelines for DTM used in 

flood inundation mapping for hilly terrain (Federal Emergency 

Management Agency, 2016). The distribution of GCP residual 

values are shown in figure 8. The majority of observed error 

is on steep slopes, incised channels, and in areas with heavy 

vegetation. These errors can be explained by the range of 

elevations associated with steep slopes compared to the 

interpolated single value of the DTM. Incised channels at 

distance or in heavy vegetation, such as the area immediately 

downstream of the bridge, may have been influenced by 

shadowing. Shadowing occurs when a feature such as a tree on 

a steep slope blocks a laser return from an area or when thick, 

low-lying vegetation prevents the laser from reflecting off the 

ground. The histogram and cumulative percentage plot (fig. 9) 

show that 81 percent of the DTM error is 0.75 ft and that the 

DTM has a slightly positive skew.
Data Acquisition and Processing 11

Base modified from National Agricultural Imagery

Program, 2016, 1:8,000 scale. Universal

Transverse Mercator, zone 11,

World Geodetic System of 1984

GRAPEVINE CANYON ROAD

117°20'40" 117°20'30" 117°20'20" 117°20'10" 117°20' 117°19'50"

37°02'

37°01'50"

37°01'40"

EXPLANATION

0 400 800 FEET

0 100 200 METERS

5-square-meter filter area

3-square-meter filter area

1-square-meter filter area

Figure 6. Terrestrial laser scanner minimum elevation filtering areas used to create the digital terrain model for Scotty’s Castle 

in Grapevine Canyon, Death Valley National Park, California.
12 Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP

Base modified from National Agricultural Imagery

Program, 2016, 1:8,000 scale. Universal

Transverse Mercator, zone 11,

World Geodetic System of 1984

G F

H

E

C B

A

D

I

J

GRAPEVINE CANYON ROAD

117°20'40" 117°20'30" 117°20'20" 117°20'10" 117°20' 117°19'50"

37°02'

37°01'50"

37°01'40"

EXPLANATION

0 400 800 FEET

0 100 200 METERS

Buildings and structures

A Gravel separator F Hacienda

B Overflow parking lot G Stable

C Castle Gate Bridge H Pools

D Chimes Tower I Visitors center and park offices

E Scotty's Castle J Main parking lot

Elevation, in feet

3,209.6

3,146.7

3,115.3

3,083.9

3,052.4

3,021

2,989.6

2,958.2

2,926.7

2,895.3

3,178.1

Figure 7. Digital terrain model for Scotty’s Castle in Grapevine Canyon, Death Valley National Park, California.
Data Acquisition and Processing 13

Base modified from National Agricultural Imagery

Program, 2016, 1:8,000 scale. Universal

Transverse Mercator, zone 11,

World Geodetic System of 1984

GRAP E V INE CANYON ROAD

117°20'40" 117°20'30" 117°20'20" 117°20'10" 117°20' 117°19'50"

37°02'

37°01'50"

37°01'40"

0 400 800 FEET

0 100 200 METERS

EXPLANATION

Ground control points difference, in feet

–7.232858 to –4.299083

–4.299082 to –1.513939

–1.513938 to –0.382107

–0.382106 to 0.204938

0.204939 to 0.951340

0.951341 to 2.309630

2.309631 to 6.909616

Figure 8. Spatial distribution of measured residual error between ground control points and the digital terrain model for Scotty’s 

Castle in Grapevine Canyon, Death Valley National Park, California.
14 Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP

0

20

40

60

80

100

120

0

50

100

150

200

250

–7.5

–7

–6.5

–6

–5.5

–5

–4.5

–4

–3.5

–3

–2.5

–2

–1.5

–1

–0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

6.5

7

7.5

Frequency

Residual error, in feet

Cumulative percentage

Frequency

Cumulative percentage

EXPLANATION

Figure 9. Histogram and cumulative percentage of residual error between ground control points and the digital terrain model for 

Scotty’s Castle in Grapevine Canyon, Death Valley National Park, California.

Hydraulic Modeling

The hydraulic modeling was done with the U.S. Army 

Corps of Engineers Hydrologic Engineering Center–River 

Analysis System (HEC–RAS), version 5.0.7 (U.S. Army 

Corps of Engineers, 2019). A one-dimensional step-backwater 

model, HEC–RAS computes open-channel streamflow using 

channel geometry and channel roughness. The streamflows 

of the computed AEP floods were used to determine water 

surface elevations for each cross section. With no hydrograph 

or water surface elevations for the varying streamflows to use 

for boundary conditions, the normal slope (Sn) was set equal 

to the channel slope (So), defining the boundary conditions for 

Grapevine Canyon downstream end (Sn=0.04). Due to the very 

steep channel, supercritical streamflow could be computed 

by the model; however, the ability of supercritical streamflow 

to occur over long distances in alluvial channels has been 

questioned (Grant, 1997). Rather, as streamflow increases, 

turbulence and the formation of bed forms cause an increase 

of roughness and subcritical or critical flow to occur (Jarrett, 

1984; Costa and Jarrett, 2008). Since supercritical flow would 

result in a lower water surface to be computed, a conservative 

approach was used and the model was run in subcritical 

model, allowing only subcritical and critical streamflow. 

Expansion and contraction coefficients were set at 0.5 and 0.0, 

respectively (Davidian, 1984).
Hydraulic Modeling 15

Model Geometry

The U.S. Army Corps of Engineers Hydrologic 

Engineering Center Geo River Analysis System 

(HEC-GeoRAS) ArcMap extension, version 10.3, was used 

to extract cross sections and delineate buildings from the 

TLS-derived DTM to define the model geometry (U.S. Army 

Corps of Engineers, 2015). A total of 539 cross sections were 

extracted for six defined model reaches and used for model 

simulations. Modifications were made to the bridge because 

the TLS scans did not adequately define the bridge structure. 

The modifications were based on manual width, length, and 

depth measurements.

Six separate model stream reaches were defined for 

the model to describe the six primary streamflow channels 

(fig. 2). Upper Grapevine Canyon was defined from the 

upstream end of the surveyed area to approximately 300 ft 

downstream of the bridge. Middle Grapevine Canyon was 

defined from approximately 300 ft downstream of the bridge 

to the main confluence with Tie Canyon. Lower Grapevine 

Canyon was defined from this confluence to the downstream 

end of the surveyed area. Upper Tie Canyon was defined from 

the upstream end of the surveyed area to just upstream of 

the gravel separator (a large historical structure used during 

the construction of Scotty’s Castle). Lower Tie Canyon was 

defined from upstream of the gravel separator to the main 

confluence with Grapevine Canyon. Side Channel was defined 

as the distributary channel from upstream of the gravel 

separator to approximately 300 ft downstream of the bridge.

Near the Tie and Grapevine Canyon confluence, Lower 

Tie Canyon, Side Channel, Middle Tie Canyon, and the lower 

portion of Upper Tie Canyon all become one continuous area 

of inundation at higher streamflows. The boundaries of these 

channels were arbitrarily set at higher locations between 

defined channels when possible, with the model assuming 

a vertical bank at this point. This was done to reduce errors 

associated with large changes in water surface between 

cross sections.

Several of the buildings at Scotty’s Castle were defined 

as obstructions. It is possible the largest streamflows could 

damage the buildings to such an extent to allow some 

conveyance of streamflow; however, the conveyance would 

be minimal compared to the entire channel. Ineffective 

streamflow areas, or areas where water would pool but not 

convey streamflow, were defined near the bridge and in 

backwater areas.

Model Hydrology

Because of the multiple confluences, AEP flows were 

assigned to each model reach in three different ways. The 

regional regression equations and the drainage areas were used 

to determine the streamflow for Upper Grapevine and Upper 

Tie Canyons. Lower Grapevine Canyon was determined 

by an addition of Upper Grapevine and Upper Tie Canyons 

streamflows. Middle Grapevine Canyon was determined by an 

addition of Upper Grapevine and Side Channel flows. Because 

Lower Tie Canyon and Side Canyon are distributaries (rather 

than tributaries) of Upper Tie Canyon, simple addition of 

streamflow could not be done. Instead, the “flow optimization 

tool” in HEC–RAS was run using the inflow from Upper Tie 

Canyon and varying the streamflow going down both Lower 

Tie Canyon and Side Channel until a balance of water surface 

and energy grade lines was reached.

Roughness Coefficients

The streamflow of a channel is controlled not just 

by the geometry (cross sections and slope) but also by 

friction with the channel bed and vegetation growing in 

the channel. Channel roughness, as defined by Manning’s 

n-value, was estimated for cross sections using tables for 

channel material (base n-value) and adjusting for channel 

irregularities, obstructions, and vegetation to determine a 

final n-value (Chow, 1959; Arcement and Schnieder, 1989). 

Where overbank areas occurred, additional n-values were 

estimated using the same process. Estimated n-values were 

also compared with photographs of streams with determined 

roughness values to verify the final values (Barnes, 1967; 

Aldridge and Garrett, 1973; Phillips and Ingersoll, 1998). 

The final selected n-values ranged from 0.017 to 0.13. The 

higher values in the specified ranges were used for areas just 

upstream of Scotty’s Castle and downstream of the bridge 

for dense riparian vegetation growing in the channel as well 

as overbank locations in Upper Tie Canyon where piles 

of railroad ties act as additional obstructions. The lower 

values were for the pavement of either the parking lot or the 

Grapevine Canyon Road.

As an additional check on roughness, the measured 

channel bed particle size was used to compute a base n-value 

(without adjustments) based on work done in California by 

Limerinos (1970)1 and a geographically diverse dataset by 

Rickenmann and Recking (2011):

n

R

R

d

b 



0 113

1 16 2 0

1 6

84

.

. . log

/

(7)

n

d b = 84

0 167

20 4

.

. (8)

where nb is the base n-value, R is the hydraulic radius in 

meters, and d84 is the particle size that exceeds that of 

84 percent of the particles in meters. The 1-AEP streamflow 

was used to compute the hydraulic radius.

1This is a metric form of the equation as given in Bray and Davar (1987).
16 Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP

Model Calibration

Because no gaging stations had been operation in the area 

before December 2016, model calibration data was limited 

to the indirect measurement surveyed for the October 18, 

2015, flood (at the upstream end of the Upper Grapevine 

Canyon model reach). The model was run using the indirect 

streamflow of 3,200 cfs in Grapevine Canyon. The modeled 

water surface was compared with the surveyed high-water 

marks (quality good to poor) from the indirect measurement 

surfaces (fig. 10). When the indirect measurement was 

computed, it was found that there was a very large decrease 

in cross-sectional area and increase in velocity in the middle 

of the reach in contrast to all other parts of the surveyed 

indirect reach. The significant difference of channel hydraulic 

properties along with photographic examination of the channel 

and weather radar data of the movement of the thunderstorm 

provided ample evidence that an unnamed side canyon had 

deposited fill in the middle of the indirect measurement reach 

after the main flood peak in Grapevine Canyon. Therefore, 

the high-water marks from the main flood peak would not 

represent the water surface for the same streamflow in 

the current channel because fill happened after the peak. 

Additionally, after the indirect measurement survey, but 

before the TLS survey, gravel and cobble fill from the road 

had been moved and placed within the main channel, further 

complicating the comparison. When impacted high-water 

marks associated with cross sections that were affected by 

the greatest fill were removed from consideration, the mean 

model water surface was found to be on average 0.22 ft. 

higher than the high-water marks. This is within the accuracy 

of the surveyed high-water marks (0.20–0.40 ft) from the 

indirect measurement survey. Because the reach was already 

computing as critical flow, lowering the n-value would not 

decrease the water surface further. For these reasons, no 

additional modifications to the model were made.

3,070

3,075

3,080

3,085

3,090

3,095

3,100

3,105

3,110

3,115

3,120

3,125

3,070 3,075 3,080 3,085 3,090 3,095 3,100 3,105 3,110 3,115 3,120 3,125

Surveyed high-water marks from October 18, 2015, flood, in feet

Modeled water surface for October 18, 2015, flood, in feet

Surveyed versus modeled water surface for October 18, 2015, flood

Impacted high water marks

1:1 agreement

Unimpacted high water marks

EXPLANATION

Figure 10. Surveyed versus modeled water surface for October 18, 2015, flood at Scotty’s Castle in Grapevine Canyon, Death Valley 

National Park, California.
Results 17

Elsewhere in Grapevine Canyon and Tie Canyons, 

removal of the high-water marks from the October 18, 2015, 

flood by weather and maintenance crews was done before the 

TLS surveys were completed; therefore, additional calibration 

points could not be determined for that flood.

After the creation and the execution of the HEC–RAS 

model, the resulting inundation areas were imported into a 

geographic information system. Near the confluence of Tie 

and Grapevine Canyons, streamflow became two-dimensional 

and was not adequately mapped using the one-dimensional 

model. Examples include additional braided channels in lower 

Tie Canyon and lower Grapevine Canyons (where streamflow 

would continue downstream, not stopping at a cross section), 

the arbitrary boundaries between channels as described above, 

and the overflow of the bridge and embankment in upper 

Grapevine Canyons (where the model computed streamflow 

was confined to the channel downstream of the bridge despite 

streamflow occurring over the top of the embankment). Areas 

were manually added to the inundation layers in locations 

where streamflow was inferred to occur; these manually added 

areas were marked as “inferred inundation area” to indicate 

additional uncertainty.

Sensitivity Analysis

In addition to the final computation as described (named 

final scenario), two other computations were run for every 

AEP to provide some indication of uncertainty. A high-water 

surface scenario was created, assuming vegetation grows 

back to the moderately to extremely dense vegetation that 

existed in the active channel of Grapevine Canyon before the 

October 18, 2015, flood. Imagery and photographs before the 

flood indicated very dense willow and mesquite extending 

from the Grapevine Canyon–Tie Canyon confluence to the 

upstream side of the bridge and from upstream side of the 

parking lot to 850 ft upstream. Downstream of the Grapevine 

Canyon–Tie Canyon confluence and distances greater than 

850 ft above the parking lot, moderately dense vegetation was 

present in the active channel. The n-values for these areas 

were mostly raised from 0.045 to 0.12. In Tie Canyon, the 

n-value was raised slightly for somewhat denser vegetation 

that was growing in the active channel before the flood.

In addition to the higher n-value for vegetation, on both 

the upstream and downstream side of the bridge, the large 

channel incision that took place during the flood was filled 

in to return the area to the pre-flood state. Because no recent 

survey data exist to determine the exact height of the land 

surface near the bridge before the flood, a flat surface with 

the surrounding land was used. This resulted in channels 

approximately 1–10.5 ft shallower than in the final scenario 

near the bridge.

A low-water-surface scenario was also created, assuming 

the channel was maintained to be clear of thick vegetation 

downstream of the bridge and upstream of the parking lot. 

The channel incision near the bridge was also kept in its 

current state. In Lower Grapevine Canyon and Tie Canyon, 

the low-water-surface scenario assumed some minor reduction 

in vegetation resulting in slightly lower roughness. These 

additional computations are plotted on the same maps as the 

final scenario computation.

Results

The flood-inundation maps are presented in 

figures 11–15. The park offices, visitor center, parts of 

Grapevine Canyon Road, and the bridge are inundated by 

the 2-AEP flood; however, none of the computed flows reach 

Scotty’s Castle proper, the Chimes Tower, or the Hacienda. 

The model computes steep, fast, critical streamflow for 

most of the study reaches for all the computed AEP flood 

streamflows. However, upstream of the bridge and in areas 

with dense vegetation, high roughness coefficients reduce 

velocities and cause subcritical streamflow to be computed.

Grapevine Canyon

All the AEP flood streamflows modeled inundate 

Grapevine Canyon Road near the upper end and lower end 

of the surveyed reach where the channel is nearly the same 

elevation as the road. Streamflow starts to reach the southeast 

corner of the visitor center and park offices at the 4-AEP flood 

(fig. 11). The 2-AEP (fig. 12), 1-AEP (fig. 13), and 0.5-AEP 

floods (fig. 14) have more streamflow directed around the 

north side of the visitor center and park offices where the 

ground is sloped toward the building itself. By the 0.2-AEP 

flood, streamflow has nearly surrounded the building (fig. 15). 

The stable also has a similar hazard on the east side. However, 

streamflow does not reach the stable until the 0.5-AEP flood.

The 4-AEP flood computed streamflow was confined to 

the bridge and pooling behind the embankment. At the 2-AEP 

flood, the bridge and embankment are overtopped, and by 

the 0.2-AEP flood, the overtopping streamflow is nearly 6 ft 

in depth.

Downstream of the embankment, the overflow parking lot 

terrace would be partially affected by all the AEP floods owing 

to streamflow from the north and northwest occurring through 

Side Channel. Without well-defined channels, streamflow 

could either spread out or incise and cut new channels. By 

the 2-AEP flood, where the embankment is overtopped, there 

would be additional streamflow on this terrace coming from 

Upper Grapevine Canyon, resulting in streamflow coming at 

very different angles.

The sensitivity analysis illustrates the effects that different 

management scenarios would have on the water levels. The 

4-AEP flood high-water scenario has streamflow reaching 

the visitor center and park offices as well as overtopping the 

bridge and embankment, whereas this does not occur in the 

final and low water scenario until the 2-AEP flood.
18 Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP

Base modified from National Agricultural Imagery

Program, 2016, 1:8,000 scale. Universal

Transverse Mercator, zone 11,

World Geodetic System of 1984

GRAPEVINE CANYON R O A D

117°20'40" 117°20'30" 117°20'20" 117°20'10" 117°20' 117°19'50"

37°02'

37°01'50"

37°01'40"

G

F

H

E

C

B A

D

I

J

GRAPEVINE CANYON ROAD

EXPLANATION

0 400 800 FEET

0 100 200 METERS

Buildings and structures

A Gravel separator Hacienda F

B Overflow parking lot Stable G

C Castle Gate Bridge Pools H

D Chimes Tower Visitors center and park offices I

E Scotty's Castle Main parking lot J

Inferred inundation area

Low-water surface scenario

Final water surface scenario

High-water surface scenario

4-percent annual exceedance probablity (AEP) streamflow

Figure 11. Flood-inundation areas for the 4-percent annual exceedance probability flood streamflow for Scotty’s Castle in 

Grapevine Canyon, Death Valley National Park, California.

Tie Canyon

All the AEP floods result in streamflow leaving the active 

channel located on the west side of the canyon and flowing 

onto the higher Upper Tie Canyon terrace on the east side. 

The 4-AEP flood (fig. 11) results in braided streamflow on 

this terrace. The terrace becomes completely inundated at 

flows greater than or equal to the 0.2-AEP flood streamflow 

(fig. 15). All the computed AEPs have streamflow leaving 

the main channel near the upstream end of Tie Canyon and 

following an old road that goes along the base of the hill to 

the overflow parking lot downstream of the bridge. Further 

downstream, approximately 45–54 percent of streamflow is 

directed southeast down the Side Channel created during the 

October 18, 2015, flood, with the percentage increasing with 

larger streamflow.

The sensitivity analyses in Tie Canyon show that the 

inundated extent is limited by the steep side slopes of the 

canyon, and the different computations result mostly in 

changes to the inundation depth.
Results 19

Base modified from National Agricultural Imagery

Program, 2016, 1:8,000 scale. Universal

Transverse Mercator, zone 11,

World Geodetic System of 1984

GRAPEVINE CANYON R O A D

117°20'40" 117°20'30" 117°20'20" 117°20'10" 117°20' 117°19'50"

37°02'

37°01'50"

37°01'40"

GRAPEVINE CANYON ROAD

G

F

H

E

C

B A

D

I

J

EXPLANATION

0 400 800 FEET

0 100 200 METERS

Buildings and structures

A Gravel separator F Hacienda

B Overflow parking lot G Stable

C Castle Gate Bridge H Pools

D Chimes Tower I Visitors center and park offices

E Scotty's Castle J Main parking lot

Inferred inundation area

Low-water surface scenario

Final water surface scenario

High-water surface scenario

2-percent annual exceedance probablity (AEP) streamflow

Figure 12. Flood-inundation areas for the 2-percent annual exceedance probability flood streamflow for Scotty’s Castle in 

Grapevine Canyon, Death Valley National Park, California.
20 Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP

Base modified from National Agricultural Imagery

Program, 2016, 1:8,000 scale. Universal

Transverse Mercator, zone 11,

World Geodetic System of 1984

GRAPEVINE CANYON R O A D

117°20'40" 117°20'30" 117°20'20" 117°20'10" 117°20' 117°19'50"

37°02'

37°01'50"

37°01'40"

GRAPEVINE CANYON ROAD

G

F

H

E

C

B A

D

I

J

EXPLANATION

0 400 800 FEET

0 100 200 METERS

Buildings and structures

A Gravel separator F Hacienda

B Overflow parking lot G Stable

C Castle Gate Bridge H Pools

D Chimes Tower I Visitors center and park offices

E Scotty's Castle J Main parking lot

Inferred inundation area

Low-water surface scenario

Final water surface scenario

High-water surface scenario

1-percent annual exceedance probablity (AEP) streamflow

Figure 13. Flood-inundation areas for the 1-percent annual exceedance probability flood streamflow for Scotty’s Castle in 

Grapevine Canyon, Death Valley National Park, California.
Results 21

Base modified from National Agricultural Imagery

Program, 2016, 1:8,000 scale. Universal

Transverse Mercator, zone 11,

World Geodetic System of 1984

GRAPEVINE CANYON R O A D

117°20'40" 117°20'30" 117°20'20" 117°20'10" 117°20' 117°19'50"

37°02'

37°01'50"

37°01'40"

GRAPEVINE CANYON ROAD

G

F

H

E

C

B A

D

I

J

EXPLANATION

0 400 800 FEET

0 100 200 METERS

Buildings and structures

A Gravel separator F Hacienda

B Overflow parking lot G Stable

C Castle Gate Bridge H Pools

D Chimes Tower I Visitors center and park offices

E Scotty's Castle J Main parking lot

Inferred inundation area

Low-water surface scenario

Final water surface scenario

High-water surface scenario

0.5-percent annual exceedance probablity (AEP) streamflow

Figure 14. Flood-inundation areas for the 0.5-percent annual exceedance probability flood streamflow for Scotty’s Castle in 

Grapevine Canyon, Death Valley National Park, California.
22 Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP

Base modified from National Agricultural Imagery

Program, 2016, 1:8,000 scale. Universal

Transverse Mercator, zone 11,

World Geodetic System of 1984

GRAPEVINE CANYON R O A D

117°20'40" 117°20'30" 117°20'20" 117°20'10" 117°20' 117°19'50"

37°02'

37°01'50"

37°01'40"

GRAPEVINE CANYON ROAD

G

F

H

E

C

B A

D

I

J

EXPLANATION

0 400 800 FEET

0 100 200 METERS

Buildings and structures

A Gravel separator Hacienda F

B Overflow parking lot Stable G

C Castle Gate Bridge Pools H

D Chimes Tower Visitors center and park offices I

E Scotty's Castle Main parking lot J

Inferred inundation area

Low-water surface scenario

Final water surface scenario

High-water surface scenario

0.2-percent annual exceedance probablity (AEP) streamflow

Figure 15. Flood-inundation areas for the 0.2-percent annual exceedance probability flood streamflow for Scotty’s Castle in 

Grapevine Canyon, Death Valley National Park, California.

Channel Bed Particle Size and Roughness

The result of the pebble counts to determine the channel 

bed particle size are presented in table 5. Median grain size 

(d50) ranged from 8 to 16 millimeters (mm), or medium gravel. 

The d84, or the particle size that exceeds that of 84 percent 

of the particles, ranged from 32 to 180 mm, or very coarse 

gravel to cobble. The computed base n-values from equations 

by Limerinos (1970) and Rickenmann and Recking (2011) are 

within the range of n-values given for gravel by Arcement and 

Schnieder (1989) apart from Tie Canyon Overbank, which had 

a larger percentage of boulders.
Discussion 23

Table 5. Results of pebble counts and computed n-values for Scotty’s Castle in 

Grapevine and Tie Canyons, Death Valley National Park, California.

[d50, particle size exceeds that of 50 percent of the particles; d84, particle size exceeds that of 

84 percent of the particles; mm, millimeter]

Location d50

(mm)

d84

(mm)

Base nvalueComputed base 

n-value1

Computed base 

n-value2

Grapevine Overbank 8 64 0.028–0.035 0.035 0.031

Grapevine Main 16 64 0.028–0.035 0.031 0.031

Tie Overbank 16 180 0.028–0.035 0.047 0.037

Tie Main 16 45 0.028–0.035 0.030 0.029

Confluence 11 32 0.028–0.035 0.027 0.028

1From Limerinos (1970).

2From Rickenmann and Recking (2011).

Discussion

The model indicates several buildings, roads, and the 

bridge remain susceptible to flooding. The largest hazards 

include the overtopping of the bridge and how side channel 

will respond to future floods.

Grapevine Canyon

None of the computed flows reach Scotty’s Castle main 

building. However, the area around Scotty’s Castle is still 

subject to gully and overland flow from the nearby hillslopes 

as occurred during the October 18, 2015, flood, which 

deposited sediment and debris in this area.

The greatest hazard is at the bridge and embankment. In 

all three streamflow scenarios, the bridge and embankment are 

overtopped. The 0.2-AEP flood has a depth of nearly 6 ft over 

the bridge and embankment. Because of the approximately 6 ft 

drop in the water surface from the upstream to the downstream 

sides of the bridge, significant amounts of erosion would be 

possible on the downstream side of the embankment. If a 

failure of the embankment were to occur2, it would cause a 

drastic drop in the water surface upstream, with a large release 

of the water, sediment, and entrained debris.

At the overflow parking lot terrace, because of the lack 

of defined channels, streamflow could either spread out or 

incise and cut new channels. Given the steep slope and large 

difference in elevation from the overflow parking lot terrace 

to the main channel, an incision working backwards into the 

terrace is possible. At AEP floods in which the embankment 

2A technical structure survey would be needed to determine the actual risk 

of embankment failure and is beyond the scope of this report.

is overtopped, there would be additional streamflow on this 

terrace coming from Upper Grapevine Canyon, resulting in 

streamflow coming at very different angles. In such an event, 

very complex interactions of the streamflow and the incision 

would occur and probably vary significantly over the course of 

the flood.

The visitor center, park offices, and stable all face unique 

hazards because the adjacent ground terrain slopes downhill 

into the buildings. The slope direction has the potential to 

be more hazardous and damaging as streamflow, sediment, 

and entrained debris are directed into the buildings, which 

occurred during the October 18, 2015, flood.

Tie Canyon

In Tie Canyon, the largest uncertainty is how Side 

Channel may respond to future streamflows. Side Channel 

appeared to have been created by streamflow following an old 

road during the 2015 flood. Lower Tie Canyon functions as an 

alluvial fan, and it is very common for streamflow to switch 

distributary channels or rapidly create new channels during 

floods on fans (National Research Council, 1996). Therefore, 

depending on the variable channel conditions on this fan, it is 

possible for Side Channel to convey significant but variable 

streamflows that could even become the primary channel 

for Tie Canyon, directing the streamflow onto the overflow 

parking lot terrace. This scenario could cause additional 

damage to the overflow parking lot, potentially resulting in 

additional fill being deposited near the exit of the bridge, and 

cause backwater conditions resulting in higher water surface 

elevations upstream of the bridge. Additionally, increased 

streamflow in Side Channel would cause higher velocities very 

close to the gravel separator that could lead to damage of the 

historic structure.
24 Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP

Uncertainties and Limitations

The hydraulic model and maps produced in this 

study have uncertainties and limitations that are detailed 

below. Uncertainties are cumulative and include limited 

understanding of the hydraulics of very steep, erodible-bed 

channels; the possibility of significant channel changes from 

both floods and management; the limits of one-dimension 

modeling; and the reliance on regional regression equations. 

The mapped inundation areas should not be viewed as 

absolute, but rather a prediction within a larger ensemble 

of possibilities.

Physical Limitations

Most significantly, the model is a snapshot of the 

conditions during the topographic data collection survey. The 

sensitivity analysis provides general guidance on how different 

management strategies could affect the flood-inundation 

areas; it does not cover every possible scenario. Changes to 

the channel or bridge geometry would affect the computed 

water surface elevations. For example, the construction of 

berms to protect an area against flooding would likely cause 

higher water surface elevations for a given streamflow for the 

remainder of the channel near the berms. Conversely, channel 

enlargement would cause lower water surface elevations.

The channel is subject to unknown scour and fill during 

flood streamflows. Scour at the peak would cause a larger 

cross-sectional area, and therefore lower water surface 

elevations, for a given streamflow, whereas fill at the peak 

would cause higher water surface elevations for a given 

streamflow. Additionally, such scour and fill would vary 

spatially and temporally with bed armoring, channel form, 

wave form, and streamflow (Hooke and Mant, 2000; Powell 

and others, 2007).

The actual channel roughness may vary from those 

used; a higher roughness would cause higher water-surface 

elevations for a given streamflow, whereas a lower roughness 

would cause lower water surface elevations for a given 

streamflow. Roughness is variable in time with seasonal 

changes to vegetation and the movement of sediment during 

floods (Bray and Davar, 1987). Finally, nearly all information 

about n-values are from lower gradient channels, which 

has been found to underestimate n-values for high gradient 

channels (Jarrett, 1984; Marcus and others, 1992).

Floods can carry substantial amounts of debris that can 

get lodged on trees, boulders, or other features. Such flood 

debris can direct streamflow in varying directions, causing 

higher velocities and erosion in places than would otherwise 

occur. Flood debris can also block streamflow and would be 

most impactful at the bridge and immediately upstream from 

the bridge, where debris would reduce conveyance and cause 

higher water surface elevations.

Model Limitations

Although most of the channel was suitable for 

one-dimensional modeling using the step-backwater method, 

the area near the confluence of Tie and Grapevine Canyons 

was not. Because of the various angles of streamflow (both 

from Side Channel and over the top of the bridge embankment 

in Grapevine Canyon), braided channels, arbitrary boundaries 

between channels that have a single inundation surface at 

higher streamflows, and streamflow over the embankment, 

one-dimensional modeling cannot fully describe the 

streamflow paths. Elsewhere, abrupt changes in the channel 

cross sections cause large changes in channel conveyance, 

which increases uncertainty that energy losses are correctly 

computed (Davidian, 1984). Finally, because of the steepness 

of the channel, large drops in the water surface occur 

between cross sections bounding channel junctions, causing 

additional uncertainty.

The regional regression equations used to compute 

modeled streamflows also have uncertainties, especially in 

desert regions with shorter period datasets, highly variable 

peak streamflow, and zero streamflow years (Gotvald and 

others, 2012). These uncertainties grow with the lower 

probability of the streamflow’s occurrence (the 4-percent 

AEP versus the 0.2-percent AEP). The previously published 

regional regression equations used by Bowers (1989) have 

computed streamflows 10–50 percent greater than Gotvald and 

others (2012), illustrating how the additional data collected 

indicates these issues.

Finally, the model does not address hazards related 

to gully and overland flow from the adjacent hillslopes. 

Currently, many gullies flow directly into building walls or 

spread onto parking lots with no established drainage. The 

erosion and deposition from these gullies and hillslopes was 

an important and possibly major cause of damage during the 

October 18, 2015, flood.

Suggestions for Future Research

Two crest-stage gages were installed at Scotty’s Castle 

in December 2016, one approximately 1,600 ft upstream 

of the bridge in Grapevine Canyon and one approximately 

1,700 ft upstream of the confluence in Tie Canyon. Long-term 

monitoring of peak flows at the site would provide additional 

calibration data and the ability to perform site specific flood 

frequency analyses (10 years are the minimum required 

[England and others, 2018]), as well as provide data from 

currently unrepresented locations for regional flood frequency 

regression equations. However, as of September 2020, no 

streamflow has occurred at the two sites.
References Cited 25

Along with the two crest-stage gages, scour chains were 

installed in both canyons. Although the measured scour at 

those points cannot be assumed to apply to the entire reach, it 

can provide information on the relative importance of scour to 

the reach. If scour is found to be significant, additional scour 

chains could be installed in indirect measurement sections 

to help to reduce uncertainties associated with scour and fill 

during floods.

One-dimensional hydraulic models, such as the 

step-backwater method, assume straight streamflow and do 

not perform routing of streamflow. In locations such as Upper 

Tie Canyon, Lower Grapevine Canyon, and Upper Grapevine 

Canyon (upstream of the bridge), streamflow is mostly 

straight, and routing should not cause appreciable changes in 

the inundation locations. In the complex areas around the Tie 

and Grapevine Canyon confluence, the use of two-dimensional 

hydraulic models to determine flood-inundation areas 

would more accurately describe the complex streamflow 

paths. If channel modifications significant enough to be 

useful for flood protection are performed, the development 

of a two-dimensional model might provide more accurate 

flood-inundation area mapping.

Summary and Conclusions

This report provides a series of updated maps for the 

flood-inundation areas near Death Valley Scotty Historic 

District in Death Valley National Park. A terrestrial laser 

scanner (TLS) was used to collect elevation data to construct 

a digital terrain model (DTM) for the area. Topographic 

and structural data were derived from this DTM and used 

in a one-dimensional hydraulic model. Annual exceedance 

probability (AEP) streamflows were computed from regional 

regression equations and used with the hydraulic model to 

determine the water surface elevation for the floods. Finally, 

these water surfaces were mapped on the DTM to create 

flood-inundation maps.

Sections of Grapevine Canyon Road are subject to 

flooding by all the computed AEP floods. For all the computed 

AEP floods, two buildings at Scotty’s Castle are also subject 

to flooding, but none of the modeled floods reached Scotty’s 

Castle main building, although it still could be affected by 

gully and overflow flow from the nearby hillslopes. The 

bridge and embankment are subject to overtopping by the 

2-percent AEP flood. Sensitivity analyses illustrate the bridge 

is sensitive to fill and vegetation growth, with overtopping 

occurring at the 4-percent AEP flood with pre-October 2015 

flood conditions. All computed floods in Tie Canyon result in 

streamflow outside the main channel with the possibility of 

future floods moving the active main channel to the east of the 

gravel separator, closer to the bridge and embankment.

Specific uncertainties with the model are lack of model 

calibration, lack of a site-specific flood frequency analysis, the 

limitations of one-dimensional modeling, and uncertainties 

about the behavior of very steep gravel bed streams during 

floods. These uncertainties should be considered when 

viewing the results of this report.

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Nevada Water Science Center

U.S. Geological Survey

2730 N. Deer Run Road

Carson City, Nevada 95819

https://www.usgs.gov/centers/nv-water

Publishing support provided by the U.S. Geological Survey 

Science Publishing Network, Sacramento Publishing Service Center
Morris and others—Delineation of Flood-Inundation Areas in Grapevine Canyon Near Scotty’s Castle, Death Valley NP—SIR 2020–5082

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20205082