7/28/2019 The Seeley and Clay Springs Fires - Impacts on Water Supply

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April1Update

TheSeeleyFireandPotentialImpactsonHuntingtonCreekWaterSupplyClaySpringsFireandPotential

ImpactsonOakCreekWaterSupply

TheSeeleyFire

TheSeeleyfireburnedabout48,000acresincentralUtahsouthofScofieldinJulyof2012,including18,500

acresof

the

Huntington

Creek

Watershed

just

below

Electric

Lake

in

the

bottom

half

of

the

basin.

This

constitutesnearlyhalf(46%)ofthetotalwatershedareaof40,100acres.

Figure1.BurnedportionoftheHuntingtonCreekWatershed.

TheimpactfireshaveonwatersupplyandstreamflowinhighreliefareasoftheintermountainWestcanbe

complex.Generallyinthefirstfewyearsafterafire,snowmeltcanbeaccelerateddueto:(1)

carbon/dust/organicmaterialdepositiononthesnowsurface;(2)thevolumeofstandingblackenedtimber

changingthealbedo(reflectivity)ofthesnowpack;and(3)thereductionincanopycoverinareasthat

formerlysustainedevergreenforest.Snowmeltcanconsequentlybeadvancedasmuchas6weeks,ormore.

Theseconditionscanalsoleadtogreatersnowpacklossestowinderosionandsublimation. Conversely,the

7/28/2019 The Seeley and Clay Springs Fires - Impacts on Water Supply

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lackofforestcovercanincreasetheamountofsnowonthegroundthatwouldnormallybeinterceptedbythe

forestcanopy,and,particularlyinthedecadeortwoafterthefire,mayleadtohigheroverallAprilJulystream

flow. However,inthefirstfewpostfireyearswithlowsnowpacksandwithlongperiodsbetweenstorms,the

neteffectcanbeloweroverallsnowwaterequivalentonthegroundwithearlymelt.Someoftherunoffthat

wouldnormallyhaveoccurredintheAprilJulytimeframecouldhappeninMarchorearlier.

HuntingtonCanyon,southfacingaspectwithallsnowpackmelted.

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Patchysnowonnorthandeastfacingaspects.

WatersupplyforecastmodelsaregearedtopredicttheAprilJulyrunoffseasonbasedonobservedsnowpack

andothervariables. TherearenodatasitesinsidetheHuntingtonCreekburnareaanddatausedinthe

hydrologicmodelsarefromnonimpactednearbysites.Assuch,weanticipatethatrunoffonHuntington

Creekwillbeshiftedtoanearliertimeframeduetotheburnconditionsinthewatershedandthatthe

AprilJulyforecastislikelytooverestimatetheAprilJulystreamflow.Theseconditionscouldpersistfor

severalyears.ItisalsoimportanttonotethattheinflowtoElectricLakeabovetheburnareawillnotbe

impacted.

Withsolittlesnowlefttomeltontheburnareathereislittleprobabilityofseriouserosionormasswasting

phenomenafromthefirearea. Theremainingsnowislikelytomeltinsmalldailyincrementsandinfiltratethe

soilsoverthenextmonthorso.Intenseprecipitationeventscouldtriggermudanddebrisflowsfromthe

burn.

WaterusersthatrelyonHuntingtonCreekareadvisedthattheAprilJulyflowwilllikelybelessthanthe50%

exceedancenumberandforplanningpurposesareadvisedtousealowerfiguresuchasthe70%exceedance

number.

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PRI CE SAN RAFAELStr eamf l ow Forecasts - Apri l 1, 2013

==================================================================================================================================| || |

For ecas t Poi nt For ecas t | ==================== Chance Of Exceedi ng * ====================== |Peri od | 90% 70% | 50% | 30% 10% | 30- Yr Avg.

| ( 1000AF) ( 1000AF) | ( 1000AF) ( % AVG. ) | ( 1000AF) ( 1000AF) | ( 1000AF)====================================================================| =======================| =====================================Fi sh Ck ab Reser voi r nr Scof i el d APR- J UL 9. 3 13. 1 | 16. 0 53 | 19. 2 25 30

| |Pri ce R nr Scof i el d Reser voi r ( 2) APR- J UL 10. 1 15. 6 | 20 49 | 25 33 41

| |Whi t e R bl Tabbyune Cr eek APR- J UL 2. 4 3. 9 | 5. 0 32 | 6. 3 8. 5 15. 5

| |

Gr een R at Gr een Ri ver, UT ( 2) APR- J UL 700 1050 | 1320 45 | 1630 2130 2960| |El ectr i c Lake I nfl ow ( 2) APR- J UL 2. 8 4. 5 | 6. 0 45 | 7. 7 10. 5 13. 3

| |Hunt i ngt on Ck nr Hunt i ngt on ( 2) APR- J UL 10. 5 14. 7 | 18. 0 45 | 22 28 40

InthisAprilreleasethe50%exceedancenumberforHuntingtonCreekis18,000acrefeetandthe70%

exceedancefigureis14,700acrefeet.Theeasywaytoreadthistable:weare90%suretoget10.5KAFor

higher,70%suretoget14.7KAF,50%toget18KAFandonly30%chanceofgetting22KAForhigher.Dueto

theburnconditionsacrossthewatershednotcapturedbymodelinput;weadviseusingalowerforecast

numbersuchasthe14.7KAFfigureinthisexample.

TheClay

Springs

Fire

(Oak

Creek

Watershed)

TheClaySpringsfirenorthofDeltaburnedabout180,000acresinmidJulyof2012.Thisfirewas,inplaces,

extremelyhotandburnedrootsbelowthegroundsurface.Theterraininthiseasttowestfacingwatershedis

verysteepwithabout50%ofthewatershedonasouthfacingaspect. Nearlytheentirewatershed(99.6%)

wasimpactedtosomedegreebythefire.

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ClaySpringsfireperimetershowninred.

TheOakCreekSNOTELsitewasdestroyedandlaterrebuilt,andiscurrentlygivinggoodinformationon

snowpack,precipitation,

temperature

and

soil

moisture.

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TheSNOTELsiteatOakCreekhascompletelymeltedoutsome3weeksearlierthanlastyearwithapproximatelythesameamountofsnowpack,illustratinghowburnedareasimpactmeltrates.(currentyearsnowpackblueline,2012,greenline)Thesiteisatanelevationof7800feetonasteepnorthfacingaspectandnormallyholdssnowwellintoMay.Atthispoint,thevastmajorityofthewatershedissnowfreeandsnowmeltrunoffisessentiallyoverfortheyear.

ThesurfacesoilsattheOakCreekSNOTELsiteareshowingpossiblesignsofhydrophobicityorwaterrepellencyasthe2inchsoilmoisturesensor(greenline)refusestowetupsubstantiallyinspiteofthesite

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meltingnearly7inchesofsnow. Thelowersensorsshowincreasedmoisturelikelyfromsourcesuphillfrom

thesensors.SnowSurveypersonnelonsiteinlateMarchreportthatthesurfacesoilswereextremelydry

eveninareasrecentlysnowcovered.Thisconditioncouldposeproblemsifhighintensityprecipitationevents

occurlaterinspringandsummer.

SouthfacingaspectoftheOakCreekWatershed.Dryanddustynorunofffromthisarea.

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NorthfacingaspectoftheOakCreekWatershedwheretheSNOTELsiteislocated.

ThisphotowastakenafewdayspriortowhentheSNOTELsitemeltedoutandiscurrentlybareofanysnow.

WaterusersthatrelyonOakCreekareadvisedthattheAprilJulyflowwilllikelybelessthanthe50%

exceedancenumberandforplanningpurposesareadvisedtousealowerfiguresuchasthe70%exceedance

number.

==================================================================================================================================LOWER SEVI ER RI VER BASI N

Str eamf l ow Forecasts - Apri l 1, 2013==================================================================================================================================

| || |

For ecas t Poi nt For ecas t | ==================== Chance Of Exceedi ng * ====================== |Peri od | 90% 70% | 50% | 30% 10% | 30- Yr Avg.

| ( 1000AF) ( 1000AF) | ( 1000AF) ( % AVG. ) | ( 1000AF) ( 1000AF) | ( 1000AF)====================================================================| =======================| =====================================Sevi er R nr Gunni son APR- J UL 6. 4 34 | 52 53 | 70 98 99

| |Chi cken Ck nr Levan APR- J UL 0. 05 1. 40 | 2. 40 53 | 3. 40 4. 50 4. 50

| |Oak Cr eek nr Oak Ci t y APR- J UL 0. 09 0. 20 | 0. 30 18 | 0. 42 0. 63 1. 66

InthisAprilreleasethe50%exceedancenumberforOakCreekis300acrefeetandthe70%exceedancefigure

is200acrefeet.Theeasywaytoreadthistable:weare90%suretoget90KAForhigher,70%suretoget200

KAF,50%toget300KAFandonly30%chanceofgetting420KAForhigher.Duetotheburnconditionsacross

thewatershednotcapturedbymodelinput,weadviseusingalowerforecastnumbersuchasthe90orthe

200KAFfigureinthisexample. Theseforecastfiguresaredramaticallylowerthanthoseissuedlastmonthdue

tothehugedeclineinsnowpackacrossthewatershed.