3.0 baseline assessment results - slcdocs.com study website/redbutte/final/6...final red butte creek...

3-1

FINAL RED BUTTE CREEK MANAGEMENT PLAN

Figure 3.1. Red Butte Creek watershed. (Map from SLCO 2009).

3.0 BASELINE ASSESSMENT RESULTS

Watershed Conditions

Size and Land Use

Red Butte Creek is locatedbetween City Creek to the northand Emigration Creek to thesouth (Figure 3.1). The uppersubwatershed, located above theUniversity of Utah, drains 5,403acres of mountainous land

primarily owned and managedby the U.S. Forest Service(USFS). Nearly 80% of thestream through the uppersubwatershed is adjacent topublic land. Public access islimited, though, as much of thearea is managed as a ResearchNatural Area with a focus onstudy and research of therelatively pristine natural forest

and riparian habitats (SLCO2009). The estimatedimpervious cover of the uppersubwatershed is 9.1%.

From its headwaters at anelevation of about 8,200 feet, thestream flows through a relativelywide canyon for just over 4 milesbefore it enters Red ButteReservoir. This approximately

3-2

SALT LAKE CITY RIPARIAN CORRIDOR STUDY

Figure 3.2. Relationship between impervious cover and surfacerunoff. Impervious cover in a watershed results in increased surface runoff. (Diagram and caption textfrom FISRWG 1998).

400-acre-foot reservoir wasoriginally constructed in 1930 bythe U.S. Army, and in2003–2004 ownership andmanagement of the dam andreservoir transferred to theCentral Utah Water ConservancyDistrict (Billman et al. 2006). The reservoir is currentlymanaged to maintain a generallyconstant reservoir elevation;during the early springtime,however, the reservoir is typicallylowered to provide some floodstorage capacity during thesnowmelt runoff period (J. Crofts2009, pers. comm.). During thenonrunoff portion of the year,reservoir inflows and outflows aretypically similar. Reservoirmanagement focuses onmaintaining habitat quality forthe refuge population ofendangered June sucker(Chasmistes liorus) that currentlyinhabit the reservoir (Billman etal. 2006).

The lower Red Butte Creeksubwatershed is much smaller,draining 1,652 acres from themouth of Red Butte Canyondownstream 2.7 miles to a pointjust west of 1100 East (SLCO2009). The creek flows throughthe University of Utah campusand research park, the Veteran’sAffairs (VA) Medical Centercomplex, Sunnyside Park, andthen though primarily residentialneighborhoods. The open-channel portion of Red ButteCreek terminates in the 1300South conduit, which conveysthe creek to the Jordan River viaa 3.4-mile-long pipe. Red ButteCreek has the most highly

urbanized lower subwatershed ofthe four streams included in theRCS, with impervious coverestimated at 31.9%.

Hydrology

Because of natural alluvialdeposition patterns, Wasatchmountain streams—includingRed Butte Creek—naturally losesome surfaceflow to groundwaterwhere the canyons transition tothe valley. Within most of theRCS study area, Red Butte Creekflows through areas mapped asprimary and secondarygroundwater recharge zones, andstudies have estimated losses togroundwater to be around 0.2cubic feet per second (cfs) in

summer and fall and up to 2.3 cfsduring spring (SLCO 2009). Inits lower reaches below 1600East, Red Butte Creek gains flowfrom various springs thatdischarge along the streambanks.

Urbanization and developmentthroughout the watershed havealtered surface water-groundwater patterns. As moreof the watershed has beenconverted to impervious surfaces,a greater proportion of stormwater runs off as surfaceflowrather than infiltrating into theground, leaving less groundwateravailable to supply baseflow tothe creek during the summer dryperiod (Figure 3.2). Red ButteCreek is classified as having

3-3


Figure 3.4. A comparison of hydrographs before and afterurbanization. The discharge curve is higher and steeperfor urban streams than for natural streams. (Diagramand caption text from FISRWG 1998).

Red Butte Creek Average Monthly Flow

0

2

4

6

8

10

12

14

October

November

December

January

February

March

April

May

June Ju

ly

August

September

Flow

(cfs)

1600 East

AboveReservoir

Figure 3.3. Monthly flows at Salt Lake County’s gage at 1600 Eastand the U.S. Geological Survey gage above Red ButteReservoir.

perennial flow upstream of RedButte Reservoir and is consideredto have “perennial-reduced” flowbelow that point, indicating thatflows are artificially reduced bystream diversions (SLCO 2009). At the RCS public workshops,residents of the lower portions ofthe creek indicated concerns oversummertime reduced flowsapparently associated withdiversion operations.

Within the study area, recordedpoints of diversion include astructure near the middle ofreach LRB_R05C (a 3.8-cfswater right) and several smallsprings on residential propertiesbetween 1100 East and 1500East (UDWRT 2010). Duringbaseline assessment field work,diversion headgates were alsoobserved at the downstream endof reach LRB_R05B.

Red Butte Creek’s hydrology ischaracterized by a distinctspringtime peak typical ofsnowmelt-driven systems. Basedon analysis of flow data recordedat the County gage near 1600East from 1984–2005, averagemonthly flow is highest in May(Figure 3.3), and peak daily flowoccurs on April 30 on average(SLCO 2009). Average annualhigh flow is 22 cfs while typicalbase flows are approximately 2cfs. Field observations duringstorm events suggest that flows inthe lower reaches of the creekare quite “flashy” with rapid,brief rises in flow during storms. This is a common hydrologicpattern in urbanized systems(Figure 3.4). An example of this

storm flow response can be seenin Figure 3.5, which plots theflows recorded at the USGS gageabove Red Butte Reservoir andat the County gage near 1600

East during a rain event in April2009. Analysis of flow records atthe two gages provides furtherevidence of the flashy hydrologyat the urbanized lower gage site,

3-4


Red Butte Creek Storm Response

0

10

20

30

40

50

60

70

0:00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 21:36 0:00

Time of day (hours) on April 25 2009

Flow

(cfs)

1600 East

AboveReservoir

Figure 3.5. Streamflow response to April 25 storm event (0.5 inchof rain between midnight and 3:30 AM) at the gagesabove the reservoir and 1600 East. At the 1600 Eastgage, which drains the urbanized lower subwatershed(31.9% impervious cover), flows increased by 30 cubicfeet per second (cfs) in response to the rain event whileflows in the upper subwatershed (9.1% impervious cover)only increased by 4 cfs.

which has rise and fall ratesabout five times greater than the undeveloped upper gage site.

As discussed above, Red ButteReservoir is managed to providesome degree of flood storage (J.Crofts 2009, pers. comm.). However, analysis of flow dataindicates that the magnitude andtiming of annual peak flows issimilar above and below thereservoir and the dam influenceon flood hydrology is relativelyminor. The potentially moresignificant dam effect is ondownstream sediment supply, asall bedload is trapped in thereservoir and only a portion ofthe suspended load is conveyeddownstream.

Water Quality

Designated beneficial uses ofupper Red Butte Creek abovethe reservoir are 1C (high-qualitydrinking water), 2B (secondarycontact recreation, and 3A (cold-water fishery). Below thereservoir the creek is designatedwith the default classifications of2B and 3D (waterfowl/shorebirdprotection). Red Butte Creek iscurrently assessed as meeting itsdesignated beneficial useclassifications (DWQ 2006). Aspart of its standard water qualitymonitoring program, the UtahDivision of Water Quality (DWQ)collects water quality data atthree monitoring stations inupper Red Butte Creek abovethe reservoir (STORET numbers

4992100, 4992110, and4992120) and at one stationbelow the reservoir at the USFSboundary (STORET number4992090; EPA 2009). Duringspring and summer 2009,additional E. coli sampling wasalso conducted by the DWQ atthe station at the USFS boundaryas part of an on-goingbacteriological sampling effort. The County also collectsmacroinvertebrate (aquaticinsect) data on Red Butte Creekas part of its Stream FunctionIndex data collection program(SLCO 2009).

No established DWQ waterquality monitoring stations arepresent on lower Red ButteCreek within the RCS study area. However, data have beencollected for several years at astation on the 1300 Southconduit (STORET 4992070). Water in the conduit originatesfrom Emigration, Parleys, andRed Butte Creeks, so the datacollected at this monitoringstation provide an indication ofwater quality conditions andstorm water effects within thelower, urbanized portions ofthese creeks. Potential nonpointsource pollution contributorswithin lower Red Butte Creekinclude urban runoff, activeconstruction sites, and managedparks and campus areas.

Geology and Soils

The surficial geology of the upperRed Butte Creek subwatershed iscomposed of various members ofthe Triassic Ankareh formation,

3-5


as well as Jurassic/TriassicNugget Sandstone (Bryant1990). Approximately50–86.2% of the soils in theupper subwatershed have severeto very severe erosion potential. Once it exits the canyon, RedButte Creek flows throughalluvial and debris fan depositsand a series of Pleistocene LakeBonneville deposits. Thesedeposits range in size fromfiner-grained silt and claydeposits to coarser sand andgravel deposits. In the lowersubwatershed, 20–35% of thesoils have severe to very severeerosion potential (SLCO 2009).

After Lake Bonneville recededapproximately 16,000 years ago,it left a series of old shorelinedeposits that now formprominent “benches” along theedges of Salt Lake Valley. Toreach its modern base level at theJordan River, Red Butte Creekhad to carve through thesedeposits. In part because of thisnatural geologic history, streamgradient is relatively steep andthe creek is entrenched betweentall slopes that extend up to theBonneville bench levels. Varioushuman-caused alterations to thecreek—including channelstraightening, installation of roadcrossing culverts, fill placement,and bank hardening—havefurther contributed to the steepgrade and entrenched shape ofthe channel.

Fish, Birds, and Wildlife

Quantitative data on fish andwildlife populations within the

urban portion of Red Butte Creekare limited. A managedpopulation of native Bonnevillecutthroat trout (Oncorhynchusclarki utah) exists in the creekabove the Red Butte Reservoir(Billman et al. 2006). Lower RedButte Creek is not reported inagency publications assupporting a fishery (SLCO2009) but RCS workshopattendees indicated that theyhave seen fish in the creek withinthe RCS study area, perhapsfrom private landowners stockingsmall numbers of trout forfishing.

Deer were observed in theSunnyside Park area during RCSfield assessment work. Duringthe Audubon Society’s 2005Christmas bird count, a total of30 different bird species wereobserved within the University ofUtah survey area, which includesportions of the Red Butte Creekriparian corridor (Carr 2009). Atthe RCS public workshops,residents reported regularlyseeing nuisance wildlife speciesincluding racoons and skunks. Reach LRB_R07, which includesthe Miller Bird Refuge andBonneville Glen park areas, is arecommended site forrecreational birding within theCounty.

Historical Conditionsand Current Trends

Red Butte Creek History

Red Butte Creek played animportant role in the initial

settlement and development ofSalt Lake City by the Mormonpioneers who entered the valleyin 1847. The creek was tappedfor water supply for homes andorchards built in the early 1850s. The pioneers also quarriedsandstone and some limestonefrom the canyon, building aquarry access road in 1848(Ehleringer et al. 1992). Someminor logging and grazingactivity also took place during theinitial settlement period.

When Fort Douglas wasestablished by the U.S. Army in1862, conflicts arose with SaltLake City over the use andquality of the Red Butte Creekwater supply (Figure 3.6). Theupper Red Butte Creekwatershed has been underFederal ownership andprotection since about 1900, andtoday functions as a USFSResearch Natural Area (RedButte Canyon RNA 2009). Because of this history ofprotection, the upper watershedremains in a relatively pristinecondition.

Early descriptions of the streamand its riparian corridor arelimited. One account describesabundant green grass growingalong the creek (LDS CHO1990). Publications suggest thestream historically supported aBonneville cutthroat trout fisherythat provided a food supply tothe pioneers (Billman et al.2006). One pioneer accountdescribes a broad, grassy marsharea at the confluence of Parleys,Emigration, and Red Butte creeks

3-6


Figure 3.6. Red Butte Creek historical timeline.

3-7


3-8


that made wagon travelchallenging (Dixon 1997). Modern descriptions of theprotected upper reaches of RedButte Creek, above the RCSstudy area, suggest that thepresence or absence of beaverdams plays a highly significantrole in the condition of thechannel and its riparian area. Prior to the 1983 spring flood,numerous beaver dams werepresent in the upper portions ofRed Butte Creek. The frequent“checks” on flow velocityprovided by the beaver damscreated pool and run habitatssurrounded by diverse, marshyriparian vegetation. Thesehabitats were greatly reducedwhen the beaver dams werewashed out by the 1983 flood(Ehleringer et al. 1992). Considerable slope slumping,streambed erosion, and gullyformation also occurred duringthe flood.

Alterations to the RiparianCorridor

Over the last 160 years, thevarious activities associated withdevelopment and populationgrowth in Salt Lake Valley haveresulted in significant alterationsto the stream channel andriparian conditions of lower RedButte Creek. Among otherfactors, systematic programs toremove beaver populations havelikely contributed to the currentlyreduced vegetation densityrelative to historical conditions. When beaver were morecommon, their dams increasedinundated streamside habitat

area, elevated the water table,reduced flood velocities anderosion, and trapped sedimentand nutrients (Gardner et al.1999).

As beaver populations werereduced, the “checks” onsediment and water created bybeaver dams also decreased,resulting in greater flow velocitiesand streambed down-cutting(Wohl 2000). Beaverpopulations flourished in RedButte Canyon (above the RCSstudy area) from 1928 until1982, when they were removedby the U.S. Army over concernsabout bacteriologicalcontamination of the watersupply to Fort Douglas. Theabsence of live beaverpopulations prior to, during, andimmediately following the 1983flood contributed to erosiondamage caused by the flood. Beaver populations appear to becurrently absent within the RCSstudy area.

Many of the direct alterations tolower Red Butte Creek haveoccurred in order to addressflooding concerns andaccommodate urbandevelopment and populationgrowth. One of the mostsignificant direct changes to thecreek was the construction of the1300 South conduit, whichconverted the westernopen-channel portions ofEmigration, Red Butte, andParleys Creeks to anunderground pipe system. Theexact date of conduitconstruction is not known but

Historical activitiesthat have altered ripariancorridor conditions:

• mining and quarrying forsandstone

• beaver trapping andremoval

• channel clearing and debrisremoval

• flow diversion for irrigationand drinking water

• development and piping ofsprings

• road and stream crossing

construction

• residential and commercialdevelopment

• introduction of invasive,nonnative plants

• piping of the creek inunderground conduits

• channel relocation/straightening

• bank armoring

• placement of fill withinfloodplain areas

• construction andmanagement of Red ButteDam and Reservoir

• development and operationof Fort Douglas

3-9


Figure 3.7. 1938 aerial photograph of Red Butte Creekfrom 900 South to 1500 East. Photograph isoverlaid with 2006 channel alignment in red; gapsin line indicate underground culverts.

Figure 3.8. 1938 aerial photograph of Red Butte Creekfrom Foothill Drive to Sunnyside Avenue.Photograph is overlaid with 2006 channelalignment in red; gaps in line indicateunderground culverts.

housing stock located over theconduit system dates to the late1920s, suggesting thatconstruction was complete priorto that time. No creek channelcan be seen west of 1100 East in1938 air photos of Salt Lake City(Bowman and Beisner 2008).

In general, the channel alignmentof Red Butte Creek does notappear to have changeddramatically since 1938. Somerelatively minor bendstraightening is evident inportions of the channel within theareas that are now BonnevilleGlen and Sunnyside Park(Figures 3.7 and 3.8 ). Anothersignificant change since 1938 hasbeen an increase in length andnumber of culvert pipes. Near1500 East, approximately 300feet of what used to be openstream channel (Bowman andBeisner 2008) is now pipedunder a parking lot (Figure 3.7). Similarly, just downstream fromFoothill Drive, approximately130 feet of what was onceforested stream channel is nowpiped under a road crossing(Figure 3.8). The construction ofculvert crossings and the pipingof portions of Red Butte Creekfacilitated urban growth but alsoreduced total channel length,resulting in greater channel slopeand higher stream velocities. The culverts have also disruptedthe connectivity of the ripariancorridor by creating barriers tofish and wildlife migration.

In some residential areas alongthe creek, it appears that treecanopy density has increased

3-10


Figure 3.9. Illustration of streambed lowering (incision) processcommon on urbanized streams. Following initialincision (B), the channel may continue to inciseand widen until a new equilibrium channel/floodplaingeometry is reached, posing a potential risk to urbandevelopment on terrace surfaces adjacent to the channel(Diagram from FISRWG 1998).

since 1938. This is most likelythe result of landscaping and treeplanting as dense residentialneighborhoods were built alongthe creek. Much of theresidential development withinthe RCS study area is estimatedto have occurred between 1915and 1940. This developmentprimarily affected areasdownstream from SunnysideAvenue (Figure 2.1). A secondphase of urbanization within theareas upstream of SunnysideAvenue began around 1970.

This second phase involveddevelopment of the VA MedicalCenter complex and University ofUtah research park facilities. Building expansion work andnew construction projectscontinue in these areas today.

Urban ChannelAdjustments

Urbanized streams have beenfound to undergo a sequence oftypical channel adjustments inresponse to changes in hydrologyand sediment supply (Wolman1967, Riley 1998, and Colosimoand Wilcock 2007). Studies ofurban channel adjustmentgenerally identify two mainstages of adjustment: an earlydepositional phase and a later,fully urbanized phase. The earlyphase occurs during initialdevelopment when activeconstruction leads to increasedfine sediment supply, increasedbar deposits, and reducedchannel size. The late/fullyurbanized phase occurs afterconstruction activities are

essentially complete and thewatershed has become stablewith a high percentage ofimpervious surface area andrunoff magnitudes and volumeshave correspondingly increased. Channels in the “late urbanized”phase are typically enlargedrelative to their original form dueto an oversupply of water relativeto sediment supply. Thesechannels have few bar depositsand are commonly down-cut(incised) with reduced floodplainaccess (Figure 3.9). Many of thereaches of Red Butte Creek thatwe assessed exhibitcharacteristics of the “late

urbanized” phase, such asevidence of down-cutting andlow bank erosion/root scour.

Other influences such as localizedsediment inputs from erodingstorm drain outfalls or sedimentdeposition near culvert inletsmodify conditions from thisgeneralized “late urbanized”channel condition. Existingchannel conditions within theRed Butte Creek corridor reflect acomplex response to a variety ofhistorical and on-goingalterations throughout the makesit difficult to distinguish whetherchannel lowering and

3-11


watershed. This complexity bank erosion observed in aspecific location are due to acorridor-scale streambedlowering trend, a localized culvertor bank treatment effect, orcombination of several factors.

Recent and AnticipatedFuture Trends

Anticipated future land usechanges are minimal within theupper Red Butte Creeksubwatershed. Within the lowersubwatershed, additionaldevelopment is primarilyanticipated to occur within theareas occupied by the Universityof Utah’s research park and theVA complex. The imperviouscover of the lower subwatershedis expected to increasesignificantly by 2030, to a totalimpervious cover value of 43.8%(SLCO 2009).

Climate change is another factorthat can be anticipated to affectthe Red Butte Creek ripariancorridor. Climate projections forthe southwestern region of theUnited States show increasedtemperatures, reduced mountainsnowpack, a 10–20% decrease inannual runoff volume, reducedspringtime precipitation amounts,and anticipated water supplyshortages (Karl et al. 2009). Therisk of drought, as well as the riskof flooding, is also expected toincrease. The changes intemperature will likely result in ashift in vegetation communities,and altered precipitation patternswill influence stream hydrologyand channel conditions. The

timing of snowmelt runoff isexpected to occur earlier in thespring, with a reduction insummertime base flowsanticipated (Karl et al. 2009).

Stream and VegetationConditions

Stream ChannelCharacteristics

Salt Lake County has classifiedthe stream reaches within thelower Red Butte Creeksubwatershed as entrenched tomoderately entrenched, meaningthe channel is vertically confined.Over 60% of the channel in thelower subwatershed received afair to poor stream stability ratingduring County stream studies;upper subwatershed reachesURB_R09 and URB_R10 bothreceived fair stability ratings (K.Collins 2009, pers. comm.). During field assessments in 2008,the County classified lower RedButte Creek as Rosgen (1996)stream types A3 and B3 betweenlower Red Butte Garden and1500 East (reaches LRB_R01through LRB_R07), and types A4and B4 below 1500 East. Stream reaches in the uppersubwatershed were assessed in2007 and the assigned streamtype for reaches URB_R09 andURB_R10 was B3 (K. Collins2009, pers. comm.). Countybankfull width estimates for thestream reaches in lower RedButte Creek ranged from 8 to 20feet, with an average of 13 feet. Estimates for reaches URB_R09and URB_R10 were 14 and 15

feet, respectively (K. Collins2009, pers. comm.).

Results of RCS field surveys andGIS analyses further illustrate thefact that the Red Butte Creekchannel is commonly entrenchedand typically inset between tall,steep slopes (Figure 3.10).Because of this characteristic,residents along the creek corridorwho attended the RCS publicworkshops often refer to thechannel as a “gully” or “ravine.”The steep side slopes also makeaccess to the creek challenging inmany areas. However, theextent of vertical confinementvaries, and in some locations thechannel shape is wider (Figure3.10). These wider areas areimportant because they allowwater to spread out horizontallyduring flood events, dissipatingvelocity and reducing erosionpotential.

Surveyed channel width valuesare quite variable, ranging fromabout 4–11 feet at low flow, withan average value of 8 feet (Table3.1). High flow surveys wereconducted at a streamflow of 19cfs, which is close to the averageannual high flow value of 22 cfs. Width at this high flow valuevaries from about 6 to 16 feet,with an average of 10 feet. Insome reaches, particularly thedownstream reaches in olderresidential neighborhoods,channel width is directly affectedby installed bank hardeningmeasures such as grouted rockwalls. Channel slope, asdetermined for each streamreach from digital elevation data,

3-12


Figure 3.10. Cross-section plots extrapolated from digital elevation data. Plots on left (in blue) exhibit a highdegree of vertical confinement between tall, steep side slopes. Plots on right (in red) exhibit lessvertical confinement.

varies from 3.1–6.7% within theRCS study area with an averagevalue of 4.6% (Figure 3.11,Table 3.1).

Red Butte Creek does not showany consistent spatial trends ingradient through the study area

because the valley slope remainssteep throughout the study area,which traverses Lake Bonnevillebench deposits. The valleybecomes significantly flatter westof 1100 East and, historically,Red Butte Creek would haveshifted to a flatter, less confined,

more sinuous channel type inthis area. However, this portionof the creek is now pipedunderground in the 1300 Southconduit.

Median (D50) streambed particlesizes at the measured cross

3-13


Table 3.1 Summary of streambed material, channel geometry, and slope data.

REACHNUMBER

MEASURED VALUES AT RIFFLE CROSS SECTIONREACH DATA

STREAMBED MATERIAL SIZE DATA CHANNEL GEOMETRY

D16(mm) a

D50(mm) a

D84(mm) a

PercentEmbedded

Low FlowWetted Width

(ft) b

WettedWidth (ft) b

at 16 cfs c

Local Slope(ft/ft) d

Reach Slope(ft/ft) d

Reach Length(ft) b

URB_R09 12 75 164 25 10.0 10.5 0.036 0.051 2297

URB_R10 - - - - - - - 0.067 827

LRB_R01 6 51 111 9 6.7 16.2 0.023 0.043 281

LRB_R02 <2 12 27 5 7.0 11.3 0.009 0.053 451

LRB_R03 5 30 181 32 10.8 11.1 0.094 0.062 1041

LRB_R04A <2 23 86 15 4.3 6.0 0.032 0.053 961

LRB_R04B 9 45 95 11 6.3 8.9 0.018 0.040 595

LRB_R04C 3 27 79 16 7.9 8.6 0.048 0.032 1294

LRB_R05A 9 42 104 6 9.9 10.4 0.054 0.055 433

LRB_R05B 12 41 104 4 8.4 10.2 0.042 0.031 1081

LRB_R05C 9 42 134 16 5.8 7.6 0.028 0.037 887

LRB_R06 - - - - - - - 0.046 492

LRB_R07 12 37 111 10 9.4 10.0 0.021 0.036 2084

LRB_R08 - - - - - - - 0.044 1059

LRB_R09 - - - - - - - 0.053 633

LRB_R10 10 32 77 3 5.8 7.4 e 0.057 0.041 1449

LRB_R11 - - - - - - - 0.043 301a The 16th, 50th, and 84th percentile values of the particle size distribution, in millimeters.b Feet.c Cubic feet per second.d Feet per feet.e Wetted width at 10.5 cubic feet per second.

sections range from 12–75millimeters, indicating thatmedium- and large-sized gravelare the dominant substrate sizesin riffle areas of Red Butte Creek(Table 3.1). At most of thecross-section riffles, fine gravelcomprises the D16 particle sizeand cobble-sized materialcomprises the D84 particle size (Table 3.1). Embeddednessvalues are highly variable. Inflatter-gradient portions of thechannel, such as run and poolareas, particle sizes are smaller

with sand and silt oftendominant. No consistentupstream-to-downstream trendsare evident in the pebble countresults; rather, bed material sizeand embeddedness appear to belargely a function of local factors such as sediment inputs fromerosion areas and composition ofbank material.

Vegetation Characteristics

Table 3.2 lists all dominant plantspecies noted on the data forms

during the mapping effort for thestudy area. Species are identifiedwith their common and scientificnames, wetland indicator status(USFWS 1988), and whether thespecies is native to Utah orintroduced (NRCS 2009). A totalof 41 different species werenoted during Red Butte Creekmapping work, with a little morethan half of the species beingnative to Utah. As seen in Table3.3, most of the nonnativespecies within the corridor occur

3-14


Red Butte Creek Longitudinal Profile

UR

B R09

UR

B R10

LRB R

01LR

B R02

LRB R

03

LRB R

04A

LRB R

04B

LRB R

04C

LRB R

05A

LRB R

05B

LRB R

05C

LRB R

06

LRB R

07 LRB R

08

LRB R

09

LRB R

10

LRB R

11

Red Butte Garden

Chipeta Way

Tennis CourtsMarriott

Foothill Dr.

VA Medical Ctr.Sunnyside Ave.

900 S.

1500 E

1300 E

1100 E

4200

4300

4400

4500

4600

4700

4800

4900

5000

5100

5200

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Distance Downstream (ft)

Elev

atio

n (ft

)

Figure 3.11. Longitudinal profile plot of Red Butte Creek streambed. Black cross marks indicate culvert inletsor outlets; red and blue lines indicate open channel stream sections.

in the canopy and understoryvegetation layers while the shrublayer is dominated entirely bynative species. The mostcommon trees along the stream-side areas of Red Butte Creek arebox elder (Acer negundo) andcottonwood (Populus sp.), withGambel oak (Quercus gambelii)dominant in undeveloped upperslope areas. Siberian elm (Ulmuspumila), an introduced invasivetree species, is fairly common inthe study area. Russian olive(Elaeagnus angustifolia), also anintroduced invasive tree, ispresent but less prominent (Table

3.3). Common shrub speciesinclude redosier dogwood(Cornus sericea), twinberryhoneysuckle (Lonicerainvolucrata), and narrowleafwillow (Salix exigua), withWoods’ rose (Rosa woodsii)common on upper portions ofslopes. The understoryvegetation layer includes nativespecies such as Western poisonivy (Toxicodendron rydbergii)and Virginia creeper(Parthenocissus quinquefolia) insome reaches, with field horsetail(Equisetum arvense) present inothers. Introduced species such

as ornamental English ivy (Hedrahelix), common periwinkle (Vincaminor), climbing nightshade(Solanum dulcamara), smoothbrome (Bromus inermis), andlesser burdock (Arctium minus)are significant components of theunderstory cover in severalreaches. In addition, the upperslope portions of some reachescontain the invasive specieswhitetop (Cardaria draba) andhoundstongue (Cynoglossumofficinale) (Table 3.3).

Canopy (tree) cover is generallyhigh throughout the study area,

3-15


Table 3.2. Dominant species noted during Red Butte Creek vegetation mapping work.

SCIENTIFIC NAME COMMON NAME WETLAND INDICATOR STATUS NATIVE TO UTAH OR INTRODUCED

Acer grandidentatum bigtooth maple no indicator native

Acer negundo box elder facultative wetland native

Agoseris glauca pale agoseris facultative upland native

Ambrosia artemisiifolia annual ragweed facultative upland native

Arctium minus lesser burdock no indicator introduced

Balsamorhiza macrophylla cutleaf balsamroot no indicator native

Balsamorhiza sagittata arrowleaf balsamroot no indicator native

Betula occidentalis water birch facultative wetland native

Bromus inermis smooth brome no indicator introduced/naturalized

Bromus tectorum cheatgrass no indicator introduced

Cardaria draba whitetop no indicator introduced

Cornus sericea redosier dogwood facultative wetland native

Cynoglossum officinale gypsyflower (houndstongue) not designated introduced

Elaeagnus angustifolia Russian olive facultative introduced

Elymus repens quackgrass facultative upland introduced

Equisetum arvense field horsetail facultative native

Fraxinus pennsylvanica green ash facultative wetland native

Gleditsia tricanthos honeylocust facultative native

Hedera helix English ivy no indicator introduced

Juglans nigra black walnut not designated native

Lonicera involucrata twinberry honeysuckle facultative native

Maianthemum racemosum feathery false lily of the valley no indicator native

Mahonia repens creeping barberry no indicator native

Maianthemum stellatum starry false lily of the valley facultative native

Melilotus officinalis yellow sweetclover facultative upland introduced

Onopordum acanthium scotch cottonthistle no indicator introduced

Parthenocissus quinquefolia Virginia creeper not designated native

Phalaris arundinacea reed canarygrass obligate wetland native

Populus angustifolia narrowleaf cottonwood facultative native

Populus deltoides eastern cottonwood facultative wetland native

Poa pratensis Kentucky bluegrass facultative upland introduced

Prunus virginiana western chokecherry facultative upland native

Quercus gambelii Gambel oak obligate upland native

Rhus trilobata skunkbush sumac no indicator native

Rosa woodsii Woods' rose facultative native

Salix exigua narrowleaf willow obligate wetland native

Solanum dulcamara climbing nightshade facultative introduced

Symphyotrichum ascendens western aster no indicator native

Toxicodendron rydbergii western poison ivy facultative upland native

Ulmus pumila Siberian elm no indicator introduced

Vinca minor common periwinkle no indicator introduced

3-16


Table 3.3. List of mapped canopy, shrub, and understory plant species found in each assessed streamreach.

PLANT SPECIES

URB_

R09

URB_

R10

LRB_

R01

LRB_

R02

LRB_

R03

LRB_

R04A

LRB_

R04B

LRB_

R04C

LRB_

R05A

LRB_

R05B

LRB_

R05C

LRB_

R06

LRB_

R07

Common Name Scientific Name

CANO

PY

Bigtooth maple Acer grandidentatum X X X

Box elder Acer negundo X X X X X X X X X X X X X

Water birch Betula occidentalis X X

Green ash Fraxinus pennsylvanica X X

Black walnut Juglans nigra X X

Narrowleaf cottonwood Populus angustifolia X X X

Eastern cottonwood Populus deltoides X X X X X X X

Gambel oak Quercus gambelii X X X X X X X X

Honeylocust Gleditsia tricanthos X X

Siberian elm a Ulmus pumila a X X X X X

Russian olive a Elaeagnus angustifolia a X X X

SH

RUB

Western chokecherry Prunus virginiana X X

Skunkbush sumac Rhus trilobata X

Redosier dogwood Cornus sericea X X X X X X X

Twinberry honeysuckle Lonicera involucrata X X X X

Woods' rose Rosa woodsii X X X X X X X X

Narrowleaf willow Salix exigua X X X

Creeping barberry Mahonia repens X X X

UNDE

RSTO

RY

Arrowleaf balsamroot Balsamorhiza sagittata X

Cutleaf balsamroot Balsamorhiza macrophylla X

Field horsetail Equisetum arvense X X

Feathery false lily of the valley Maianthemum racemosum X

Starry false lily of the valley Maianthemum stellatum X

Virginia creeper Parthenocissus quinquefolia X X

Kentucky bluegrass Poa pratensis X X

Climbing nightshade Solanum dulcamara X

Western aster Symphyotrichum ascendens X

Western poison ivy Toxicodendron rydbergii X X X X

Smooth brome b Bromus inermis b X X

Lesser burdock a Arctium minus a X X X X

Whitetop a Cardaria draba a X X X X

Quackgrass a Elymus repens a X

Scotch cottonthistle a Onopordum acanthium a X

Gypsyflower (Houndstongue) a Cynoglossum officinale a X

Cheatgrass c Bromus tectorum c X X

Common periwinkle c Vinca minor c X X

English ivy c Hedera helix c X X

Yellow sweetclover b Melilotis officianalis b X

Pale agoseris Agoseris glauca X

Reed canarygrass Phalaris arundinacea X

Annual ragweed Ambrosia artemisiifolia X

a State- or city-listed, nonnative, noxious weed species.b Species not native to Utah.c Nonnative, invasive species.

3-17


with all but six of the mappedvegetation polygons having apercent canopy cover greaterthan 75%. Because of the highquality tree cover within the RedButte Creek riparian corridor, theriparian functions of shading andwater temperature control arebeing met to a high degree withinthe corridor. In contrast, plantcover within the lower structurallayers is typically much lower,with 23 and 21 of the mappedpolygons having cover of 50% orless in the shrub and understorycommunities, respectively (Table3.4). Invasive species cover wasvariable throughout the studyarea, with about half of thevegetation polygons having aninvasive species class of “low” or“none” (i.e., 5% cover or less),with the other half classified asmoderate, high, or majorityinvasive cover (Table 3.4).

Issues AffectingRiparian Functions

During the baseline assessmentwork, several common issueswere observed to be affectingand limiting riparian functions inthe Red Butte Creek corridor.

These issues are discussed byfunction below.

Aesthetics

Although many visuallyappealing portions of Red ButteCreek exist, the presence of trashand debris degrades corridoraesthetics in a number oflocations. Common types oftrash include miscellaneous smallitems such as bottles, cans, foodwrappers, plywood, plasticcontainers, tarps, etc. Anothercommon category of trash isremnant/obsolete infrastructuresuch as pieces of concrete andasphalt, broken fencing, oldpipes and barrels, obsoleteerosion-control devices such asfailing silt fence, etc. In manyinstances the concrete pieces areassociated with prior bankstabilization efforts that havefailed due to the concrete beingundermined by scour orstreambed lowering. Twelveindividual, significant litter areaswere mapped in the study areaduring RCS baseline assessmentwork.

Vegetationassociations presentin the study area:

• Bigtooth Maple /Gambel Oak Forest

• Box Elder - EasternCottonwood / RedosierDogwood Forest

• Box Elder - EasternCottonwood Semi-natural Woodland

• Box Elder - NarrowleafCottonwood / RedosierDogwood Forest

• Box Elder / GambelOak Woodland

• Box Elder Forest

• Box Elder Semi-naturalWoodland

• Designed OrnamentalSemi-natural PerennialMix

• Gambel Oak /

Skunkbush SumacWoodland

• Gambel Oak Forest

• Introduced Trees,Shrubs and Grasses

• Mixed Semi-naturalIntroduced Forbes andGrasses

3-18


Table 3.4. Percent cover and invasive species class for mapped vegetation polygons.

REACHPOLYGONNUMBER

PERCENT CANOPYCOVER

PERCENT SHRUBCOVER

PERCENTUNDERSTORY

COVER

INVASIVESPECIES CLASS

LRB_R01 1 76—100+ 76—100+ 0 none

LRB_R02 2 76—100+ 0 0 none

LRB_R02/3 3 76—100+ 51—75 1—5 low

LRB_R03 4 51—75 51—75 26—50 low

LRB_R04A 5 76—100+ 51—75 51—75 moderate

LRB_R04A 6 76—100+ 0 26—50 none

LRB_R04B 7 76—100+ 51—75 6—25 none

LRB_R04B 8 76—100+ 6—25 0 none

LRB_R04B 9 76—100+ 26—50 6—25 none

LRB_R04B 10 76—100+ 26—50 6—25 none

LRB_R04C 11 51—75 26—50 26—50 none

LRB_R04C 13 76—100+ 26—50 76—100+ high

LRB_R04C 14 76—100+ 26—50 76—100+ high

LRB_R05A 15 76—100+ 0 26—50 high

LRB_R05B 16 76—100+ 6—25 6—25 moderate

LRB_R05B 17 76—100+ 6—25 6—25 low

LRB_R05C 18 76—100+ 26—50 0 moderate

LRB_R05C 19 76—100+ 51—75 6—25 moderate

LRB_R07 20 76—100+ 0 26—50 high

LRB_R07 21 76—100+ 26—50 76—100+ majority

LRB_R06 22 76—100+ 6—25 51—75 majority

URB_R10 23 0 0 76—100+ none

URB_R10 24 51—75 51—75 6—25 moderate

URB_R09 25 76—100+ 6—25 51—75 low

URB_R09 26 76—100+ 76—100+ 51—75 moderate

LRB_R04A 60 76—100+ 51—75 26—50 none

LRB_R05C 201 26—50 0 76—100+ high

LRB_R05C 202 76—100+ 0 76—100+ high

LRB_R05C 203 26—50 0 76—100+ moderate

LRB_R05C 204 76—100+ 26—50 6—25 moderate

LRB_R05C 205 76—100+ 26—50 6—25 moderate

LRB_R05C 206 76—100+ 26—50 6—25 low

3-19


Wildlife Habitatand Connectivity

A wide range of native bird andmammal species rely on nativeinsects as a key food source(Tallamy 2009). These insectsmust share an evolutionaryhistory with plants in order torecognize them and use them asa food source. Therefore,healthy native plant communitiesare necessary for a ripariancorridor to function to itsmaximum potential in terms ofwildlife habitat. As discussedabove, invasive nonnative plantspecies are a concern in abouthalf of the study reaches withinthe Red Butte Creek corridor,and they affect the compositionof the understory and canopyvegetation layers. In some areasinvasive species comprise themajority plant cover within avegetative layer, limiting theability of native plants to thriveand support native insects, birds,and wildlife. The lack ofunderstory and shrub cover inmany reaches also limits habitatquality in terms of structuraldiversity, which is particularlyimportant for bird populations.

Another issue affecting wildlifehabitat, as well as riparianconnectivity, is the presence ofstream crossing culverts. Twelveculvert crossings were mappedwithin the study area (Figure3.11). Several of these culvertsimpede or block fish passage dueto steep vertical drops at theiroutlets and high flow velocities

within the smooth concrete pipes. This limits the ability of fishpopulations to use Red ButteCreek as a continuous travelcorridor. The small diameter ofthe culverts also blocks passageby mammal species such as deer. Within the study area, a totallength of 0.35 mile of stream iscontained in culvert pipes,limiting the overall length of openchannel stream available asaquatic habitat. The longestcontinuous segments of stream inthe study area include studyreach URB_R09, which is 2,300feet long; reach LRB_R07, whichis 2,080 feet long; a 1,700-foot-long segment between 1500 Eastand 1300 East; and a 1,500-foot-long segment between Red ButteGarden and Chipeta Way (Figure3.11).

Nutrient Filtrationand Sediment Trapping

As discussed above, many areasof the Red Butte Creek corridorlack the dense understory andshrub cover that are needed tomaximize the ability of theriparian corridor to filtersediment, nutrients, andpollutants from storm runoff. Insome areas, understory cover ishigh but the community isdominated by invasive periwinkleor ivy vines. Because these vineshave shallow, low-density rootand stem systems, they do notserve the filtration function aswell as native grass and forbcommunities would.

Invasive plantsof concern in the studyarea:

• Russian olive

• Siberian elm

• tree of heaven

• lesser burdock

• whitetop

• periwinkle vine

• English ivy

• cheatgrass

• quackgrass

• Scotch thistle

• houndstongue

Factors limiting shrub and understory cover:

• oversteepened slopes

• inadequate revegetationefforts followingconstruction

• soil compaction fromheavy foot traffic

• uncontrolled runoff fromupland areas

3-20


Stream Stability

A number of different issues werenoted as affecting stream stabilitywithin the Red Butte Creekriparian corridor. Specific issuesare discussed in the subsectionsbelow.

Stream Crossing CulvertsLocalized erosion and depositionproblems were noted at severalof the stream crossing culvertswithin the study area. Most ofthe culverts have diameters of 3to 7 feet (Table 3.5), which issignificantly smaller than the 13-foot average bankfull channelwidth. Because of this widthdiscrepancy, a hydraulicconstriction occurs at culvertinlets, slowing flow velocities andleading to deposition and accumulation of sediment anddebris. At three crossings withinthe study area, the size of theopenings at the culvert inlets andthe conveyance capacities of thestructures have been substantiallyreduced as a result of thisdeposition process. During RCSpublic workshops andstakeholder meetings, no onereported experiencing anyflooding problems on Red ButteCreek since the 1983 floods;however, problems may occur inthe future unless measures aretaken to restore the conveyancecapacities of these crossingstructures.

The size and design of the streamcrossing culverts also contributeto stability concerns at some ofthe culvert outlets. During highflows, velocities at the outlets of

the longer culverts areaccelerated because of widthconstriction and a lack of bedroughness within the smoothconcrete pipe material. Scourproblems and vertical drops werenoted at three of the assessedcrossing outlets within the studyarea (Table 3.5).

Storm Drain OutfallsErosion was commonly observedat storm drain pipe outfalls withinthe study area. These outfallsdeliver storm water runoff to thecreek from streets, gutters, and

rooftops. The outfalls often lackadequate outlet protection todissipate runoff velocities andprotect against erosion. Evenwhere outlet protection isprovided, stabilized conveyancechannels are typically lackingbetween the protected outlet andthe main Red Butte Creekchannel and evidence of rillerosion in these areas iscommon. Of the 25 mappedoutfall locations, 12 were rankedas medium- or high-priority areasfor stability improvements.

Top left: Debris and sediment accumulation at culvert inlet. Top right:Erosion at storm drain outfall. Bottom left: Invasive vines onstreambank. Bottom right: Scour at culvert outlet.

3-21


Table 3.5. Size and condition of stream crossing culverts in the study area.CrossingLocation/Description

ReachNumber(s)

ApproximateCulvert

Length (ft) a

Vertical Drop from Inlet

to Outlet b (ft) aCulvert Type

ApproximateCulvert Size/

Diameter (ft) aInlet Condition Outlet Condition

Trail at south endof Red ButteGarden

betweenLRB_R01

and LRB_R0250 2 3 round pipes 2.5 each

fair; affected by siltfence/construction

at timeof assessment

good; minimal scour

Chipeta Waybetween

LRB_R03and LRB_R04A

108 5 concrete arch 6.5 H x 5.5 W c fair; sticks placedacross inlet good; minimal scour

Crossing neartennis courts

betweenLRB_R04A

and LRB_R04B90 4 concrete arch 7 H x 6 W c fair; boards

partially block inlet good

Crossing nearMarriot

betweenLRB_R04B

and LRB_R04C72 4 concrete arch 6 H x 6 W c

fair; partiallyblocked

by sediment/debrisaccumulation

good

Foothill Drivebetween

LRB_R04Cand LRB_R05A

192 9

concrete box(inlet);

eliptical metalpipe (outlet)

6.5 H x 6 W (inlet); 6 H x 7 W

(outlet) c

fair; bare slopesaround concrete

headwall

poor; scour and bankerosion; 2-foot dropfrom pipe to water

surface

Hall Streetbetween

LRB_R05Aand LRB_R05B

128 5 roundconcrete pipe

6

fair; some bareslopes/erosion

aroundconcreteheadwall

fair; scour poolpresent below

concrete apron

Crossingwithin VAMedicalCentercomplex

neardownstream

endof LRB_R05B

20 1 concrete arch 5poor; nearly blocked

by sedimentand debris

poor; 2/3 of archfilled with sediment

SunnysideAvenue

betweenLRB_R05C

and LRB_R06180 10

two verticallystackedconcrete

boxes

each 3 H x 3 W c good not assessed

900 Southbetween

LRB_R06and LRB_R07

210 9round metal

pipe 3 not assessedfair; some scour/

undercutting

Trail in MillerPark

middleof LRB_R07

16 N/A d open-bottomarch

9 H x 12 W c excellent excellent

1500 Eastbetween

LRB_R07and LRB_R08

400 14round

concrete pipe 4stable; concrete

and rip-rap not assessed

1300 Eastbetween

LRB_R09and LRB_R10

260 14round

concrete pipe 3 or 4 not assessed not assessed

1100 EastbetweenLRB_R10

and LRB_R1190 1.5

roundconcrete pipe 3 or 4 stable; all concrete stable; all concrete

a Feet.b Elevation change between inlet and outlet based on digital elevation data.c H = height, W = width.d Not applicable.

3-22


Streambank ErosionLateral erosion of streambanks isa natural process in streamchannels, which are dynamicsystems. Erosion and sedimenttransport are necessary for thecreation and maintenance ofimportant habitat features suchas scour pools, undercut banks,and spawning gravels. Deposition of sediment ontofloodplain areas is alsoimportant, as it provides freshsubstrate for the growth of willowand cottonwood seedlings thatare needed to maintain nativeriparian forests. However,excessive amounts of erosion ordeposition can degrade habitatand water quality, and threatenmunicipal infrastructure andresidential homes.

Several types of bank erosionwere observed in the study area. Low bank erosion/root zonescour are evident in nearly allstudy reaches and are associatedwith the flashy urban hydrologythat produces frequent, erosiverunoff events during storms. Insome areas, it appears thatstreambed lowering is alsocontributing to low bank erosionby causing the toe of the slope tobecome undermined. In somereaches tall, vertical, bare banksare present where the creek hasmigrated laterally into a fine-grained Bonneville terracedeposit. This type of terraceerosion at the outside of bends isa natural process, but it is aconcern where it poses a risk toinfrastructure. Localized bankerosion caused by direct channelalterations is another type of

erosion problem observed in thestudy area. In several locations,bank erosion problems wereobserved in unprotected areasopposite or adjacent to banksthat have been hardened withrock or concrete. This type ofproblem can occur when bank

stabilization efforts are notimplemented comprehensivelythroughout a reach becausemeasures taken to fix erosion inone location may alter channelshape and flow hydraulics andinadvertently create erosion in adifferent location.

Top: Terrace erosion at outside of bend. Bottom: Low bank/root zoneerosion.

3.0 baseline assessment results - slcdocs.com study website/redbutte/final/6...final red butte creek...

Documents