ora-polk-mitchell1_Bridge_TSL_Hydraulics_Memo-combined-v1.pdf

Memorandum

Western Federal Lands Highway Division 610 E. Fifth Street

Vancouver, WA 98661-3801

LITTLE LUCKIAMUTE RIVER BRIDGE

TSL BRIDGE HYDRAULICS MEMO

To: Matthew Miller, WFLHD Project Manager From: Sven Leon, P.E., WFLHD Hydraulics Engineer Date: January 9, 2020 Project: OR POLK 2016(1) – Black Rock Road Reconstruction

Background Polk County, Oregon, is replacing a bridge over Little Luckiamute River on Black Rock Road (Fig. 1).

The single span, single lane, steel truss, 85 feet long bridge was constructed in 1963. Polk County maintains the road and bridge structure. Western Federal Lands Highway Division (WFLHD) is designing the new bridge. Final recommendations for bridge waterway width, skew angle, minimum low chord elevation, riprap scour control, and scour elevations are presented.

Recommendations

• Minimum low chord elevation 437.5 feet (project datum) (100-year water surface plus 3 feet freeboard for woody debris passage).

• Locate new 110-foot long bridge slightly upstream of the existing road alignment (begin station 39+73.5, end station 40+86.5).

• 60 feet channel bottom width.

• 2(h):1(v) channel sideslopes.

• 89 feet minimum perpendicular distance between vertical abutment wall faces.

• Angle between bridge centerline and channel centerline 30.0 degrees.

• Cross centerline channel with centerline road at station 40+31.5 feet.

• Riprap Class 4 (FHWA FP-14, method B), 4 feet thick, crest 436.0 feet, bottom on bedrock.

• Use separation-stabilization geotextile, Class 1, Type C, under all riprap not directly bearing on bedrock.

• Align riprap with bridge abutment face.

• Place partially-grouted riprap along bedrock surface for keying riprap to the bedrock surface.

• Place conserved streambed material over the new riprap for covering the riprap and creating a natural appearing bank-line.

• Based on scour calculations, set abutment bottom elevations on bedrock.

• Slope bridge 1.0 percent minimum longitudinal and 2.0 percent minimum cross slope towards the northeast bridge corner.

Memo to: Matthew Miller, WFLHD Project Manager January 9, 2020

• Install Class 1 riprap, method A, 20 feet by 10 feet, 30 cubic yards at each bridge corner for transitioning to the finished road embankment grade.

• Remove the existing riprap abutment protection, bridge abutments, and road embankment fill for opening the waterway and establishing an unrestricted channel.

Construction Work within the ordinary-high-water limits can be performed July 1 to October 15. Avoid working within the ordinary-high-water limits when the stream is flooding. Isolate abutments as needed for the work. Do no block channel completely. Maintain flow always when instream work is performed.

Temporary flow deflectors or diversion berms placed for isolating the work area and diverting the stream flow in place October 16 through June 30 must have minimum;

• Flow capacity equal to the 2-year discharge, 1,870 cubic feet per second (cfs).

• Minimum height of 5 feet above the stream bottom and be stable assuming 10 feet per second

(fps) parallel flow.

Temporary flow deflectors or diversion berms placed for isolating the work area and diverting the stream flow in place July 1 to October 15 must have minimum;

• Flow capacity equal to 500 cfs.

• Minimum height of 4 feet above the stream bottom and be stable assuming 8 fps parallel flow.

Use plastic-lined channels or pipes for temporally conveying stream flow through the construction area.

Protect the outfalls from erosion. Fish passage downstream through the temporary flow diversions is required. Ensure fish can pass smoothly from the upstream diversion point to the downstream diversion point. Locate diversion points in the main stream channel. Fish passage upstream is not required. Before installing the flow deflectors, remove fish from the work area to the level and methods specified in the environmental permits.

Full construction area dewatering is expected up to the groundwater level for excavation and installing the bridge abutments and riprap. Water pumped from work area must be discharged at an upland area near the site. Access for abutment installation work can be accomplished within the existing road embankment footprint. Temporary access route adjacent to the road embankment is needed for installing flow barriers and completing bridge installation work. Constructing the proposed bridge and in-stream work may require heavy track-mounted equipment operating on the stream bed, possibly in water up to 3 feet deep.

The State of Oregon may restrict the release of turbidity from the work areas into the stream. The agencies require turbidity control and monitoring, and should be contacted for specific requirements and allowable discharge limits.

Stream Impacts The proposed bridge is expected to improve stream flow conveyance, sediment transport, and woody debris transport.

A moderate amount of turbidity and sediment is expected to be released when the flow barriers are removed and stream flow is introduced into the newly constructed channel. The amount of turbidity and sediment will be reduced by removing the flow barriers gradually introducing the stream flow over an extended two to three-hour time.

Operation and Maintenance Riprap placed for controlling bank erosion should be inspected annually and after each extreme flood event. Replace or reposition dislodged stone. The presence of woody debris trapped upstream, beneath, and downstream of the bridge should be inspected annually and after each extreme flood event. Remove woody debris as needed for maintaining flow conveyance capacity and preventing logs deflecting flow towards the riprap or abutments.

Floodplain and Flood-rise Impacts

Flood limits and elevations have been mapped by the National Flood Insurance Program for the Little Luckiamute River near the site (FIRM FIS 41053C0355F, effective 12/19/2006). Immediately downstream of the bridge site the stream is mapped as Zone A, a special flood hazard area subject to inundation by the 1 percent annual chance flood event with no base flood elevations determined.

Upstream of the Zone A area, the stream is designated Zone X, areas determined to be outside the 0.2 percent annual chance floodplain. Polk County is the local floodplain administrator. FHWA Policy 23 CFR 650A allows up to 1 foot rise between the pre- and post-project water-surface profile hydraulic models.

Insurable structures are found 100 to 800 feet upstream of the bridge site. The proposed bridge will improve hydraulic conveyance and is expected to reduce potential flooding at and upstream of the bridge site. Differences in 100-year water surface elevations and flow velocities between the existing bridge and proposed bridge conditions are shown in Figures 2 and 3.

Site Conditions The stream is aligned approximately 30 degrees to the roadway (Photos 1, 2, 3, and 4). Channel confined against right bank immediately downstream or bridge site. Riprap has been placed under both bridge abutments for controlling embankment erosion. Some riprap dislodgement and road embankment erosion has occurred (Photos 5 and 6). The riprap and embankment fill encroaches into the waterway.

Hard, scour resistant bedrock is observed throughout the stream bottom and banks (Photos 7 and 8). It prevents the stream channel from degrading. A bedrock outcrop encroaches into the waterway 250 feet downstream of the bridge (Fig. 2, Photo 2). The encroachment is enough to backwater the bridge site during extreme floods. Zero to 2 feet of streambed material is seen on the bedrock.

Streambanks are moderately well defined. Measurements for estimating bankfull width were taken upstream and downstream of the bridge. Measurements indicate natural bankfull width is 30 to 40 feet.

Bankfull depth (ordinary-high-water) is 4 to 5 feet. Flood-prone width is 50 to 70 feet. Flood-prone depth is 6 to 8 feet. Channel slope is 1 to 3 percent. Pool-riffle is the dominant bed form. Boulder, cobble, and gravel is the dominant bed material. Streambed gradation was measured visually upstream of the bridge. Resulting gradation is D100 18 inches, D85 12 inches, D50 3 inches, and D15 1 inches (Photo 9).

The stream is moderately entrenched and has a relatively low sinuosity. Alignment is structurally controlled by relatively high, steep mountainous terrain. Banks are coarse alluvium, well vegetated, and appear moderately stable. Risk for bank migration or channel avulsion is low. Large woody debris recruitment and transports potential is high. Debris flow potential is low.

Hydrology Little Luckiamute River originates in the Oregon Coast Range and flows east to merge with Luckiamute River, which eventually flows into the Willamette River.

USGS gage station 14190100 is located approximately 0.5 miles upstream of the bridge site. Record period is 1966 to 2000. StreamStats, version 4.3.11, was used to delineate the drainage area, perform a Bulletin 17C peak discharge estimate for the USGS gage station, and develop peak discharges for the project site using USGS regression equations from “Estimation of Peak Discharges for Rural, Unregulated Streams in Western Oregon", USGS SIR 2005-5116, 2005. Peak discharge estimates are included in Table 1. USGS data set is too short and does not cover heavy flooding in the 2000’s. The peak discharge estimates using the USGS regression equations were used for the bridge design.

Drainage area for the bridge site is 22.8 square miles (Fig. 4). Elevations range from 436 feet at the bridge site to 3,320 feet with a mean of 1,780 feet. Mean annual precipitation is 102 inches. Percent forest cover is 91.5 percent. The watershed is in mixed private, state forest, and BLM land use. No major development occurs. There are no lake areas or water diversions.

Extreme flooding typically occurs with snow-melt and heavy rainfall in November, April, May, and June.

Lowest flows typically occur July through October.

Water Surface Elevations and Flow Velocities Hydrologic Engineering Center River Analysis System (HEC-RAS 5.0.7) two-dimensional, unsteady flow model was used for estimating the proposed bridge water surface elevations, flow depths, and flow velocities. Terrain for the proposed bridge model was created by modifying existing ground topography obtained from project mapping to reflect the proposed bridge and road embankment. The model uses a mesh with 4 feet by 4 feet grid spacing extending 220 feet upstream and 480 feet downstream (Fig. 5).

Normal flow depth with 0.015 feet/feet friction slope was set for the downstream boundary condition.

Fourteen-hour duration, 1-minute interval hydrograph was used for the upstream boundary condition.

The hydrograph includes the 2, 5, 10, 25, 50, 100, and 500-year flood flows. Manning’s Roughness Coefficients of 0.05 were selected for the main channel area. The overbank areas are densely vegetated with willow and alder shrubs. Peak flooding occurs in April, May, and June before the dense wetland vegetation on the floodplain is fully leafed. A Manning’s Roughness Coefficients of 0.1 was selected for the overbank areas. The model was calibrated with apparent bankfull and high-water levels determined in the field. The model uses a 10 second computation interval, full momentum equation set, and 2-hour warmup time. Flow depths, water surface elevations, and design flow velocities are summarized in Table 2 and Figures 6, 7, and 8. Differences in 100-year water surface elevations and flow velocities between the existing bridge and proposed bridge conditions are shown in Figures 2 and 3.

Scour Hard, scour resistant bedrock is observed along the stream bottom and both banks. Channel degradation is controlled by the bedrock. Scour depth was assumed to bedrock.

Riprap Sizing The riprap was sized using the approach from USACE EM 1110-2-1601, June 1994. Based on the two-dimensional HECRAS modeling, maximum expected flow velocity at the downstream bridge face is approximately 10 feet/sec for the 100-year flood event (Fig. 4). A stability factor of 0.3 was used for angular rock. Specific gravity of the stone was assumed to be 2.65. Slope of finished riprap surface is 2(h):1(v). To account for unknown flow impingement angles caused by shifting debris and mid-channel sediment deposits, a design factor-of-safety of 1.5 was selected. Class 4 (FHWA, FP-14) riprap, minimum 4 feet thickness was selected. Keying the riprap to the smooth bedrock will be difficult and will require partial grouting for stability.

attachments: Tables 1 and 2 Figures 1 to 8 Photographs 1 to 9 Drawings H.1 and H.2 Peak Discharge Estimates

Estimate Drainage

Method Area (mi2) 2 5 10 25 50 100 500

USGS Streamstats 22.8 1870 2580 3060 3680 4140 4610 5710

USGS 14190100 22.4 1930 2730 3320 4100 4730 5390 7070

DESIGN 22.8 1870 2580 3060 3680 4140 4610 5710

Notes:

1. USGS Regression Equations, “Estimation of Peak Discharges for Rural, Unregulated Streams in

Western Oregon", USGS SIR 2005-5116, 2005.

Table 1. Peak Discharges (ft3/sec)

Recurrence Intervals (years)

HYDRAULIC & HYDROLOGIC SUMMARY Hydraulic Model: HECRAS 5.0.7

Flood Frequency Yr 2 10 25 50 100 500

Exceedance Probability % 50 10 4 2 1 0.2

Discharge - USGS Regression Equations cfs 1870 3060 3680 4140 4610 5710

Modeled Water Surface Elevation Elev 431.6 433 433.6 434 434.5 435.4

Elevation Datum Conversion Ft 0 0 0 0 0 0

Project Water Surface Elevation Elev 431.6 433 433.6 434 434.5 435.4

Clearance above WS Ft 5.9 4.5 3.9 3.5 3 2.1

Existing Water Surface Elevation Elev 431.8 433.4 434 434.5 435 436

Predicted Flood Rise Ft -0.2 -0.4 -0.4 -0.5 -0.5 -0.6

Design Flow Velocity Ft/sec 6.5 7.6 8.7 9.3 10 10.8

Scour Base Elevation (Channel Thalweg) Elev 426 426

Contraction Scour Depth Ft 0 0

Stream Degradation Depth Ft 0 0

Left Abutment Scour Depth Ft 0 0

Right Abutment Scour Depth Ft 0 0

Total Left Abutment Scour Elevation ** Elev 425 425

Total Right Abutment Scour Elevation ** Elev 430 430

Pier Scour Depth Ft

Total Pier Scour Elevation ** Elev* 0

* or to bedrock when present.

** includes contraction and stream degradation scour.

Streambed material grain size (inches) D100/D85/D50/D15/D5 18 12 3 1

Scour Design Basis

Project Elevation Datum

RECOMMENDED SCOUR COUNTERMEASURES

Type

Top Elevation 436.0 Slope (H:V) 2:1

Bottom Elevation 425.0 Toe Width (Ft) 0.0

Thick (Ft) 4.0 Toe Thickness (Ft) 0.0

Riprap Design Basis

HEC-18

Project

Riprap, Class 4 (FHWA FP-14)

HEC-23

Table 2. Bridge Hydraulics & Scour Summary

1. USGS Regression Equations, “Estimation of Peak Discharges for Rural, Unregulated Streams in Western

Oregon", USGS SIR 2005-5116, 2005.

Black Rock Road_Bridge-Hydraulics-Scour_Summary-2.xls

Bridge Location

Project Site Location

Image from Google Earth Pro, image date 7/26/2018

N

44.870 / -123.451

FIGURE 1

LITTLE LUCKIAMUTE BRIDGE

SITE LOCATION

0 300 feet

Map printed from Google Earth Pro, image date 7/2015.

FIGURE 2

LITTLE LUCKIAMUTE BRIDGE

100-YR EXIST. VS PROP.

Map printed from Google Earth Pro, image date 7/2015.

FIGURE 3

LITTLE LUCKIAMUTE BRIDGE

100-YR EXIST. VS PROP.

Map printed from Google Earth Pro, image date 7/26/2018.

N

USGS 14190100

FIGURE 4

LITTLE LUCKIAMUTE BRIDGE

DRAINAGE AREA

0 2 miles

Bridge

Little Luckiamute River

DA = 22.8 sq. mi.

Bank Stabilization

HECRAS 5.0.7 - Two-Dimensional hydraulic model.

N

US Hydro Boundary

Mesh

FIGURE 5

LITTLE LUCKIAMUTE BRIDGE

HECRAS 2-D MODEL

DS Normal Depth Boundary

Flow Velocity (Feet/sec)

N

Design Value Location

FIGURE 6

LITTLE LUCKIAMUTE BRIDGE

100-YEAR FLOW VELOCITY

2-yr

500-yr 100-yr50-yr

25-yr 10-yr

5-yr

Flow Depth (Feet)

N

Design Value Location

FIGURE 7

LITTLE LUCKIAMUTE BRIDGE

100-YEAR FLOW DEPTH

2-yr

500-yr

100-yr 50-yr

25-yr

431.5

432.5

433.5

434.5

435.5

Water Surface Elevation (Feet)

N

Design Value Location

FIGURE 8

LITTLE LUCKIAMUTE BRIDGE

100-YEAR WATER SURFACE

2-yr

500-yr

100-yr 50-yr

25-yr

Photos Little Luckiamute River Bridge

PHOTO 1

PHOTO 2

PHOTO 3

6/14/2018

Channel skewed 30 degrees to roadway, bedrock exposed along stream bottom and banks. Riprap and road fill material encroaches into waterway.

Channel skewed 30 degrees to roadway, bedrock exposed along stream bottom and banks.

Downstream channel looking upstream at bridge.

Channel upstream bridge.

Channel skewed 30 degrees to roadway, bedrock exposed along stream bottom and banks.

Channel downstream bridge.

PHOTO 4

PHOTO 5

PHOTO 6

6/14/2018

Channel skewed 30 degrees to roadway, bedrock exposed along stream bottom and banks. Riprap and road fill material encroaches into waterway.

Upstream channel looking downstream at bridge.

Channel skewed 30 degrees to roadway, bedrock exposed along stream bottom and banks. Riprap and road fill material encroaches into waterway.

Right bank under bridge.

Channel skewed 30 degrees to roadway, bedrock exposed along stream bottom and banks. Riprap and road fill material encroaches into waterway.

Left bank under bridge.

PHOTO 7

PHOTO 8

PHOTO 9

6/14/2018

Sand, gravel, cobble, small boulder streambed material. Yellow dots are spaced 3 feet.

Upstream channel at old bridge crossing foundation.

Sand, gravel, cobble, small boulder streambed material. Bedrock exposed along stream bottom and banks.

Upstream channel.

Upstream channel streambed material gradation location.

Channel straight. Banks and floodplain well vegetated. Sand, gravel, cobble, small boulder streambed material.

Bedrock exposed along stream bottom and banks.

CL

CL

P

10006

CP

Wingwall A

Wingwall C

Wingwall D

Wingwall A

10 200510

SCALE IN FEET

N

PLAN

SCOUR MITIGATION

LITTLE LUCKIAMUTE BRIDGE

H.1

STATE PROJECT

NUMBER

SHEET

I n t_ ft

D c p w w o r k d v

B la c k

R o c k

R o a d

B r id g e r ip r a p

L O I n t_ ft

D .d g n

OR POLK 2016(1)

A

M

J a n u a r y

C h e c k e d b y

D e s ig n e d b y

F lo w

Existing grade contour

Stream edge

Proposed road C

Existing road C

A

A

20'-0"

B

B

Placed riprap, method B, class 4

Placed riprap, method B, class 4

R e g ra d e b a n k a re a

R e g ra d e b a n k a re a

14'- 0"

11'- 0"

Proposed bridge

Align riprap with bridge abutment face

11'- 0"

4'-0

Proposed bridge footing

Proposed bridge abutment face shape to finished road embankment

10 cy for grade transition, Placed riprap, method A, class 1, abutment

Remove existing bridge

NO SCALE

ELEVATION

CL

CL CL

15 ft left of C

Existing ground at C

Existing ground elev. 437.44

Low chord

Proposed ground

-1.00% Grade on rock (elev. 425.0)

Concrete spread footing

Proposed profile grade on rock (elev. 430.0)

Concrete spread footing

DESCRIPTIONITEM NO. UNIT QUANTITY

RIPRAP QUANTITIES

25101-0500

25101-0100

20701-0300

Placed riprap, method B, class 4

Placed riprap, method A, class 1

Separation- stabilization geotextile, class 1, type C

280CUYD

CUYD

SQYD

SECTIONS

SCOUR MITIGATION

LITTLE LUCKIAMUTE BRIDGE

100-year W.S. Elev 434.5

OHW Elev 431.6

Abut. 1 Abut. 2

H.2

STATE PROJECT

NUMBER

SHEET

I n t_ ft

D c p w w o r k d v

B la c k

R o c k

R o a d

B r id g e r ip r a p

L O I n t_ ft

D .d g n

OR POLK 2016(1)

A

M

J a n u a r y

B

V in c e n t

S

L e o n

C h e c k e d b y

D e s ig n e d b y

Varies

Excavation limit

Existing grade

Abutmant wingwall

Conserved streambed material

24'-0" geotextile, class 1, type C

Separation-stabilization

Placed riprap, method B, class 4

SECTION B-B

Concrete spread footing on bedrock

SECTION A-A

Placed riprap, method B, class 4 geotextile, class 1, type C

Separation-stabilization elev 436.0'

Riprap crest, Proposed grade

Existing stream bottom

Proposed abutment wingwall

Proposed profile grade

Proposed bridge

Existing grade

Placed riprap, method B, class 4

4'-0"

Placed partially-grouted riprap for keying into bedrock

'-0

Approximate bedrock surface

Abutment wingwall face

Match abutment wingwall face

Placed riprap, method B, class 4

14'-0" 11'-0" 4'-0"11'-0"

Concrete spread footing on bedrock

Conserved streambed material

15 ft right of C Existing ground

Conserved streambed material m in

Placed riprap, method A, class 1

Placed riprap, method A, class 1

11'4' to 14' shape to finished road embankment

10 cy for grade transition, Placed riprap, method A, class 1, 1/2/2020 StreamStats https://streamstats.usgs.gov/ss/ 1/5

Black Rock Road Bridge - StreamStats Report

Basin Characteristics

Parameter Code Parameter Description Value Unit

DRNAREA Area that drains to a point on a stream 22.8 square miles

I24H2Y Maximum 24-hour precipitation that occurs on average once in 2 years - Equivalent to precipitation intensity index

4.43 inches

SOILPERM Average Soil Permeability 1.13 inches per hour

JANMAXT2K Mean Maximum January Temperature from 2K resolution PRISM 1961-1990 data

43.4 degrees F

Region ID: OR Workspace ID: OR20200102235525986000 Clicked Point (Latitude, Longitude): 44.86995, -123.45133 Time: 2020-01-02 15:55:42 -0800 https://streamstats.usgs.gov/ss/ 2/5

Parameter Code Parameter Description Value Unit

WATCAPORC Available water capacity from STATSGO data using methods from SIR 2005-5116

0.15 inches

ORREG2 Oregon Region Number 10001 dimensionless

BSLOPD Mean basin slope measured in degrees 14.2 degrees

JANMINT2K Mean Minimum January Temperature from 2K resolution PRISM PRISM 1961-1990 data

32.3 degrees F

ELEV Mean Basin Elevation 1780 feet

ASPECT basin average of topographic slope compass directions from elevation grid

157 degrees

DRNDENSITY Basin drainage density defined as total stream length divided by drainage area.

0.92 dimensionless

ELEVMAX Maximum basin elevation 3320 feet

FOREST Percentage of area covered by forest 91.5 percent

IMPERV Percentage of impervious area 0 percent

JANAVPRE2K Mean January Precipitation 18.6 inches

JANMAXTMP Mean Maximum January Temperature 43.4 degrees F

JANMINTMP Mean Minimum January Temperature 32.2 degrees F

JULAVPRE2K Mean July Average Precipitation 0.77 inches

LC11BARE Percentage of barren from NLCD 2011 class 31 5 percent

LC11CRPHAY Percentage of cultivated crops and hay, classes 81 and 82, from NLCD 2011

0 percent

LC11DEVHI Percentage of area developed, high intensity, NLCD 2011 class 24

0 percent

LC11DVLO Percentage of developed area, low intensity, from NLCD 2011 class 22

0 percent

LC11DVMD Percentage of area developed, medium intensity, NLCD 2011 class 23

0 percent

LC11DVOPN Percentage of developed open area from NLCD 2011 class 21

7 percent

LC11FORSHB Percentage of forests and shrub lands, classes 41 to 52, from NLCD 2011

79 percent

LC11HERB Percentage of herbaceous from NLCD 2011 classes 71-74

8 percent https://streamstats.usgs.gov/ss/ 3/5

Parameter Code Parameter Description Value Unit

LC11IMP Average percentage of impervious area determined from NLCD 2011 impervious dataset

0.6 percent

LC11WATER Percent of open water, class 11, from NLCD 2011 0 percent

LC11WETLND Percentage of wetlands, classes 90 and 95, from

NLCD 2011

1 percent

MAJ_ROADS Length of non-state major roads in basin 0 miles

MAXBSLOPD Maximum basin slope, in degrees, using ArcInfo Grid with NHDPlus 30-m resolution elevation data.

51.8 degrees

MAXTEMP Mean annual maximum air temperature over basin area from PRISM 1971-2000 800-m grid

57.7 degrees F

MINBELEV Minimum basin elevation 436 feet

MINBSLOPD Minimum basin slope, in degrees, using ArcInfo Grid with NHDPlus 30-m resolution elevation data.

0.00955 degrees

MINTEMP Mean annual minimum air temperature over basin surface area as defined in SIR 2008-5126

40.3 degrees F

MIN_ROADS Length of non-state minor roads in basin 82.2 miles

OR_HIPERMA Percent basin surface area containing high permeability aquifer units as defined in SIR 2008-

0 percent

OR_HIPERMG Percent basin surface area containing high permeability geologic units as defined in SIR 2008-

0 percent

PRECIP Mean Annual Precipitation 102 inches

RELIEF Maximum - minimum elevation 2890 feet

STATE_HWY Length of state highways in basin 0 miles

STATSGODEP Area-weighted average soil depth from NRCS STATSGO database

45 inches

STRMTOT total length of all mapped streams (1:24,000-scale) in the basin

33.9 miles

WATCAPORR Available water capacity from STATSGO data using methods from SIR 2008-5126

0.15 inch per inch

Peak-Flow Statistics Parameters[100 Percent (22.8 square miles) Reg 2B Western Interior LT 3000 ft Cooper] https://streamstats.usgs.gov/ss/ 4/5

Parameter Code Parameter Name Value Units Min Limit Max Limit Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 22.8 square miles 0.37 7270

BSLOPD Mean Basin Slope degrees 14.2 degrees 5.62 28.3

I24H2Y 24 Hour 2 Year Precipitation 4.43 inches 1.53 4.48

ELEV Mean Basin Elevation 1780 feet

ORREG2 Oregon Region Number 10001 dimensionless

Peak-Flow Statistics Flow Report[100 Percent (22.8 square miles) Reg 2B Western Interior LT 3000 ft Cooper]

PIl: Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE:

Standard Error (other -- see report)

Statistic Value Unit PIl PIu SE SEp Equiv. Yrs.

2 Year Peak Flood 1870 ft^3/s 1100 3190 32.6 32.6 2

5 Year Peak Flood 2580 ft^3/s 1520 4390 32.4 32.4 2.8

10 Year Peak Flood 3060 ft^3/s 1790 5260 33 33 3.6

25 Year Peak Flood 3680 ft^3/s 2110 6430 34.1 34.1 4.8

50 Year Peak Flood 4140 ft^3/s 2330 7370 35.1 35.1 5.5

100 Year Peak Flood 4610 ft^3/s 2550 8340 36.2 36.2 6.2

500 Year Peak Flood 5710 ft^3/s 3020 10800 39.1 39.1 7.5

Peak-Flow Statistics Citations

Cooper, R.M.,2005, Estimation of Peak Discharges for Rural, Unregulated Streams in Western Oregon: U.S. Geological Survey Scientific Investigations Report 2005-5116, 76 p.

(http://pubs.usgs.gov/sir/2005/5116/pdf/sir2005-5116.pdf)

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http://pubs.usgs.gov/sir/2005/5116/pdf/sir2005-5116.pdf https://streamstats.usgs.gov/ss/ 5/5

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Application Version: 4.3.11