Aerial view of Casandro Wash Dam near its peak impoundment at approximately 7:15 pm; Courtesy of ABC15 News

Flood Control District of Maricopa County
Engineering Division, Flood Warning Branch

Storm Report : July 18, 2015
Vicinity of Wickenburg, AZ
Revision 1 – Sep. 4, 2015
 Revised the discharge hydrograph for Hassayampa River at I-10 (#5283)
 Added Figure 34 – Where Did All The Wickenburg Water Go?
 Added Appendix A – Indirect Flood Discharge Measurement for Cemetery Wash

TABLE OF CONTENTS
Meteorology ....................................................................... 3
Precipitation ...................................................................... 8
Runoff ............................................................................ 13
Event Timeline .................................................................. 25
Selected Data Sources ........................................................ 28

TABLES
Table 1
Table 2
Table 3
Table 4
Table 5

FCDMC Hourly Quantitative Precipitation Forecast ............................. 4
Peak Rainfall Amounts and Calculated Return Periods ......................... 8
Summary of Measured Peak Discharges at FCD Stream Stations ............. 13
Summary of Measured Peak Stages at FCD Impoundment Stations .......... 13
Travel Times between Various Stream Gages in the Wickenburg Area ...... 19

FIGURES
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
Figure 14
Figure 15
Figure 16
Figure 17
Figure 18
Figure 19
Figure 20
Figure 21
Figure 22
Figure 23
Figure 24
Figure 25
Figure 26
Figure 27
Figure 28
Figure 29
Figure 30
Figure 31
Figure 32
Figure 33
Figure 34
Appendix A

True-color Visible Satellite Photo of Arizona ..................................... 5
True-color Visible Satellite Photo of the Eastern Pacific ....................... 5
4-Panel Synoptic Setup - 5:00 PM MST 07/18/2015 .............................. 6
Observed Skew-T/log P Diagram for Phoenix, 7/18/15 5:00 PM .............. 7
Rainfall Hyetograph for Twin Peaks Rain Gage ................................... 9
Rainfall Hyetograph for Vulture Mine Rd. Rain Gage ............................ 9
Rainfall Hyetograph for Casandro Wash Rain Gage .............................. 9
Rainfall Hyetograph for Powder House Wash Rain Gage ........................ 9
Rainfall Map - Isohyetal and Point Values ........................................ 10
Sea Surface Temperatures, Eastern Pacific, 7/1/2015 ......................... 11
The MCSSI Scale ........................................................................ 12
MCSSI Calculation Template ........................................................ 12
MCSSI Storm Map ...................................................................... 12
Antelope Creek Hydrograph ........................................................ 14
Box Wash Hydrograph ................................................................ 14
Casandro Wash Hydrograph ......................................................... 15
Casandro Dam Hydrograph .......................................................... 15
Flying E Wash Hydrograph ........................................................... 16
Hartman Wash Hydrograph ......................................................... 16
Hassayampa R. @ Box Canyon Hydrograph ....................................... 17
Hassayampa R. @ US 60 Hydrograph .............................................. 17
Hassayampa R. near Morristown Hydrograph .................................... 18
Hassayampa R. @ I-10 ................................................................ 18
Plot of Hassayampa River Peaks & Travel Times ................................ 19
Martinez Creek Hydrograph .......................................................... 20
Powder House Wash Hydrograph ................................................... 20
Sols Wash near Matthie Hydrograph ............................................... 21
Sunnycove FRS Hydrograph ......................................................... 21
Sunset FRS Hydrograph .............................................................. 22
Vulture Mine Road Hydrograph ..................................................... 22
Photo - Box Wash, Left Bank, 5/14/2015 ........................................ 23
Photo - Box Wash, Left Bank, 7/20/2015 ........................................ 23
Photo - Debris Flow on Vulture Mine Rd. ......................................... 24
Hydrographs – Where Did All The Wickenburg Water Go? ..................... 24
– Indirect Flood Discharge Measurement for Cemetary Wash .................. 28

METEOROLOGY
An unstable atmosphere largely aided by tropical moisture associated with the remnants of
Hurricane Dolores led to the development of an organized thunderstorm complex which dropped
torrential rains over northwestern Maricopa County during the evening of Saturday July 18th.
These storms produced anywhere from 2.00”-5.00” of rain over a three hour period with many
gages registering the bulk of that rainfall during a brief 60-90 minute window. Heavy rain from
this event ultimately led to significant flash flooding in and around the Town of Wickenburg.
Synopsis:
In the days leading up to the event, District staff as well as many other Federal agencies began
keeping close tabs on the track of the 4th named tropical system, Dolores, to develop in the
eastern Pacific. Dolores organized into a tropical storm early the morning of July 12th, quickly
intensified into a hurricane the following afternoon, and became the third major hurricane of
the season on July 15th. Forecast tracks projected the hurricane to move northwest toward the
southern tip of Baja California (BC) by Friday July 17th before continuing northwest and
weakening well off the west of coast of the BC Spur (geographical feature on the west coast of
the BC peninsula) on Saturday July 18th. A loop of all forecasts tracks produced by the National
Hurricane Center (NHC) can be viewed here. While the circulation center of Dolores was never
forecast to make landfall in the southwestern US, numerical weather guidance continued to
favor a deep surge of tropical moisture to move north out of the Gulf of California into southern
AZ/CA Friday into Saturday.
The synoptic setup on the evening of the event is shown in Figure 3 (page 6). The upper level
images (C and D) depict the Monsoon ridge suppressed across southeastern TX and a large scale
trough off the western coast of CA; meanwhile the remnants of Dolores are seen off the west
coast of BC in each of the four images. It’s worth noting that this persistent upper-level pattern
was evident days before the event and was one of the main drivers helping to draw the tropical
system and subsequent moisture north. Looking at the mid-levels, moist south/southwesterly
flow was evident in both the 700mb and 850mb maps. Surface moisture values were rather high
with area dewpoints running in the mid to upper 60s across much of west central AZ, image
(courtesy of NWS Storm Prediction Center at 00Z, 5:00pm MST). Precipitable water values were
measured throughout the day as the deep surge of tropical moisture moved north into southern
AZ/CA. A value of 1.73” was observed on the 00Z, 5:00pm MST, KPSR sounding (Figure 2, below)
which according to the Storm Prediction Sounding Climatology page (can be viewed here) was a
period of record daily max.
Mesoanalysis data across CA/AZ in the near storm environment on Saturday afternoon revealed a
favorable setup for scattered to widespread heavy rain producing thunderstorms. Evidence of
this is shown by the 23Z (4:00pm MST) RAP model mesoanalysis images shown here (gathered
from NWS Storm Prediction Center archives). Thermodynamic variables/indices of note are
included in images A and B: the high CAPE/low CIN profile maximized across southwestern AZ
and largely negative lifted indices. The wind profile, shown in image C, was characterized by
effective bulk shear values in the 20-35 knot range out of the southwest across the lower
Colorado River Valley and extending into west-central AZ. The distribution of precipitable water
is shown in image D. Further description of the favorable setup for heavy rain and flash flooding
potential was conveyed an hour earlier by the Weather Prediction Center through its 2:59pm MST
mesoscale precipitation discussion here . Table 1 shows values from the District’s hourly
Convective Quantitative Precipitation Forecast (QPF) at 5:06pm MST which was generated just as
the complex of storms moved into the Wickenburg area. Of note are the abnormally large 1-hr,
30-min, and 10-min potential rainfall rates within the two forecast zones encompassing
northwestern Maricopa County. The QPF with multiplier values, which indicate a severe storm
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able to utilize the full moisture profile, were remarkably accurate when compared to rain gage
observations around the region.
Storm Summary and Radar Imagery
Strong downdraft winds from elevated t-storms over northern portions of the Sierra Estrella
Mountains (web cam and radar image) kicked off a northward propagating outflow boundary
around 3:00pm MST. Over the next hour this gust front helped initiate several rounds of weaker
convection as it traversed the West Valley before generating a line of stronger storms just north
of the White Tank Mountains extending northeast across Hwy74 in the Northwest Valley (image).
After 4:30pm MST, the line strengthened as it continued to move north/northwest along US
60/93 dropping brief heavy rain along with pea-sized hail and severe downburst winds toppling
power poles in and around the Morristown area. Resulting damage ultimately led to the brief
closure of US 60 between mile posts 122-124.
The severe complex of thunderstorms continued to propagate north/northwest into a highly
favorable environment for rapid intensification just after 5:00pm MST. Storm updrafts were
further enhanced from upslope propagation over the higher terrain as well as from a strong area
of low-level convergence associated with outflow boundary interaction from a large line of
organized storms moving east out of the Lower Colorado River Valley into the region. From 5:006:00pm MST, torrential rain fell in and around the Town of Wickenburg with most District rain
gages picking up 2.00” to more than of 4.00” (image). Significant flash flooding was underway
as area washes, some of which were already moistened by rain the prior evening, began
conveying runoff downstream into larger waterways. Residents living along Cemetery and
Powder House Washes were hit particularly hard as runoff spilled onto area roadways and into
neighborhoods. The heavy rain began to taper off after 7:00pm MST, though larger streams such
as the Hassayampa River continued to register flows well into the overnight hours. A radar loop
spanning the entire event, courtesy of the NWS Phoenix WFO, can be viewed using the following
links (regional loop, Maricopa County loop); also local NWS storm reports can be viewed here.

TABLE 1: Hourly Quantitative Precipitation Forecast, Valid 05:06 pm MST 07/18/15
Convective QPF (in)
MSP Weather Station
1-hr
30-min
10-min
Wickenburg
Upper Centennial

MSP Weather Station
Wickenburg
Upper Centennial

1.99
2.19

1.39
1.53

0.84
0.92

Convective QPF w/multiplier (in)
1-hr
30-min
10-min
3.98
4.38

2.79
3.07

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1.67
1.84

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FIGURE 1

True-color visible
satellite photo of AZ
from GOES West – 5PM
MST on July 18th. Red
ellipse denotes the
location of the
Wickenburg storm.

FIGURE 2

True-color
visible
satellite photo
of the eastern
Pacific from
GOES West –
5PM MST on
July 18th.
Note position
and influence
of Hurricane
Delores.

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4-Panel 00Z Synoptic Setup 07/19/2015
(5:00 PM MST 07/18/2015)

FIGURE 3

Figure 3 depicts the synoptic setup at 5:00 PM MST on July 18th 2015. The images are from the
Storm Prediction Center upper air maps archive. A) is the 850mb map: the black lines are
heights, the red dashed lines are isotherms, the green lines are isodrosotherms, blue barbs are
wind speed, and station observations are plotted at each available location. B) is the 700mb
map: variables colored the same as A. C) is the 500mb map: variables colored the same as in A.
D) is the 300mb map: the black lines are stream lines, the yellow lines are divergence, and
station observations are plotted at each available location.

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FIGURE 4

Figure 4: Observed Skew-T/log P (vertical profile of the atmosphere above Phoenix) diagram at
5:00pm MST on July, 18th, 2015. Sounding generated from NOAA/SPC. The vertical axis is
pressure in (hPa) and the horizontal axis is temperature in (°C). The thick solid red line is the
temperature profile. The thick solid green line is the moisture profile. The dashed red lines are
the atmospheric parcel profiles. The vertical axis on the right displays the wind speed and
direction at each level in knots. Thin solid brown lines sloping from upper left to lower right are
constant potential temperature (°K). Thin dashed brown and blue lines sloping from right to left
are isotherms (°C). Thin dashed green lines sloping from right to left are mixing ratio (g/kg).
The table in the top left displays various parcel attributes and thermodynamic indices.

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PRECIPITATION
Table 2 presents rainfall as recorded by area FCDMC ALERT rain gages – peak amounts and return
periods for selected durations. These 3-hour totals match the values displayed on Figure 9:

TABLE 2
Rain Gage Names and Locations, Links to Station History Pages (also see Figure 9):
5225
7110
5230
5245
7130
7040
7090
5305
7100
7080
5260
7120
7165
7010
7060
7070
5250
5320
7000

– Hassayampa River @ US 60; southwest corner of the old bridge.
– Powder House Wash; 0.8 miles NE of confluence with Hassayampa R., 0.3 mi. N of Constellation Rd.
– Sunset FRS; 0.2 miles SE of the intersection of US 60 and Mariposa Dr.
– Sunnycove FRS; 0.2 miles NW of the intersection of Kellis Rd. and Turtleback Ln.
– Casandro Wash Dam; 0.2 miles NW of the intersection of US 60 and Mariposa Dr.
– Sols Wash near Matthie; 1.3 miles NNW of Sols Wash crossing of Vulture Mine Rd.
– Casandro Wash; US 60 at Lazy Fox Drive.
– Hassayampa River at Box Canyon; 5.3 miles NNE of Wickenburg.
– Constellation Road; at Sportsman’s Gun Club, 1.4 miles ENE of Hassayampa R. at US 60.
– Flying E Wash; 250 ft. west of Park Ave. on US 60.
– Vulture Mine Road; Vulture Mine Rd. at Duffy Drive.
– Wickenburg Airport; 125 yards west of the Airport entrance road.
– Antelope Creek; 2.3 miles NNE of the US 93 / US 89 junction.
– Martinez Creek; 0.9 miles NE of the US 93 / US 89 junction.
– Hartman Wash; 1.4 miles west of Wickenburg Airport
– Flying E Tank; 2.1 miles SSW of Wickenburg Airport.
– Twin Peaks; off Vulture Mine Road; 6.2 miles SSW of Vulture Mine Rd. at US 60
– O’Brien Gulch; 12.8 miles NE of Wickenburg
– Stanton; at Stanton RV Park, 6.6 miles east of Congress

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15-minute time distributions for selected rain gages are shown in Figures 5-8 below:
FIGURE 5

FIGURE 6

FIGURE 7

FIGURE 8

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FIGURE 9
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Precipitation Synopsis
Table 2 presents precipitation frequency statistical estimates from NOAA Atlas 14 at nineteen
precipitation measuring points. All are FCDMC ALERT-format rain gages using 1mm tipping
buckets. The gages transmit an incremented count for each recorded millimeter of rain during
an event. Some of the increment counts are lost during an event of this magnitude due to
collision of transmissions occurring at the same time, or when more than one ‘tip’ occurs in the
30 second hold-off time for transmission. When subjecting the data to QA/QC editing prior to
development of this report, it appeared that data loss was on the order of 20-30%. This can lead
to slight inaccuracies in the calculation of intensities, but overall the intensity calculations, and
therefore the frequency calculations, can be considered good. The 20-30% data loss will be
reduced to nearly zero as these stations are converted to the ALERT2 format in the coming year.
Of the nineteen gages analyzed for this report, 13 of them set new records for 30-minute, 1 hour
or 3 hour durations. Their record lengths range from 20 to 34 years. Two all-time records were
set for FCDMC rain gages – both at the Twin Peaks gage. Its 1-hour total was 4.25 inches and its
3-hour total was 5.00 inches. The old records were 3.58” at Vulture Mine Road on 7/21/1986
and 4.21” at Waterman Wash @ Rainbow Valley Road on 9/8/2014 respectively. Together with
the 15-minute record of 1.77” at Congress on 9/9/2006, it is interesting that all these short-term
records occurred within about 20 miles of each other.
In reviewing Table 2, for durations from 30 minutes to 2 hours:
11 gages had return periods of 100 years or more,
7 gages had return periods of 500 years or more,
5 gages had return periods of 1,000 years or more.
As was experienced in Maricopa County during several storms in the summer of 2014, 1,000-year
return period rainfall amounts were measured in this storm. This is undoubtedly the result of
entrained tropical moisture from Hurricane Delores, but an unusual phenomenon during the
month of July. Warmer-than-normal sea-surface temperatures in the Eastern Pacific courtesy of
El Niño are a likely contributor to these early-season tropical storms and their ability to
influence weather so far north of their origin.

FIGURE 10

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Maricopa County Storm Severity Index (MCS2I), developed by FCDMC
MCS2I is an index that classifies the severity of a storm based on the area covered, the average rainfall
over that area (from gage-adjusted radar estimates), and the storm duration. For this storm, we chose
the area inside the 1-inch contour on the 3-hour duration storm map. The storm scores an MCS2I of 7.3,
categorized as Major on the MCS2I Scale. If a smaller area near the most instense portion of the storm had
been selected, say to the southwest of US 93, it would have certainly scored more than an 8.

FIGURE 11

FIGURE 13

FIGURE 14

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RUNOFF
Very intense rainfall occurred on Saturday July 18, 2015 from remnants of Hurricane Dolores.
Table 3 below gives a summary of the streamgages affected by the heavy rainfall in and around
the Wickenburg area. The peaks in the two tables below have been verified in the field by
either verifying high water marks from staff gages, crest-stage gages, or surveying of high water
marks. Values highlighted in yellow are period-of-record peaks. “Peak Q” is discharge in cubic
feet per second and “GH” is gage height in feet from an arbitrary datum, often (but not always)
the bottom of the stream bed.

TABLE 3
Site
Antelope Creek
Box Wash
Casandro Wash
Flying E Wash
Hartman Wash
Hassayampa River at Box Canyon
Hassayampa River at US60 Bridge
Hassayampa River near Morristown
Hassayampa River at I-10 Bridge
Martinez Creek
Powder House Wash
Sols Wash near Matthie
Vulture Mine Road
Cemetary Wash east of 323rd Ave.

ID
7168
5273
7093
7083
7063
5308
5228
5223
5283
7013
7113
7043
5263
None

Peak Q
4,430
4,160
670
5,250
2,465
9,601
9,123
15,606
6,456
10,562
2,300
5,240
102
~10,000

Peak GH
4.79
5.65
8.01
7.07
6.62
10.80
3.45
14.19
3.22
11.43
2.42
4.40
2.83
6.40

Time / Date
07/18/2015 18:48
07/18/2015 18:33
07/18/2015 18:18
07/18/2015 19:03
07/18/2015 18:55
07/18/2015 19:05
07/18/2015 18:22
07/18/2015 21:00
07/19/2015 02:36
07/18/2015 19:07
07/18/2015 17:36
07/18/2015 19:26
07/18/2015 17:35
Time Unknown

Additionally, the three impoundment structures in Wickenburg also experienced record levels
from this precipitation event. All structures were empty prior to this storm.

TABLE 4

Site
Casandro Dam
Sunnycove FRS
Sunset FRS

ID
7133
5248
5233

Peak
GH
(feet)

Peak
Vol
(ac-ft)

% Full

Time / Date of
Peak

Time from
empty to Peak

18.64
31.85
16.78

113
145
64

85.2
66.9
74.8

07/18/2015 19:16
07/18/2015 20:21
07/18/2015 19:19

125 minutes
195 minutes
136 minutes

Previous to this event, none of these structures had filled to a capacity of 50 percent. Casandro
Dam previously reached 48.8 percent full and Sunset FRS reached 39.5 percent full during the
1997 Hurricane Nora storm. Sunnycove FRS had had a maximum of 24.5 percent in 1992. Using
design studies and anecdotal information, the authors believe that Casandro Wash Dam’s pool
and spillway were designed to impound the 6-hour, 100-year storm (3.35 inches) at a future
condition which included a 35% impervious watershed – much higher than existed in 1995 or even
today. Sunset and Sunnycove were designed by the (then) Soil Conservation Service to impound
the 10-day, 100-year rainfall of 6.50 inches, also using Curve Numbers to simulate rainfall losses
that represented a future-condition watershed.
Discussion
All the gaged washes in Wickenburg flowed in response to the large amount of rainfall that
occurred on Saturday July 18, 2015. Five of these washes experienced their highest-ever
recorded peak discharge. Following are hydrographs for each of the gaged washes and
impoundment structures, in alphabetical order:
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Antelope Creek (ID #7168)
This gage is located about 1.7 miles upstream from the Martinez Creek gage (7013). It flows into
Martinez Creek about one quarter mile upstream from the Martinez Creek gage station. The
flow here was the second largest flow of record since installation in 2003 – probably the result of
rain and streamflow the previous day. Peak discharge high water marks were verified by survey.

FIGURE 14

Box Wash (ID #5273)
Box Wash is located south of Wickenburg, but its watershed is adjacent to those for Flying E
Wash and Hartman Wash. It experienced similar high flows for the event. The flow here was
4,160 cfs at 5.65 feet gage height. It is by far the largest discharge recorded since installation in
2003. Peak discharge high water marks were verified by survey.

FIGURE 15

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Casandro Wash (ID #7093)
This gage is located on the upstream side of the US60 culverts about one half mile east of
Vulture Mine Road. The culverts are two 6-foot high by 6-foot wide boxes. The water level in
the channel at the entrance to the culvert exceeded the top of the culvert but did not overtop
the roadway. The rating was developed using an HY-8 culvert analysis and is considered good.
Peak stage was a record 8.01 feet gage height, and the peak discharge was a record 668 cfs.
Peak stage was verified using high water marks on the upstream side of the bridge. The creststage gage was overtopped during the event.

FIGURE 16

Casandro Dam (ID #7133)
This dam downstream from the Casandro Wash stream station received a record amount of
inflow and had a peak impoundment that reached 85% capacity, within 1.6 feet of the
emergency spillway crest, and the highest recorded since its construction in 1996.

FIGURE 17

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Flying E Wash (ID #7083)
This gaged wash is located about one-half mile west of Vulture Mine Road on US 60. The
watershed had high intensity rainfall, but the transducer gage failed to measure the peak. High
water marks were recovered from the crest-stage gage and from a survey of the site. Peak
discharge was an estimated 5,250 cfs at 7.07 feet gage height. This is the highest flow recorded
since installation in 1994.

FIGURE 18

Hartman Wash (ID #7063)
This wash is located about 2 miles west of Flying E Wash, also along US60. This point on the
wash is also monitored by the USGS. The transducer gage at this location also did not work
correctly. High water marks were recovered from crest-stage gages and a survey. Best estimate
is that the peak stage was at about 6.5 feet gage height upstream, and about 5.0 feet in the
culvert. The discharge for this water level is 2,490 cfs.

FIGURE 19

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Hassayampa River at Box Canyon (ID #5308)
This station is upstream of the town and all major tributaries. It is about 8 miles upstream from
the US60 bridge. This station recorded a flow of 9,601 cfs at 10.80 feet gage height. There have
been a number of flows of greater magnitude over the long period of record for this gage. Peak
stage was not verified for this event.

FIGURE 20

Hassayampa River at US60 (ID #5228)
This gage is located near the center of the town of Wickenburg and is downstream of tributary
inflow from the upper watershed including Antelope Creek, Martinez Creek, Hartman Wash,
Flying E Wash, Sols Wash near Matthie, and Powder House Wash. This gage had a peak discharge
of 9,123 cfs at 3.45 feet gage height. The peak stage could not verified as of publication of this
report. However, analysis of peak discharge and time of peaks for the upstream stations would
indicate this peak discharge to be reasonable.

FIGURE 21

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Hassayampa River near Morristown (ID #5223)
This station is approximately 7.4 miles downstream form the US 60 bridge. The USGS also
operates a gage at this location. The peak at this station was 15,606 cfs and a stage of 14.19
feet gage height. The peak occurred about 2.5 hours after the peak passed the US 60 bridge.

FIGURE 22

Hassayampa River at I-10 (ID #5283)
This last station on the Hassayampa River is about 20 miles downstream from the Morristown
gage. This station received a small flow, likely as a result of the flows upstream. Using an
average velocity and channel distance, the flow was estimated to arrive at this station at
07/19/2015 03:00. The actual arrival time was 07/19/2015 at 02:36, which confirmed that the
flow originated from the Wickenburg event. Much of the flow from Morristown did not go the
full 20 mile trip – it soaked into the river bottom. The peak at I-10 was 6,456 cfs and 3.22 feet
gage height.

FIGURE 23

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TABLE 5

Table 5 shows distances and travel times between various stream gages in the Wickenburg area.
The average velocity was taken from HEC-2 and HEC-RAS hydraulic models. Since US 60 peaked
before Box Canyon, the peak could not have come from there. US 60 peaked before every other
contributing gage except Powder House, so its peak likely came from Powder House and other
small upstream washes, plus a contribution from Sols Wash and its tributaries below the Matthie
gage. The estimated arrival and actual times over the 20.24 miles from Morristown to I-10 were
remarkably close – the actual average velocity was 5.3 feet/second.

FIGURE 24

Figure 24 shows the peaks at the four Hassayampa River gages and when they occurred in time.
Inflow from ungaged washes downstream of US 60, especially Cemetery Wash, contributed to the
much higher peak at Morristown.

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Martinez Creek (ID #7013)
The Martinez Creek gage is located about one mile upstream of Scenic Loop Road. Flow at this
gage is from Martinez Creek and Antelope Creek, both of which have large watersheds. Peak
stage values tend to be very large here due to a 90 degree bend the water must make at the
gage location. The peak discharge was estimated in a contraction about 300 feet upstream from
the level gage. Peak discharge for this event is 10,300 cfs which is the highest recorded to date.

FIGURE 25

Powder House Wash (ID #7113)
This gage is on a small watershed east of the Hassayampa River. It is a very steep wash that
discharges into the Hassayampa River just above the US 60 bridge. Runoff from the event
produced the largest flow of record since 1995 when the gage was installed. The peak stage was
2.42 feet, with a computed discharge of 2,300 cfs. High water mark data were verified with a
survey and from the crest-stage gage.

FIGURE 26

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Sols Wash near Matthie (ID #7043)
This gage is located about one mile upstream from Vulture Mine Road, and about 4.5 miles
upstream from the US 60 bridge. The peak discharge at this station was 5,240 cfs at 4.40 feet
gage height. High water marks were verified from a survey of the site following the event.

FIGURE 27

Sunnycove FRS (ID #5248)
This dam is located southwest of the downtown area of Wickenburg, near the town cemetery.
Sunnycove FRS recorded a record impoundment, reaching a peak of 31.85 feet gage height, or
about 67% of spillway capacity, which is the highest known impoundment.

FIGURE 28

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Sunset FRS (ID #5233)
Sunset FRS is located on the south side of US 60 west of downtown Wickenburg. This dam also
recorded its highest known impoundment. Records have been kept since 1989. The peak stage
was 16.78 feet gage height - about 75% of spillway capacity.

FIGURE 29
FIGURE 28

Vulture Mine Road (ID #5263)
This gage is located on a part of Casandro Wash on a small upper watershed. It had a small flow
during the event, 102 cfs. There have been larger flows in the past.

FIGURE 30
FIGURE 28

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Additional Information of Interest
Significant changes to streams occur as a result of high flows. At Box Wash, a significant amount
of vegetation was destroyed. The photos below show the scour power of water. The top picture
shows the left bank of Box Wash upstream from the gage, taken in May 2015. The bottom photo
is the same left bank upstream of the gage, taken on July 20, 2015. Much of the vegetation has
been removed and the bank scoured.

FIGURE 31
FIGURE 30

FIGURE 28

Box Wash, Left bank, May 14, 2015

FIGURE 32
FIGURE 30

FIGURE 28

Box Wash, Left bank, July 20, 2015

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The photo below shows a large debris flow that occurred on a tributary wash to Box Wash that
crosses a paved portion of Vulture Mine Road. Notice the large boulder in the center of the
road. The boulder is about 2.5 feet wide and over a foot in height.

FIGURE 33
FIGURE 30

Debris Flow on Vulture Mine Road, south of Box Wash crossing, July 19, 2015

FIGURE 28

2801 W. Durango St., Phoenix, AZ 85009 (602) 506-1501; Rev. 1, 9/4/2015

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EVENT TIMELINE
Friday, 7/17/2015
11:10 AM

FCDMC MSP issues a Message 2 Flash Flood Watch for all MSP Forecast Zones from 5pm Friday
7/17 through 11pm Saturday 7/18.

6:10 PM

FCDMC MSP issues a Message 1 Alert for the Wickenburg Forecast Zone.

8:00 PM

FCDMC MSP issues a Message 3 Flash Flood Warning for Antelope Creek and Martinez Creek.

8:03 PM

Flow at Antelope Creek gage peaks at 2,830 cfs.

8:08 PM

FCDMC ALERT Room called Wickenburg Police Dispatch – “Expect flow to come down
Martinez Creek and into the Hassayampa River”.

8:23 PM

Flow at Martinez Creek gage peaks at 4,700 cfs.

9:36 PM

Flow at Hassayampa River at US 60 peaks at 1,170 cfs.

Saturday, 7/18/2015 (not all rain / stream alarms are included)
1:52 PM

FCDMC MSP issues a Message 1 Alert for the Gila Bend Forecast Zone.

3:00 PM

FCDMC MSP issues a Message 1 Alert for the Rainbow Valley Forecast Zone.

3:12 PM

FCDMC MSP issues a Message 1 Alert for the West Valley Forecast Zone.

4:01 PM

FCDMC MSP issues a Message 1 Alert for the Northwest Valley Forecast Zone.

4:40 PM

FCDMC MSP issues a Lake Alert for Lake Pleasant.

4:55 PM

Heavy rain begins falling in Wickenburg.

5:00 PM

FCDMC MSP issues a Message 1 Alert for the Wickenburg Forecast Zone.

5:04 PM

Impoundment begins at Sunset FRS.

5:07 PM

Impoundment begins at Sunnycove FRS.

5:10 PM

First of the Wickenburg rainfall alarms activated – Casandro Dam. Five more rainfall alarms
sound before 5:13 PM.

5:12 PM

Impoundment begins at Casandro Dam.

5:13 PM

First Wickenburg stream gage alarm activated - Casandro Wash reached 1.9 ft. / 50 cfs.

5:20 PM

FCDMC MSP issues a Message 3 Flash Flood Warning for the Wickenburg Forecast Zone.

5:22 PM

Powder House Wash stream gage alarm activated - reached 0.8 ft. / 220 cfs.

5:23 PM

FCDMC ALERT Room called Wickenburg Police Dispatch – “Be sure to keep an eye on Powder
House Wash, gage is showing flow”.

5:24 PM

Sunset FRS 10% alarm activated, stage is 6.48 feet (10% filled in 20 minutes).

5:30 PM

Casandro Dam 10% alarm activated, stage is 4.54 feet (10% in 18 minutes).

5:32 PM

Twin Peaks 20-min. rainfall alarm sounds – 1.77 inches

5:33 PM

FCDMC ALERT Room called MCDOT Barricade Section – “Send a crew to Wickenburg via
Vulture Mine Rd”.

5:35 PM

Vulture Mine Road stream gage (above Sunnycove FRS) peaked at 2.8 feet / 102 cfs.

5:36 PM

Sunset FRS at 25%, stage is 9.83 feet (15% filled in 12 minutes, 25% full in 32 minutes).

5:37 PM

Box Wash stream gage alarm - above 2.73 feet / 700 cfs.

5:37 PM

Powder House Wash stream gage peaks at 2.42 feet / 1,800 cfs.

5:40 PM

FCDMC ALERT Room notified FCD O&M – “Sunset FRS at 25%”.

5:50 PM

FCDMC ALERT Room notified FCDMC AOC Chief

5:55 PM

Flying E Wash stream gage alarm - 1.90 feet / 315 cfs

6:01 PM

Casandro Dam at 25%, stage is 10.5 feet (15% filled in 31 minutes, 25% full in 49 minutes).

6:08 PM

Sunset FRS at 50%, stage is 14.1 feet (25% filled in 32 minutes, 50% full in 64 minutes).

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6:00 PM

Antelope Creek stream gage alarm - 3.00 feet / 750 cfs

6:02 PM

Hassayampa R. @ Box Canyon stream gage alarm - 7.25 feet / 1,600 cfs.

6:12 PM

Major flash flood hits Sunnycove FRS. In three minutes the stage goes from 9.2 feet (3%) to
24.6 feet (34%).

6:14 PM

Twin Peaks 1-hour rainfall alarm sounds – 3.23 inches.

6:17 PM

Hassayampa R. @ US 60 stream gage alarm - above 2.80 feet / 5,245 cfs.

6:18 PM

Casandro Wash stream gage peaks at 8.0 feet / 665 cfs.

6:23 PM

Hassayampa R. @ US 60 peaks at 3.45 feet / 9,100 cfs.

6:26 PM

Casandro Dam at 50%, stage is 14.6 feet (25% filled in 25 minutes, 50% full in 74 minutes).

6:30 PM

FCDMC AOC Chief arrives at AOC.

6:31 PM

Flying E Tank 1-hour rainfall alarm sounds - 2.44 inches.

6:32 PM

Hartman Wash stream gage alarm - 3.0 feet / 730 cfs.

6:37 PM

Sunnycove FRS at 50%, 28.6 feet (50% full in 90 minutes).

6:37 PM

Martinez Creek stream gage alarm - 4.90 feet / 1,900 cfs.

6:48 PM

Wickenburg Airport 1-hour rainfall alarm sounds - 2.48 inches.

6:59 PM

Hassayampa R. near Morristown stream gage alarm - 10.1 feet / 2,415 cfs

6:59 PM

Casandro Dam at 75%, 17.6 feet (25% filled in 33 minutes, 75% full in 1 hour 47 minutes).

7:03 PM

Sols Wash near Matthie stream gage alarm - 1.75 feet / 500 cfs.

7:03 PM

Hassayampa R. @ Box Canyon stream gage peaked at 10.8 feet / 9,600 cfs.

7:04 PM

Martinez Creek stream gage peaks at 11.4 feet / 10,562 cfs.

7:17 PM

Casandro Dam peaks at 18.64 feet, 85.2% (10% filled in 18 minutes, 85.2% full in 2 hours 5
minutes). ALERT gage does not check in for 1 hour and 35 minutes. A level pool was
assumed because at this time the Casandro Wash stream gage had dropped to 100 cfs.

7:20 PM

Sunset FRS peaks at 75%, 16.8 feet, (25% filled in 72 minutes, 75% full in 2 hrs. 16 min.).

7:38 PM

First FCD staff (our MCSO Deputy) arrives at Casandro Dam, reports a staff gage reading of
19.0 feet.

8:13 PM

Hassayampa R. near Morristown stream gage peaks at 14.2 feet / 15,600 cfs.

8:22 PM

Sunnycove FRS peaks at 67%, 31.85 feet (17% filled in 105 minutes, 67% full in 3 hours 15
minutes.

8:32 PM

Casandro Dam - MCSO Deputy reports a staff gage reading of 18.5 feet – this value was
entered manually into the ALERT database.

8:42 PM

Casandro Dam pool gage finally sends a reading of 18.34 feet / 82.%.

9:11 PM

Patton Rd. @ Hassayampa River flashing warning signs activate.

10:00 PM

FCDMC AOC closed.

Sunday, 7/19/2015
0:00 AM

Sunset FRS has dropped to 15.1 feet / 60%, Sunnycove has dropped to 31.4 feet / 64.5%, and
Casandro Dam has dropped to 17.4 feet / 75%.

2:36 AM

Hassayampa River @ I-10 stream gage alarm peaked at 3.22 feet / 6,456 cfs.

Monday, 7/20/2015
5:38 AM

Hassayampa R. near Morristown stream gage drops to zero; Patton Rd. @ Hassayampa River
flashing warning signs deactivate.

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SELECTED DATA SOURCES

1.

National Atmospheric and Oceanic Administration, National Climatic Data Center,
Asheville, NC – Radar Data Archive and Climate and Weather Toolkit:
http://www.ncdc.noaa.gov/oa/radar/radardata.html

2.

Strong winds and Heavy Rain in Wickenburg Saturday 18 July 2015: National
Weather Service, Phoenix, AZ WFO:
http://www.wrh.noaa.gov/psr/pns/2015/July/18JulyStorms.php

3.

National Weather Service, Storm Prediction Center, Norman, OK:
http://www.spc.noaa.gov/obswx/maps/

4.

Flood Control District of Maricopa County, Phoenix, AZ:
http://www.fcd.maricopa.gov

5.

National Weather Service, National Hurricane Center, Miami, FL:
http://www.nhc.noaa.gov/?epac

6.

National Weather Service, Weather Prediction Center, College Park, MY:
http://www.wpc.ncep.noaa.gov/

7.

US Naval Research Laboratory, Marine Meteorology Division; NEXSAT NRL/NPOESS
Next-Generation Weather Satellite Demonstration Project
http://www.nrlmry.navy.mil/

8.

National Weather Service, Hydrometeorological Design Studies Center, Silver
Spring, MD - Precipitation Frequency Data Server for Arizona:
http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=az

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Cemetery Wash
Indirect Flood Discharge Measurement
Flood Date: 18 July 2015
Survey Date: 04 August 2015
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Summary
A significant flood event occurred on Cemetery Wash in Wickenburg, AZ on July 18,
2015. The wash is not gaged at any location. Field data were collected on August 4,
2015. Data collected included high water marks on left and right banks, and cross
section geometry. High water marks were of fair to excellent quality.
Based on analysis of the collected data, the peak discharge for the event is computed to
be an estimated 10,000 cubic feet per second. The most recent estimate of the 1%
chance flood discharge at the surveyed location on the wash is 7,561 cfs.
Introduction
A large precipitation event occurred on the late afternoon of Saturday July 18, 2015 in
and around Wickenburg. Precipitation in the 7.6 square mile Cemetery Wash watershed
was in the range of 3.5 to 4.5 inches in about 2 hours. Rain in this quantity and short
duration will produce significant runoff. Runoff in Cemetery Wash was significant, and it
was desired to determine the peak discharge of the runoff. Cemetery Wash is not gaged
at any location along its watercourse.
Discussion
A survey was conducted to acquire data to determine the peak discharge from the July
18 event. First a suitable reach was examined from aerial photos. It was decided to
survey a part of the wash that was accessible from Ocotillo Drive. The specific site was
about one half mile downstream from 323rd Drive. The approximate coordinates are
latitude 33.9466, longitude -112.7494. An aerial of the surveyed area is below.

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The channel in this section has a well-defined main bed composed of fine sand. There
was only a small left over-bank with a wide, heavily vegetated right over-bank. The
photo below is of the channel downstream from the furthest upstream cross section
surveyed.

It was desired to select three cross sections to survey. However, due to significant
variability of the channel (expanding, contracting, bends, etc.) only two cross sections
were surveyed in this fairly straight, and somewhat uniform section of the channel. The
reach length between the two cross sections is about 215 feet.
Data were collected, analyzed, plotted, and used to create a Slope Area Computation
(SAC) model. Channel roughness values (n-values) were selected in the field based on
observation and experience of the hydrologist. For the main channel, n-values of 0.028
to 0.030 were used. In the over-banks, the n value selected was 0.065 to 0.090 due to
heavy vegetation.
The SAC program was run with various parameters. The table below summarizes the
findings.
RUN

WSEL
US

WSEL
DS

MAIN N

RB N

LB N

1
2
3
4
5
6

96.40
96.40
96.40
97.06
96.36
96.40

93.50
93.50
93.50
92.91
93.16
93.50

0.03
0.03
0.028
0.028
0.03
0.028

0.065
0.075
0.075
0.09
0.075
0.075

0.08
0.08
0.08
0.09
0.08
0.09

US - DS
COMPUTED
COMPUTED
DISCHARGE
FROUDE #
1.31-1.39
10,683
1.26-1.37
10,048
1.32-1.44
10,383
0.94-1.52
8,648
1.17-1.39
9,191
1.32-1.45
10,403

Run 4 used the actual high water marks as surveyed, whereas the first 3 runs and run 6
used water surface slope among all the high water marks on each bank. Run 5 used
average high water marks between the left and right banks. At the upstream cross
section, the left bank high water mark was higher by 1.4 feet, whereas at the
downstream cross section the right bank high water mark was about 0.9 feet higher than
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the left bank. Furthermore, no previous information was available about past runoff
events or the amount of channel scour that occurs. For this analysis, the scour is not
considered significant, though that may be in error.
A hand computation for the main channel at the downstream cross section only, gives
velocities of 19.7 feet-per-second (n=0.03) to 21.1 fps (n=0.028). Either n value is
reasonable, but the lower one is probably justified for use in this case. These high
velocities produced nearly 7,000 cfs in the main channel alone (hand calculation).
Given both the SAC results and the hand calculation showing a high discharge, it is not
unreasonable to conclude that the peak discharge was about 10,000 cfs. More likely, the
peak discharge was in the range of 9,500 – 10,500 cfs for this event. The most recent
estimate of a 1%, or 100-year discharge for Cemetery Wash @ 323rd Ave., based on a 100year, 24-hour rainfall of 4.5 inches, is 7,571 cfs.

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