U. LlvengoodD. CederburgL,HenJeyGJenoerB. LaneJ. MurdochC. PearsonN. RjjihR. RoroerS. Stilling |

Gale Wm. Fnser, II, P.E.Gmnl UiMotr/Cr* Engnttr

BOARD OF DIRECTORS

Lance M. MaloneChairman

CK rk County

Cresent HardyVet-Chairman

City of M«quite

Larry BrownGtyofUsMgu

Jan Laverty JonesCity of las Vtgas

Bryan A. NixCity erf Boulder City

John K. RhodesCity of North Us Wou

David WoodQty of H«r>dtr»on

Bruce L. WoodburyCUrk County

C I A I K C O U N T Y

REGDNAL FLOOD CONTROL DISTRICT RECEIVEDOCT 0 7 1998

c.c.p.w.DIRECTORS OFFICE

SFUND RECORDS CTR

2095948TO: Distribution

FROM: Timothy E. Sutko, Senior Hydrologist

SUBJECT: September 11, 1998 Flooding

DATE: October 2, 1998

Attached please find a copy of the Rainfall Event Report for the September 11,1998 event.Please don't hesitate to contact me if you have any questions or require additionalinformation.

Distribution: RFCD Board membersRFCD TAG membersRFCD CAC MembersLarry Jensen, NWSRon McQueen, NWSJohn James, State ClimatologistMike Turnipseed, State EngineerBob Cullins, Emergency Management Coordinator, City of Las VegasJack Finney, Emergency Management Coordinator, City of HendersonBob Andrews, Emergency Management Coordinator, Clark CountyVicki Taylor, Public Information Officer, City of HendersonTom Warden, Public Information Officer, Clark CountyPhu Simpson, Clark County Community DevelopmentCurt Chandler, City of HendersonDennis Moyer, City of Las VegasLenny Badger, City of North Las Vegas

301 E. Clark Avenue, Suite 301 • Las Vegas, Nevada 89101(702) 455-3139 • FAX: (702) 455-3870

RAINFALL EVENT REPORTSeptember 11,1998

prepared byTimothy E. SutkoSenior Hydrologist

Clark County Regional Flood Control DistrictClark County, Nevada

Severe weather moved through the Las Vegas Valley and northeast Clark County beginning latein the morning on September 11,1998 causing wide-spread drainage problems and other damages.While the rainfall intensities and depths recorded in many pans of the County were not atypicalof warm season convective storms in the region, perhaps the most notable feature of this stormsystem was the size of the area which was impacted. Based on weather radar images it isestimated that 40% of the county may have received up to one inch of rainfall or more. Therainfall was accompanied by hail throughout much of the Las Vegas Valley as well as reports oftornadoes in the Henderson area. In the Las Vegas Valley the largest rainfall depths appear tohave occurred in the Green Valley area of Henderson and the east part of the Valley extendingnorth to the Nellis AFB area. The Green Valley rainfall caused significant flow in Pittman Washand Duck Creek, perhaps the largest flows recorded in those drainages in recent years. On theeastside of the Valley, the Sloan Channel, Flamingo Wash, and Las Vegas Wash all experiencedsignificant flows. Flood flows from the entire Valley combined above Lake Las Vegas where thepreliminary peak flow is estimated to have been in the 7000-9000 cfs range.

The rainfall depths recorded in the California Wash and Muddy River drainages were far moreimpressive than those recorded in the Las Vegas Valley. For the twelve hour period ending atmidnight on September 11, four RFCD rain gages in that area recorded in excess of two inchesof rainfall, and one of those recorded more than three inches of rain. The resulting runoff in theCalifornia Wash at the Hidden Valley Road may have been up to 10,000 cfs. This flow combinedwith flow in the Muddy River above Glendale and overtopped SR 168 at Glendale, washed outthe Gubler Avenue crossing of the Muddy River in Logandale, and caused some residentialflooding in Overton. There was one swift-water rescue which took place on Hidden Valley Roadas flood waters from the California Wash overwhelmed a delivery van which attempted to crossthe flooded dip-section.

This storm system moved generally from the southwest to the northeast across the southern andeastern portions of the Las Vegas Valley before moving into the California Wash and MuddyRiver drainage areas. In the Las Vegas Valley, rainfall began to move into the south end of theValley between 11:30 am and noon. At approximately 11:30 am, the National Weather Service(NWS) office issued a Severe Thunderstorm Warning for Northeast Clark County, including theMoapa Valley, Mesquite and Bunkerville. Shortly thereafter (11:50 am), a Severe ThunderstormWarning was issued for the Las Vegas Valley as weather radar indicated increasing rainfallintensities moving into the area and marble-sized hail was reported at the NWS offices. The firstFlash Flood Warning was issued by the NWS at approximately 12:15 pm. These warnings were

repeatedly extended and expanded by the NWS throughout the remainder of the day. District staffprovided updates to the local public works departments as the NWS issued or extended theweather statements. District staff also advised both Clark County Public Works and the ClarkCounty Sanitation District of the possibility of significant flows in lower Duck Creek as therainfall began entering the Las Vegas Valley.

Owing to the location and movement of this storm, most of the runoff occurred in streets andwashes and did not, with the exception of the Range Wash/Confluence Detention Basin andCarey/Lake Mead Detention Basin, enter any of the regional detention basins. Flow in the LasVegas Wash at Vegas Valley Drive was observed to have been within one foot of the maximumchannel capacity. The following listing presents estimates of the peak flows at various locationsin the Las Vegas Valley as determined by the US Geological Survey (USGS) and/or RegionalFlood Control District. These values are preliminary estimates and are subject to change as betterinformation is developed.

Location Peak Discharge

Pittman Wash at Wigwam Ave 1430 cfsDuck Creek at Eastern Avenue 650 cfsDuck Creek near Hollywood Blvd 3000 cfsFlamingo Wash at Decatur Blvd 130 cfsFlamingo Wash at Eastern Avenue 920 cfsFlamingo Wash at Nellis Blvd 1500-2000 cfsRange Wash Tributary at Las Vegas Blvd 920 cfsSloan Channel at Charleston Blvd 1230 cfsLas Vegas Wash near Sahara Ave 2240 cfsLas Vegas Wash below confluence with Flamingo

Wash 5000-8000 cfsLas Vegas Wash at Lake Las Vegas 7000-9000 cfs

The peak flow adopted for Flood Insurance Study purposes in the Las Vegas Wash at VegasValley Drive is 7100 cfs. Based upon these flow estimates, it appears that in some reaches ofthe Las Vegas Wash this event may have approximated a 100-year flood.

The lower end of Duck Creek experienced high lows for at least the third time this summer. Inthe vicinity of the Stadium Mobile Home Park, approximately 100 feet of block wall collapsed,an 18-inch water line and a sanitary sewer line ruptured, and almost 300 feet of a 28-inch naturalgas line was exposed by the flooding. At Lake Las Vegas, the rate of flow in the Wash farexceeded the capacity of the two by-pass pipelines and a large fraction of the Wash flow spilledinto the Lake. The two low level bladder dams were deflated and the lake drain was opened inorder to allow the storm flows to discharge from the Lake.

There have been numerous reports in the media regarding erosion in the Sunrise MountainLandfill area. Operators of the landfill have informed District staff that rainfall depths of 2.2-,2.25-, and 2.5-inches were collected by the three NWS-type rain gages located at the landfill site.While this type of gage does not record rainfall intensities, the operators stated that the rainfalloccurred in less than a one hour period.

The rainfall cells appeared to have intensified as they left the Las Vegas Valley to the northeast.Rainfall, flow rates and damages were higher in the Moapa Valley area than they were in the LasVegas Valley. While the rainfall in the Las Vegas Valley generally took place within a two-hourperiod, in the drainages impacting the Moapa Valley intense cells appear to have built and re-builta few times throughout the afternoon and evening. Four RFCD rain gages recorded more than2-inches of rainfall, and one of those recorded over 3-inches. Each of these gages recordedrainfall rates of 1.15 inches per hour or more. This rainfall generated flows in the CaliforniaWash which washed out 150-feet of the paved road east of the Byron exit from 1-15. At sometimeduring this storm, runoff was flowing over 1-15 in the vicinity of the rest area south of theGlendale/Moapa exit. Flows in the California Wash at Hidden Valley Road may have been in the7000-10,000 cfs range (the 100-year flow rate for the California Wash in this area is 14,600 cfs).A swift water rescue was successfully performed at this location by the volunteer Fire Departmentshortly before the driver's van was completed submerged by the flow. Flows in the Muddy Riveralso over-topped Hidden Valley Road on the northside of the Hidden Valley Dairy. The flowsin these two watercourses effectively isolated the dairy for over 12 hours.

Flows in the Muddy River overtopped the SR-168 bridge in Glendale and washed out the lowlevel crossing at Gubler Avenue in Logandale. According to the damage assessment preparedby the American Red Cross, thirteen homes in the Overton area suffered major damages and twomobile homes in the Glendale/Moapa area were destroyed by flooding. The preliminary USGSestimate of the Muddy River flows two miles below Glendale is 6500 cfs. The Clark CountyPublic Works Department has estimated that the area suffered approximately $400,000 in damagesto roadways.

While a significant amount of rainfall was not recorded by any of the District's rain gages locatednorth of Mesquite, this same storm system which impacted the Las Vegas Valley and MoapaValley must have moved through that area, as the water level behind the Jim Wilson (aka TownWash) Detention Basin rose to over 10 feet before receding. The Red Cross damage assessmentindicates that 5 homes in Bunkerville suffered major flood damages.

Attached to this report are summaries of the rainfall data collected by the District.

RAINFALL TOTALS (inches)FOR SEPTEMBER 11, 1998

upR

Channe

rain

nuit

?!P

I'man@W

5minuit

71HR2 4

09/98 DYll->8 10 12 14 16 18 20 22

an. oU

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•30.32

. 30

A Q. 4B

no.32

. 16

r\

4739 IIPRR f.HANNF.T, M."*4"J

H

. . . . ii4K14 nriPK- PRKRK AT RARTRRM ( T . 7 f V |

i . f . « _ _ ! .

4734 PITTMAN WASH AT WIGWAM (1.85-,

r •4 7 4 4 SOUTH HENDERSON (1.30")

T

-

n

rn t n • r , - t t .

rflIn . . , . . .

-.

£ . . .___

f t h . . . . .

•

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.80

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it. 16 He

3 D

rain ^

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on E80

e >i 164 g

jrt **"48 £n«o . .32 U

itA e no16 n.e

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rain

»

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.80

5 -64

m .„i .48nu .32

it

rain

.80A5 *m A0i .48n

n

4114 RANGE WASH AT LAS VEGAS BLVD (1.897)

r

_

4074 LAS VEGAS WASH AT T.AKE MEAD

n , ,J_ JLT . .

n'

t • t • •

1.34")

rTV,rT

-i

4 ? H 4 LAS VEGAS WASH AT LAMB _LJ,38")

-

n4379 VAN BUSKIRK nB (1.38")

.al..

,, nHKll

H R 2 4 6 809/98 DYll->

10 12 14 16 18 20 22 0

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4174 SLOAN CHANNEL AT CHARLESTON (0

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4084 LAS VEGAS WASH NEAR SAHARA

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4394 FLAMINGO WASH AT NELLIS (.0_.

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4^74 FT.aMTM^n WA<;H AT RQPTP.PM ( n . m l f i

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09/98HR2 B 10 12 14 16 18 20 22

Lincoln County

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09/98

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£ . 11 n. n .rfi n. n

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3064 WEISER WASH (1.30'M

3384 MEADOW VALLEY WASH (2 .24" )

f • . « 1 1

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8 10 12 14 16 16 20 22

Clark County Regional Flood Control DistrictSeptember 11. 1998 (Green V a l l e y )

DevicelD 4704D r e c i o

Uni ts in

4744 4734prec i P orec i p

in in

4739orec i p

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4644orec i p

in

4624preci p

in

4634preci D

in

4774preci D

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09/11/98143014151400134513301315130012451230121512001145

TOTALS:

47044744473447394644462446344774

0 . 000.000.000 . 000.000.000.000.040. 120.040.040.04

0.28 •

NDOT vehicl1 1/2 miles

0.000.000.000 . 000.000.000.040.310.550.080.280.00

1 .26

e insoectiSouth of

Wiqwam Avenue 1/2 milUPRR ChanneNWS OfficesParadise RdEastern AveTIHET facil

1 at Greenon Indust1/4 mi le1/4 mi 1 e

0.000.000.040.080. 120.080.550.200.040.670.080. 00

1.85

on s tat i

0.000.000.000.040.040. 120.390 .040. 160.S10.000 . 00

1.30

on near

0.000.000.000.000.040. 160.000.040.000.040.240.04

0.55

Town of

000000000000

0

Si oan

.00

.00

.00

.00

.00

.00

.20

. 16

.04

.24

. 16

.04

.83

000000000000

1

.00 .

.00

.00

.00

.00

.04

.24

. 12

.00

.67

.20

.00

.26

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0

.00

.00

.00

.00

.04

.08

.51

. 16

.04

.00

.00

.00

.83

Sky Harbor Airporte East oVal lev

rial RdNorth ofSouth of

f EasteParkwayNorth oWi ndmi

rn Avenue

f Blue Di11 Lane

amond Rd

V/arm Sprinns Rdi t v in Henderson

r

c

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(

Clark Countv Regional Flood Control DisSeptember 11. 1998 (E. LV Vallev)

.ct

DevicelD 4379 4374 4394 4084 4174Datatype precip precip precip precip precipUnits in in in in in

4284 4074preci p prec i p

in in

4114prec i p

in

4154preci p

i n

09/11/98143014151400134513301315130012451230121512001145

TOTALS:

437943744394408441744284407441144154

0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.000.24 0.35 0.04 0.00 0.000.08 0.04 0.12 0.08 0.040.12 0.00 0.08 0.04 0.080.04 0.04 0.16 0.20 0.200.16 0.08 0.04 ' 0.04 0.000.08 0.04 0.08 0.08 0.240.12 0.08 0.39 0.43 0.390.55 0.16 0.04 0.04 0.000.00 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00

1.38 0.79 0.94 0.91 0.94

Van Buskirk Detention Basin near Harmon/MacLeodnear intersection of Eastern Avenue and twainN e l l i s Blvd 1/4 m i l e South of Sahara Avenue

0.000.000.470.390. 160.080.000.040. 160.080.000.00

1.38

0.000.390.510. 160.080.040.000.040.080.040.000 .00

1 .34

0.000.510.590.350.2O0.040.040.040. 120.000.000 . 00

1 .89

0.000 .000. 200. 040.080.120.040.280.080.000.000.00

0.83

on Desert Rose Golf Course 1/4 m i l e South of Sahara Avenueon Sloan Channel at Charleston Blvdnear intersection of Washington Avenue and Lambat intersection of Lake Mead Blvd and Pecos RdLas Vecias Blvd North 1/4 East of Lamb BlvdConfluence Detetnion Basin

Blvd

r

Clark Countv Regional Flood Control DistrictSeptember 11. 1998 (California Wash)

Devi celD 3144DataTvoe precipUni ts in

09/123002245223022152200214521302115210020452O30201520001945193019151900184518301815180017451730171517001645163016151600154515301515150014451430141514001345133013151300124512301215120011451130

1/980.000.040 . 000.000.200.000.000.000.120.000.000.000.000.080.390. 120.000.000. 160.000.000.000.000.000.000.000.00o.oo0.000.000.000. 160. 350.040.000.000.350.390. 550.000.000.000 . 000.240.000.000.00

TOTALS: 3.19

31443164318432643384306432343244T?Q<!

Cal i forniaCal i forniaCal i f orni aMuddy R i v eMeadow Val7 m i l e s M

3164Dree i D

in

O.OO0.000.000 .000.040.000.O00.000.000.000.000 .000.000.080.000 .000.000.080.040.000.000.000.000.080 . 000.000.000.000.000.080.080. 160.000.000.00 '0.200.470.28

' 0.200.000.000.000.000.000.000.000.00

1.77

Wash. 13W a s h . 7 m

3184p r e c i p

i n

o.oo"0. 12 ' •0/000.00 :0.000.000.000.040.000.000.000.000.080.040.08.0.000.080.08

• 0.080. 120.040. 160.000.000.000.000.000.000.000. 160. 120.310.000.000.240.470.240.350.000.000.000.000.000.0-10.000.000.00

2 .S3

3264 3384precip precip

in

• ' 0.000.000.000.000.000.000.00O.OO0.000.000.000.040. 120.000.000.000.000.000.040.040.000.000.040.280.000.000.000.000.000.000.000.000.040.000.080.080.790.200.000.000.000.040.310.000.000.000.00

2.09

m i l e s SSW of Glendai l e s SSW

Wash . 4 m i l e s SWr at Warm Springslev Wash, 11 m i l e sof Gl endal e

of Glendal

in

0.000.000.000.000.000.000.000.000.000.000 .000.000.080.000.000.040.000.000.000.000.000.000.040.000.000.000.000.000. 160.000.390.200.000 . 000. 160.590.390.000.080.000.040.000.080.000.000.000.00

2.24

lee

of GlendaleRd: 6 miles NW ofNNW of Glendale

3064precl D

in

0.000.000.000.000.000.000.000.000.000.000.000.080.080.000.000.040.080.000.000.040.000.000.280.000.00O.000.000.000. 120.000.00O.040.000.000.200.240.080 .000.000.000.000.000.040.000.000.000.00

1.30

Gl enda 1 e

3234preci p

in

0.000.000.000.000.000 .000.000.000.000.000.000.000.000.000.000.000.000 . 000 .000.000.000.000.000.000.080.080.000. 160. 160 . 000.00O.00

' 0.000 . 000.000.000.040.000 . 000:000.000.040.000.000.O4.0.080.00

0.67

3244prec i p

in

0.080.040.390. 160.000.000.000.000.000.000.000 . 000.000.00 '0.000.000.000.000.000.000.000.000.000.000.000.O00.000.000.000.000.000.000 . 000.000.55O.OOo.oo0.000.000.000.000.000.000.000.000.000.00

1 .22

3294prec i p

in

0. 160.080.000.000.000 .000.000.000.000. 000.000.000.000 . 000.000.000.000.000.000.000.000.000.000 . 000.000.000.040.000.000.000.000.04.0.000.000.000.000.000.000.000.000.000.000.000.040.000.000.00

0. 35

15 miles NW of Glendale3 mi les MEOi/*»rtnn A i

of Bowmanrno r t

R e s e v o i r

Figure la (above) and Ib (below). Las Vegas Wash looking north and south from Vegas ValleyDrive. The channel is approximately 100-fcct wide and 8-feet deep; discharge is approximately 9000cfs. (September 11,1998)

Figure 2a (above) and 2b (below). Muddy River Bridge at SR-168 in Glendale. High Hows in theMuddy River were 2-3 feet deep across the roadway on September 11,1998.

Figure 3. Wash out of paved road east of 1-15 at the Ute exit resulting from flows in the CaliforniaWash September 11, 1998.

Figure 4. Debris washed up 18-inchcs on fence at rest area on 1-15 south of Moapa/Glendale exit fromflow in California Wash drainage across the Interstate on September 11, 1998.

Figure 5. Muddy River below Gubler Avenue crossing. Note shed perched on bank in left center ofphoto after flows of September 11, 1998.